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Sample records for accelerometer wear time

  1. Effects of Varying Epoch Lengths, Wear Time Algorithms, and Activity Cut-Points on Estimates of Child Sedentary Behavior and Physical Activity from Accelerometer Data

    PubMed Central

    Banda, Jorge A.; Haydel, K. Farish; Davila, Tania; Desai, Manisha; Haskell, William L.; Matheson, Donna; Robinson, Thomas N.

    2016-01-01

    Objective To examine the effects of accelerometer epoch lengths, wear time (WT) algorithms, and activity cut-points on estimates of WT, sedentary behavior (SB), and physical activity (PA). Methods 268 7–11 year-olds with BMI ≥ 85th percentile for age and sex wore accelerometers on their right hips for 4–7 days. Data were processed and analyzed at epoch lengths of 1-, 5-, 10-, 15-, 30-, and 60-seconds. For each epoch length, WT minutes/day was determined using three common WT algorithms, and minutes/day and percent time spent in SB, light (LPA), moderate (MPA), and vigorous (VPA) PA were determined using five common activity cut-points. ANOVA tested differences in WT, SB, LPA, MPA, VPA, and MVPA when using the different epoch lengths, WT algorithms, and activity cut-points. Results WT minutes/day varied significantly by epoch length when using the NHANES WT algorithm (p < .0001), but did not vary significantly by epoch length when using the ≥ 20 minute consecutive zero or Choi WT algorithms. Minutes/day and percent time spent in SB, LPA, MPA, VPA, and MVPA varied significantly by epoch length for all sets of activity cut-points tested with all three WT algorithms (all p < .0001). Across all epoch lengths, minutes/day and percent time spent in SB, LPA, MPA, VPA, and MVPA also varied significantly across all sets of activity cut-points with all three WT algorithms (all p < .0001). Conclusions The common practice of converting WT algorithms and activity cut-point definitions to match different epoch lengths may introduce significant errors. Estimates of SB and PA from studies that process and analyze data using different epoch lengths, WT algorithms, and/or activity cut-points are not comparable, potentially leading to very different results, interpretations, and conclusions, misleading research and public policy. PMID:26938240

  2. Assessment of Differing Definitions of Accelerometer Nonwear Time

    ERIC Educational Resources Information Center

    Evenson, Kelly R.; Terry, James W., Jr.

    2009-01-01

    Measuring physical activity with objective tools, such as accelerometers, is becoming more common. Accelerometers measure acceleration multiple times within a given frequency and summarize this as a count over a pre-specified time period or epoch. The resultant count represents acceleration over the epoch length. Accelerometers eliminate biases…

  3. Identification of Accelerometer Nonwear Time and Sedentary Behavior

    ERIC Educational Resources Information Center

    Oliver, Melody; Badland, Hannah M.; Schofield, Grant M.; Shepherd, Janine

    2011-01-01

    The primary aim of the current study was to investigate the accuracy of various automated rules for determining accelerometer nonwear time in a sample of predominantly desk-based office workers (using their self-reported nonwear times as a criterion). Second, the authors examined the effect of applying these rules to accelerometer data retention…

  4. ACCELEROMETER

    DOEpatents

    Pope, K.E.

    1958-11-25

    A device, commonly known as an accelerometer, is described which may be utllized for measuring acceleratlon with high sensitivity and accuracy tbroughout a relatively wlde range of values. In general, the accelerometer consists of an assembly, including an electric motor stator and a mass element located away from the axis of rotation of the stator, rotatably mounted on a support, and an electric motor rotor positioned within the stator and rotatable thereln. An electrlcal switching circuit controlled by the movement of the stator lntermittently energizes the rotor winding and retards move ment of the stator, and a centrifugal switch is rotatable with the rotor to operate upon attainment of a predetermined rotor rotational velocity.

  5. Extracting Time-Accurate Acceleration Vectors From Nontrivial Accelerometer Arrangements.

    PubMed

    Franck, Jennifer A; Blume, Janet; Crisco, Joseph J; Franck, Christian

    2015-09-01

    Sports-related concussions are of significant concern in many impact sports, and their detection relies on accurate measurements of the head kinematics during impact. Among the most prevalent recording technologies are videography, and more recently, the use of single-axis accelerometers mounted in a helmet, such as the HIT system. Successful extraction of the linear and angular impact accelerations depends on an accurate analysis methodology governed by the equations of motion. Current algorithms are able to estimate the magnitude of acceleration and hit location, but make assumptions about the hit orientation and are often limited in the position and/or orientation of the accelerometers. The newly formulated algorithm presented in this manuscript accurately extracts the full linear and rotational acceleration vectors from a broad arrangement of six single-axis accelerometers directly from the governing set of kinematic equations. The new formulation linearizes the nonlinear centripetal acceleration term with a finite-difference approximation and provides a fast and accurate solution for all six components of acceleration over long time periods (>250 ms). The approximation of the nonlinear centripetal acceleration term provides an accurate computation of the rotational velocity as a function of time and allows for reconstruction of a multiple-impact signal. Furthermore, the algorithm determines the impact location and orientation and can distinguish between glancing, high rotational velocity impacts, or direct impacts through the center of mass. Results are shown for ten simulated impact locations on a headform geometry computed with three different accelerometer configurations in varying degrees of signal noise. Since the algorithm does not require simplifications of the actual impacted geometry, the impact vector, or a specific arrangement of accelerometer orientations, it can be easily applied to many impact investigations in which accurate kinematics need to

  6. A Pilot Study Using an Accelerometer to Evaluate a Caregiver's Interpretation of an Infant or Toddler's Activity Level as Recorded in a Time Activity Diary

    ERIC Educational Resources Information Center

    Tulve, Nicolle S.; Jones, Paul A.; McCurdy, Thomas; Croghan, Carry W.

    2007-01-01

    The objectives of this study were to: (a) determine if very young children will wear an accelerometer for relatively long periods of time and comply with the protocol for its use; (b) evaluate how well a caregiver can estimate the activity level of his/her infant or toddler when completing an exposure-oriented time activity diary; and (c) compare…

  7. Ngram time series model to predict activity type and energy cost from wrist, hip and ankle accelerometers: implications of age.

    PubMed

    Strath, Scott J; Kate, Rohit J; Keenan, Kevin G; Welch, Whitney A; Swartz, Ann M

    2015-11-01

    To develop and test time series single site and multi-site placement models, we used wrist, hip and ankle processed accelerometer data to estimate energy cost and type of physical activity in adults. Ninety-nine subjects in three age groups (18-39, 40-64, 65 +  years) performed 11 activities while wearing three triaxial accelereometers: one each on the non-dominant wrist, hip, and ankle. During each activity net oxygen cost (METs) was assessed. The time series of accelerometer signals were represented in terms of uniformly discretized values called bins. Support Vector Machine was used for activity classification with bins and every pair of bins used as features. Bagged decision tree regression was used for net metabolic cost prediction. To evaluate model performance we employed the jackknife leave-one-out cross validation method. Single accelerometer and multi-accelerometer site model estimates across and within age group revealed similar accuracy, with a bias range of -0.03 to 0.01 METs, bias percent of -0.8 to 0.3%, and a rMSE range of 0.81-1.04 METs. Multi-site accelerometer location models improved activity type classification over single site location models from a low of 69.3% to a maximum of 92.8% accuracy. For each accelerometer site location model, or combined site location model, percent accuracy classification decreased as a function of age group, or when young age groups models were generalized to older age groups. Specific age group models on average performed better than when all age groups were combined. A time series computation show promising results for predicting energy cost and activity type. Differences in prediction across age group, a lack of generalizability across age groups, and that age group specific models perform better than when all ages are combined needs to be considered as analytic calibration procedures to detect energy cost and type are further developed. PMID:26449155

  8. The timing of scour and fill in a gravel-bedded river measured with buried accelerometers

    NASA Astrophysics Data System (ADS)

    Gendaszek, Andrew S.; Magirl, Christopher S.; Czuba, Christiana R.; Konrad, Christopher P.

    2013-07-01

    A device that measures the timing of streambed scour and the duration of sediment mobilization at specific depths of a streambed was developed using data-logging accelerometers placed within the gravel substrate of the Cedar River, Washington, USA. Each accelerometer recorded its orientation every 20 min and remained stable until the surrounding gravel matrix mobilized as sediment was transported downstream and scour reached the level of the accelerometer. The accelerometer scour monitors were deployed at 26 locations in salmon-spawning habitat during the 2010-2011 flood season to record when the streambed was scoured to the depth of typical egg-pocket deposition. Scour was recorded at one location during a moderate high-flow event (65 m3/s; 1.25-1.5-year recurrence interval) and at 17 locations during a larger high-flow event (159 m3/s; 7-year recurrence interval). Accelerometer scour monitors recorded periods of intermittent sediment mobilization and stability within a high-flow event providing insight into the duration of scour. Most scour was recorded during the rising limb and at the peak of a flood hydrograph, though some scour occurred during sustained high flows following the peak of the flood hydrograph.

  9. The timing of scour and fill in a gravel-bedded river measured with buried accelerometers

    USGS Publications Warehouse

    Gendaszek, Andrew S.; Magirl, Christopher S.; Czuba, Christiana R.; Konrad, Christopher P.

    2013-01-01

    A device that measures the timing of streambed scour and the duration of sediment mobilization at specific depths of a streambed was developed using data-logging accelerometers placed within the gravel substrate of the Cedar River, Washington, USA. Each accelerometer recorded its orientation every 20 min and remained stable until the surrounding gravel matrix mobilized as sediment was transported downstream and scour reached the level of the accelerometer. The accelerometer scour monitors were deployed at 26 locations in salmon-spawning habitat during the 2010–2011 flood season to record when the streambed was scoured to the depth of typical egg-pocket deposition. Scour was recorded at one location during a moderate high-flow event (65 m3/s; 1.25–1.5-year recurrence interval) and at 17 locations during a larger high-flow event (159 m3/s; 7-year recurrence interval). Accelerometer scour monitors recorded periods of intermittent sediment mobilization and stability within a high-flow event providing insight into the duration of scour. Most scour was recorded during the rising limb and at the peak of a flood hydrograph, though some scour occurred during sustained high flows following the peak of the flood hydrograph.

  10. Falls classification using tri-axial accelerometers during the five-times-sit-to-stand test.

    PubMed

    Doheny, Emer P; Walsh, Cathal; Foran, Timothy; Greene, Barry R; Fan, Chie Wei; Cunningham, Clodagh; Kenny, Rose Anne

    2013-09-01

    The five-times-sit-to-stand test (FTSS) is an established assessment of lower limb strength, balance dysfunction and falls risk. Clinically, the time taken to complete the task is recorded with longer times indicating increased falls risk. Quantifying the movement using tri-axial accelerometers may provide a more objective and potentially more accurate falls risk estimate. 39 older adults, 19 with a history of falls, performed four repetitions of the FTSS in their homes. A tri-axial accelerometer was attached to the lateral thigh and used to identify each sit-stand-sit phase and sit-stand and stand-sit transitions. A second tri-axial accelerometer, attached to the sternum, captured torso acceleration. The mean and variation of the root-mean-squared amplitude, jerk and spectral edge frequency of the acceleration during each section of the assessment were examined. The test-retest reliability of each feature was examined using intra-class correlation analysis, ICC(2,k). A model was developed to classify participants according to falls status. Only features with ICC>0.7 were considered during feature selection. Sequential forward feature selection within leave-one-out cross-validation resulted in a model including four reliable accelerometer-derived features, providing 74.4% classification accuracy, 80.0% specificity and 68.7% sensitivity. An alternative model using FTSS time alone resulted in significantly reduced classification performance. Results suggest that the described methodology could provide a robust and accurate falls risk assessment.

  11. Validating Pedometer-Based Physical Activity Time against Accelerometer in Middle School Physical Education

    ERIC Educational Resources Information Center

    Gao, Zan; Lee, Amelia M.; Solmon, Melinda A.; Kosma, Maria; Carson, Russell L.; Zhang, Tao; Domangue, Elizabeth; Moore, Delilah

    2010-01-01

    The purpose of this study was to validate physical activity time in middle school physical education as measured by pedometers in relation to a criterion measure, namely, students' accelerometer determined moderate to vigorous physical activity (MVPA). Participants were 155 sixth to eighth graders participating in regularly scheduled physical…

  12. Impact of Advertising on Tampon Wear-time Practices

    PubMed Central

    Woeller, Kara E.; Miller, Kenneth W.; Robertson-Smith, Amy L.; Bohman, Lisa C.

    2015-01-01

    OBJECTIVES (1) To determine whether advertising nighttime tampon use for up to eight hours was understood to be consistent with label recommendations and (2) to determine whether television and print advertising with this message affected tampon wear times in adults and teens. METHODS (1) A comprehension study (online advertising and follow-up questionnaire) among women aged 14–49 years (300 per group) who viewed either the test or a control advertising message; (2) Diary-based surveys of tampon wear times performed prior to (n = 292 adults, 18–49 years, 74 teens, 12–17 years) and after (n = 287 adults, 104 teens) the launch of national advertising. RESULTS Significantly more test message viewers than controls stated tampons should be worn less than or equal to eight hours (93.6% vs. 88.6%, respectively, P = 0.049). A directionally higher percentage of test message viewers said they would use a pad if sleeping longer than eight hours (52% vs. 42% of controls). Among the women who used tampons longer than eight hours when sleeping, 52% reported they would wake up and change compared with 45% of controls. No significant difference between baseline and follow-up diary surveys was found among teens or adults in various measures of tampon wear time (mean wear times; usage intervals from less than two hours to more than 10 hours; percentage of tampons used for more than or equal to eight hours; frequency of wearing at least one tampon more than eight hours). CONCLUSIONS Advertising nighttime tampon wear for up to eight hours effectively communicated label recommendations but did not alter tampon wear times. The informational intervention had limited impact on established habits. PMID:26688668

  13. Accelerometer data requirements for reliable estimation of habitual physical activity and sedentary time of children during the early years - a worked example following a stepped approach.

    PubMed

    Bingham, Daniel D; Costa, Silvia; Clemes, Stacy A; Routen, Ash C; Moore, Helen J; Barber, Sally E

    2016-10-01

    This study presents a worked example of a stepped process to reliably estimate the habitual physical activity and sedentary time of a sample of young children. A total of 299 children (2.9 ± 0.6 years) were recruited. Outcome variables were daily minutes of total physical activity, sedentary time, moderate to vigorous physical activity and proportional values of each variable. In total, 282 (94%) provided 3 h of accelerometer data on ≥1 day and were included in a 6-step process: Step-1: determine minimum wear-time; Step-2: process 7-day-data; Step-3: determine the inclusion of a weekend day; Step-4: examine day-to-day variability; Step-5: calculate single day intraclass correlation (ICC) (2,1); Step-6: calculate number of days required to reach reliability. Following the process the results were, Step-1: 6 h was estimated as minimum wear-time of a standard day. Step-2: 98 (32%) children had ≥6 h wear on 7 days. Step-3: no differences were found between weekdays and weekend days (P ≥ 0.05). Step-4: no differences were found between day-to-day variability (P ≥ 0.05). Step-5: single day ICC's (2,1) ranged from 0.48 (total physical activity and sedentary time) to 0.53 (proportion of moderate to vigorous physical activity). Step-6: to reach reliability (ICC = 0.7), 3 days were required for all outcomes. In conclusion following a 7 day wear protocol, ≥6 h on any 3 days was found to have acceptable reliability. The stepped-process offers researchers a method to derive sample-specific wear-time criterion.

  14. Accelerometer Adherence and Performance in a Cohort Study of US Hispanic Adults

    PubMed Central

    Evenson, Kelly R.; Sotres-Alvarez, Daniela; Deng, Yu; Marshall, Simon J.; Isasi, Carmen R.; Esliger, Dale W.; Davis, Sonia

    2014-01-01

    Purpose This study described participant adherence to wearing the accelerometer and accelerometer performance in a cohort study of adults. Methods From 2008-2011, 16,415 United States (US) Hispanic/Latino adults age 18-74 years enrolled in the Hispanic Community Health Study/Study of Latinos. Immediately following the baseline visit, participants wore an Actical accelerometer for one week. This study explored correlates of accelerometer participation and adherence, defined as wearing it for at least 3 of a possible days for >=10 hours/day. Accelerometer performance was assessed by exploring the number of different values of accelerometer counts/minute for each participant. Results Overall, 92.3% (n=15,153) had at least one day with accelerometer data and 77.7% (n=12,750) were adherent. Both accelerometer participation and adherence were higher among participants who were married or partnered, reported a higher household income, were first generation immigrants, or reported lower sitting time. Participation was also higher among those with no stair limitations. Adherence was higher among participants who were male, older, employed or retired, not US born, preferred Spanish over English, reported higher work activity or lower recreational activity, and those with a lower body mass index. Among the sample that met the adherence definition, the maximum recorded count/minute was 12,000, and there were a total of 5,846 different counts/minute. On average, participants had 112.5 different counts/minute over 6 days (median 106, interquartile range 91-122). The number of different counts/minute were higher among men, younger ages, normal weight, and those with higher accelerometer assessed physical activity. Conclusion Several correlates differed between accelerometer participation and adherence. These characteristics could be targeted in future studies to improve accelerometer wear. The performance of the accelerometer provided insight into creating a more accurate non-wear

  15. Time- and Computation-Efficient Calibration of MEMS 3D Accelerometers and Gyroscopes

    PubMed Central

    Stančin, Sara; Tomažič, Sašo

    2014-01-01

    We propose calibration methods for microelectromechanical system (MEMS) 3D accelerometers and gyroscopes that are efficient in terms of time and computational complexity. The calibration process for both sensors is simple, does not require additional expensive equipment, and can be performed in the field before or between motion measurements. The methods rely on a small number of defined calibration measurements that are used to obtain the values of 12 calibration parameters. This process enables the static compensation of sensor inaccuracies. The values detected by the 3D sensor are interpreted using a generalized 3D sensor model. The model assumes that the values detected by the sensor are equal to the projections of the measured value on the sensor sensitivity axes. Although this finding is trivial for 3D accelerometers, its validity for 3D gyroscopes is not immediately apparent; thus, this paper elaborates on this latter topic. For an example sensor device, calibration parameters were established using calibration measurements of approximately 1.5 min in duration for the 3D accelerometer and 2.5 min in duration for the 3D gyroscope. Correction of each detected 3D value using the established calibration parameters in further measurements requires only nine addition and nine multiplication operations. PMID:25123469

  16. Time- and computation-efficient calibration of MEMS 3D accelerometers and gyroscopes.

    PubMed

    Stančin, Sara; Tomažič, Sašo

    2014-01-01

    We propose calibration methods for microelectromechanical system (MEMS) 3D accelerometers and gyroscopes that are efficient in terms of time and computational complexity. The calibration process for both sensors is simple, does not require additional expensive equipment, and can be performed in the field before or between motion measurements. The methods rely on a small number of defined calibration measurements that are used to obtain the values of 12 calibration parameters. This process enables the static compensation of sensor inaccuracies. The values detected by the 3D sensor are interpreted using a generalized 3D sensor model. The model assumes that the values detected by the sensor are equal to the projections of the measured value on the sensor sensitivity axes. Although this finding is trivial for 3D accelerometers, its validity for 3D gyroscopes is not immediately apparent; thus, this paper elaborates on this latter topic. For an example sensor device, calibration parameters were established using calibration measurements of approximately 1.5 min in duration for the 3D accelerometer and 2.5 min in duration for the 3D gyroscope. Correction of each detected 3D value using the established calibration parameters in further measurements requires only nine addition and nine multiplication operations.

  17. Factors associated with participant compliance in studies using accelerometers.

    PubMed

    Lee, Paul H; Macfarlane, Duncan J; Lam, T H

    2013-09-01

    Participant compliance is an important issue in studies using accelerometers. Some participants wear the accelerometer for the duration specified by the researchers but many do not. We investigated a range of demographic factors associated with participant compliance in obtaining analyzable accelerometer data. A total of 3601 participants (aged 47.6±13.1 years, 44.6% male) were included. They were asked to wear an accelerometer (ActiGraph) for four consecutive days after completing a household survey during March 2009-January 2011 in Hong Kong. Participants wore the accelerometer on average for 13.9h in a 24-h day. No significant difference was found between males and females (p=0.38). Using log-linear regression, it was found that older participants (0.5% more wearing hours for each year of age, p<0.001), those with full-time job (p<0.01), with tertiary education (p<0.01), non-smokers (p<0.01) and with high self-reported health (p<0.05) wore the accelerometer for more hours. These results provide details for estimating compliance rates for samples with different characteristics and thus sample size calculation to account for participant compliance. PMID:23688408

  18. Accelerometer-Measured Physical Activity and Sedentary Time Differ According to Education Level in Young Adults.

    PubMed

    Kantomaa, Marko T; Tikanmäki, Marjaana; Kankaanpää, Anna; Vääräsmäki, Marja; Sipola-Leppänen, Marika; Ekelund, Ulf; Hakonen, Harto; Järvelin, Marjo-Riitta; Kajantie, Eero; Tammelin, Tuija H

    2016-01-01

    This study examined the association of education level with objectively measured physical activity and sedentary time in young adults. Data from the Finnish ESTER study (2009-2011) (n = 538) was used to examine the association between educational attainment and different subcomponents of physical activity and sedentary time measured using hip-worn accelerometers (ActiGraph GT1M) for seven consecutive days. Overall physical activity, moderate-to-vigorous physical activity (MVPA), light-intensity physical activity and sedentary time were calculated separately for weekdays and weekend days. A latent profile analysis was conducted to identify the different profiles of sedentary time and the subcomponents of physical activity. The educational differences in accelerometer-measured physical activity and sedentary time varied according to the subcomponents of physical activity, and between weekdays and weekend days. A high education level was associated with high MVPA during weekdays and weekend days in both sexes, high sedentary time during weekdays in both sexes, and a low amount of light-intensity physical activity during weekdays in males and during weekdays and weekend days in females. The results indicate different challenges related to unhealthy behaviours in young adults with low and high education: low education is associated with a lack of MVPA, whereas high education is associated with a lack of light-intensity physical activity and high sedentary time especially during weekdays. PMID:27403958

  19. Accelerometer-Measured Physical Activity and Sedentary Time Differ According to Education Level in Young Adults

    PubMed Central

    Kantomaa, Marko T.; Tikanmäki, Marjaana; Kankaanpää, Anna; Vääräsmäki, Marja; Sipola-Leppänen, Marika; Ekelund, Ulf; Hakonen, Harto; Järvelin, Marjo-Riitta; Kajantie, Eero; Tammelin, Tuija H.

    2016-01-01

    This study examined the association of education level with objectively measured physical activity and sedentary time in young adults. Data from the Finnish ESTER study (2009–2011) (n = 538) was used to examine the association between educational attainment and different subcomponents of physical activity and sedentary time measured using hip-worn accelerometers (ActiGraph GT1M) for seven consecutive days. Overall physical activity, moderate-to-vigorous physical activity (MVPA), light-intensity physical activity and sedentary time were calculated separately for weekdays and weekend days. A latent profile analysis was conducted to identify the different profiles of sedentary time and the subcomponents of physical activity. The educational differences in accelerometer-measured physical activity and sedentary time varied according to the subcomponents of physical activity, and between weekdays and weekend days. A high education level was associated with high MVPA during weekdays and weekend days in both sexes, high sedentary time during weekdays in both sexes, and a low amount of light-intensity physical activity during weekdays in males and during weekdays and weekend days in females. The results indicate different challenges related to unhealthy behaviours in young adults with low and high education: low education is associated with a lack of MVPA, whereas high education is associated with a lack of light-intensity physical activity and high sedentary time especially during weekdays. PMID:27403958

  20. Accelerometer data reduction in adolescents: effects on sample retention and bias

    PubMed Central

    2013-01-01

    Background Accelerometry is increasingly being recognized as an accurate and reliable method to assess free-living physical activity (PA) in children and adolescents. However, accelerometer data reduction criteria remain inconsistent, and the consequences of excluding participants in for example intervention studies are not well described. In this study, we investigated how different data reduction criteria changed the composition of the adolescent population retained in accelerometer data analysis. Methods Accelerometer data (Actigraph GT3X), anthropometric measures and survey data were obtained from 1348 adolescents aged 11–14 years enrolled in the Danish SPACE for physical activity study. Accelerometer data were analysed using different settings for each of the three key data reduction criteria: (1) number of valid days; (2) daily wear time; and (3) non-wear time. The effects of the selected setting on sample retention and PA counts were investigated and compared. Ordinal logistic regression and multilevel mixed-effect linear regression models were used to analyse the impact of differing non-wear time definitions in different subgroups defined by body mass index, age, sex, and self-reported PA and sedentary levels. Results Increasing the minimum requirements for daily wear time and the number of valid days and applying shorter non-wear definitions, resulted in fewer adolescents retained in the dataset. Moreover, the different settings for non-wear time significantly influenced which participants would be retained in the accelerometer data analyses. Adolescents with a higher BMI (OR:0.93, CI:0.87-0.98, p=0.015) and older adolescents (OR:0.68, CI:0.49-0.95, p=0.025) were more likely to be excluded from analysis using 10 minutes of non-wear compared to longer non-wear time periods. Overweight and older adolescents accumulated more daily non-wear time if the non-wear time setting was short, and the relative difference between groups changed depending on the non-wear

  1. A MEMS accelerometer-based real-time motion-sensing module for urological diagnosis and treatment.

    PubMed

    Sun, Hongzhi; Fu, Guoqing; Xie, Huikai

    2013-02-01

    This paper reports a real-time motion-sensing module, which is realized by incorporating multiple MEMS accelerometers into a standard Foley catheter, for assisting diagnosis and treatment of stressed urinary incontinence. The accelerometers measure the orientations of the catheter at multiple points, so the shape of the urethra and movement of the bladder neck can be tracked in real time. An algorithm for extracting tilting, position and shape information from 3-axis MEMS accelerometers has been developed. The model of measurement errors for both static and dynamic testing is also established. The experimental results indicate that the module tracks the movement of the Foley catheter successfully in a real-time environment and the absolute error for static measurement is no more than 1.1° within the operation range. PMID:23360195

  2. Estimation of Physiological Tremor from Accelerometers for Real-Time Applications

    PubMed Central

    Veluvolu, Kalyana C.; Ang, Wei Tech

    2011-01-01

    Accurate filtering of physiological tremor is extremely important in robotics assisted surgical instruments and procedures. This paper focuses on developing single stage robust algorithms for accurate tremor filtering with accelerometers for real-time applications. Existing methods rely on estimating the tremor under the assumption that it has a single dominant frequency. Our time-frequency analysis on physiological tremor data revealed that tremor contains multiple dominant frequencies over the entire duration rather than a single dominant frequency. In this paper, the existing methods for tremor filtering are reviewed and two improved algorithms are presented. A comparative study is conducted on all the estimation methods with tremor data from microsurgeons and novice subjects under different conditions. Our results showed that the new improved algorithms performed better than the existing algorithms for tremor estimation. A procedure to separate the intended motion/drift from the tremor component is formulated. PMID:22163783

  3. Real-time estimation of daily physical activity intensity by a triaxial accelerometer and a gravity-removal classification algorithm.

    PubMed

    Ohkawara, Kazunori; Oshima, Yoshitake; Hikihara, Yuki; Ishikawa-Takata, Kazuko; Tabata, Izumi; Tanaka, Shigeho

    2011-06-01

    We have recently developed a simple algorithm for the classification of household and locomotive activities using the ratio of unfiltered to filtered synthetic acceleration (gravity-removal physical activity classification algorithm, GRPACA) measured by a triaxial accelerometer. The purpose of the present study was to develop a new model for the immediate estimation of daily physical activity intensities using a triaxial accelerometer. A total of sixty-six subjects were randomly assigned into validation (n 44) and cross-validation (n 22) groups. All subjects performed fourteen activities while wearing a triaxial accelerometer in a controlled laboratory setting. During each activity, energy expenditure was measured by indirect calorimetry, and physical activity intensities were expressed as metabolic equivalents (MET). The validation group displayed strong relationships between measured MET and filtered synthetic accelerations for household (r 0·907, P < 0·001) and locomotive (r 0·961, P < 0·001) activities. In the cross-validation group, two GRPACA-based linear regression models provided highly accurate MET estimation for household and locomotive activities. Results were similar when equations were developed by non-linear regression or sex-specific linear or non-linear regressions. Sedentary activities were also accurately estimated by the specific linear regression classified from other activity counts. Therefore, the use of a triaxial accelerometer in combination with a GRPACA permits more accurate and immediate estimation of daily physical activity intensities, compared with previously reported cut-off classification models. This method may be useful for field investigations as well as for self-monitoring by general users.

  4. Accelerometer body sensor network improves systolic time interval assessment with wearable ballistocardiography.

    PubMed

    Wiens, Andrew D; Inan, Omer T

    2015-01-01

    Systolic time intervals (STI) are non-invasive measures of cardiac function. Due to the fact that STI can be measured noninvasively outside the clinic, STI are a promising method for long-term monitoring of patients with cardiovascular disease. In particular, the pre-ejection period (PEP) has been measured successfully from body vibrations of the beating heart, a technique called ballistocardiography (BCG), using a weighing scale. Similar measurements can be made with on-body accelerometers, however these wearable BCG signals are typically more challenging to interpret than whole-body BCG. In this paper, we conducted a small pilot study with four subjects to investigate whether a body sensor network of four accelerometers positioned on the wrist, arm, sternum, and head could improve beat-by-beat PEP prediction beyond that of each sensor alone. Linear models were fitted from the R-J and R-I intervals of the four BCG signals to PEP measured with impedance cardiography from 5-minute recordings after isometric lower-body exercise. Specifically, we found that (i) the RMS error of PEP estimation from the wearable BCG sensors can be reduced by using double integration, (ii) the standard deviation of PEP estimates from R-I intervals was smaller than from R-J intervals, and (iii) linear models combining both R-J and R-I measurements from all sensors resulted in the best average correlation (r(2) = 0.96 ± 0.01) and lowest average root mean square error (2.5 ± 0.8 ms) from 5×2-fold cross validation.

  5. Accelerometer-measured sedentary time among Hispanic adults: Results from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL).

    PubMed

    Merchant, Gina; Buelna, Christina; Castañeda, Sheila F; Arredondo, Elva M; Marshall, Simon J; Strizich, Garrett; Sotres-Alvarez, Daniela; Chambers, Earle C; McMurray, Robert G; Evenson, Kelly R; Stoutenberg, Mark; Hankinson, Arlene L; Talavera, Gregory A

    2015-01-01

    Excessive sedentary behavior is associated with negative health outcomes independent of physical activity. Objective estimates of time spent in sedentary behaviors are lacking among adults from diverse Hispanic/Latino backgrounds. The objective of this study was to describe accelerometer-assessed sedentary time in a large, representative sample of Hispanic/Latino adults living in the United States, and compare sedentary estimates by Hispanic/Latino background, sociodemographic characteristics and weight categories. This study utilized baseline data from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) that included adults aged 18-74 years from four metropolitan areas (N = 16,415). Measured with the Actical accelerometer over 6 days, 76.9% (n = 12,631) of participants had > 10 h/day and > 3 days of data. Participants spent 11.9 h/day (SD 3.0), or 74% of their monitored time in sedentary behaviors. Adjusting for differences in wear time, adults of Mexican background were the least (11.6 h/day), whereas adults of Dominican background were the most (12.3 h/day), sedentary. Women were more sedentary than men, and older adults were more sedentary than younger adults. Household income was positively associated, whereas employment was negatively associated, with sedentary time. There were no differences in sedentary time by weight categories, marital status, or proxies of acculturation. To reduce sedentariness among these populations, future research should examine how the accumulation of various sedentary behaviors differs by background and region, and which sedentary behaviors are amenable to intervention.

  6. Accelerometer-measured sedentary time among Hispanic adults: Results from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL)

    PubMed Central

    Merchant, Gina; Buelna, Christina; Castañeda, Sheila F.; Arredondo, Elva M.; Marshall, Simon J.; Strizich, Garrett; Sotres-Alvarez, Daniela; Chambers, Earle C.; McMurray, Robert G.; Evenson, Kelly R.; Stoutenberg, Mark; Hankinson, Arlene L.; Talavera, Gregory A.

    2015-01-01

    Excessive sedentary behavior is associated with negative health outcomes independent of physical activity. Objective estimates of time spent in sedentary behaviors are lacking among adults from diverse Hispanic/Latino backgrounds. The objective of this study was to describe accelerometer-assessed sedentary time in a large, representative sample of Hispanic/Latino adults living in the United States, and compare sedentary estimates by Hispanic/Latino background, sociodemographic characteristics and weight categories. This study utilized baseline data from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) that included adults aged 18–74 years from four metropolitan areas (N = 16,415). Measured with the Actical accelerometer over 6 days, 76.9% (n = 12,631) of participants had > 10 h/day and > 3 days of data. Participants spent 11.9 h/day (SD 3.0), or 74% of their monitored time in sedentary behaviors. Adjusting for differences in wear time, adults of Mexican background were the least (11.6 h/day), whereas adults of Dominican background were the most (12.3 h/day), sedentary. Women were more sedentary than men, and older adults were more sedentary than younger adults. Household income was positively associated, whereas employment was negatively associated, with sedentary time. There were no differences in sedentary time by weight categories, marital status, or proxies of acculturation. To reduce sedentariness among these populations, future research should examine how the accumulation of various sedentary behaviors differs by background and region, and which sedentary behaviors are amenable to intervention. PMID:26844159

  7. Implementation of a real-time human movement classifier using a triaxial accelerometer for ambulatory monitoring.

    PubMed

    Karantonis, Dean M; Narayanan, Michael R; Mathie, Merryn; Lovell, Nigel H; Celler, Branko G

    2006-01-01

    The real-time monitoring of human movement can provide valuable information regarding an individual's degree of functional ability and general level of activity. This paper presents the implementation of a real-time classification system for the types of human movement associated with the data acquired from a single, waist-mounted triaxial accelerometer unit. The major advance proposed by the system is to perform the vast majority of signal processing onboard the wearable unit using embedded intelligence. In this way, the system distinguishes between periods of activity and rest, recognizes the postural orientation of the wearer, detects events such as walking and falls, and provides an estimation of metabolic energy expenditure. A laboratory-based trial involving six subjects was undertaken, with results indicating an overall accuracy of 90.8% across a series of 12 tasks (283 tests) involving a variety of movements related to normal daily activities. Distinction between activity and rest was performed without error; recognition of postural orientation was carried out with 94.1% accuracy, classification of walking was achieved with less certainty (83.3% accuracy), and detection of possible falls was made with 95.6% accuracy. Results demonstrate the feasibility of implementing an accelerometry-based, real-time movement classifier using embedded intelligence.

  8. Use of Accelerometers to Examine Sedentary Time on an Acute Stroke Unit

    PubMed Central

    Mattlage, Anna E.; Redlin, Sara A.; Rippee, Michael A.; Abraham, Michael G.; Rymer, Marilyn M.; Billinger, Sandra A.

    2015-01-01

    Background and Purpose Observational studies demonstrate low levels of physical activity during in-patient stroke rehabilitation. There is no objective measure of sedentary time on the acute stroke unit and whether sedentary time is related to functional outcomes. The purpose of this study was to characterize sedentary time after acute stroke and determine whether there is a relationship to functional performance at discharge. Methods Thirty-two individuals (18 males; 56.5 ± 12.7 years) with acute stroke were enrolled within 48 hours of hospital admission. An accelerometer was placed on the stroke-affected ankle to measure 24-hour activity and was worn for 4 days or until discharge from the hospital. Performance of activities of daily living, walking endurance, and functional mobility was assessed using the Physical Performance Test (PPT), Six-Minute Walk Test (6MWT), and Timed-Up and Go (TUG), respectively. Results Mean percent time spent sedentary was 93.9 ± 4.1% and percent time in light activity was 5.1 ± 2.4%. When controlling for baseline performance, the mean time spent sedentary per day was significantly related to PPT performance at discharge (r = −0.37; p = 0.05), but not the 6MWT or TUG. Discussion and Conclusions Patients with acute stroke were sedentary most of their hospital stay. To minimize the potential negative effects of inactivity, our data suggest that there should be an emphasis towards increasing physical activity during the hospital stay. Video Abstract available for more insights from the authors (See Video, Supplemental Digital Content 1). PMID:26035120

  9. Quasi-Real Time Estimation of Angular Kinematics Using Single-Axis Accelerometers

    PubMed Central

    Caroselli, Alessio; Bagalà, Fabio; Cappello, Angelo

    2013-01-01

    In human movement modeling, the problem of multi-link kinematics estimation by means of inertial measurement units has been investigated by several authors through efficient sensor fusion algorithms. In this perspective a single inertial measurement unit per link is required. This set-up is not cost-effective compared with a solution in which a single-axis accelerometer per link is used. In this paper, a novel fast technique is presented for the estimation of the sway angle in a multi-link chain by using a single-axis accelerometer per segment and by setting the boundary conditions through an ad hoc algorithm. The technique, based on the windowing of the accelerometer output, was firstly tested on a mechanical arm equipped with a single-axis accelerometer and a reference encoder. The technique is then tested on a subject performing a squat task for the knee flexion-extension angle evaluation by using two single-axis accelerometers placed on the thigh and shank segments, respectively. A stereo-photogrammetric system was used for validation. RMSEs (mean ± std) are 0.40 ± 0.02° (mean peak-to-peak range of 147.2 ± 4.9°) for the mechanical inverted pendulum and 1.01 ± 0.11° (mean peak-to-peak range of 59.29 ± 2.02°) for the knee flexion-extension angle. Results obtained in terms of RMSE were successfully compared with an Extended Kalman Filter applied to an inertial measurement unit. These results suggest the usability of the proposed algorithm in several fields, from automatic control to biomechanics, and open new opportunities to increase the accuracy of the existing tools for orientation evaluation. PMID:23322097

  10. Quasi-real time estimation of angular kinematics using single-axis accelerometers.

    PubMed

    Caroselli, Alessio; Bagalà, Fabio; Cappello, Angelo

    2013-01-15

    In human movement modeling, the problem of multi-link kinematics estimation by means of inertial measurement units has been investigated by several authors through efficient sensor fusion algorithms. In this perspective a single inertial measurement unit per link is required. This set-up is not cost-effective compared with a solution in which a single-axis accelerometer per link is used. In this paper, a novel fast technique is presented for the estimation of the sway angle in a multi-link chain by using a single-axis accelerometer per segment and by setting the boundary conditions through an ad hoc algorithm. The technique, based on the windowing of the accelerometer output, was firstly tested on a mechanical arm equipped with a single-axis accelerometer and a reference encoder. The technique is then tested on a subject performing a squat task for the knee flexion-extension angle evaluation by using two single-axis accelerometers placed on the thigh and shank segments, respectively. A stereo-photogrammetric system was used for validation. RMSEs (mean ± std) are 0.40 ± 0.02° (mean peak-to-peak range of 147.2 ± 4.9°) for the mechanical inverted pendulum and 1.01 ± 0.11° (mean peak-to-peak range of 59.29 ± 2.02°) for the knee flexion-extension angle. Results obtained in terms of RMSE were successfully compared with an Extended Kalman Filter applied to an inertial measurement unit. These results suggest the usability of the proposed algorithm in several fields, from automatic control to biomechanics, and open new opportunities to increase the accuracy of the existing tools for orientation evaluation.

  11. Evaluation of a single accelerometer based biofeedback system for real-time correction of neck posture in computer users.

    PubMed

    Breen, Paul P; Nisar, Aamer; Olaighin, Gearoid

    2009-01-01

    The worldwide adoption of computers is closely linked to increased prevalence in neck and shoulder pain. Many ergonomic interventions are available; however, the lifetime prevalence of neck pain is still estimated as high as 80%. This paper introduces a biofeedback system using a novel single accelerometer placement. This system allows the user to react and correct for movement into a position of bad posture. The addition of visual information provides artificial proprioceptive information on the cranial-vertebral angle. Six subjects were tested for 5 hours with and without biofeedback. All subjects had a significant decrease in the percentage of time spent in bad posture when using biofeedback. PMID:19965101

  12. Passive Accelerometer

    NASA Technical Reports Server (NTRS)

    Naumann, Robert J.; Baugher, Charles; Alexander, Iwan

    1992-01-01

    Motion of ball in liquid indicates acceleration. Passive accelerometer measures small accelerations along cylindrical axis. Principle of operation based on Stokes' law. Provides accurate measurements of small quasi-steady accelerations. Additional advantage, automatically integrates out unwanted higher-frequency components of acceleration.

  13. Association between accelerometer-measured physical activity intensities and sedentary time in 8- to 10-year-old children.

    PubMed

    Herman, Katya M; Paradis, Gilles; Mathieu, Marie-Eve; O'Loughlin, Jennifer; Tremblay, Angelo; Lambert, Marie

    2014-02-01

    This study examines the association between objectively-measured physical activity (PA) intensities and sedentary behavior (SED) in a cohort of 532 children aged 8-10 y. PA and SED were assessed by accelerometer over 7-days. Television and computer/video-game use were self-reported. Associations between PA intensities and SED variables were assessed by Spearman correlations and adjusted multiple linear regression. Higher mean daily moderate-to-vigorous and vigorous PA (MVPA, VPA) were negatively associated with mean daily SED (r = -0.47 and -0.37; p < .001), and positively associated with mean daily total PA (r = .58 and 0.46; p < .001). MVPA was also positively associated with light PA (LPA; r = .26, p < .001). MVPA and VPA were not significantly associated with TV, computer/video or total screen time; accelerometer SED was only weakly associated with specific SED behaviors. On average, for each additional 10 min daily MVPA, children accumulated >14 min less SED, and for each additional 5 min VPA, 11 min less SED. Thus, over the course of a week, higher mean daily MVPA may displace SED time and is associated with higher total PA over and above the additional MVPA, due to concomitant higher levels of LPA. Public health strategies should target both MVPA and SED to improve overall PA and health in children. PMID:24018974

  14. Investigation of the time-dependent wear behavior of veneering ceramic in porcelain fused to metal crowns during chewing simulations.

    PubMed

    Guo, Jiawen; Tian, Beimin; Wei, Ran; Wang, Weiguo; Zhang, Hongyun; Wu, Xiaohong; He, Lin; Zhang, Shaofeng

    2014-12-01

    The excessive abrasion of occlusal surfaces in ceramic crowns limits the service life of restorations and their clinical results. However, little is known about the time-dependent wear behavior of ceramic restorations during the chewing process. The aim of this in vitro study was to investigate the dynamic evolution of the wear behavior of veneering porcelain in PFM crowns as wear progressed, as tested in a chewing simulator. Twenty anatomical metal-ceramic crowns were prepared using Ceramco III as the veneering porcelain. Stainless steel balls served as antagonists. The specimens were dynamically loaded in a chewing simulator with 350N up to 2.4×10(6) loading cycles, with additional thermal cycling between 5 and 55°C. During the testing, several checkpoints were applied to measure the substance loss of the crowns' occlusal surfaces and to evaluate the microstructure of the worn areas. After 2.4×10(6) cycles, the entire wear process of the veneering porcelain in the PFM crowns revealed three wear stages (running-in, steady and severe wear stages). The occlusal surfaces showed traces of intensive wear on the worn areas during the running-in wear stage, and they exhibited the propagation of cracks in the subsurface during steady wear stage. When the severe wear stage was reached, the cracks penetrated the ceramic layer, causing the separation of porcelain pieces. It also exhibited a good correlation among the microstructure, the wear loss and the wear rate of worn ceramic restorations. The results suggest that under the conditions of simulated masticatory movement, the wear performance of the veneering porcelain in PFM crowns indicates the apparent similarity of the tribological characteristics of the traditional mechanical system. Additionally, the evaluation of the wear behavior of ceramic restorations should be based on these three wear stages. PMID:25194522

  15. Investigation of the time-dependent wear behavior of veneering ceramic in porcelain fused to metal crowns during chewing simulations.

    PubMed

    Guo, Jiawen; Tian, Beimin; Wei, Ran; Wang, Weiguo; Zhang, Hongyun; Wu, Xiaohong; He, Lin; Zhang, Shaofeng

    2014-12-01

    The excessive abrasion of occlusal surfaces in ceramic crowns limits the service life of restorations and their clinical results. However, little is known about the time-dependent wear behavior of ceramic restorations during the chewing process. The aim of this in vitro study was to investigate the dynamic evolution of the wear behavior of veneering porcelain in PFM crowns as wear progressed, as tested in a chewing simulator. Twenty anatomical metal-ceramic crowns were prepared using Ceramco III as the veneering porcelain. Stainless steel balls served as antagonists. The specimens were dynamically loaded in a chewing simulator with 350N up to 2.4×10(6) loading cycles, with additional thermal cycling between 5 and 55°C. During the testing, several checkpoints were applied to measure the substance loss of the crowns' occlusal surfaces and to evaluate the microstructure of the worn areas. After 2.4×10(6) cycles, the entire wear process of the veneering porcelain in the PFM crowns revealed three wear stages (running-in, steady and severe wear stages). The occlusal surfaces showed traces of intensive wear on the worn areas during the running-in wear stage, and they exhibited the propagation of cracks in the subsurface during steady wear stage. When the severe wear stage was reached, the cracks penetrated the ceramic layer, causing the separation of porcelain pieces. It also exhibited a good correlation among the microstructure, the wear loss and the wear rate of worn ceramic restorations. The results suggest that under the conditions of simulated masticatory movement, the wear performance of the veneering porcelain in PFM crowns indicates the apparent similarity of the tribological characteristics of the traditional mechanical system. Additionally, the evaluation of the wear behavior of ceramic restorations should be based on these three wear stages.

  16. Wear rate quantifying in real-time using the charged particle surface activation

    NASA Astrophysics Data System (ADS)

    Alexandreanu, B.; Popa-Simil, L.; Voiculescu, D.; Racolta, P. M.

    1997-02-01

    Surface activation, commonly known as Thin Layer Activation (TLA), is currently employed in over 30 accelerator laboratories around the world for wear and/or corrosion monitoring in industrial plants [1-6]. TLA was primarily designed and developed to meet requirements of potential industrial partners, in order to transfer this technique from research to industry. The method consists of accelerated ion bombardment of a surface of interest, e.g., a machine part subjected to wear. Loss of material owing to wear, erosive corrosion or abrasion is characterized by monitoring the resultant changes in radioactivity. In principle, depending upon the case at hand, one may choose to measure either the remnant activity of the component of interest or to monitor the activity of the debris. For applications of the second type, especially when a lubricating agent is involved, dedicated installations have been constructed and adapted to an engine or a tribological testing stand in order to assure oil circulation around an externally placed detection gauge. This way, the wear particles suspended in the lubricant can be detected and the material loss rates quantified in real time. Moreover, in specific cases, such as the one presented in this paper, remnant activity measurements prove to be useful tools for complementary results. This paper provides a detailed presentation of such a case: in situ resistance-to-wear testing of two types of piston rings.

  17. Wear-time recording during early Class III facemask treatment using TheraMon chip technology.

    PubMed

    Stocker, Bruce; Willmann, Jan H; Wilmes, Benedict; Vasudavan, Sivabalan; Drescher, Dieter

    2016-09-01

    Successful intervention in a developing Class III malocclusion with facemask protraction therapy depends on a patient's ability to adhere to the recommendations for duration of appliance wear. In this article, we report the introduction of a novel approach for tracking of the duration of application of a protraction facemask, with the incorporation of a "FaceMon" sensor (TheraMon, microelectronic system; MC Technology GmbH, Hargelsberg, Austria) to track wear time. A 9-year-old boy with a Class III malocclusion was successfully treated with a modified alternate rapid maxillary expansion and constriction protocol and intermittent application of a hybrid hyrax-protraction facemask combination. The average duration of wear of the facemask was measured at 10.8 hours per day. The use of an objective measuring device may have implications for the development of treatment strategies, since patient responses may be able to calibrated in relation to compliance. PMID:27585783

  18. Varying the Wear Time of the Methylphenidate Transdermal System in Children with Attention-Deficit/Hyperactivity Disorder

    ERIC Educational Resources Information Center

    Wilens, Timothy E.; Boellner, Samuel W.; Lopez, Frank A.; Turnbow, John M.; Wigal, Sharon B.; Childress, Ann C.; Abikoff, Howard B.; Manos, Michael J.

    2008-01-01

    A study investigated the impact of variable wear times of the methylphenidate transdermal system in children with attention-deficit/hyperactivity disorder (ADHD). It was concluded that duration of medication effect was directly related to the wear time of the methylphenidate transdermal system patch.

  19. Python microgravity accelerometer system

    NASA Astrophysics Data System (ADS)

    Nijhawan, V.; Arrott, A. P.; Grimes, R. S.

    1989-01-01

    A microgravity accelerometer system developed for use in the Space Shuttle middeck locker is described. The system, known as PYTHON, is a microcomputer-based digital acceleration-measurement system that uses primarily off-the-shelf qualified space hardware and modular software. It can be operated on-board in real time and on the ground either during the flight or post-flight. The sensor head consists of an accelerometer, which measures acceleration in three orthogonal axes, and an internal thermister for temperature compensation; threshold and resolution are better than 0.000001 g. The results of acceleration measurements with PYTHON carried out during parabolic maneuvers aboard the NASA's KC-135 aircraft are presented.

  20. Towards Real-Time Detection of Freezing of Gait Using Wavelet Transform on Wireless Accelerometer Data

    PubMed Central

    Rezvanian, Saba; Lockhart, Thurmon E.

    2016-01-01

    Injuries associated with fall incidences continue to pose a significant burden to persons with Parkinson’s disease (PD) both in terms of human suffering and economic loss. Freezing of gait (FOG), which is one of the symptoms of PD, is a common cause of falls in this population. Although a significant amount of work has been performed to characterize/detect FOG using both qualitative and quantitative methods, there remains paucity of data regarding real-time detection of FOG, such as the requirements for minimum sensor nodes, sensor placement locations, and appropriate sampling period and update time. Here, the continuous wavelet transform (CWT) is employed to define an index for correctly identifying FOG. Since the CWT method uses both time and frequency components of a waveform in comparison to other methods utilizing only the frequency component, we hypothesized that using this method could lead to a significant improvement in the accuracy of FOG detection. We tested the proposed index on the data of 10 PD patients who experience FOG. Two hundred and thirty seven (237) FOG events were identified by the physiotherapists. The results show that the index could discriminate FOG in the anterior–posterior axis better than other two axes, and is robust to the update time variability. These results suggest that real time detection of FOG may be realized by using CWT of a single shank sensor with window size of 2 s and update time of 1 s (82.1% and 77.1% for the sensitivity and specificity, respectively). Although implicated, future studies should examine the utility of this method in real-time detection of FOG. PMID:27049389

  1. The Effects of Daily Weather on Accelerometer-measured Physical Activity among Adults with Arthritis

    PubMed Central

    Feinglass, Joe; Lee, Julia; Dunlop, Dorothy; Song, Jing; Semanik, Pam; Chang, Rowland W.

    2010-01-01

    Background This study analyzes Chicago-area weather effects on objectively measured physical activity over a three year period among a cohort of 241 participants in an on-going arthritis physical activity trial. Methods Uniaxial accelerometer counts and interview data were analyzed for up to six weekly study waves involving 4823 days of wear. The effects of temperature, rainfall, snowfall and daylight hours were analyzed after controlling for participant characteristics, day of the week, and daily accelerometer wear hours in a mixed effects linear regression model. Results Daylight hours, mean daily temperature <20 or ≥ 75 degrees and light or heavy rainfall (but not snowfall) were all significantly associated with lower physical activity after controlling for the significant effects of weekends, accelerometer wear hours, age, sex, type of arthritis, employment, Hispanic ethnicity, obesity, and SF36 physical and mental health scores. Conclusions The cumulative effects of weather are reflected in a 38.3% mean monthly difference in daily counts between November and June, reflecting over three additional hours of sedentary time. Physical activity promotion programs for older persons with chronic conditions need lifestyle physical activity plans adapted to weather extremes. PMID:21885884

  2. Does Wearing Textured Insoles during Non-class Time Improve Proprioception in Professional Dancers?

    PubMed

    Steinberg, N; Tirosh, O; Adams, R; Karin, J; Waddington, G

    2015-11-01

    This study sought to determine whether textured insoles inserted in the sports shoes of young dancers improved their inversion and eversion ankle movement discrimination. 26 ballet dancers (14 female, 12 male) from the Australian Ballet School, ages 14-19 years, were divided into 2 groups according to sex and class levels. During the first 4 weeks, the first intervention group (GRP1) was asked to wear textured insoles in their sports shoes during non-class periods, and the second intervention group (GRP2) followed standard practice. In the next 4 weeks, GRP2 was asked to wear the textured insoles and GRP1 did not wear the textured insoles. Participants were tested pre-intervention, after 4 weeks, and at 8 weeks for both inversion and eversion ankle discrimination. In both inversion and eversion testing positions, interaction was found between the 2 groups and the 3 testing times (p<0.001), with significant differences between the first testing and the second testing (p=0.038 and p=0.019, respectively), and between the third testing and the second testing (p=0.003 and p=0.029, respectively). In conclusion, the stimulation to the proprioceptive system arising from textured insoles worn for 4 weeks was sufficient to improve the ankle proprioception of ballet dancers, in both inversion and eversion movements.

  3. Multimilling-Insert Wear Assessment Using Non-Linear Virtual Sensor, Time-Frequency Distribution and Neural Networks

    NASA Astrophysics Data System (ADS)

    James Li, C.; Tzeng, Tzong-Chyi

    2000-11-01

    The objective of this study is to establish a signal processing methodology that can infer the state of milling insert wear from translational vibration measured on the spindle housing of a milling machine. First, the tool wear signature in a translational vibration is accentuated by mapping the translational vibration into a torsional vibration using a previously identified non-linear relationship between the two, i.e. a virtual sensor. Second, a time-frequency distribution, i.e. a Choi-Williams distribution, is calculated from the torsional vibration. Third, scattering matrices and orthogonalisation are employed to identify the time-frequency components that are best correlated to the state of wear. Fourth, a neural network is trained to estimate the extent of wear from these critical time frequency components. The combination of the virtual sensor, time-frequency analysis and neural network is then validated with data obtained from real cutting tests.

  4. Physiological tolerance times while wearing explosive ordnance disposal protective clothing in simulated environmental extremes.

    PubMed

    Stewart, Ian B; Stewart, Kelly L; Worringham, Charles J; Costello, Joseph T

    2014-01-01

    Explosive ordnance disposal (EOD) technicians are required to wear protective clothing to protect themselves from the threat of overpressure, fragmentation, impact and heat. The engineering requirements to minimise these threats results in an extremely heavy and cumbersome clothing ensemble that increases the internal heat generation of the wearer, while the clothing's thermal properties reduce heat dissipation. This study aimed to evaluate the heat strain encountered wearing EOD protective clothing in simulated environmental extremes across a range of differing work intensities. Eight healthy males [age 25 ± 6 years (mean ± sd), height 180 ± 7 cm, body mass 79 ± 9 kg, VO2max 57 ± 6 ml(.) kg(-1.)min(-1)] undertook nine trials while wearing an EOD9 suit (weighing 33.4 kg). The trials involved walking on a treadmill at 2.5, 4 and 5.5 km ⋅ h(-1) at each of the following environmental conditions, 21, 30 and 37 °C wet bulb globe temperature (WBGT) in a randomised controlled crossover design. The trials were ceased if the participants' core temperature reached 39 °C, if heart rate exceeded 90% of maximum, if walking time reached 60 minutes or due to fatigue/nausea. Tolerance times ranged from 10-60 minutes and were significantly reduced in the higher walking speeds and environmental conditions. In a total of 15 trials (21%) participants completed 60 minutes of walking; however, this was predominantly at the slower walking speeds in the 21 °C WBGT environment. Of the remaining 57 trials, 50 were ceased, due to attainment of 90% maximal heart rate. These near maximal heart rates resulted in moderate-high levels of physiological strain in all trials, despite core temperature only reaching 39 °C in one of the 72 trials. PMID:24586228

  5. Physiological Tolerance Times while Wearing Explosive Ordnance Disposal Protective Clothing in Simulated Environmental Extremes

    PubMed Central

    Stewart, Ian B.; Stewart, Kelly L.; Worringham, Charles J.; Costello, Joseph T.

    2014-01-01

    Explosive ordnance disposal (EOD) technicians are required to wear protective clothing to protect themselves from the threat of overpressure, fragmentation, impact and heat. The engineering requirements to minimise these threats results in an extremely heavy and cumbersome clothing ensemble that increases the internal heat generation of the wearer, while the clothing’s thermal properties reduce heat dissipation. This study aimed to evaluate the heat strain encountered wearing EOD protective clothing in simulated environmental extremes across a range of differing work intensities. Eight healthy males [age 25±6 years (mean ± sd), height 180±7 cm, body mass 79±9 kg, V˙O2max 57±6 ml.kg−1.min−1] undertook nine trials while wearing an EOD9 suit (weighing 33.4 kg). The trials involved walking on a treadmill at 2.5, 4 and 5.5 km⋅h−1 at each of the following environmental conditions, 21, 30 and 37°C wet bulb globe temperature (WBGT) in a randomised controlled crossover design. The trials were ceased if the participants’ core temperature reached 39°C, if heart rate exceeded 90% of maximum, if walking time reached 60 minutes or due to fatigue/nausea. Tolerance times ranged from 10–60 minutes and were significantly reduced in the higher walking speeds and environmental conditions. In a total of 15 trials (21%) participants completed 60 minutes of walking; however, this was predominantly at the slower walking speeds in the 21°C WBGT environment. Of the remaining 57 trials, 50 were ceased, due to attainment of 90% maximal heart rate. These near maximal heart rates resulted in moderate-high levels of physiological strain in all trials, despite core temperature only reaching 39°C in one of the 72 trials. PMID:24586228

  6. Wearable accelerometer in clinical use.

    PubMed

    Tamura, Toshiyo

    2005-01-01

    To improve the equality of life, we must prevent the falls in both healthy elderly and patients with the cerebrovascular diseases. Wearable accelerometer was applied to monitor. In this paper, we introduced two different clinical applications. On is fall detector and the other is monitoring device for screening test. 1) We have developed body-worn accelerometer with data loggers and monitored the daily of life in patient with Parkinson disease. The patients wore the device and monitored falls while walking and standing. As a result, we could obtain fall times for a long period. 2) The ability of walking and standing have been evaluated by Timed up & go test. We used telemetry with accelerometer. The stability of walking could be evaluated by the acceleration signals. The simple body-won device can be useful for fall study.

  7. Detection of brake wear aerosols by aerosol time-of-flight mass spectrometry

    NASA Astrophysics Data System (ADS)

    Beddows, D. C. S.; Dall'Osto, M.; Olatunbosun, O. A.; Harrison, Roy M.

    2016-03-01

    Brake dust particles were characterised using an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) operated using two inlet configurations, namely the aerodynamic lens (AFL) inlet and countersunk nozzle inlet. Laboratory studies show that dust particles are characterised by mass spectra containing ions deriving from Fe and Ba and although highly correlated to each other, the Fe and Ba signals were mostly detected using the nozzle inlet with relatively high laser desorption energies. When using the AFL, only [56Fe] and [-88FeO2] ions were observed in brake dust spectra generated using lower laser desorption pulse energies, and only above 0.75 mJ was the [138Ba] ion detected. When used with the preferred nozzle inlet configuration, the [-88FeO2] peak was considered to be the more reliable tracer peak, because it is not present in other types of dust (mineral, tyre, Saharan etc). As shown by the comparison with ambient data from a number of locations, the aerodynamic lens is not as efficient in detecting brake wear particles, with less than 1% of sampled particles attributed to brake wear. Five field campaigns within Birmingham (background, roadside (3) and road tunnel) used the nozzle inlet and showed that dust particles (crustal and road) accounted for between 3.1 and 65.9% of the particles detected, with the remaining particles being made up from varying percentages of other constituents.

  8. Radiological Outcomes and Operative Time following Total Knee Arthroplasty using Accelerometer-based, Portable Navigation versus Conventional Inter-Medullary Alignment Guides

    PubMed Central

    MacDessi, Samuel; Solayar, GN; Thatcher, N; Chen, Darren B

    2016-01-01

    Objectives: Accelerometer-based, portable navigation instrumentation is a new method of achieving desired resection alignments in total knee arthroplasty (TKA). Methods: After randomisation and the application of exclusion criteria, 79 knees were analysed. 42 patients which underwent TKA using conventional intra-medullary (IM) alignment guides were compared to 37 patients with the use of accelerometer-based, portable navigation device (KneeAlign; OrthoAlign Inc, Aliso Viejo, California). Radiographic results were obtained from post-operative computer-tomography following the CT Perth Protocol. Results: In the IM cohort, 81.0% of patients had a coronal alignment within 3° of a neutral mechanical axis (vs 83.8% with KneeAlign, p=0.74), 81.0% had a femoral coronal alignment within 2° of perpendicular to the femoral mechanical axis (vs 89.2% with KneeAlign, p=0.31), and 92.9% had a tibial coronal alignment within 2° of perpendicular to the tibial mechanical axis (vs 81.1% with KneeAlign, p=0.12). Regarding sagittal alignment, the IM cohort had 90.5% of patients with femoral component alignment within 2° of optimum (vs 91.9% with KneeAlign, p=0.83) and 92.9% had a tibial component alignment within 2° of the optimal tibial slope (vs 89.2% with KneeAlign, p=0.57). The mean tourniquet time (from incision to completion of coronal bone resections) in the IM cohort was 16.5± 8.9 minutes vs 22.2 ± 7.6 minutes in the KneeAlign cohort (p<0.003). Conclusion: Accelerometer-based, portable navigation has a statistically similar outcome in alignment following TKA as IM guides. It is noted that using the portable navigation device does prolong surgical time compared to conventional IM surgery and this may be due to the learning curve.

  9. Understanding wear in dentistry.

    PubMed

    Mair, L H

    1999-01-01

    Tooth wear is an increasing problem in dentistry. Traditionally, it has been divided into three categories: abrasion, attrition, and erosion. However, most clinical cases of tooth wear involve more than one of these processes. It is often easier to make a diagnosis by looking for the signs of the fundamental wear processes rather than trying to categorize the individual case. Wear can be caused by direct surface-to-surface wear, an intervening slurry, or a corrosive environment. Wear occurs during mastication, but also at other times, often at night. Although it may be possible to institute a preventive regimen, this will not always help the patient if his or her prime concern is esthetics. The same processes that cause tooth wear will cause wear to restorative materials. To diagnose and prevent wear, its processes must be understood.

  10. Assessing Stride Variables and Vertical Stiffness with GPS-Embedded Accelerometers: Preliminary Insights for the Monitoring of Neuromuscular Fatigue on the Field

    PubMed Central

    Buchheit, Martin; Gray, Andrew; Morin, Jean-Benoit

    2015-01-01

    The aim of the present study was to examine the ability of a GPS-imbedded accelerometer to assess stride variables and vertical stiffness (K), which are directly related to neuromuscular fatigue during field-based high-intensity runs. The ability to detect stride imbalances was also examined. A team sport player performed a series of 30-s runs on an instrumented treadmill (6 runs at 10, 17 and 24 km·h-1) with or without his right ankle taped (aimed at creating a stride imbalance), while wearing on his back a commercially-available GPS unit with an embedded 100-Hz tri-axial accelerometer. Contact (CT) and flying (FT) time, and K were computed from both treadmill and accelerometers (Athletic Data Innovations) data. The agreement between treadmill (criterion measure) and accelerometer-derived data was examined. We also compared the ability of the different systems to detect the stride imbalance. Biases were small (CT and K) and moderate (FT). The typical error of the estimate was trivial (CT), small (K) and moderate (FT), with nearly perfect (CT and K) and large (FT) correlations for treadmill vs. accelerometer. The tape induced very large increase in the right - left foot ∆ in CT, FT and K measured by the treadmill. The tape effect on CT and K ∆ measured with the accelerometers were also very large, but of lower magnitude than with the treadmill. The tape effect on accelerometer-derived ∆ FT was unclear. Present data highlight the potential of a GPS-embedded accelerometer to assess CT and K during ground running. Key points GPS-embedded tri-axial accelerometers may be used to assess contact time and vertical stiffness during ground running. These preliminary results open new perspective for the field monitoring of neuromuscular fatigue and performance in run-based sports PMID:26664264

  11. A real-time and self-calibrating algorithm based on triaxial accelerometer signals for the detection of human posture and activity.

    PubMed

    Curone, Davide; Bertolotti, Gian Mario; Cristiani, Andrea; Secco, Emanuele Lindo; Magenes, Giovanni

    2010-07-01

    Assessment of human activity and posture with triaxial accelerometers provides insightful information about the functional ability: classification of human activities in rehabilitation and elderly surveillance contexts has been already proposed in the literature. In the meanwhile, recent technological advances allow developing miniaturized wearable devices, integrated within garments, which may extend this assessment to novel tasks, such as real-time remote surveillance of workers and emergency operators intervening in harsh environments. We present an algorithm for human posture and activity-level detection, based on the real-time processing of the signals produced by one wearable triaxial accelerometer. The algorithm is independent of the sensor orientation with respect to the body. Furthermore, it associates to its outputs a "reliability" value, representing the classification quality, in order to launch reliable alarms only when effective dangerous conditions are detected. The system was tested on a customized device to estimate the computational resources needed for real-time functioning. Results exhibit an overall 96.2% accuracy when classifying both static and dynamic activities.

  12. The effect of real-time aging on the oxidation and wear of highly cross-linked UHMWPE acetabular liners.

    PubMed

    Wannomae, Keith K; Christensen, Steven D; Freiberg, Andrew A; Bhattacharyya, Shayan; Harris, William H; Muratoglu, Orhun Kamil

    2006-03-01

    Irradiation decreases the wear of ultra-high molecular weight polyethylene (UHMWPE) but generates residual free radicals, precursors to long-term oxidation. Melting or annealing is used in quenching free radicals. We hypothesized that irradiated and once-annealed UHMWPE would oxidize while irradiated and melted UHMWPE would not, and that the oxidation in the former would increase wear. Acetabular liners were real-time aged by immersion in an aqueous environment that closely mimicked the temperature and oxygen concentration of synovial fluid. After 95 weeks of real-time aging, once-annealed components were oxidized; the melted components were not. The wear rate of the real-time aged irradiated and once-annealed components was higher than the literature reported values of other contemporary highly cross-linked UHMWPEs. Single annealing after irradiation used with terminal gamma sterilization may adversely affect the long-term oxidative stability of UHMWPE components.

  13. New accelerometers under development

    NASA Technical Reports Server (NTRS)

    Wald, Jerry; Tehrani, M.

    1990-01-01

    The commercial viability of the Space Station requires that it provide a micro-g, or submicro-g environment to users. This represents significant improvement over existing systems. Attainment of the lowest micro-g levels requires isolation systems. Passive and active systems have been evaluated. Best performance is achieved using active approaches where accelerometer sensors close feedback loops. Two emerging accelerometer technologies are presented that have promise for meeting performance goals while achieving reductions of package size, weight, and power. The technologies addressed are Honeywell's design concept for an optical cavity locking accelerometer and the recent development of an integrated silicon accelerometer for government applications.

  14. Using RFID and accelerometer-embedded tracers to measure probabilities of bed load transport, step lengths, and rest times in a mountain stream

    NASA Astrophysics Data System (ADS)

    Olinde, Lindsay; Johnson, Joel P. L.

    2015-09-01

    We present new measurements of bed load tracer transport in a mountain stream over several snowmelt seasons. Cumulative displacements were measured using passive tracers, which consisted of gravel and cobbles embedded with radio frequency identification tags. The timing of bed load motion during 11 transporting events was quantified with active tracers, i.e., accelerometer-embedded cobbles. Probabilities of cobble transport increased with discharge above a threshold, and exhibited slight to moderate hysteresis during snowmelt hydrographs. Dividing cumulative displacements by the number of movements recorded by each active tracer constrained average step lengths. Average step lengths increased with discharge, and distributions of average step lengths and cumulative displacements were thin tailed. Distributions of rest times followed heavy-tailed power law scaling. Rest time scaling varied somewhat with discharge and with the degree to which tracers were incorporated into the streambed. The combination of thin-tailed displacement distributions and heavy-tailed rest time distributions predict superdiffusive dispersion.

  15. Hybridizing matter-wave and classical accelerometers

    SciTech Connect

    Lautier, J.; Volodimer, L.; Hardin, T.; Merlet, S.; Lours, M.; Pereira Dos Santos, F.; Landragin, A.

    2014-10-06

    We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performance without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely, the dead times between consecutive measurements.

  16. Hybridizing matter-wave and classical accelerometers

    NASA Astrophysics Data System (ADS)

    Lautier, J.; Volodimer, L.; Hardin, T.; Merlet, S.; Lours, M.; Pereira Dos Santos, F.; Landragin, A.

    2014-10-01

    We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performance without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely, the dead times between consecutive measurements.

  17. Ultracold-Atom Accelerometers

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1995-01-01

    Proposed class of accelerometers and related motion sensors based on use of ultracold atoms as inertial components of motion transducers. Ultracold atoms supplant spring-and-mass components of older accelerometers. As used here, "ultracold atoms" means atoms with kinetic energies equivalent to temperatures equal to or less than 20 mK. Acclerometers essentially frictionless. Primary advantage high sensitivity.

  18. Validation of a wireless accelerometer network for energy expenditure measurement.

    PubMed

    Montoye, Alexander H K; Dong, Bo; Biswas, Subir; Pfeiffer, Karin A

    2016-11-01

    The purpose of this study was to validate a wireless network of accelerometers and compare it to a hip-mounted accelerometer for predicting energy expenditure in a semi-structured environment. Adults (n = 25) aged 18-30 engaged in 14 sedentary, ambulatory, exercise, and lifestyle activities over a 60-min protocol while wearing a portable metabolic analyser, hip-mounted accelerometer, and wireless network of three accelerometers worn on the right wrist, thigh, and ankle. Participants chose the order and duration of activities. Artificial neural networks were created separately for the wireless network and hip accelerometer for energy expenditure prediction. The wireless network had higher correlations (r = 0.79 vs. r = 0.72, P < 0.01) but similar root mean square error (2.16 vs. 2.09 METs, P > 0.05) to the hip accelerometer. Measured (from metabolic analyser) and predicted energy expenditure from the hip accelerometer were significantly different for the 3 of the 14 activities (lying down, sweeping, and cycle fast); conversely, measured and predicted energy expenditure from the wireless network were not significantly different for any activity. In conclusion, the wireless network yielded a small improvement over the hip accelerometer, providing evidence that the wireless network can produce accurate estimates of energy expenditure in adults participating in a range of activities.

  19. Obtaining Accelerometer Data in a National Cohort of Black and White Adults

    PubMed Central

    Howard, Virginia J.; Rhodes, J. David; Mosher, Aleena; Hutto, Brent; Stewart, Margaret S.; Colabianchi, Natalie; Vena, John E.; Blair, Steven N.; Hooker, Steven P.

    2014-01-01

    Purpose To report methodological details and feasibility of conducting an accelerometer ancillary study in a large U.S. cohort being followed for stroke and cognitive decline. Methods REGARDS is a national, population-based study of 30,239 blacks and whites, aged ≥ 45 years, enrolled January 2003–October 2007. Baseline evaluations were conducted through computer-assisted telephone interview (CATI) and an in-home visit. Participants are followed by CATI every 6 months. Starting with May 2009 follow-up, contingent on accelerometer availability, participants were invited to wear an accelerometer for 7 days. Device inventory was 1,150. Accelerometer, instructions, log sheet and stamped addressed return envelope were mailed to consenting participants. Postcard acknowledgement and reminders, and ≤ two calls were made to encourage compliance. Results Between May 2009 and January 2013, 20,076 were invited to participate; 12,146 (60.5%) consented. Participation rates by race-sex groups were similar: black women 58.6%, black men 59.6%, white women 62.3% and white men 60.5%. Mean age of the 12,146 participants to whom devices were shipped was 63.5 ± 8.7 years. Return rate was 92%. Of 11,174 returned, 1,187 were not worn, 14 had device malfunction, and of 9,973 with data, 8,096 (81.2%) provided usable data, defined as ≥ 4 days of 10+ hours of wear time, ranging from 74.4% among black women to 85.2% among white men. Conclusions Using mail and telephone methods, it is feasible to obtain objective measures of physical activity from a sizeable proportion of a national cohort of adults, with similar participation rates among blacks and whites. Linked with the clinical health information collected through follow-up, these data will allow future analyses on the association between objectively-measured sedentary time, physical activity and health outcomes. PMID:25333247

  20. Activity recognition using a single accelerometer placed at the wrist or ankle

    PubMed Central

    Mannini, Andrea; Intille, Stephen S.; Rosenberger, Mary; Sabatini, Angelo M.; Haskell, William

    2013-01-01

    PURPOSE Large physical activity surveillance projects such as the UK Biobank and NHANES are using wrist-worn accelerometer-based activity monitors that collect raw data. The goal is to increase wear time by asking subjects to wear the monitors on the wrist instead of the hip, and then to use information in the raw signal to improve activity type and intensity estimation. The purpose of this work is obtaining an algorithm to process wrist and ankle raw data and classify behavior into four broad activity classes: ambulation, cycling, sedentary and other. METHODS Participants (N = 33) wearing accelerometers on the wrist and ankle performed 26 daily activities. The accelerometer data were collected, cleaned, and preprocessed to extract features that characterize 2 s, 4 s, and 12.8 s data windows. Feature vectors encoding information about frequency and intensity of motion extracted from analysis of the raw signal were used with a support vector machine classifier to identify a subject’s activity. Results were compared with categories classified by a human observer. Algorithms were validated using a leave-one-subject-out strategy. The computational complexity of each processing step was also evaluated. RESULTS With 12.8 s windows, the proposed strategy showed high classification accuracies for ankle data (95.0%) that decreased to 84.7% for wrist data. Shorter (4 s) windows only minimally decreased performances of the algorithm on the wrist to 84.2%. CONCLUSIONS A classification algorithm using 13 features shows good classification into the four classes given the complexity of the activities in the original dataset. The algorithm is computationally-efficient and could be implemented in real-time on mobile devices with only 4 s latency. PMID:23604069

  1. Predicting Human Movement with Multiple Accelerometers Using Movelets

    PubMed Central

    He, Bing; Bai, Jiawei; Zipunnikov, Vadim V.; Koster, Annemarie; Caserotti, Paolo; Lange-Maia, Brittney; Glynn, Nancy W.; Harris, Tamara B.; Crainiceanu, Ciprian M.

    2014-01-01

    Purpose The study aims were: 1) to develop transparent algorithms that use short segments of training data for predicting activity types; and 2) to compare prediction performance of proposed algorithms using single accelerometers and multiple accelerometers. Methods Sixteen participants (age, 80.6 yr (4.8 yr); BMI, 26.1 kg·m−2 (2.5 kg·m−2)) performed fifteen life-style activities in the laboratory, each wearing three accelerometers at the right hip, left and right wrists. Triaxial accelerometry data were collected at 80 Hz using Actigraph GT3X+. Prediction algorithms were developed, which, instead of extracting features, build activity specific dictionaries composed of short signal segments called movelets. Three alternative approaches were proposed to integrate the information from the multiple accelerometers. Results With at most several seconds of training data per activity, the prediction accuracy at the second-level temporal resolution was very high for lying, standing, normal/fast walking, and standing up from a chair (the median prediction accuracy ranged from 88.2% to 99.9% based on the single-accelerometer movelet approach). For these activities wrist-worn accelerometers performed almost as well as hip-worn accelerometers (the median difference in accuracy between wrist and hip ranged from −2.7% to 5.8%). Modest improvements in prediction accuracy were achieved by integrating information from multiple accelerometers. Discussion and conclusions It is possible to achieve high prediction accuracy at the secondlevel temporal resolution with very limited training data. To increase prediction accuracy from the simultaneous use of multiple accelerometers, a careful selection of integrative approaches is required. PMID:25134005

  2. Compact Circuit Preprocesses Accelerometer Output

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr.

    1993-01-01

    Compact electronic circuit transfers dc power to, and preprocesses ac output of, accelerometer and associated preamplifier. Incorporated into accelerometer case during initial fabrication or retrofit onto commercial accelerometer. Made of commercial integrated circuits and other conventional components; made smaller by use of micrologic and surface-mount technology.

  3. Double resonator cantilever accelerometer

    DOEpatents

    Koehler, Dale R.

    1984-01-01

    A digital quartz accelerometer includes a pair of spaced double-ended tuning forks fastened at one end to a base and at the other end through a spacer mass. Transverse movement of the resonator members stresses one and compresses the other, providing a differential frequency output which is indicative of acceleration.

  4. Double resonator cantilever accelerometer

    DOEpatents

    Koehler, D.R.

    1982-09-23

    A digital quartz accelerometer includes a pair of spaced double-ended tuning forks fastened at one end to a base and at the other end through a spacer mass. Transverse movement of the resonator members stresses one and compresses the other, providing a differential frequency output which is indicative of acceleration.

  5. Superconducting Rebalance Accelerometer

    NASA Technical Reports Server (NTRS)

    Torti, R. P.; Gerver, M.; Leary, K. J.; Jagannathan, S.; Dozer, D. M.

    1996-01-01

    A multi-axis accelerometer which utilizes a magnetically-suspended, high-TC proof mass is under development. The design and performance of a single axis device which is stabilized actively in the axial direction but which utilizes ring magnets for passive radial stabilization is discussed. The design of a full six degree-of-freedom device version is also described.

  6. CHAMP Tracking and Accelerometer Data Analysis Results

    NASA Technical Reports Server (NTRS)

    Lemoine, Frank G.; Luthcke, S. B.; Rowlands, D. D.; Pavlis, D. E.; Colombo, O. L.; Ray, Richard D.; Thompson, B.; Nerem, R. S.; Williams, Teresa A.; Smith, David E. (Technical Monitor)

    2002-01-01

    The CHAMP (Challenging Minisatellite Payload) mission's unique combination of sensors and orbit configuration will enable unprecedented improvements in modeling and understanding the Earth's static gravity field and its temporal variations. CHAMP is the first of two missions (GRACE (Gravity Recovery and Climate Experiment) to be launched in the later part of '01) that combine a new generation of GPS (Global Positioning System) receivers, a high precision three axis accelerometer, and star cameras for the precision attitude determination. In order to isolate the gravity signal for science investigations, it is necessary to perform a detailed reduction and analysis of the GPS and SLR tracking data in conjunction with the accelerometer and attitude data. Precision orbit determination based on the GPS and SLR (Satellite Laser Ranging) tracking data will isolate the orbit perturbations, while the accelerometer data will be used to distinguish the surface forces from those due to the geopotential (static, and time varying). In preparation for the CHAMP and GRACE missions, extensive modifications have been made to NASA/GSFC's GEODYN orbit determination software to enable the simultaneous reduction of spacecraft tracking (e.g. GPS and SLR), three axis accelerometer and precise attitude data. Several weeks of CHAMP tracking and accelerometer data have been analyzed and the results will be presented. Precision orbit determination analysis based on tracking data alone in addition to results based on the simultaneous reduction of tracking and accelerometer data will be discussed. Results from a calibration of the accelerometer will be presented along with the results from various orbit determination strategies. Gravity field modeling status and plans will be discussed.

  7. The effect of feeding time on dispersal of Virola seeds by toucans determined from GPS tracking and accelerometers

    NASA Astrophysics Data System (ADS)

    Kays, Roland; Jansen, Patrick A.; Knecht, Elise M. H.; Vohwinkel, Reinhard; Wikelski, Martin

    2011-11-01

    Seed dispersal is critical to understanding forest dynamics but is hard to study because tracking seeds is difficult. Even for the best-studied dispersal system of the Neotropics, Virola nobilis, the dispersal kernel remains unknown. We combined high-resolution GPS/3D-acceleration bird tracking, seed-retention experiments, and field observations to quantify dispersal of V. nobilis by their principal dispersers, Ramphastos toucans. We inferred feeding events from movement data, and then estimated spatio-temporally explicit seed-dispersal kernels. Wild toucans moved an average of 1.8 km d -1 with two distinct activity peaks. Seed retention time in captive toucans averaged 25.5 min (range 4-98 min). Estimated seed dispersal distance averaged 144 ± 147 m, with a 56% likelihood of dispersal >100 m, two times further than the behaviour-naive estimate from the same data. Dispersal was furthest for seeds ingested in the morning, and increased with seed retention time, but only up to 60 min after feeding. Our study supports the long-standing hypothesis that toucans are excellent dispersers of Virola seeds. To maximize seed dispersal distances trees should ripen fruit in the morning when birds move the most, and produce fruits with gut-processing times around 60 min. Our study demonstrates how new tracking technology can yield nuanced seed dispersal kernels for animals that cannot be directly observed.

  8. Context-Specific Outdoor Time and Physical Activity among School-Children Across Gender and Age: Using Accelerometers and GPS to Advance Methods

    PubMed Central

    Klinker, Charlotte Demant; Schipperijn, Jasper; Kerr, Jacqueline; Ersbøll, Annette Kjær; Troelsen, Jens

    2014-01-01

    Introduction: Being outdoors has a positive influence on health among children. Evidence in this area is limited and many studies have used self-reported measures. Objective context-specific assessment of physical activity patterns and correlates, such as outdoor time, may progress this field. Aims: To employ novel objective measures to assess age and gender differences in context-specific outdoor weekday behavior patterns among school-children [outdoor time and outdoor moderate to vigorous physical activity (MVPA)] and to investigate associations between context-specific outdoor time and MVPA. Methods: A total of 170 children had at least one weekday of 9 h combined accelerometer and global positioning system data and were included in the analyses. The data were processed using the personal activity and location measurement system (PALMS) and a purpose-built PostgreSQL database resulting in context-specific measures for outdoor time, outdoor MVPA, and overall daily MVPA. In addition, 4 domains (leisure, school, transport, and home) and 11 subdomains (e.g., urban green space and sports facilities) were created and assessed. Multilevel analyses provided results on age and gender differences and the association between outdoor time and MVPA. Results: Girls compared to boys had fewer outdoor minutes (p < 0.05), spent a smaller proportion of their overall daily time outdoors (p < 0.05), had fewer outdoor MVPA minutes during the day (p < 0.001) and in 11 contexts. Children compared to adolescents had more outdoor minutes (p < 0.05). During school and within recess, children compared to adolescents had more outdoor MVPA (p < 0.001) and outdoor time (p < 0.001). A 1-h increase in outdoor time was associated with 9.9 more minutes of MVPA (p < 0.001). Conclusion: A new methodology to assess the context-specific outdoor time and physical activity patterns has been developed and can be expanded to other populations. Different context

  9. An Attachable Electromagnetic Energy Harvester Driven Wireless Sensing System Demonstrating Milling-Processes and Cutter-Wear/Breakage-Condition Monitoring.

    PubMed

    Chung, Tien-Kan; Yeh, Po-Chen; Lee, Hao; Lin, Cheng-Mao; Tseng, Chia-Yung; Lo, Wen-Tuan; Wang, Chieh-Min; Wang, Wen-Chin; Tu, Chi-Jen; Tasi, Pei-Yuan; Chang, Jui-Wen

    2016-02-23

    An attachable electromagnetic-energy-harvester driven wireless vibration-sensing system for monitoring milling-processes and cutter-wear/breakage-conditions is demonstrated. The system includes an electromagnetic energy harvester, three single-axis Micro Electro-Mechanical Systems (MEMS) accelerometers, a wireless chip module, and corresponding circuits. The harvester consisting of magnets with a coil uses electromagnetic induction to harness mechanical energy produced by the rotating spindle in milling processes and consequently convert the harnessed energy to electrical output. The electrical output is rectified by the rectification circuit to power the accelerometers and wireless chip module. The harvester, circuits, accelerometer, and wireless chip are integrated as an energy-harvester driven wireless vibration-sensing system. Therefore, this completes a self-powered wireless vibration sensing system. For system testing, a numerical-controlled machining tool with various milling processes is used. According to the test results, the system is fully self-powered and able to successfully sense vibration in the milling processes. Furthermore, by analyzing the vibration signals (i.e., through analyzing the electrical outputs of the accelerometers), criteria are successfully established for the system for real-time accurate simulations of the milling-processes and cutter-conditions (such as cutter-wear conditions and cutter-breaking occurrence). Due to these results, our approach can be applied to most milling and other machining machines in factories to realize more smart machining technologies.

  10. An Attachable Electromagnetic Energy Harvester Driven Wireless Sensing System Demonstrating Milling-Processes and Cutter-Wear/Breakage-Condition Monitoring

    PubMed Central

    Chung, Tien-Kan; Yeh, Po-Chen; Lee, Hao; Lin, Cheng-Mao; Tseng, Chia-Yung; Lo, Wen-Tuan; Wang, Chieh-Min; Wang, Wen-Chin; Tu, Chi-Jen; Tasi, Pei-Yuan; Chang, Jui-Wen

    2016-01-01

    An attachable electromagnetic-energy-harvester driven wireless vibration-sensing system for monitoring milling-processes and cutter-wear/breakage-conditions is demonstrated. The system includes an electromagnetic energy harvester, three single-axis Micro Electro-Mechanical Systems (MEMS) accelerometers, a wireless chip module, and corresponding circuits. The harvester consisting of magnets with a coil uses electromagnetic induction to harness mechanical energy produced by the rotating spindle in milling processes and consequently convert the harnessed energy to electrical output. The electrical output is rectified by the rectification circuit to power the accelerometers and wireless chip module. The harvester, circuits, accelerometer, and wireless chip are integrated as an energy-harvester driven wireless vibration-sensing system. Therefore, this completes a self-powered wireless vibration sensing system. For system testing, a numerical-controlled machining tool with various milling processes is used. According to the test results, the system is fully self-powered and able to successfully sense vibration in the milling processes. Furthermore, by analyzing the vibration signals (i.e., through analyzing the electrical outputs of the accelerometers), criteria are successfully established for the system for real-time accurate simulations of the milling-processes and cutter-conditions (such as cutter-wear conditions and cutter-breaking occurrence). Due to these results, our approach can be applied to most milling and other machining machines in factories to realize more smart machining technologies. PMID:26907297

  11. An Attachable Electromagnetic Energy Harvester Driven Wireless Sensing System Demonstrating Milling-Processes and Cutter-Wear/Breakage-Condition Monitoring.

    PubMed

    Chung, Tien-Kan; Yeh, Po-Chen; Lee, Hao; Lin, Cheng-Mao; Tseng, Chia-Yung; Lo, Wen-Tuan; Wang, Chieh-Min; Wang, Wen-Chin; Tu, Chi-Jen; Tasi, Pei-Yuan; Chang, Jui-Wen

    2016-01-01

    An attachable electromagnetic-energy-harvester driven wireless vibration-sensing system for monitoring milling-processes and cutter-wear/breakage-conditions is demonstrated. The system includes an electromagnetic energy harvester, three single-axis Micro Electro-Mechanical Systems (MEMS) accelerometers, a wireless chip module, and corresponding circuits. The harvester consisting of magnets with a coil uses electromagnetic induction to harness mechanical energy produced by the rotating spindle in milling processes and consequently convert the harnessed energy to electrical output. The electrical output is rectified by the rectification circuit to power the accelerometers and wireless chip module. The harvester, circuits, accelerometer, and wireless chip are integrated as an energy-harvester driven wireless vibration-sensing system. Therefore, this completes a self-powered wireless vibration sensing system. For system testing, a numerical-controlled machining tool with various milling processes is used. According to the test results, the system is fully self-powered and able to successfully sense vibration in the milling processes. Furthermore, by analyzing the vibration signals (i.e., through analyzing the electrical outputs of the accelerometers), criteria are successfully established for the system for real-time accurate simulations of the milling-processes and cutter-conditions (such as cutter-wear conditions and cutter-breaking occurrence). Due to these results, our approach can be applied to most milling and other machining machines in factories to realize more smart machining technologies. PMID:26907297

  12. Low G accelerometer testing

    NASA Technical Reports Server (NTRS)

    Vaughan, M. S.

    1972-01-01

    Eight different types of low-g accelerometer tests are covered on the Bell miniature electrostatically suspended accelerometer (MESA) which is known to be sensitive to less than 10 to the minus 7th power earth's gravity. These tests include a mass attracting scheme, Leitz dividing head, Wild theodolite, precision gage blocks, precision tiltmeters, Hilger Watts autocollimator, Razdow Mark 2 autocollimator, and laser interferometer measuring system. Each test is described and a comparison of the results is presented. The output of the MESA was as linear and consistent as any of the available devices were capable of measuring. Although the extent of agreement varied with the test equipment used, it can only be concluded that the indicated errors were attributable to the test equipment coupled with the environmental conditions.

  13. Piezoelectric accelerometers for ultrahigh temperature application

    NASA Astrophysics Data System (ADS)

    Zhang, Shujun; Jiang, Xiaoning; Lapsley, Michael; Moses, Paul; Shrout, Thomas R.

    2010-01-01

    High temperature sensors are of major importance to aerospace and energy related industries. In this letter, a high temperature monolithic compression-mode piezoelectric accelerometer was fabricated using YCa4O(BO3)3 (YCOB) single crystals. The performance of the sensor was tested as function of temperature up to 1000 °C and over a frequency range of 100-600 Hz. The accelerometer prototype was found to possess sensitivity of 2.4±0.4 pC/g, across the measured temperature and frequency range, indicating a low temperature coefficient. Furthermore, the sensor exhibited good stability over an extended dwell time at 900 °C, demonstrating that YCOB piezoelectric accelerometers are promising candidates for high temperature sensing applications.

  14. Piezoelectric accelerometers for ultrahigh temperature application

    SciTech Connect

    Zhang Shujun; Moses, Paul; Shrout, Thomas R.; Jiang Xiaoning; Lapsley, Michael

    2010-01-04

    High temperature sensors are of major importance to aerospace and energy related industries. In this letter, a high temperature monolithic compression-mode piezoelectric accelerometer was fabricated using YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) single crystals. The performance of the sensor was tested as function of temperature up to 1000 deg. C and over a frequency range of 100-600 Hz. The accelerometer prototype was found to possess sensitivity of 2.4+-0.4 pC/g, across the measured temperature and frequency range, indicating a low temperature coefficient. Furthermore, the sensor exhibited good stability over an extended dwell time at 900 deg. C, demonstrating that YCOB piezoelectric accelerometers are promising candidates for high temperature sensing applications.

  15. ATS-6 - Flight accelerometers

    NASA Technical Reports Server (NTRS)

    Mattson, R.; Honeycutt, G.; Lindner, F.

    1975-01-01

    The Applications Technology Satellite-6 (ATS-6) flight accelerometers were designed to provide data for verifying the basic spacecraft vibration modes during launch, to update the analytical model of the ATA structure, and to provide a capability for detection and diagnosis of inflight and anomalies. The experiment showed accelerations less than 2.5 g during liftoff and 1.1 g or less during staging with frequencies below 80 Hz. Measured values were generally within 1 g of predicted.

  16. Fiber optic micro accelerometer

    SciTech Connect

    Swierkowski, Steve P.

    2005-07-26

    An accelerometer includes a wafer, a proof mass integrated into the wafer, at least one spring member connected to the proof mass, and an optical fiber. A Fabry-Perot cavity is formed by a partially reflective surface on the proof mass and a partially reflective surface on the end of the optical fiber. The two partially reflective surfaces are used to detect movement of the proof mass through the optical fiber, using an optical detection system.

  17. Passive Accelerometer System Measurements on MIR

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.

    1997-01-01

    The Passive Accelerometer System (PAS) is a simple moving ball accelerometer capable of measuring the small magnitude steady relative acceleration that occurs in a low earth orbit spacecraft due to atmospheric drag and the earth's gravity gradient. The acceleration is measured by recording the average velocity of the spherical ball over a suitable time increment. A modified form of Stokes law is used to convert the average velocity into an acceleration. PAS was used to measure acceleration on the MIR space station and on the first United States Microgravity Laboratory (USML-1). The PAS measurement on MIR revealed remarkably low acceleration levels in the SPEKTR module.

  18. Levitated micro-accelerometer.

    SciTech Connect

    Warne, Larry Kevin; Schmidt, Carrie Frances; Peterson, Kenneth Allen; Kravitz, Stanley H.; Renn, Rosemarie A.; Peter, Frank J.; Kinney, Ragon D.; Gilkey, Jeffrey C.

    2004-06-01

    The objective is a significant advancement in the state-of-the-art of accelerometer design for tactical grade (or better) applications. The design goals are <1 milli-G bias stability across environments and $200 cost. This quantum leap in performance improvement and cost reduction can only be achieved by a radical new approach, not incremental improvements to existing concepts. This novel levitated closed-loop accelerometer is implemented as a hybrid micromachine. The hybrid approach frees the designer from the limitations of any given monolithic process and dramatically expands the available design space. The design can be tailored to the dynamic range, resolution, bandwidth, and environmental requirements of the application while still preserving all of the benefits of monolithic MEMS fabrication - extreme precision, small size, low cost, and low power. An accelerometer was designed and prototype hardware was built, driving the successful development and refinement of several 'never been done before' fabrication processes. Many of these process developments are commercially valuable and are key enablers for the realization of a wide variety of useful micro-devices. While controlled levitation of a proof mass has yet to be realized, the overall design concept remains sound. This was clearly demonstrated by the stable and reliable closed-loop control of a proof mass at the test structure level. Furthermore, the hybrid MEMS implementation is the most promising approach for achieving the ambitious cost and performance targets. It is strongly recommended that Sandia remain committed to the original goal.

  19. A Simple Accelerometer Calibrator

    NASA Astrophysics Data System (ADS)

    Salam, R. A.; Islamy, M. R. F.; Munir, M. M.; Latief, H.; Irsyam, M.; Khairurrijal

    2016-08-01

    High possibility of earthquake could lead to the high number of victims caused by it. It also can cause other hazards such as tsunami, landslide, etc. In that case it requires a system that can examine the earthquake occurrence. Some possible system to detect earthquake is by creating a vibration sensor system using accelerometer. However, the output of the system is usually put in the form of acceleration data. Therefore, a calibrator system for accelerometer to sense the vibration is needed. In this study, a simple accelerometer calibrator has been developed using 12 V DC motor, optocoupler, Liquid Crystal Display (LCD) and AVR 328 microcontroller as controller system. The system uses the Pulse Wave Modulation (PWM) form microcontroller to control the motor rotational speed as response to vibration frequency. The frequency of vibration was read by optocoupler and then those data was used as feedback to the system. The results show that the systems could control the rotational speed and the vibration frequencies in accordance with the defined PWM.

  20. Combination of High Rate, Real-time GNSS and Accelerometer Observations - Preliminary Results Using a Shake Table and Historic Earthquake Events.

    NASA Astrophysics Data System (ADS)

    Jackson, Michael; Passmore, Paul; Zimakov, Leonid; Raczka, Jared

    2014-05-01

    One of the fundamental requirements of an Earthquake Early Warning (EEW) system (and other mission critical applications) is to quickly detect and process the information from the strong motion event, i.e. event detection and location, magnitude estimation, and the peak ground motion estimation at the defined targeted site, thus allowing the civil protection authorities to provide pre-programmed emergency response actions: Slow down or stop rapid transit trains and high-speed trains; shutoff of gas pipelines and chemical facilities; stop elevators at the nearest floor; send alarms to hospitals, schools and other civil institutions. An important question associated with the EEW system is: can we measure displacements in real time with sufficient accuracy? Scientific GNSS networks are moving towards a model of real-time data acquisition, storage integrity, and real-time position and displacement calculations. This new paradigm allows the integration of real-time, high-rate GNSS displacement information with acceleration and velocity data to create very high-rate displacement records. The mating of these two instruments allows the creation of a new, very high-rate (200 Hz) displacement observable that has the full-scale displacement characteristics of GNSS and high-precision dynamic motions of seismic technologies. It is envisioned that these new observables can be used for earthquake early warning studies and other mission critical applications, such as volcano monitoring, building, bridge and dam monitoring systems. REF TEK a Division of Trimble has developed the integrated GNSS/Accelerograph system, model 160-09SG, which consists of REF TEK's fourth generation electronics, a 147-01 high-resolution ANSS Class A accelerometer, and Trimble GNSS receiver and antenna capable of real time, on board Precise Point Positioning (PPP) techniques with satellite clock and orbit corrections delivered to the receiver directly via L-band satellite communications. The test we

  1. Designing Electrostatic Accelerometers for Next Gravity Missions

    NASA Astrophysics Data System (ADS)

    Huynh, Phuong-Anh; Foulon, Bernard; Christophe, Bruno; Liorzou, Françoise; Boulanger, Damien; Lebat, Vincent

    2016-04-01

    Square cuboid electrostatic accelerometers sensor core have been used in various combinations in recent and still flying missions (CHAMP, GRACE, GOCE). ONERA is now in the process of delivering such accelerometers for the GRACE Follow-On mission. The goal is to demonstrate the performance benefits of an interferometry laser ranging method for future low-low satellite to satellite missions. The electrostatic accelerometer becoming thus the system main performance limiter, we propose for future missions a new symmetry which will allow for three ultrasensitive axes instead of two. This implies no performance ground testing, as the now cubic proof-mass will be too heavy, but only free fall tests in catapult mode, taking advantage of the additional microgravity testing time offered by the updated ZARM tower. The updated mission will be in better adequacy with the requirements of a next generation of smaller and drag compensated micro-satellites. In addition to the measurement of the surface forces exerted on the spacecraft by the atmospheric drag and by radiation pressures, the accelerometer will become a major part of the attitude and orbit control system by acting as drag free sensor and by accurately measuring the angular accelerations. ONERA also works on a hybridization of the electrostatic accelerometer with an atomic interferometer to take advantage of the absolute nature of the atomic interferometer acceleration measurement and its great accuracy in the [5-100] mHz bandwidth. After a description of the improvement of the GRACE-FO accelerometer with respect to the still in-orbit previous models and a status of its development, the presentation will describe the new cubic configuration and how its operations and performances can be verified in the Bremen drop tower.

  2. Improved Signal Processing Technique Leads to More Robust Self Diagnostic Accelerometer System

    NASA Technical Reports Server (NTRS)

    Tokars, Roger; Lekki, John; Jaros, Dave; Riggs, Terrence; Evans, Kenneth P.

    2010-01-01

    The self diagnostic accelerometer (SDA) is a sensor system designed to actively monitor the health of an accelerometer. In this case an accelerometer is considered healthy if it can be determined that it is operating correctly and its measurements may be relied upon. The SDA system accomplishes this by actively monitoring the accelerometer for a variety of failure conditions including accelerometer structural damage, an electrical open circuit, and most importantly accelerometer detachment. In recent testing of the SDA system in emulated engine operating conditions it has been found that a more robust signal processing technique was necessary. An improved accelerometer diagnostic technique and test results of the SDA system utilizing this technique are presented here. Furthermore, the real time, autonomous capability of the SDA system to concurrently compensate for effects from real operating conditions such as temperature changes and mechanical noise, while monitoring the condition of the accelerometer health and attachment, will be demonstrated.

  3. Capacitive Position Sensor For Accelerometer

    NASA Technical Reports Server (NTRS)

    Vanzandt, Thomas R.; Kaiser, William J.; Kenny, Thomas W.

    1995-01-01

    Capacitive position sensor measures displacement of proof mass in prototype accelerometer described in "Single-Crystal Springs for Accelerometers" (NPO-18795). Sensor is ultrasensitive, miniature device operating at ultra-high frequency and described in more detail in "Ultra-High-Frequency Capacitive Displacement Sensor," (NPO-18675). Advances in design and fabrication of prototype accelerometer also applicable to magnetometers and other sensors in which sensed quantities measured in terms of deflections of small springs.

  4. Wearing gloves in the hospital

    MedlinePlus

    Infection control - wearing gloves; Patient safety - wearing gloves; Personal protective equipment - wearing gloves; PPE - wearing gloves; Nosocomial infection - wearing gloves; Hospital acquired infection - wearing gloves

  5. Associations between Accelerometer-derived Physical Activity and Regional Adiposity in Young Men and Women

    PubMed Central

    Smith, H A; Storti, K L; Arena, VC; Kriska, A M; Gabriel, K K Pettee; Sutton-Tyrrell, K; Hames, K C; Conroy, M B

    2013-01-01

    Objective Empirical evidence supports an inverse relationship between physical activity (PA) and adiposity, but studies using detailed measures of both are scarce. We described the relationship between regional adiposity and accelerometer-derived PA in men and women. Design and Methods Cross-sectional analysis included 253 participants from a weight loss study limited to ages 20–45 years and BMI 25–39.9 kg/m2. PA data were collected with accelerometers and expressed as total accelerometer counts and average amount of time per day accumulated in different intensity levels (sedentary, light-, and moderate- to vigorous- intensity PA (MVPA)). Accumulation of time spent above 100 counts was expressed as total active time. Computed tomography (CT) was used to measure abdominal and adipose tissue (AT). Multivariate linear regression analyses were used to assess the relationship between regional adiposity (dependent variable) and the various PA levels (independent variable), and were executed separately for men and women, adjusting for wear time, age, race, education, and BMI. Results Among males light activity was inversely associated with total AT (β=−0.19; p=0.02) as well as visceral AT (VAT) (β=−0.30; p=0.03). Among females sedentary time was positively associated with VAT (β=0.11; p=0.04) and total active time was inversely associated with VAT (β=−0.12; p=0.04). Conclusions Findings from this study suggest that PA intensity level may influence regional adiposity differently in men and women. Additional research is needed in larger samples to clarify the difference in these associations by sex, create recommendations for the frequency, duration and intensity of PA needed to target fat deposits, and determine if these recommendations should differ by sex. PMID:23408709

  6. The novel use of a SenseCam and accelerometer to validate training load and training information in a self-recall training diary.

    PubMed

    O Connor, Siobhan; McCaffrey, Noel; Whyte, Enda; Moran, Kieran

    2016-01-01

    Self-recall training diaries are a frequently used tool to quantify training load and training information. While accelerometers are predominantly used to validate training diaries, they are unable to validate contextual training information. Thus this study aimed to examine the novel use of data fusion from a wearable camera device (SenseCam) and accelerometer to validate a self-recall training diary. Thirty participants filled in a training diary for 1 day while simultaneously wearing a SenseCam and accelerometer. The training diary was validated using Bland-Altman plots, Spearman's rank-order correlation, percentage agreement and κ measure of agreement between the diary and the SenseCam and accelerometer. The results demonstrated overall agreement, and no bias, between the training diary and the accelerometer for training intensity, and the SenseCam for duration of activity and travel time. A positive correlation was found for duration (r = 0.82, P < 0.001) and intensity (r = 0.67, P < 0.001). Hundred per cent agreement was found between the SenseCam and training diary for activity, training surface and footwear (κ = 1, P < 0.0001), with a lower agreement noted for sports played (97.3%, κ = 0.91, P < 0.0001). The self-recall training diary was found to be a valid measure of capturing training load and training information using the combined wearable camera device and accelerometer.

  7. Intermonitor variability of GT3X accelerometer.

    PubMed

    Santos-Lozano, A; Torres-Luque, G; Marín, P J; Ruiz, J R; Lucia, A; Garatachea, N

    2012-12-01

    The main purpose of this study was to assess the inter-monitor reliability of the tri-axial GT3X Actigraph accelerometer over a range of physical activities (PA). This device collects motion data on each of the vertical (Y), horizontal right-left (X), and horizontal front-back (Z) axes and also calculates the vector summed value √X(2)+Y(2)+Z(2) known as 'vector magnitude' (VM). 8 GT3X accelerometers were worn at the same time by the same participant. Accelerometers were placed back-to-front, all facing forward and in sets of 4 securely taped together, attached to a belt and allocating each block above either left or right hip at waist level. Inter-monitor reliability was assessed during 6 conditions: rest, walking (4 and 6 km·h(-1)), running (8 and 10 km·h(-1)) and repeated sit-to-stand (40 times·min(-1)). The intra-class correlation coefficients were high for X, Y and Z axes (i.e., all ≥ 0.925) and for VM (≥ 0.946). In conclusion, we found good inter-instrument reliability of the GT3X accelerometer across all planes, yet our results also suggest that the X and Z axes do not provide further benefits over the 'traditional' Y-axis to assess the movement in typical PA.

  8. Assessment of gait kinetics using triaxial accelerometers.

    PubMed

    Fortune, Emma; Morrow, Melissa M; Kaufman, Kenton R

    2014-10-01

    Repeated durations of dynamic activity with high ground reaction forces (GRFs) and loading rates (LRs) can be beneficial to bone health. To fully characterize dynamic activity in relation to bone health, field-based measurements of gait kinetics are desirable to assess free-living lower-extremity loading. The study aims were to determine correlations of peak vertical GRF and peak vertical LR with ankle peak vertical accelerations, and of peak resultant GRF and peak resultant LR with ankle peak resultant accelerations, and to compare them to correlations with tibia, thigh, and waist accelerations. GRF data were collected as ten healthy subjects (26 [19-34] years) performed 8-10 walking trials at velocities ranging from 0.19 to 3.05 m/s while wearing ankle, tibia, thigh, and waist accelerometers. While peak vertical accelerations of all locations were positively correlated with peak vertical GRF and LR (r² > .53, P < .001), ankle peak vertical accelerations were the most correlated (r² > .75, P < .001). All peak resultant accelerations were positively correlated with peak resultant GRF and LR (r² > .57, P < .001), with waist peak resultant acceleration being the most correlated (r² > .70, P < .001). The results suggest that ankle or waist accelerometers give the most accurate peak GRF and LR estimates and could be useful tools in relating physical activity to bone health.

  9. Assessment of gait kinetics using triaxial accelerometers.

    PubMed

    Fortune, Emma; Morrow, Melissa M; Kaufman, Kenton R

    2014-10-01

    Repeated durations of dynamic activity with high ground reaction forces (GRFs) and loading rates (LRs) can be beneficial to bone health. To fully characterize dynamic activity in relation to bone health, field-based measurements of gait kinetics are desirable to assess free-living lower-extremity loading. The study aims were to determine correlations of peak vertical GRF and peak vertical LR with ankle peak vertical accelerations, and of peak resultant GRF and peak resultant LR with ankle peak resultant accelerations, and to compare them to correlations with tibia, thigh, and waist accelerations. GRF data were collected as ten healthy subjects (26 [19-34] years) performed 8-10 walking trials at velocities ranging from 0.19 to 3.05 m/s while wearing ankle, tibia, thigh, and waist accelerometers. While peak vertical accelerations of all locations were positively correlated with peak vertical GRF and LR (r² > .53, P < .001), ankle peak vertical accelerations were the most correlated (r² > .75, P < .001). All peak resultant accelerations were positively correlated with peak resultant GRF and LR (r² > .57, P < .001), with waist peak resultant acceleration being the most correlated (r² > .70, P < .001). The results suggest that ankle or waist accelerometers give the most accurate peak GRF and LR estimates and could be useful tools in relating physical activity to bone health. PMID:25010675

  10. Dual-Cantilever-Beam Accelerometer

    NASA Technical Reports Server (NTRS)

    Reynolds, Emmitt A.; Speckhart, Frank H.

    1988-01-01

    Sensitivity to velocity changes along beam axis reduced. Weighted-end cantilever beams of accelerometer deflected equally by acceleration in y direction. When acceleration to right as well as up or down, right beam deflected more, while left beam deflected less. Bridge circuit averages outputs of strain gauges measuring deflections, so cross-axis sensitivity of accelerometer reduced. New device simple and inexpensive.

  11. Instrument sequentially samples ac signals from several accelerometers

    NASA Technical Reports Server (NTRS)

    Chapman, C. P.

    1967-01-01

    Scanner circuit sequentially samples the ac signals from accelerometers used in conducting noise vibration tests, and provides a time-averaged output signal. The scanner is used in conjunction with other devices for random noise vibration tests.

  12. MGRA: Motion Gesture Recognition via Accelerometer

    PubMed Central

    Hong, Feng; You, Shujuan; Wei, Meiyu; Zhang, Yongtuo; Guo, Zhongwen

    2016-01-01

    Accelerometers have been widely embedded in most current mobile devices, enabling easy and intuitive operations. This paper proposes a Motion Gesture Recognition system (MGRA) based on accelerometer data only, which is entirely implemented on mobile devices and can provide users with real-time interactions. A robust and unique feature set is enumerated through the time domain, the frequency domain and singular value decomposition analysis using our motion gesture set containing 11,110 traces. The best feature vector for classification is selected, taking both static and mobile scenarios into consideration. MGRA exploits support vector machine as the classifier with the best feature vector. Evaluations confirm that MGRA can accommodate a broad set of gesture variations within each class, including execution time, amplitude and non-gestural movement. Extensive evaluations confirm that MGRA achieves higher accuracy under both static and mobile scenarios and costs less computation time and energy on an LG Nexus 5 than previous methods. PMID:27089336

  13. MGRA: Motion Gesture Recognition via Accelerometer.

    PubMed

    Hong, Feng; You, Shujuan; Wei, Meiyu; Zhang, Yongtuo; Guo, Zhongwen

    2016-01-01

    Accelerometers have been widely embedded in most current mobile devices, enabling easy and intuitive operations. This paper proposes a Motion Gesture Recognition system (MGRA) based on accelerometer data only, which is entirely implemented on mobile devices and can provide users with real-time interactions. A robust and unique feature set is enumerated through the time domain, the frequency domain and singular value decomposition analysis using our motion gesture set containing 11,110 traces. The best feature vector for classification is selected, taking both static and mobile scenarios into consideration. MGRA exploits support vector machine as the classifier with the best feature vector. Evaluations confirm that MGRA can accommodate a broad set of gesture variations within each class, including execution time, amplitude and non-gestural movement. Extensive evaluations confirm that MGRA achieves higher accuracy under both static and mobile scenarios and costs less computation time and energy on an LG Nexus 5 than previous methods. PMID:27089336

  14. Movement Prediction Using Accelerometers in a Human Population

    PubMed Central

    Xiao, Luo; He, Bing; Koster, Annemarie; Caserotti, Paolo; Lange-Maia, Brittney; Glynn, Nancy W.; Harris, Tamara B.; Crainiceanu, Ciprian M.

    2015-01-01

    Summary We introduce statistical methods for predicting the types of human activity at sub-second resolution using triaxial accelerometry data. The major innovation is that we use labeled activity data from some subjects to predict the activity labels of other subjects. To achieve this, we normalize the data across subjects by matching the standing up and lying down portions of triaxial accelerometry data. This is necessary to account for differences between the variability in the position of the device relative to gravity, which are induced by body shape and size as well as by the ambiguous definition of device placement. We also normalize the data at the device level to ensure that the magnitude of the signal at rest is similar across devices. After normalization we use overlapping movelets (segments of triaxial accelerometry time series) extracted from some of the subjects to predict the movement type of the other subjects. The problem was motivated by and is applied to a laboratory study of 20 older participants who performed different activities while wearing accelerometers at the hip. Prediction results based on other people’s labeled dictionaries of activity performed almost as well as those obtained using their own labeled dictionaries. These findings indicate that prediction of activity types for data collected during natural activities of daily living may actually be possible. PMID:26288278

  15. Single-Axis Accelerometer

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis Stephen (Inventor); Capo-Lugo, Pedro A. (Inventor)

    2016-01-01

    A single-axis accelerometer includes a housing defining a sleeve. An object/mass is disposed in the sleeve for sliding movement therein in a direction aligned with the sleeve's longitudinal axis. A first piezoelectric strip, attached to a first side of the object and to the housing, is longitudinally aligned with the sleeve's longitudinal axis. The first piezoelectric strip includes a first strip of a piezoelectric material with carbon nanotubes substantially aligned along a length thereof. A second piezoelectric strip, attached to a second side of the object and to the housing, is longitudinally aligned with the sleeve's longitudinal axis. The second piezoelectric strip includes a second strip of the piezoelectric material with carbon nanotubes substantially aligned along a length thereof. A voltage sensor is electrically coupled to at least one of the first and second piezoelectric strips.

  16. Ultraminiature resonator accelerometer

    SciTech Connect

    Koehler, D.R.; Kravitz, S.H.; Vianco, P.T.

    1996-04-01

    A new family of microminiature sensors and clocks is being developed with widespread application potential for missile and weapons applications, as biomedical sensors, as vehicle status monitors, and as high-volume animal identification and health sensors. To satisfy fundamental technology development needs, a micromachined clock and an accelerometer have initially been undertaken as development projects. A thickness-mode quartz resonator housed in a micromachined silicon package is used as the frequency-modulated basic component of the sensor family. Resonator design philosophy follows trapped energy principles and temperature compensation methodology through crystal orientation control, with operation in the 20--100 MHz range, corresponding to quartz wafer thicknesses in the 75--15 micron range. High-volume batch-processing manufacturing is utilized, with package and resonator assembly at the wafer level. Chemical etching of quartz, as well as micromachining of silicon, achieves the surface and volume mechanical features necessary to fashion the resonating element and the mating package. Integration of the associated oscillator and signal analysis circuitry into the silicon package is inherent to the realization of a size reduction requirement. A low temperature In and In/Sn bonding technology allows assembly of the dissimilar quartz and silicon materials, an otherwise challenging task. Unique design features include robust vibration and shock performance, capacitance sensing with micromachined diaphragms, circuit integration, capacitance-to-frequency transduction, and extremely small dimensioning. Accelerometer sensitivities were measured in the 1--3 ppm/g range for the milligram proof-mass structures employed in the prototypes evaluated to date.

  17. Self Diagnostic Accelerometer Testing on the C-17 Aircraft

    NASA Technical Reports Server (NTRS)

    Tokars, Roger P.; Lekki, John D.

    2013-01-01

    The self diagnostic accelerometer (SDA) developed by the NASA Glenn Research Center was tested for the first time in an aircraft engine environment as part of the Vehicle Integrated Propulsion Research (VIPR) program. The VIPR program includes testing multiple critical flight sensor technologies. One such sensor, the accelerometer, measures vibrations to detect faults in the engine. In order to rely upon the accelerometer, the health of the accelerometer must be ensured. The SDA is a sensor system designed to actively determine the accelerometer structural health and attachment condition, in addition to vibration measurements. The SDA uses a signal conditioning unit that sends an electrical chirp to the accelerometer and recognizes changes in the response due to changes in the accelerometer health and attachment condition. To demonstrate the SDAs flight worthiness and robustness, multiple SDAs were mounted and tested on a C-17 aircraft engine. The engine test conditions varied from engine off, to idle, to maximum power. The SDA attachment conditions were varied from fully tight to loose. The newly developed SDA health algorithm described herein uses cross correlation pattern recognition to discriminate a healthy from a faulty SDA. The VIPR test results demonstrate for the first.

  18. Recent Results from CHAMP Tracking and Accelerometer Data Analysis

    NASA Technical Reports Server (NTRS)

    Luthcke, S. B.; Rowlands, D. D.; Lemoine, F. G.; Nerem, R. S.; Thompson, B.; Pavlis, E.; Williams, T. A.; Colombo, O. L.; Chao, Benjamin F. (Technical Monitor)

    2002-01-01

    The CHAMP mission's unique combination of sensors and orbit configuration will enable unprecedented improvements in modeling and understanding the Earth's static gravity field and its temporal variations. CHAMP is the first of two missions (GRACE to be launched in the early part of 02') that combine a new generation of Global Positioning System (GPS) receivers, a high precision three-axis accelerometer, and star cameras for the precision attitude determination. In order to isolate the gravity signal for science investigations, it is necessary to perform a detailed reduction and analysis of the GPS and Satellite Laser Ranging (SLR) tracking data in conjunction with the accelerometer and attitude data. Precision orbit determination based on the GPS and SLR tracking data will isolate the orbit perturbations, while the accelerometer data will be used to distinguish the non-gravitational forces from those due to the geopotential (static, and time varying). In preparation for the CHAMP and GRACE missions, extensive modifications have been made to NASA/GSFC's GEODYN orbit determination software to enable the simultaneous reduction of spacecraft tracking (e.g. GPS and SLR), three-axis accelerometer and precise attitude data. Several weeks of CHAMP tracking and accelerometer data have been analyzed and the results will be presented. Precision orbit determination analysis based on tracking data alone in addition to results based on the simultaneous reduction of tracking and accelerometer data will be discussed. Results from a calibration of the accelerometer will be presented along with the results from various orbit determination strategies.

  19. Accelerometer Data Analysis and Presentation Techniques

    NASA Technical Reports Server (NTRS)

    Rogers, Melissa J. B.; Hrovat, Kenneth; McPherson, Kevin; Moskowitz, Milton E.; Reckart, Timothy

    1997-01-01

    The NASA Lewis Research Center's Principal Investigator Microgravity Services project analyzes Orbital Acceleration Research Experiment and Space Acceleration Measurement System data for principal investigators of microgravity experiments. Principal investigators need a thorough understanding of data analysis techniques so that they can request appropriate analyses to best interpret accelerometer data. Accelerometer data sampling and filtering is introduced along with the related topics of resolution and aliasing. Specific information about the Orbital Acceleration Research Experiment and Space Acceleration Measurement System data sampling and filtering is given. Time domain data analysis techniques are discussed and example environment interpretations are made using plots of acceleration versus time, interval average acceleration versus time, interval root-mean-square acceleration versus time, trimmean acceleration versus time, quasi-steady three dimensional histograms, and prediction of quasi-steady levels at different locations. An introduction to Fourier transform theory and windowing is provided along with specific analysis techniques and data interpretations. The frequency domain analyses discussed are power spectral density versus frequency, cumulative root-mean-square acceleration versus frequency, root-mean-square acceleration versus frequency, one-third octave band root-mean-square acceleration versus frequency, and power spectral density versus frequency versus time (spectrogram). Instructions for accessing NASA Lewis Research Center accelerometer data and related information using the internet are provided.

  20. Wearing weighted backpack dilates subjective visual duration: the role of functional linkage between weight experience and visual timing.

    PubMed

    Jia, Lina; Shi, Zhuanghua; Feng, Wenfeng

    2015-01-01

    Bodily state plays a critical role in our perception. In the present study, we asked the question whether and how bodily experience of weights influences time perception. Participants judged durations of a picture (a backpack or a trolley bag) presented on the screen, while wearing different weight backpacks or without backpack. The results showed that the subjective duration of the backpack picture was dilated when participants wore a medium weighted backpack relative to an empty backpack or without backpack, regardless of identity (e.g., color) of the visual backpack. However, the duration dilation was not manifested for the picture of trolley bag. These findings suggest that weight experience modulates visual duration estimation through the linkage between the wore backpack and to-be-estimated visual target. The congruent action affordance between the wore backpack and visual inputs plays a critical role in the functional linkage between inner experience and time perception. We interpreted our findings within the framework of embodied time perception. PMID:26441748

  1. Multi-Axis Accelerometer Calibration System

    NASA Technical Reports Server (NTRS)

    Finley, Tom; Parker, Peter

    2010-01-01

    A low-cost, portable, and simplified system has been developed that is suitable for in-situ calibration and/or evaluation of multi-axis inertial measurement instruments. This system overcomes facility restrictions and maintains or improves the calibration quality for users of accelerometer-based instruments with applications in avionics, experimental wind tunnel research, and force balance calibration applications. The apparatus quickly and easily positions a multi-axis accelerometer system into a precisely known orientation suitable for in-situ quality checks and calibration. In addition, the system incorporates powerful and sophisticated statistical methods, known as response surface methodology and statistical quality control. These methods improve calibration quality, reduce calibration time, and allow for increased calibration frequency, which enables the monitoring of instrument stability over time.

  2. The GRADIO accelerometer - Design and development status

    NASA Astrophysics Data System (ADS)

    Bernard, A.; Touboul, P.

    The concept of Satellite Gravity Gradiometry based on differential microaccelerometry has been proposed by ONERA in the early eighties. Since 1986, an important effort is devoted to the development of the GRADIO accelerometers. Their configuration has been optimized for the ARISTOTELES mission with the objective of 0.01 Eotvos resolution for an integrating time of 4 s. The achieved resolution, better than 10 exp -9 G, is limited by the actual stability of alignments on the testing equipment.

  3. Research on the effect of wear-ring clearances to the performance of centrifugal pump

    NASA Astrophysics Data System (ADS)

    Zhao, W. G.; Li, Y. B.; Wang, X. Y.; Sun, J. P.; Wu, G. X.

    2012-11-01

    In order to study the effect of wear-ring clearance on the performance of centrifugal pump, based on the Reynolds Time-Averaged N-S equations and RNG k-ε turbulence model, a centrifugal pump was simulated with three variable styles of the wear-rings: Only the clearance of the front wear-ring was changed, only the clearance of the back wear-ring was changed and both were changed. Numerical results agree well with the experimental results. In the three changing styles of the clearance, the variable of the clearance of front wear-ring has the most influence on the performance of centrifugal pump. The existence of wear-ring not only has an effect on the volumetric loss of the centrifugal pump, but also on the performance of the centrifugal pump. Relative to the experimental studies, numerical simulation methods have some advantages, such as low cost, fast and efficient, and easy to get the detailed structure of the internal flow characteristics, so it has been widely used in the fluid machinery study. In order to study the effect of wear-ring clearance on the performance of centrifugal pump, based on the Reynolds Time-Averaged N-S equations and RNG k-ε turbulence model, a centrifugal pump was simulated with three variable styles of the wear-rings: Only the clearance of the front wear-ring was changed, only the clearance of the back wear-ring was changed and both were changed. Numerical results agree well with the experimental results. In the three changing styles of the clearance, the variable of the clearance of front wear-ring has the most influence on the performance of centrifugal pump.

  4. A novel differential optical fiber accelerometer

    NASA Astrophysics Data System (ADS)

    Pi, Shaohua; Zhao, Jiang; Hong, Guangwei; Jia, Bo

    2013-08-01

    The development of sensitive fiber-optic accelerometers is a subject of continuing interest. To acquire high resolution, Michelson phase interferometric techniques are widely adopted. Among the variety structures, the compliant cylinder approach is particularly attractive due to its high sensitivity that is defined as the induced phase shift per applied acceleration. While the two arms of Michelson interferometer should be at the same optical path, it is inconvenient to adjust the two arms' length to equal, also the polarization instability and phase random drift will cause a signal decline. To overcome these limitations, a novel optical fiber accelerometer based on differential interferometric techniques is proposed and investigated. The interferometer is a Sagnac-like white light interferometer, which means the bandwidth of laser spectrum can be as wide as tens nanometers. This interferometer was firstly reported by Levin in 1990s. Lights are divided to two paths before entering the coupler. To induce time difference, one passes through a delay arm and another goes a direct arm. After modulated by the sensing component, they reflect to opposite arm. The sensing part is formed by a seismic mass that is held to only one compliant cylinder, where the single-mode optical fiber is wrapped tightly. When sticking to vibrations, the cylinder compresses or stretches as a spring. The corresponding changes in cylinder circumference lead to strain in the sensing fibers, which is detected as an optical phase shift by the interferometer. The lights from two arms reach the vibration source at different time, sensing a different accelerate speed; produce a different optic path difference. Integrating the dissimilarity of the accelerated speed by time can obtain the total acceleration graph. A shaker's vibration has been tested by the proposed accelerometer referring to a standard piezoelectric accelerometer. A 99.8% linearity of the optical phase shift to the ground acceleration

  5. Characterization of accelerometer mountings in shock environments

    SciTech Connect

    Boatman, V.I.; Solomon, O.M. Jr.

    1986-08-01

    This report describes the shock test characterization of four accelerometer mounting techniques which are: adiprene and wax, polysulfide rubber and wax, restrained adiprene, and hard mount. The mountings have all been used in field tests, and the shock testing provides some simulation of the field test environments. The characteristics of these mountings are analyzed in the time-domain and in the frequency-domain and are compared to the response of a reference accelerometer at two different shock levels, approximately 2 kg and 7 kg. While soft mounting techniques can be used to guarantee acceleratometers survival in severe mechanical environments, this report documents the tested mounting materials to be highly nonlinear. These nonlinearities result in significant data distortion at frequencies above a few hundred hertz.

  6. Accurate Telescope Mount Positioning with MEMS Accelerometers

    NASA Astrophysics Data System (ADS)

    Mészáros, L.; Jaskó, A.; Pál, A.; Csépány, G.

    2014-08-01

    This paper describes the advantages and challenges of applying microelectromechanical accelerometer systems (MEMS accelerometers) in order to attain precise, accurate, and stateless positioning of telescope mounts. This provides a completely independent method from other forms of electronic, optical, mechanical or magnetic feedback or real-time astrometry. Our goal is to reach the subarcminute range which is considerably smaller than the field-of-view of conventional imaging telescope systems. Here we present how this subarcminute accuracy can be achieved with very cheap MEMS sensors and we also detail how our procedures can be extended in order to attain even finer measurements. In addition, our paper discusses how can a complete system design be implemented in order to be a part of a telescope control system.

  7. Micromachined accelerometer design, modeling and validation

    SciTech Connect

    Davies, B.R.; Bateman, V.I.; Brown, F.A.; Montague, S.; Murray, J.R.; Rey, D.; Smith, J.H.

    1998-04-01

    Micromachining technologies enable the development of low-cost devices capable of sensing motion in a reliable and accurate manner. The development of various surface micromachined accelerometers and gyroscopes to sense motion is an ongoing activity at Sandia National Laboratories. In addition, Sandia has developed a fabrication process for integrating both the micromechanical structures and microelectronics circuitry of Micro-Electro-Mechanical Systems (MEMS) on the same chip. This integrated surface micromachining process provides substantial performance and reliability advantages in the development of MEMS accelerometers and gyros. A Sandia MEMS team developed a single-axis, micromachined silicon accelerometer capable of surviving and measuring very high accelerations, up to 50,000 times the acceleration due to gravity or 50 k-G (actually measured to 46,000 G). The Sandia integrated surface micromachining process was selected for fabrication of the sensor due to the extreme measurement sensitivity potential associated with integrated microelectronics. Measurement electronics capable of measuring at to Farad (10{sup {minus}18} Farad) changes in capacitance were required due to the very small accelerometer proof mass (< 200 {times} 10{sup {minus}9} gram) used in this surface micromachining process. The small proof mass corresponded to small sensor deflections which in turn required very sensitive electronics to enable accurate acceleration measurement over a range of 1 to 50 k-G. A prototype sensor, based on a suspended plate mass configuration, was developed and the details of the design, modeling, and validation of the device will be presented in this paper. The device was analyzed using both conventional lumped parameter modeling techniques and finite element analysis tools. The device was tested and performed well over its design range.

  8. Effects of liquid cooling garments on recovery and performance time in individuals performing strenuous work wearing a firefighter ensemble.

    PubMed

    Kim, Jung-Hyun; Coca, Aitor; Williams, W Jon; Roberge, Raymond J

    2011-07-01

    This study investigated the effects of body cooling using liquid cooling garments (LCG) on performance time (PT) and recovery in individuals wearing a fully equipped prototype firefighter ensemble (PFE) incorporating a self-contained breathing apparatus (SCBA). Six healthy male participants (three firefighters and three non-firefighters) completed six experimental sessions in an environmental chamber (35°C, 50% relative humidity), consisting of three stages of 15 min exercise at 75% VO2max, and 10 min rest following each exercise stage. During each session, one of the following six conditions was administered in a randomized order: control (no cooling, CON); air ventilation of exhaust SCBA gases rerouted into the PFE (AV); top cooling garment (TCG); TCG combined with AV (TCG+AV); a shortened whole body cooling garment (SCG), and SCG combined with AV (SCG+AV). Results showed that total PT completed was longer under SCG and SCG+AV compared with CON, AV, TCG, and TCG+AV (p<0.01). Magnitude of core temperature (Tc) elevation was significantly decreased when SCG was utilized (p<0.01), and heart rate recovery rate (10 min) was enhanced under SCG, SCG+AV, TCG, and TCG+AV compared with CON (p<0.05). Estimated Esw rate (kg·h(-1)) was the greatest in CON, 1.62 (0.37), and the least in SCG+AV 0.98 (0.44): (descending order: CON>AV>TCG=TCG+AV>SCG>SCG+AV) without a statistical difference between the conditions (p<0.05). Results of the present study suggest that the application of LCG underneath the PFE significantly improves the recovery during a short period of rest and prolongs performance time in subsequent bouts of exercise. LCG also appears to be an effective method for body cooling that promotes heat dissipation during uncompensable heat stress.

  9. The LISA accelerometer

    NASA Astrophysics Data System (ADS)

    Rodrigues, M.; Touboul, P.

    2003-10-01

    In the frame of investigating the fundamental nature of gravity, the Laser Interferometer Space Antenna (LISA) mission could open the way to a new kind of observations unreachable from ground. The experiment, based on a V-formation of six drag-free spacecraft, uses the cubic proof masses of inertial sensors to reflect the laser light, acting as reference mirrors of a 5 × 10 9 m arm length interferometer. The proof masses are also used as inertial references for the drag-free control of the spacecraft which constitute in return a shield against external forces. Derived from space electrostatic accelerometers developed at ONERA, such as GRADIO for the ESA ARISTOTELES and now GOCE mission (Bernard and Touboul, 1991), the proposed LISA sensor should shield its proof mass from any accelerometric disturbance at a level of 10 -15ms-2Hz- 1/2. The accurate capacitive sensing of the mass provides its position relative to the satellite with a resolution better than 10 -9m Hz- 1/2 in order to control the satellite orbit and to minimise the disturbances induced by the satellite self gravity or by the proof mass charge. The sensor configuration and accomodation has to be specifically optimised for the mission requirements. Fortunately, the sensor will benefit from the thermal stability of the LISA optical bench environment, i.e. 10 -6K Hz- 1/2, and of the selected materials that exhibit a very low coefficient of thermal expansion (CTE), ensuring a high geometrical stability. Apart from the modeling and the evaluation of the flight characteristics, the necessary indirect ground demonstration of the performance and the interfaces with the drag-free control will have to be considered in detail in the future.

  10. MEMS accelerometers in accurate mount positioning systems

    NASA Astrophysics Data System (ADS)

    Mészáros, László; Pál, András.; Jaskó, Attila

    2014-07-01

    In order to attain precise, accurate and stateless positioning of telescope mounts we apply microelectromechanical accelerometer systems (also known as MEMS accelerometers). In common practice, feedback from the mount position is provided by electronic, optical or magneto-mechanical systems or via real-time astrometric solution based on the acquired images. Hence, MEMS-based systems are completely independent from these mechanisms. Our goal is to investigate the advantages and challenges of applying such devices and to reach the sub-arcminute range { that is well smaller than the field-of-view of conventional imaging telescope systems. We present how this sub-arcminute accuracy can be achieved with very cheap MEMS sensors. Basically, these sensors yield raw output within an accuracy of a few degrees. We show what kind of calibration procedures could exploit spherical and cylindrical constraints between accelerometer output channels in order to achieve the previously mentioned accuracy level. We also demonstrate how can our implementation be inserted in a telescope control system. Although this attainable precision is less than both the resolution of telescope mount drive mechanics and the accuracy of astrometric solutions, the independent nature of attitude determination could significantly increase the reliability of autonomous or remotely operated astronomical observations.

  11. Computational wear prediction of artificial knee joints based on a new wear law and formulation.

    PubMed

    Abdelgaied, Abdellatif; Liu, Feng; Brockett, Claire; Jennings, Louise; Fisher, John; Jin, Zhongmin

    2011-04-01

    Laboratory joint wear simulator testing has become the standard means for preclinical evaluation of wear resistance of artificial knee joints. Recent simulator designs have been advanced and become successful at reproducing the wear patterns observed in clinical retrievals. However, a single simulator test can be very expensive and take a long time to run. On the other hand computational wear modelling is an alternative attractive solution to these limitations. Computational models have been used extensively for wear prediction and optimisation of artificial knee designs. However, all these models have adopted the classical Archard's wear law, which was developed for metallic materials, and have selected wear factors arbitrarily. It is known that such an approach is not generally true for polymeric bearing materials and is difficult to implement due to the high dependence of the wear factor on the contact pressure. Therefore, these studies are generally not independent and lack general predictability. The objective of the present study was to develop a new computational wear model for the knee implants, based on the contact area and an independent experimentally determined non-dimensional wear coefficient. The effects of cross-shear and creep on wear predictions were also considered. The predicted wear volume was compared with the laboratory simulation measurements. The model was run under two different kinematic inputs and two different insert designs with curved and custom designed flat bearing surfaces. The new wear model was shown to be capable of predicting the difference of the wear volume and wear pattern between the two kinematic inputs and the two tibial insert designs. Conversely, the wear factor based approach did not predict such differences. The good agreement found between the computational and experimental results, on both the wear scar areas and volumetric wear rates, suggests that the computational wear modelling based on the new wear law and the

  12. Measurement of Impact Acceleration: Mouthpiece Accelerometer Versus Helmet Accelerometer

    PubMed Central

    Higgins, Michael; Halstead, P. David; Snyder-Mackler, Lynn; Barlow, David

    2007-01-01

    Context: Instrumented helmets have been used to estimate impact acceleration imparted to the head during helmet impacts. These instrumented helmets may not accurately measure the actual amount of acceleration experienced by the head due to factors such as helmet-to-head fit. Objective: To determine if an accelerometer attached to a mouthpiece (MP) provides a more accurate representation of headform center of gravity (HFCOG) acceleration during impact than does an accelerometer attached to a helmet fitted on the headform. Design: Single-factor research design in which the independent variable was accelerometer position (HFCOG, helmet, MP) and the dependent variables were g and Severity Index (SI). Setting: Independent impact research laboratory. Intervention(s): The helmeted headform was dropped (n = 168) using a National Operating Committee on Standards for Athletic Equipment (NOCSAE) drop system from the standard heights and impact sites according to NOCSAE test standards. Peak g and SI were measured for each accelerometer position during impact. Main Outcome Measures: Upon impact, the peak g and SI were recorded for each accelerometer location. Results: Strong relationships were noted for HFCOG and MP measures, and significant differences were seen between HFCOG and helmet g measures and HFCOG and helmet SI measures. No statistically significant differences were noted between HFCOG and MP g and SI measures. Regression analyses showed a significant relationship between HFCOG and MP measures but not between HFCOG and helmet measures. Conclusions: Upon impact, MP acceleration (g) and SI measurements were closely related to and more accurate in measuring HFCOG g and SI than helmet measurements. The MP accelerometer is a valid method for measuring head acceleration. PMID:17597937

  13. FPGA-Based Fused Smart-Sensor for Tool-Wear Area Quantitative Estimation in CNC Machine Inserts

    PubMed Central

    Trejo-Hernandez, Miguel; Osornio-Rios, Roque Alfredo; de Jesus Romero-Troncoso, Rene; Rodriguez-Donate, Carlos; Dominguez-Gonzalez, Aurelio; Herrera-Ruiz, Gilberto

    2010-01-01

    Manufacturing processes are of great relevance nowadays, when there is a constant claim for better productivity with high quality at low cost. The contribution of this work is the development of a fused smart-sensor, based on FPGA to improve the online quantitative estimation of flank-wear area in CNC machine inserts from the information provided by two primary sensors: the monitoring current output of a servoamplifier, and a 3-axis accelerometer. Results from experimentation show that the fusion of both parameters makes it possible to obtain three times better accuracy when compared with the accuracy obtained from current and vibration signals, individually used. PMID:22319304

  14. Dual-Element Tunneling Accelerometer

    NASA Technical Reports Server (NTRS)

    Kaiser, William J.; Kenny, Thomas W.; Rockstad, Howard K.; Reynolds, Joseph K.

    1994-01-01

    Improved micromachined tunneling accelerometer contains two deflecting transducer elements: One an elastically supported proof mass having relatively low resonant frequency; other cantilever tunneling transducer that tracks displacement of proof mass and has relatively high resonant frequency ({sup a} 10 kHz). Deflection voltage generated by circuit like described in "Wideband Feedback Circuit for Tunneling Sensor" (NPO-18866). Accelerometers of this type suited for underwater acoustic measurements, detecting vibrations associated with malfunctions in vehicles, detecting seismic signals, monitoring and controlling vibrations in structures, and other applications.

  15. System Wide Joint Position Sensor Fault Tolerance in Robot Systems Using Cartesian Accelerometers

    NASA Technical Reports Server (NTRS)

    Aldridge, Hal A.; Juang, Jer-Nan

    1997-01-01

    Joint position sensors are necessary for most robot control systems. A single position sensor failure in a normal robot system can greatly degrade performance. This paper presents a method to obtain position information from Cartesian accelerometers without integration. Depending on the number and location of the accelerometers. the proposed system can tolerate the loss of multiple position sensors. A solution technique suitable for real-time implementation is presented. Simulations were conducted using 5 triaxial accelerometers to recover from the loss of up to 4 joint position sensors on a 7 degree of freedom robot moving in general three dimensional space. The simulations show good estimation performance using non-ideal accelerometer measurements.

  16. Accelerometer having integral fault null

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr. (Inventor)

    1995-01-01

    An improved accelerometer is introduced. It comprises a transducer responsive to vibration in machinery which produces an electrical signal related to the magnitude and frequency of the vibration; and a decoding circuit responsive to the transducer signal which produces a first fault signal to produce a second fault signal in which ground shift effects are nullified.

  17. Evaluation of infrared thermography body temperature and collar-mounted accelerometer and acoustic technology for predicting time of ovulation of cows in a pasture-based system.

    PubMed

    Talukder, S; Thomson, P C; Kerrisk, K L; Clark, C E F; Celi, P

    2015-03-01

    This study was conducted to test the hypothesis that the specificity of infrared thermography (IRT) in detecting cows about to ovulate could be improved using different body parts that are less likely to be contaminated by fecal matter. In addition, the combined activity and rumination data captured by accelerometers were evaluated to provide a more accurate indication of ovulation than the activity and rumination data alone. Thermal images of 30 cows were captured for different body areas (eye, ear, muzzle, and vulva) twice daily after AM and PM milking sessions during the entire experimental period. Milk progesterone data and insemination records were used to determine the date of ovulation. Cows were fitted with SCR heat and rumination long-distance tags (SCR HR LD) for 1 month. Activity- and rumination-based estrus alerts were initially identified using default threshold values set by the manufacturer; however, a range of thresholds was also created and tested for both activity and rumination to determine the potential for higher levels of accuracy of ovulation detection. Visual assessment of mounting indicators resulted in 75% sensitivity (Se), 100% specificity (Sp), and 100% positive predictive value (PPV). Overall, IRT showed poor performance for detecting cows about to ovulate. Vulval temperature resulted in the greatest (80%) Sp but the poorest (21%) Se compared with the IRT temperatures of other body areas. The SCR HR LD tags default threshold value resulted in 78% Se, 57% Sp, and 70% PPV. Lowering the activity threshold from the default value improved the sensitivity but created a large number of false positives, which resulted in a decrease in specificity. Lowering the activity threshold to 20 resulted in a detection performance of 80% Se, 94% Sp, and 67% PPV, whereas the rumination levels achieved 35% Se, 69% Sp, and 14% PPV. The area under the curve for the activity level, rumination level, and the combined measures of activity and rumination levels

  18. The GRADIO accelerometer: Design and development status

    NASA Astrophysics Data System (ADS)

    Bernard, Alain; Touboul, M. P.

    1991-12-01

    The concept of Satellite Gravity Gradiometry (SGG) based on differential microaccelerometry as proposed in the early eighties is summarized. Work devoted to the development of the GRADIO accelerometers is described. The configuration was optimized for the Aristoteles mission with the objective of increasing resolution for an integrating time of 4 s. Thanks to the selected three axis configuration, very sensitive differential tests were carried out between two very representative laboratory models, in directions perpendicular to gravity. The resolution of these tests, limited by the actual stability of alignments of the testing equipment is described.

  19. Multiple-stage integrating accelerometer

    DOEpatents

    Devaney, Howard F.

    1986-01-01

    An accelerometer assembly is provided for use in activating a switch in response to multiple acceleration pulses in series. The accelerometer includes a housing forming a chamber. An inertial mass or piston is slidably disposed in the chamber and spring biased toward a first or reset position. A damping system is also provided to damp piston movement in response to first and subsequent acceleration pulses. Additionally, a cam, including a Z-shaped slot, and cooperating follower pin slidably received therein are mounted to the piston and the housing. The middle or cross-over leg of the Z-shaped slot cooperates with the follower pin to block or limit piston movement and prevent switch activation in response to a lone acceleration pulse. The switch of the assembly is only activated after two or more separate acceleration pulses are sensed and the piston reaches the end of the chamber opposite the reset position.

  20. Multiple-stage integrating accelerometer

    DOEpatents

    Devaney, H.F.

    1984-06-27

    An accelerometer assembly is provided for use in activating a switch in response to multiple acceleration pulses in series. The accelerometer includes a housing forming a chamber. An inertial mass or piston is slidably disposed in the chamber and spring biased toward a first or reset position. A damping system is also provided to damp piston movement in response to first and subsequent acceleration pulses. Additionally, a cam, including a Z-shaped slot, and cooperating follower pin slidably received therein are mounted to the piston and the housing. The middle or cross-over leg of the Z-shaped slot cooperates with the follower pin to block or limit piston movement and prevent switch activation in response to a lone acceleration pulse. The switch of the assembly is only activated after two or more separate acceleration pulses are sensed and the piston reaches the end of the chamber opposite the reset position.

  1. Accelerometer Method and Apparatus for Integral Display and Control Functions

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr. (Inventor)

    1996-01-01

    Method and apparatus for detecting mechanical vibrations and outputting a signal in response thereto. Art accelerometer package having integral display and control functions is suitable for mounting upon the machinery to be monitored. Display circuitry provides signals to a bar graph display which may be used to monitor machine conditions over a period of time. Control switches may be set which correspond to elements in the bar graph to provide an alert if vibration signals increase in amplitude over a selected trip point. The circuitry is shock mounted within the accelerometer housing. The method provides for outputting a broadband analog accelerometer signal, integrating this signal to produce a velocity signal, integrating and calibrating the velocity signal before application to a display driver, and selecting a trip point at which a digitally compatible output signal is generated.

  2. Accelerometer Method and Apparatus for Integral Display and Control Functions

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr. (Inventor)

    1998-01-01

    Method and apparatus for detecting mechanical vibrations and outputting a signal in response thereto is discussed. An accelerometer package having integral display and control functions is suitable for mounting upon the machinery to be monitored. Display circuitry provides signals to a bar graph display which may be used to monitor machine conditions over a period of time. Control switches may be set which correspond to elements in the bar graph to provide an alert if vibration signals increase in amplitude over a selected trip point. The circuitry is shock mounted within the accelerometer housing. The method provides for outputting a broadband analog accelerometer signal, integrating this signal to produce a velocity signal, integrating and calibrating the velocity signal before application to a display driver, and selecting a trip point at which a digitally compatible output signal is generated.

  3. The effects of metabolic work rate and ambient environment on physiological tolerance times while wearing explosive and chemical personal protective equipment.

    PubMed

    Costello, Joseph T; Stewart, Kelly L; Stewart, Ian B

    2015-01-01

    This study evaluated the physiological tolerance times when wearing explosive and chemical (>35 kg) personal protective equipment (PPE) in simulated environmental extremes across a range of differing work intensities. Twelve healthy males undertook nine trials which involved walking on a treadmill at 2.5, 4, and 5.5 km·h(-1) in the following environmental conditions, 21, 30, and 37°C wet bulb globe temperature (WBGT). Participants exercised for 60 min or until volitional fatigue, core temperature reached 39°C, or heart rate exceeded 90% of maximum. Tolerance time, core temperature, skin temperature, mean body temperature, heart rate, and body mass loss were measured. Exercise time was reduced in the higher WBGT environments (WBGT37 < WBGT30 < WBGT21; P < 0.05) and work intensities (5.5 < 4 < 2.5 km·h(-1); P < 0.001). The majority of trials (85/108; 78.7%) were terminated due to participant's heart rate exceeding 90% of their maximum. A total of eight trials (7.4%) lasted the full duration. Only nine (8.3%) trials were terminated due to volitional fatigue and six (5.6%) due to core temperatures in excess of 39°C. These results demonstrate that physiological tolerance times are influenced by the external environment and workload and that cardiovascular strain is the limiting factor to work tolerance when wearing this heavy multilayered PPE.

  4. The effects of metabolic work rate and ambient environment on physiological tolerance times while wearing explosive and chemical personal protective equipment.

    PubMed

    Costello, Joseph T; Stewart, Kelly L; Stewart, Ian B

    2015-01-01

    This study evaluated the physiological tolerance times when wearing explosive and chemical (>35 kg) personal protective equipment (PPE) in simulated environmental extremes across a range of differing work intensities. Twelve healthy males undertook nine trials which involved walking on a treadmill at 2.5, 4, and 5.5 km·h(-1) in the following environmental conditions, 21, 30, and 37°C wet bulb globe temperature (WBGT). Participants exercised for 60 min or until volitional fatigue, core temperature reached 39°C, or heart rate exceeded 90% of maximum. Tolerance time, core temperature, skin temperature, mean body temperature, heart rate, and body mass loss were measured. Exercise time was reduced in the higher WBGT environments (WBGT37 < WBGT30 < WBGT21; P < 0.05) and work intensities (5.5 < 4 < 2.5 km·h(-1); P < 0.001). The majority of trials (85/108; 78.7%) were terminated due to participant's heart rate exceeding 90% of their maximum. A total of eight trials (7.4%) lasted the full duration. Only nine (8.3%) trials were terminated due to volitional fatigue and six (5.6%) due to core temperatures in excess of 39°C. These results demonstrate that physiological tolerance times are influenced by the external environment and workload and that cardiovascular strain is the limiting factor to work tolerance when wearing this heavy multilayered PPE. PMID:25866818

  5. The Effects of Metabolic Work Rate and Ambient Environment on Physiological Tolerance Times While Wearing Explosive and Chemical Personal Protective Equipment

    PubMed Central

    Costello, Joseph T.; Stewart, Kelly L.; Stewart, Ian B.

    2015-01-01

    This study evaluated the physiological tolerance times when wearing explosive and chemical (>35 kg) personal protective equipment (PPE) in simulated environmental extremes across a range of differing work intensities. Twelve healthy males undertook nine trials which involved walking on a treadmill at 2.5, 4, and 5.5 km·h−1 in the following environmental conditions, 21, 30, and 37°C wet bulb globe temperature (WBGT). Participants exercised for 60 min or until volitional fatigue, core temperature reached 39°C, or heart rate exceeded 90% of maximum. Tolerance time, core temperature, skin temperature, mean body temperature, heart rate, and body mass loss were measured. Exercise time was reduced in the higher WBGT environments (WBGT37 < WBGT30 < WBGT21; P < 0.05) and work intensities (5.5 < 4 < 2.5 km·h−1; P < 0.001). The majority of trials (85/108; 78.7%) were terminated due to participant's heart rate exceeding 90% of their maximum. A total of eight trials (7.4%) lasted the full duration. Only nine (8.3%) trials were terminated due to volitional fatigue and six (5.6%) due to core temperatures in excess of 39°C. These results demonstrate that physiological tolerance times are influenced by the external environment and workload and that cardiovascular strain is the limiting factor to work tolerance when wearing this heavy multilayered PPE. PMID:25866818

  6. Friction and Wear

    NASA Technical Reports Server (NTRS)

    Pomey, Jacques

    1952-01-01

    From the practical point of view, this analysis shows that each problem of friction or wear requires its particular solution. There is no universal solution; one or other of the factors predominates and defines the choice of the solution. In certain cases, copper alloys of great thermal conductivity are preferred; in others, plastics abundantly supplied with water. Sometimes, soft antifriction metals are desirable to distribute the load; at other times, hard metals with high resistance to abrasion or heat.

  7. Optimal GPS/accelerometer integration algorithm for monitoring the vertical structural dynamics

    NASA Astrophysics Data System (ADS)

    Meng, Xiaolin; Wang, Jian; Han, Houzeng

    2014-11-01

    The vertical structural dynamics is a crucial factor for structural health monitoring (SHM) of civil structures such as high-rise buildings, suspension bridges and towers. This paper presents an optimal GPS/accelerometer integration algorithm for an automated multi-sensor monitoring system. The closed loop feedback algorithm for integrating the vertical GPS and accelerometer measurements is proposed based on a 5 state extended KALMAN filter (EKF) and then the narrow moving window Fast Fourier Transform (FFT) analysis is applied to extract structural dynamics. A civil structural vibration is simulated and the analysed result shows the proposed algorithm can effectively integrate the online vertical measurements produced by GPS and accelerometer. Furthermore, the accelerometer bias and scale factor can also be estimated which is impossible with traditional integration algorithms. Further analysis shows the vibration frequencies detected in GPS or accelerometer are all included in the integrated vertical defection time series and the accelerometer can effectively compensate the short-term GPS outages with high quality. Finally, the data set collected with a time synchronised and integrated GPS/accelerometer monitoring system installed on the Nottingham Wilford Bridge when excited by 15 people jumping together at its mid-span are utilised to verify the effectiveness of this proposed algorithm. Its implementations are satisfactory and the detected vibration frequencies are 1.720 Hz, 1.870 Hz, 2.104 Hz, 2.905 Hz and also 10.050 Hz, which is not found in GPS or accelerometer only measurements.

  8. Emotion recognition based on customized smart bracelet with built-in accelerometer

    PubMed Central

    Zhang, Zhan; Song, Yufei; Cui, Liqing

    2016-01-01

    Background: Recently, emotion recognition has become a hot topic in human-computer interaction. If computers could understand human emotions, they could interact better with their users. This paper proposes a novel method to recognize human emotions (neutral, happy, and angry) using a smart bracelet with built-in accelerometer. Methods: In this study, a total of 123 participants were instructed to wear a customized smart bracelet with built-in accelerometer that can track and record their movements. Firstly, participants walked two minutes as normal, which served as walking behaviors in a neutral emotion condition. Participants then watched emotional film clips to elicit emotions (happy and angry). The time interval between watching two clips was more than four hours. After watching film clips, they walked for one minute, which served as walking behaviors in a happy or angry emotion condition. We collected raw data from the bracelet and extracted a few features from raw data. Based on these features, we built classification models for classifying three types of emotions (neutral, happy, and angry). Results and Discussion: For two-category classification, the classification accuracy can reach 91.3% (neutral vs. angry), 88.5% (neutral vs. happy), and 88.5% (happy vs. angry), respectively; while, for the differentiation among three types of emotions (neutral, happy, and angry), the accuracy can reach 81.2%. Conclusions: Using wearable devices, we found it is possible to recognize human emotions (neutral, happy, and angry) with fair accuracy. Results of this study may be useful to improve the performance of human-computer interaction. PMID:27547564

  9. New wear resistant composite material

    SciTech Connect

    Angers, R.; Champagne, B.; Fiset, M.; Chollet, P.

    1983-01-01

    A composite material consisting of WC-Co particles in a steel matrix was fabricated by sintering mixtures of WC-Co particles and a steel powder and infiltrating the sintered pieces with a copper alloy. Its wear resistance and mechanical properties were studied as a function of the content in WC-Co particles and other characteristics of the composite material microstructure. Infiltration provided a simple means to obtain a strong cohesion between WC-Co particles and the steel matrix. An effective matrix protection against wear is obtained with relatively low additions of particles especially with a silica abrasive which is soft with respect to cemented carbide. The experimental results show that this material has good mechanical properties and wear resistance. Depending upon abrasion resistance, wear losses are reduced up to 10 times by a 30 vol% addition of cemented carbide particles.

  10. Statistical analysis of accelerometer data in the online monitoring of a power slip ring in a wind turbine

    NASA Astrophysics Data System (ADS)

    Soua, S.; Bridge, B.; Cebulski, L.; Gan, T.-H.

    2012-03-01

    The use of a shock accelerometer for the continuous in-service monitoring of wear of the slip ring on a wind turbine generator is proposed and supporting results are presented. Five wear defects in the form of out-of-round circumference acceleration data with average radial dimensions in the range 5.9-25 µm were studied. A theoretical model of the acceleration at a point on the circumference of a ring as a function of the defect profile is presented. Acceleration data as a continuous function of time have been obtained for ring rotation frequencies that span the range of frequencies arising with the variation of wind speeds experienced under all in-service conditions. As a result, the measured RMS acceleration is proven to follow an overall increasing trend with frequency for all defects at all brush pressures. A statistical analysis of the root mean square of the time acceleration data as a function of the defect profiles, rotation speeds and brush contact pressure has been performed. The detection performance is considered in terms of the achievement of a signal to noise ratio exceeding 3 (99.997% defect detection probability). Under all conditions of rotation speed and pressure, this performance was achieved for average defect sizes as small as 10 µm, which is only 0.004% of the ring diameter. These results form the basis of a very sensitive defect alarm system.

  11. High shock, high frequency characteristics of a mechanical isolator for a piezoresistive accelerometer

    SciTech Connect

    Bateman, V.I.; Brown, F.A.; Davie, N.T.

    1995-07-01

    A mechanical isolator has been developed for a piezoresistive accelerometer. The purpose of the isolator is to mitigate high frequency shocks before they reach the accelerometer because the high frequency shocks may cause the accelerometer to resonate. Since the accelerometer is undamped, it often breaks when it resonates. The mechanical isolator was developed in response to impact test requirements for a variety of structures at Sandia National Laboratories. An Extended Technical Assistance Program with the accelerometer manufacturer has resulted in a commercial isolator that will be available to the general public. This mechanical isolator has ten times the bandwidth of any other commercial isolator and has acceptable frequency domain performance from DC to 10 kHz ({plus_minus} 10%) over a temperature range of -65{degrees}F to +185{degrees}F as demonstrated in this paper.

  12. Comparison of Four Actigraph Accelerometers During Walking and Running

    PubMed Central

    John, Dinesh; Tyo, Brian; Bassett, David R.

    2009-01-01

    Currently, researchers can use the Actigraph 7164 or one of three different versions of the Actigraph GT1M to objectively measure physical activity. Purpose To determine if differences exist between activity counts from the Actigraph 7164 and the three versions of the GT1M at given walking and running speeds. Methods Ten male participants (23.6 ± 2.7 yrs) completed treadmill walking and running at ten different speeds (3-minute stages) while wearing either the Actigraph 7164 and the latest GT1M (GT1M-V3) or GT1M version one (GT1M-V1) and GT1M version two (GT1M-V2). Participants walked at 3, 5, and at 7 km˙hr−1 followed by running at 8, 10, 12, 14, 16, 18, and 20 km˙hr−1. The accelerometers were worn on an elastic belt around the waist over the left and right hips. Testing was performed on different days using a counterbalanced within-subjects design to account for potential differences attributable to accelerometer placement. At each speed, a one-way repeated measures ANOVA was used to examine differences between activity counts in counts˙min−1(cpm). Post-hoc pairwise comparisons with Bonferroni adjustments were used where appropriate. Results There were no significant differences between activity counts at any given walking or running speed (p<0.05). At all running speeds, activity counts from the Actigraph 7164 and GT1M-V2 displayed the lowest and highest values, respectively. Output from all accelerometers peaked at 14 km˙hr−1 (mean range: 8974 ± 677 to 9412 ± 982 cpm) and then gradually declined at higher speeds. The mean difference score at peak output between the Actigraph 7164 and GT1M-V2 was 439 ± 565 cpm. Conclusions There were no statistically significant differences between outputs from all the accelerometers indicating that researchers can select any of the four Actigraph accelerometers to do research. PMID:19927022

  13. Validation of an accelerometer for measuring sport performance.

    PubMed

    Sato, Kimitake; Smith, Sarah L; Sands, William A

    2009-01-01

    Weightlifting technique is a well-studied subject with regard to standard biomechanical analysis that includes barbell velocity as well as barbell trajectory, but kinematic data such as barbell acceleration have not often been reported. Real-time or near-real-time feedback can be more helpful to coaches and athletes than delayed feedback. The purpose of this study was to validate measures obtained by a commercially available accelerometer in comparison with kinematic data derived from video. The hypothesis was that there would be a high positive relationship between accelerometer data and acceleration measures derived from video records of a barbell high-pull movement. Accelerometer values and kinematic data from high-speed video were obtained from 7 volunteers performing 2 trials each of a barbell high-pull. The results showed that the accelerometer measures were highly correlated with derived acceleration data from video (r = 0.94-0.99). On the basis of these results, the device was considered to be validated; thus, the unit may be a useful tool to measure acceleration during real-time training sessions rather than only reserved for collecting data in a laboratory setting. This device can be a valuable tool to provide instant feedback to coaches and athletes to assess individual barbell acceleration performance.

  14. Speech activity detection using accelerometer.

    PubMed

    Matic, Aleksandar; Osmani, Venet; Mayora, Oscar

    2012-01-01

    The level of social activity is linked to the overall wellbeing and to various disorders, including stress. In this regard, a myriad of automatic solutions for monitoring social interactions have been proposed, usually including audio data analysis. Such approaches often face legal and ethical issues and they may also raise privacy concerns in monitored subjects thus affecting their natural behaviour. In this paper we present an accelerometer-based speech detection which does not require capturing sensitive data while being an easily applicable and a cost-effective solution.

  15. SeismoGeodesy: Combination of High Rate, Real-time GNSS and Accelerometer Observations and Rapid Seismic Event Notification for Earth Quake Early Warning and Volcano Monitoring

    NASA Astrophysics Data System (ADS)

    Jackson, Michael; Zimakov, Leonid; Moessmer, Matthias

    2015-04-01

    Scientific GNSS networks are moving towards a model of real-time data acquisition, epoch-by-epoch storage integrity, and on-board real-time position and displacement calculations. This new paradigm allows the integration of real-time, high-rate GNSS displacement information with acceleration and velocity data to create very high-rate displacement records. The mating of these two instruments allows the creation of a new, very high-rate (200 Hz) displacement observable that has the full-scale displacement characteristics of GNSS and high-precision dynamic motions of seismic technologies. It is envisioned that these new observables can be used for earthquake early warning studies, volcano monitoring, and critical infrastructure monitoring applications. Our presentation will focus on the characteristics of GNSS, seismic, and strong motion sensors in high dynamic environments, including historic earthquakes replicated on a shake table over a range of displacements and frequencies. We will explore the optimum integration of these sensors from a filtering perspective including simple harmonic impulses over varying frequencies and amplitudes and under the dynamic conditions of various earthquake scenarios. We will also explore the tradeoffs between various GNSS processing schemes including real-time precise point positioning (PPP) and real-time kinematic (RTK) as applied to seismogeodesy. In addition we will discuss implementation of a Rapid Seismic Event Notification System that provides quick delivery of digital data from seismic stations to the acquisition and processing center and a full data integrity model for real-time earthquake notification that provides warning prior to significant ground shaking.

  16. Micromachined low frequency rocking accelerometer with capacitive pickoff

    DOEpatents

    Lee, Abraham P.; Simon, Jonathon N.; McConaghy, Charles F.

    2001-01-01

    A micro electro mechanical sensor that uses capacitive readout electronics. The sensor involves a micromachined low frequency rocking accelerometer with capacitive pickoff fabricated by deep reactive ion etching. The accelerometer includes a central silicon proof mass, is suspended by a thin polysilicon tether, and has a moving electrode (capacitor plate or interdigitated fingers) located at each end the proof mass. During movement (acceleration), the tethered mass moves relative to the surrounding packaging, for example, and this defection is measured capacitively by a plate capacitor or interdigitated finger capacitor, having the cooperating fixed electrode (capacitor plate or interdigitated fingers) positioned on the packaging, for example. The micromachined rocking accelerometer has a low frequency (<500 Hz), high sensitivity (.mu.G), with minimal power usage. The capacitors are connected to a power supply (battery) and to sensor interface electronics, which may include an analog to digital (A/D) converter, logic, RF communication link, antenna, etc. The sensor (accelerometer) may be, for example, packaged along with the interface electronics and a communication system in a 2".times.2".times.2" cube. The proof mass may be asymmetric or symmetric. Additional actuating capacitive plates may be used for feedback control which gives a greater dynamic range.

  17. Validation study of Polar V800 accelerometer

    PubMed Central

    Hernández-Vicente, Adrián; De Cocker, Katrien; Garatachea, Nuria

    2016-01-01

    Background The correct quantification of physical activity (PA) and energy expenditure (EE) in daily life is an important target for researchers and professionals. The objective of this paper is to study the validity of the Polar V800 for the quantification of PA and the estimation of EE against the ActiGraph (ActiTrainer) in healthy young adults. Methods Eighteen Caucasian active people (50% women) aged between 19–23 years wore an ActiTrainer on the right hip and a Polar V800 on the preferred wrist during 7 days. Paired samples t-tests were used to analyze differences in outcomes between devices, and Pearson’s correlation coefficients to examine the correlation between outcomes. The agreement was studied using the Bland-Altman method. Also, the association between the difference and the magnitude of the measurement (heteroscedasticity) was examined. Sensitivity, specificity and area under the receiver operating characteristic curve (ROC-AUC value) were calculated to evaluate the ability of the devices to accurately define a person who fulfills the recommendation of 10,000 daily steps. Results The devices significantly differed from each other on all outcomes (P<0.05), except for Polar V800’s alerts vs. ActiTrainer’s 1 hour sedentary bouts (P=0.595) and Polar V800’s walking time vs. ActiTrainer’s lifestyle time (P=0.484). Heteroscedasticity analyses were significant for all outcomes, except for Kcal and sitting time. The ROC-AUC value was fair (0.781±0.048) and the sensitivity and specificity was 98% and 58%, respectively. Conclusions The Polar V800 accelerometer has a comparable validity to the accelerometer in free-living conditions, regarding “1 hour sedentary bouts” and “V800’s walking time vs. ActiTrainer’s lifestyle time” in young adults. PMID:27570772

  18. Integrated SeismoGeodetic Systsem with High-Resolution, Real-Time GNSS and Accelerometer Observation For Earthquake Early Warning Application.

    NASA Astrophysics Data System (ADS)

    Passmore, P. R.; Jackson, M.; Zimakov, L. G.; Raczka, J.; Davidson, P.

    2014-12-01

    The key requirements for Earthquake Early Warning and other Rapid Event Notification Systems are: Quick delivery of digital data from a field station to the acquisition and processing center; Data integrity for real-time earthquake notification in order to provide warning prior to significant ground shaking in the given target area. These two requirements are met in the recently developed Trimble SG160-09 SeismoGeodetic System, which integrates both GNSS and acceleration measurements using the Kalman filter algorithm to create a new high-rate (200 sps), real-time displacement with sufficient accuracy and very low latency for rapid delivery of the acquired data to a processing center. The data acquisition algorithm in the SG160-09 System provides output of both acceleration and displacement digital data with 0.2 sec delay. This is a significant reduction in the time interval required for real-time transmission compared to data delivery algorithms available in digitizers currently used in other Earthquake Early Warning networks. Both acceleration and displacement data are recorded and transmitted to the processing site in a specially developed Multiplexed Recording Format (MRF) that minimizes the bandwidth required for real-time data transmission. In addition, a built in algorithm calculates the τc and Pd once the event is declared. The SG160-09 System keeps track of what data has not been acknowledged and re-transmits the data giving priority to current data. Modified REF TEK Protocol Daemon (RTPD) receives the digital data and acknowledges data received without error. It forwards this "good" data to processing clients of various real-time data processing software including Earthworm and SeisComP3. The processing clients cache packets when a data gap occurs due to a dropped packet or network outage. The cache packet time is settable, but should not exceed 0.5 sec in the Earthquake Early Warning network configuration. The rapid data transmission algorithm was tested

  19. Superconducting six-axis accelerometer

    NASA Technical Reports Server (NTRS)

    Paik, H. J.

    1990-01-01

    A new superconducting accelerometer, capable of measuring both linear and angular accelerations, is under development at the University of Maryland. A single superconducting proof mass is magnetically levitated against gravity or any other proof force. Its relative positions and orientations with respect to the platform are monitored by six superconducting inductance bridges sharing a single amplifier, called the Superconducting Quantum Interference Device (SQUID). The six degrees of freedom, the three linear acceleration components and the three angular acceleration components, of the platform are measured simultaneously. In order to improve the linearity and the dynamic range of the instrument, the demodulated outputs of the SQUID are fed back to appropriate levitation coils so that the proof mass remains at the null position for all six inductance bridges. The expected intrinsic noise of the instrument is 4 x 10(exp -12)m s(exp -2) Hz(exp -1/2) for linear acceleration and 3 x 10(exp -11) rad s(exp -2) Hz(exp -1/2) for angular acceleration in 1-g environment. In 0-g, the linear acceleration sensitivity of the superconducting accelerometer could be improved by two orders of magnitude. The design and the operating principle of a laboratory prototype of the new instrument is discussed.

  20. Assessment of Gait Kinetics Using Tri-Axial Accelerometers

    PubMed Central

    Fortune, Emma; Morrow, Melissa M. B.; Kaufman, Kenton R.

    2015-01-01

    Repeated durations of dynamic activity with high ground reaction forces (GRFs) and loading rates (LRs) can be beneficial to bone health. To fully characterize dynamic activity in relation to bone health, field-based measurements of gait kinetics are desirable to assess free-living lower-extremity loading. The study aims were to determine correlations of peak vertical GRF and peak vertical LR with ankle peak vertical accelerations, and of peak resultant GRF and peak resultant LR with ankle peak resultant accelerations and to compare them to correlations with tibia, thigh, and waist accelerations. GRF data were collected as ten healthy subjects (26 (19–34) years) performed 8–10 walking trials at velocities ranging from 0.19–3.05 m/s, wearing ankle, tibia, thigh, and waist accelerometers. While peak vertical accelerations of all locations were positively correlated with peak vertical GRF and LR (r2>0.53, P<0.001), ankle peak vertical accelerations were the most correlated (r2>0.75, P<0.001). All peak resultant accelerations were positively correlated with peak resultant GRF and LR (r2>0.57, P<0.001) with waist peak resultant acceleration being the most correlated (r2>0.70, P<0.001). The results suggest that ankle or waist accelerometers give the most accurate peak GRF and LR estimates and could be useful tools in relating physical activity to bone health. PMID:25010675

  1. The development of an optical fiber accelerometer

    NASA Astrophysics Data System (ADS)

    Casalnuovo, S. A.; Sleefe, G. E.; James, C. E.

    1992-01-01

    We describe the design and operation of an optical fiber accelerometer intended for environments inhospitable to electronic components. An overview of the device is presented along with descriptions of the optical, electronic, and mechanical components. The performance of the current prototype is equivalent to state of the art piezoelectric accelerometers. Improvements to the current design are discussed.

  2. Display-And-Alarm Circuit For Accelerometer

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr.

    1995-01-01

    Compact accelerometer assembly consists of commercial accelerometer retrofit with display-and-alarm circuit. Provides simple means for technician attending machine to monitor vibrations. Also simpifies automatic safety shutdown by providing local alarm or shutdown signal when vibration exceeds preset level.

  3. Interinstrument Reliability of the RT3 Accelerometer

    ERIC Educational Resources Information Center

    Reneman, Michiel

    2010-01-01

    The objective of this study was to assess the interinstrument reliability of six RT3 accelerometers for measuring physical activities. Each of the six healthy participants, mean age 36.1 years (SD 9.4), carried six RT3 accelerometers (same type and same producer) simultaneously placed ventrally at the waist belt. The participants performed three…

  4. Wear and Tear - Mechanical

    NASA Technical Reports Server (NTRS)

    Swanson, Theodore

    2008-01-01

    The focus of this chapter is on the long term wear and tear, or aging, of the mechanical subsystem of a spacecraft. The mechanical subsystem is herein considered to be the primary support structure (as in a skeleton or exoskeleton) upon which all other spacecraft systems rest, and the associated mechanisms. Mechanisms are devices which have some component that moves at least once, in response to some type of passive or active control system. For the structure, aging may proceed as a gradual degradation of mechanical properties and/or function, possibly leading to complete structural failure over an extended period of time. However, over the 50 years of the Space Age such failures appear to be unusual. In contrast, failures for mechanisms are much more frequent and may have a very serious effect on mission performance. Just as on Earth, all moving devices are subject to normal (and possibly accelerated) degradation from mechanical wear due to loss or breakdown of lubricant, misalignment, temperature cycling effects, improper design/selection of materials, fatigue, and a variety of other effects. In space, such environmental factors as severe temperature swings (possibly 100's of degrees C while going in and out of direct solar exposure), hard vacuum, micrometeoroids, wear from operation in a dusty or contaminated environment, and materials degradation from radiation can be much worse. In addition, there are some ground handling issues such as humidity, long term storage, and ground transport which may be of concern. This chapter addresses the elements of the mechanical subsystem subject to wear, and identifies possible causes. The potential impact of such degradation is addressed, albeit with the recognition that the impact of such wear often depends on when it occurs and on what specific components. Most structural elements of the mechanical system typically are conservatively designed (often to a safety factor of greater than approximately 1.25 on yield for

  5. Diurnal Cycles of Tree Mass Obtained Using Accelerometers

    NASA Astrophysics Data System (ADS)

    Llamas, R. A.; Niemeier, J. J.; Kruger, A.; Lintz, H. E.; Kleinknecht, G. J.; Miller, R. A.

    2013-12-01

    We used a non-invasive technique to estimate the mass of trees using accelerometers. The technique was inspired by Selker et al., 2011 who performed experiments with an oak tree to estimate the time-varying canopy mass. The technique consists of placing an accelerometer on the trunk of a live tree. The resonance frequency is related to the mass of the tree. Wind drives the tree and the accelerometer data are analyzed to obtain estimates of the resonance frequency and mass of the tree. In addition to wind speed and direction, we also collected ambient temperature and rain accumulation using co-located instruments. We collected data for 3 months using several accelerometers configured for different sampling rates. Analysis of the data revealed diurnal cycles in temperature, wind speed, and tree mass derived from the tree resonance frequency. We used the Welch method for power spectral density estimation to obtain hourly estimates of the tree resonance frequency. Our hypothesis is that the mass diurnal cycle is related to the tree water content.

  6. Duration and breaks in sedentary behaviour: accelerometer data from 1566 community-dwelling older men (British Regional Heart Study)

    PubMed Central

    Jefferis, Barbara J; Sartini, Claudio; Shiroma, Eric; Whincup, Peter H; Wannamethee, S Goya; Lee, I-Min

    2015-01-01

    Background Sedentary behaviours are increasingly recognised as raising the risk of cardiovascular disease events, diabetes and mortality, independently of physical activity levels. However, little is known about patterns of sedentary behaviour in older adults. Methods Cross-sectional study of 1566/3137 (50% response) men aged 71–91 years from a UK population-based cohort study. Men wore a GT3x accelerometer over the hip for 1 week in 2010–2011. Mean daily minutes of sedentary behaviours, percentage of day in sedentary behaviours, sedentary bouts and breaks were calculated and summarised by health and demographic characteristics. Results 1403 ambulatory men aged 78.4 years (SD=4.6 years) with ≥600 min of accelerometer wear on ≥3 days had complete data on covariables. Men spent on average 618 min (SD=83), or 72% of their day in sedentary behaviours (<100 counts/min). On average, men accumulated 72 spells of sedentary behaviours per day, with 7 breaks in each sedentary hour. Men had on average 5.1 sedentary bouts of ≥30 min, which accounted for 43% of sedentary time, and 1.4 bouts of ≥60 min, which accounted for 19% of daily sedentary time. Men who were over 80 years old, obese, depressed and had multiple chronic conditions accumulated more sedentary time and spent more time in longer sedentary bouts. Conclusions Older men spend nearly three quarters of their day in sedentary behaviours, mostly accumulated in short bouts, although bouts lasting ≥30 min accounted for nearly half of the sedentary time each day. Men with medical risk factors were more likely to also display sedentary behaviour. PMID:25232029

  7. Accelerometer method and apparatus for integral display and control functions

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr. (Inventor)

    1992-01-01

    Vibration analysis has been used for years to provide a determination of the proper functioning of different types of machinery, including rotating machinery and rocket engines. A determination of a malfunction, if detected at a relatively early stage in its development, will allow changes in operating mode or a sequenced shutdown of the machinery prior to a total failure. Such preventative measures result in less extensive and/or less expensive repairs, and can also prevent a sometimes catastrophic failure of equipment. Standard vibration analyzers are generally rather complex, expensive, and of limited portability. They also usually result in displays and controls being located remotely from the machinery being monitored. Consequently, a need exists for improvements in accelerometer electronic display and control functions which are more suitable for operation directly on machines and which are not so expensive and complex. The invention includes methods and apparatus for detecting mechanical vibrations and outputting a signal in response thereto. The apparatus includes an accelerometer package having integral display and control functions. The accelerometer package is suitable for mounting upon the machinery to be monitored. Display circuitry provides signals to a bar graph display which may be used to monitor machine condition over a period of time. Control switches may be set which correspond to elements in the bar graph to provide an alert if vibration signals increase over the selected trip point. The circuitry is shock mounted within the accelerometer housing. The method provides for outputting a broadband analog accelerometer signal, integrating this signal to produce a velocity signal, integrating and calibrating the velocity signal before application to a display driver, and selecting a trip point at which a digitally compatible output signal is generated. The benefits of a vibration recording and monitoring system with controls and displays readily

  8. An electrostatically rebalanced micromechanical accelerometer

    NASA Astrophysics Data System (ADS)

    Boxenhorn, Burton; Greiff, Paul

    The design and test performance of a low-cost micromechanical accelerometer (MA) with integral electrodes, developed for use with the vibratory micromechanical gyro described by Boxenhorn and Greiff (1988), are reported. The MA is a monolithic Si device of size 300 x 600 microns and comprises a torsional pendulum with capacitive readout and an electrostatic torquer. Data from 360-deg sweep tests performed in a g-field are presented in tables and graphs and discussed in detail. Results include bandwidth about 1 Hz, scale-factor error 480 ppm, stable bias of 260 microg over 203 min, and temperature effect 2100 microg/C on bias and -123 ppm/C on scale factor.

  9. 22 CFR 1203.735-212 - Wearing of uniforms.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... RESPONSIBILITIES AND CONDUCT Ethical and Other Conduct and Responsibilities of Employees § 1203.735-212 Wearing of... States to wear a uniform, care shall be taken that the uniform is worn only at authorized times and...

  10. A triaxial accelerometer monkey algorithm for optimal sensor placement in structural health monitoring

    NASA Astrophysics Data System (ADS)

    Jia, Jingqing; Feng, Shuo; Liu, Wei

    2015-06-01

    Optimal sensor placement (OSP) technique is a vital part of the field of structural health monitoring (SHM). Triaxial accelerometers have been widely used in the SHM of large-scale structures in recent years. Triaxial accelerometers must be placed in such a way that all of the important dynamic information is obtained. At the same time, the sensor configuration must be optimal, so that the test resources are conserved. The recommended practice is to select proper degrees of freedom (DOF) based upon several criteria and the triaxial accelerometers are placed at the nodes corresponding to these DOFs. This results in non-optimal placement of many accelerometers. A ‘triaxial accelerometer monkey algorithm’ (TAMA) is presented in this paper to solve OSP problems of triaxial accelerometers. The EFI3 measurement theory is modified and involved in the objective function to make it more adaptable in the OSP technique of triaxial accelerometers. A method of calculating the threshold value based on probability theory is proposed to improve the healthy rate of monkeys in a troop generation process. Meanwhile, the processes of harmony ladder climb and scanning watch jump are proposed and given in detail. Finally, Xinghai NO.1 Bridge in Dalian is implemented to demonstrate the effectiveness of TAMA. The final results obtained by TAMA are compared with those of the original monkey algorithm and EFI3 measurement, which show that TAMA can improve computational efficiency and get a better sensor configuration.

  11. Effectiveness of ice-vest cooling in prolonging work tolerance time during heavy exercise in the heat for personnel wearing Canadian forces chemical defense ensembles

    SciTech Connect

    Bain, B.

    1991-01-01

    Effectiveness of a portable, ice-pack cooling vest (Steelevest) in prolonging work tolerance time in chemical defense clothing in the heat (33 C dry bulb, 33% relative humidity or 25 C WBGT) was evaluated while subjects exercised at a metabolic rate of approx. 700 watts. Subjects were six male volunteers. The protocol consisted of a 20 minute treadmill walk at 1.33 m/s. and 7.5% grade, followed by 15 minutes of a lifting task, 5 minutes rest, then another 20 minutes of lifting task for a total of one hour. The lifting task consisted of lifting of 20 kg box, carrying it 3 meters and setting it down. This was followed by a 6 m walk (3m back to the start point and 3 m back to the box) 15 sec after which the lifting cycle began again. The work was classified as heavy as previously defined. This protocol was repeated until the subjects were unable to continue or they reached a physiological endpoint. Time to voluntary cessation or physiological endpoint was called the work tolerance time. Physiological endpoints were rectal temperature of 39 C, heart rate exceeding 95% of maximum for two consecutive minutes or visible loss of motor control or nausea. The cooling vest had no effect on work tolerance time, rate of rise of rectal temperature or sweat loss. It was concluded that the Steelvest ice-vest is ineffective in prolonging work tolerance time and preventing increases in rectal temperature while wearing chemical protective clothing.

  12. What Is the Effect on Obesity Indicators from Replacing Prolonged Sedentary Time with Brief Sedentary Bouts, Standing and Different Types of Physical Activity during Working Days? A Cross-Sectional Accelerometer-Based Study among Blue-Collar Workers

    PubMed Central

    Gupta, Nidhi; Heiden, Marina; Aadahl, Mette; Korshøj, Mette; Jørgensen, Marie Birk; Holtermann, Andreas

    2016-01-01

    Introduction The aim of the study was to investigate if (a) substituting total sedentary time or long sedentary bouts with standing or various types of physical activity and (b) substituting long sedentary bouts with brief sedentary bouts; is associated with obesity indicators using a cross sectional isotemporal substitution approach among blue-collar workers. Methods A total of 692 workers from transportation, manufacturing and cleaning sectors wore an Actigraph GT3X+ accelerometer on the thigh for 1–4 working days. The sedentary (sit and lie), standing, walking, and moderate to vigorous physical activity (MVPA) time on working days was computed using validated Acti4 software. The total sedentary time and uninterrupted sedentary time spent in brief (≤5 mins), moderate (>5 and ≤30 mins), and long (>30mins) bouts, were determined for the whole day and during work and non-work time separately. The obesity indicators, BMI (kg/m2), waist circumference (cm) and fat percentage were objectively measured. Isotemporal substitution modelling was utilized to determine the linear association with obesity indicators of replacing 30 min of total sedentary time or long sedentary bouts with standing, walking or MVPA and separately replacing 30 min of long sedentary bouts with brief sedentary bouts. Results Workers [mean (standard deviation, SD); age = 45.1 (9.9) years, BMI = 27.5 (4.9) kg/m2, %BF = 29.6 (9.5), waist circumference = 94.4 (13.0) cm] sat for 2.4 hours (~32% of the measured time, SD = 1.8 hours) across the day during work period and 5.5 hours (~62% of the measured time, SD = 1.5 hours) during non-work period. Most of the sedentary time was accrued in moderate bouts [work = 1.40 (SD = 1.09) hours] during work and in long bouts during non-work [2.7 (SD = 1.4) hours], while least in long sedentary bouts during work [work = 0.5 (SD = 0.9)] and in brief sedentary bouts [0.5 hours (SD = 0.3)] during non-work. Significant associations with all obesity indicators were

  13. Association of physical activity measured by accelerometer, knee joint abnormalities and cartilage T2-measurements obtained from 3T MRI: Data from the Osteoarthritis Initiative

    PubMed Central

    Kretzschmar, M.; Lin, W.; Nardo, L.; Joseph, G. B.; Dunlop, D. D.; Heilmeier, U.; Nevitt, M. C.; Alizai, H.; McCulloch, C. E.; Lynch, J. A.; Link, T. M.

    2015-01-01

    Objective To study the cross-sectional association between physical activity measured with an accelerometer, structural knee abnormalities and cartilage T2-values assessed with 3T MRI. Methods We included 274 subjects from the Osteoarthritis Initiative cohort without definite radiographic osteoarthritis (KL 0 and 1) and at most mild pain, stiffness and functional limitation in the study knee (WOMAC 0–1), which had not limited their activity due to knee pain. Physical activity was measured over seven days with an ActiGraph GT1M accelerometer. Subjects were categorized by quartile of physical activity based on the average daily minutes of moderate/vigorous activity (mv-PA). MR images of the right knee (at 48-months visit) were assessed for structural abnormalities using a modified WORMS score and for T2-relaxation times derived from segmented cartilage of 4 femorotibial regions and the patella. WORMS-grades and T2-measurements were compared between activity quartiles using a linear regression model. Covariates included age, sex, BMI, knee injury, family history of knee replacement, knee symptoms, hip and ankle pain and daily wear time of the accelerometer. Results Higher mv-PA was associated with increased severity (p=0.0087) and number of lesions of the medial meniscus (p=0.0089) and severity of bone marrow edema lesions (p=0.0053). No association between cartilage lesions and mv-PA was found. T2-values of cartilage (loss, damage, abnormalities) tended to be greater in the higher quartiles of mv-PA, but the differences were non-significant. Conclusion In knees without radiographic osteoarthritis in subjects with no or mild knee pain, higher physical activity levels were associated with increases in meniscal and BMEP lesions. PMID:25777255

  14. GRADIO three-axis electrostatic accelerometers

    NASA Technical Reports Server (NTRS)

    Bernard, A.

    1987-01-01

    Dedicated accelerometers for satellite gravity gradiometry (GRADIO project) are described. The design profits from experience acquired with the CACTUS accelerometer payload of the satellite CASTOR-D5B and studies of highly accurate accelerometers for inertial navigation. The principle of operation, based on a three-axis electrostatic suspension of a cubic proof mass, is well suited for the measurements of accelerations less than 0.0001 m/sec/sec. A resolution better than 10 to the minus 11th power m/sec/sec/sq root Hz is expected.

  15. Single-Crystal Springs For Accelerometers

    NASA Technical Reports Server (NTRS)

    Vanzandt, Thomas R.; Kaiser, William J.; Kenny, Thomas W.

    1995-01-01

    Thermal noise reduced, enabling use of smaller proof masses. Spring-and-mass accelerometers in which springs made of single-crystal material being developed. In spring-and-mass accelerometer, proof mass attached to one end of spring, and acceleration of object at other end of spring measured in terms of deflection of spring, provided frequency spectrum of acceleration lies well below resonant frequency of spring-and-proof-mass system. Use of single-crystal spring materials instead of such polycrystalline spring materials as ordinary metals makes possible to construct highly sensitive accelerometers (including seismometers) with small proof masses.

  16. Study on real-time wear measurement of piston-ring and cylinder-bore in an engine using thin layer activation method.

    PubMed

    Donghui, Huang; Pingsheng, Wang; Weizhi, Tian; Dequan, Zhao; Guangzhou, Cao; Bangfa, Ni; Xiuhua, Zhang; Lin, Li; Guiying, Zhang; Cunxiong, Liu; Dehong, Li

    2008-08-01

    The instantaneous wear rates for both the top compression piston-ring and the cylinder-bore, in a ZS1105 diesel engine, were measured in situ using the method of thin layer activation (TLA). The experimental arrangement and methods for calibrating the test specimens are described. During a 300 s counting interval, the minimum detectable wear depths for the cylinder-bore and piston-ring were 9 and 75 nm, respectively. These values reflect average recession depths and may not reflect localized differences in wear damage. Nevertheless, such in situ techniques can be usefully employed in engine development. PMID:18424051

  17. High sensitivity cymbal-based accelerometer

    SciTech Connect

    Sun Chengliang; Lam, K.H.; Choy, S.H.; Chan, H.L. W.; Zhao, X.-Z.; Choy, C.L.

    2006-03-15

    A high sensitivity piezoelectric accelerometer has been developed by replacing the conventional piezoelectric rings with a cymbal transducer. The sensitivity of the cymbal-based accelerometers containing cymbal transducers with different endcap thicknesses and different seismic masses has been measured as a function of driving frequency. Due to the high d{sub 33}{sup '} coefficient of the cymbal transducers, the cymbal-based accelerometers have a high sensitivity of {approx}97 pC/ms{sup -2} with the amplitude rise of 2.85% (<1 dB) at one-third of the mounted resonance frequency (3.38 kHz). The effect of the seismic mass, the resonance frequency, and d{sub 33}{sup '} coefficient of the cymbal transducers on the sensitivity and the frequency range of the cymbal-based accelerometers are reported.

  18. Accelerometer Measurements in the Amusement Park.

    ERIC Educational Resources Information Center

    Reno, Charles; Speers, Robert R.

    1995-01-01

    Describes the use of the Texas Instruments' calculator-based laboratory (CBL) and Vernier accelerometer for measuring the vector sum of the gravitational field and the acceleration of amusement park rides. (JRH)

  19. Interactions among friction wear, and system stiffness. Part 3. Wear model

    SciTech Connect

    Aronov, V.; D'Souza, A.F.; Kalpakjian, S.; Shareef, I.

    1983-01-01

    It is shown that wear is an increasing function of system stiffness. The increase in the frequency of the applied load oscillations in normal direction causes increase of number of loading cycles per unit time that, in turn, causes increased rate of wear particles formation due to fatigue. A wear model has been developed which accounts for slider oscillation in the normal direction. Experimental data correlate very well with the theoretical analysis. 11 references, 7 figures, 3 tables.

  20. Analysis of wear debris from full-scale bearing fatigue tests using the Ferrograph

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Loewenthal, S. H.

    1980-01-01

    The Ferrograph was used to determine the types of quantities of wear particles generated during full-scale bearing fatigue tests. Deep-groove ball bearings made from AISI 52100 steel were used. A MIL-L-23699 tetraester lubricant was used in a recirculating lubrication system containing a 49-micron absolute filter. Test conditions included a maximum Hertz stress of 2.4 GPa, a shaft speed of 15,000 rpm and a lubricant supply temperature of 74 C (165 F). Four fatigue failures were detected by accelerometers in this test set. In general, the Ferrograph was more sensitive (up to 23 h) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis (SOAP). Four particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments.

  1. Analysis of wear-debris from full-scale bearing fatigue tests using the ferrograph

    NASA Technical Reports Server (NTRS)

    Jones, W. R.; Loewenthal, S. H.

    1980-01-01

    The ferrograph was used to determine the types and quantities of wear particles generated during full-scale bearing fatigue tests. Deep-groove ball bearings made from AISI 52100 steel were used. A MIL-L-23699 tetraester lubricant was used in a recirculating lubrication system containing a 49 mm absolute filter. Test conditions included a maximum Hertz stress of 2.4 GPa, a shaft speed of 15,000 rpm, and a lubricant supply temperature of 74 C (165 F). Four fatigue failures were detected by accelerometers in this test set. In general, the ferrograph was more sensitive (up to 23 hr) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis. Four particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments.

  2. Accelerometers for Precise GNSS Orbit Determination

    NASA Astrophysics Data System (ADS)

    Hugentobler, Urs; Schlicht, Anja

    2016-07-01

    The solar radiation pressure is the largest non-gravitational acceleration on GNSS satellites limiting the accuracy of precise orbit models. Other non-gravitational accelerations may be thrusts for station keeping maneuvers. Accelerometers measure the motion of a test mass that is shielded against satellite surface forces with respect to a cage that is rigidly connected to the satellite. They can thus be used to measure these difficult-to-model non-gravitational accelerations. Accelerometers however typically show correlated noise as well as a drift of the scaling factors converting measured voltages to accelerations. The scaling thus needs to be regularly calibrated. The presented study is based on several simulated scenarios including orbit determination of accelerometer-equipped Galileo satellites. It shall evaluate different options on how to accommodate accelerometer measurements in the orbit integrator, indicate to what extent currently available accelerometers can be used to improve the modeling of non-gravitational accelerations on GNSS satellites for precise orbit determination, and assess the necessary requirements for an accelerometer that can serve this purpose.

  3. Portable, real-time alloy identification of metallic wear debris from machinery lubrication systems: laser-induced breakdown spectroscopy versus x-ray fluorescence

    NASA Astrophysics Data System (ADS)

    Suresh, Pooja

    2014-05-01

    Alloy identification of oil-borne wear debris captured on chip detectors, filters and magnetic plugs allows the machinery maintainer to assess the health of the engine or gearbox and identify specific component damage. Today, such identification can be achieved in real time using portable, at-line laser-induced breakdown spectroscopy (LIBS) and Xray fluorescence (XRF) instruments. Both techniques can be utilized in various industries including aviation, marine, railways, heavy diesel and other industrial machinery with, however, some substantial differences in application and instrument performance. In this work, the performances of a LIBS and an XRF instrument are compared based on measurements of a wide range of typical aerospace alloys including steels, titanium, aluminum and nickel alloys. Measurement results were analyzed with a staged correlation technique specifically developed for the purposes of this study - identifying the particle alloy composition using a pre-recorded library of spectral signatures. The analysis is performed in two stages: first, the base element of the alloy is determined by correlation with the stored elemental spectra and then, the alloy is identified by matching the particle's spectral signature using parametric correlation against the stored spectra of all alloys that have the same base element. The correlation analysis has achieved highly repeatable discrimination between alloys of similar composition. Portable LIBS demonstrates higher detection accuracy and better identification of alloys comprising lighter elements as compared to that of the portable XRF system, and reveals a significant reduction in the analysis time over XRF.

  4. Magnetic torquer induced disturbing signals within GRACE accelerometer data

    NASA Astrophysics Data System (ADS)

    Peterseim, Nadja; Flury, Jakob; Schlicht, Anja

    2012-05-01

    The GRACE (Gravity Recovery And Climate Experiment) gravity field satellite mission was launched in 2002. Although many investigations have been carried out, not all disturbances and perturbations upon satellite instruments and sensors are resolved yet. In this work the issue of acceleration disturbances onboard of GRACE due to magnetic torquers is investigated and discussed. Each of the GRACE satellites is equipped with a three-axes capacitive accelerometer to measure non-gravitational forces acting on the spacecraft. We used 10 Hz Level 1a raw accelerometer data in order to determine the impact of electric current changes on the accelerometer. After reducing signals which are induced by highly dominating processes in the low frequency range, such as thermospheric drag and solar radiation pressure, which can easily be done by applying a high-pass filter, disturbing signals from onboard instruments such as thruster firing events or heater switch events need to be removed from the previously filtered data. Afterwards the spikes which are induced by the torquers can be very well observed. Spikes vary in amplitude with respect to an increasing or decreasing current used for magnetic torquers, and can be as large as 20 nm/s2. Furthermore, we were able to set up a model for the spikes of each scenario with which we were able to compute model spike time series. With these time series the spikes can successfully be removed from the 10 Hz raw accelerometer data. Spectral analysis of the time series reveal that an influence onto gravity field determination due to these effects is very unlikely, but can theoretically not be excluded.

  5. Detecting gunshots using wearable accelerometers.

    PubMed

    Loeffler, Charles E

    2014-01-01

    Gun violence continues to be a staggering and seemingly intractable issue in many communities. The prevalence of gun violence among the sub-population of individuals under court-ordered community supervision provides an opportunity for intervention using remote monitoring technology. Existing monitoring systems rely heavily on location-based monitoring methods, which have incomplete geographic coverage and do not provide information on illegal firearm use. This paper presents the first results demonstrating the feasibility of using wearable inertial sensors to recognize wrist movements and other signals corresponding to firearm usage. Data were collected from accelerometers worn on the wrists of subjects shooting a number of different firearms, conducting routine daily activities, and participating in activities and tasks that could be potentially confused with firearm discharges. A training sample was used to construct a combined detector and classifier for individual gunshots, which achieved a classification accuracy of 99.4 percent when tested against a hold-out sample of observations. These results suggest the feasibility of using inexpensive wearable sensors to detect firearm discharges.

  6. Variometric Tests for Accelerometer Sensors

    NASA Astrophysics Data System (ADS)

    D'Urso, M. G.; Barbati, N.

    2012-08-01

    We present a comprehensive review of several variometric tests recently carried out on a home-made measurement system composed of a tern of low-cost accelerometer sensors of MEMS (Micro-Electro-Mechanical Systems) type equipped with autonomous electric supply and wireless transmission. The most important parameters characterizing the systematic errors, i.e. bias, scale factor and thermal correction factor, have been evaluated by calibration tests based upon the so-called "six -positions" static test proposed by the IEEE 517 Standard. In this way the system optimal configuration has been defined in terms of data acquisition frequency and of scale factor. In addition to such tests, partly documented elsewhere, the results of some sensitivity tests on the influence of external environmental factors are also presented. With the aim of employing the proposed MEMS-based system as a device for monitoring the onset of slope landslides, some further tests have been carried out in order to measure the inclination of rigid objects which the sensors have been fixed to. The most significant results of the tests are illustrated and discussed.

  7. Optomechanical accelerometers and gravity gradiometers

    NASA Astrophysics Data System (ADS)

    Guzman, Felipe

    2016-04-01

    Compact optical cavities can be combined with highly stable mechanical oscillators to yield accelerometers and gravity gradiometers of exquisite sensitivity, which are also traceable to the SI. We have incorporated Fabry-Pérot fiber-optic micro-cavities onto low-loss monolithic fused-silica mechanical oscillators for gradiometry, acceleration, and force sensing. These devices consist solely of a glass oscillator and fiber optics to inject and read out the coherent optical signal, making them very simple and compatible with space applications. We have demonstrated displacement sensitivities better than 200 am/√Hz with these fiber-optic micro-sensors. This translates into broadband acceleration noise floors below 100 nano-g/√Hz over a 10kHz, when combined with compact high frequency mechanical oscillators. Similarly, we have developed monolithic oscillators with resonance frequencies near and below 10 Hz, yielding measurement sensitivities better than 10-9 m/s2. We will introduce our sensor concepts and present results on our fiber-optic displacement sensors and novel optomechanical devices.

  8. Detecting Gunshots Using Wearable Accelerometers

    PubMed Central

    Loeffler, Charles E.

    2014-01-01

    Gun violence continues to be a staggering and seemingly intractable issue in many communities. The prevalence of gun violence among the sub-population of individuals under court-ordered community supervision provides an opportunity for intervention using remote monitoring technology. Existing monitoring systems rely heavily on location-based monitoring methods, which have incomplete geographic coverage and do not provide information on illegal firearm use. This paper presents the first results demonstrating the feasibility of using wearable inertial sensors to recognize wrist movements and other signals corresponding to firearm usage. Data were collected from accelerometers worn on the wrists of subjects shooting a number of different firearms, conducting routine daily activities, and participating in activities and tasks that could be potentially confused with firearm discharges. A training sample was used to construct a combined detector and classifier for individual gunshots, which achieved a classification accuracy of 99.4 percent when tested against a hold-out sample of observations. These results suggest the feasibility of using inexpensive wearable sensors to detect firearm discharges. PMID:25184416

  9. High G MEMS integrated accelerometer

    SciTech Connect

    Davies, B.R.; Barron, C.C.; Montague, S.; Smith, J.H.; Murray, J.R.; Christenson, T.R.; Bateman, V.I.

    1996-12-31

    This paper describes the design and implementation of a surface micromachined accelerometer for measuring very high levels of acceleration (up to 50,000 G). Both the mechanical and electronic portions of the sensor were integrated on a single substrate using a process developed at Sandia National Laboratories. In this process, the mechanical components of the sensor were first fabricated at the bottom of a trench etched into the water substrate. The trench was then filled with oxide and sealed to protect the mechanical components during subsequent microelectronics processing. The wafer surface was then planarized in preparation for CMOS processing using Chemical Mechanical Polishing (CMP). Next, the CMOS electronics were fabricated on areas of the wafer adjacent to the embedded structures. Finally, the mechanical structures were released and the sensor tested. The mechanical structure of the sensor consisted of two polysilicon plate masses suspended by multiple springs (cantilevered beam structures) over corresponding polysilicon plates fixed to the substrate to form two parallel plate capacitors. The first polysilicon plate mass was suspended using compliant springs (cantilever beams) and acted as a variable capacitor during sensor acceleration. The second polysilicon plate mass was suspended using very stiff springs and acted as a fixed capacitor during acceleration. Acceleration was measured by comparing the capacitance of the variable capacitor (compliant suspension) with the fixed capacitance (stiff suspension).

  10. A panorama of tooth wear during the medieval period.

    PubMed

    Esclassan, Rémi; Hadjouis, Djillali; Donat, Richard; Passarrius, Olivier; Maret, Delphine; Vaysse, Frédéric; Crubézy, Eric

    2015-01-01

    Tooth wear is a natural phenomenon and a universal occurrence that has existed from the origin of humankind and depends on the way of life, especially diet. Tooth wear was very serious in ancient populations up to the medieval period. The aim of this paper is to present a global view of tooth wear in medieval times in Europe through different parameters: scoring systems, quantity and direction of wear, gender, differences between maxilla and mandible, relations with diet, caries, tooth malpositions and age.

  11. A Novel Digital Closed Loop MEMS Accelerometer Utilizing a Charge Pump.

    PubMed

    Chu, Yixing; Dong, Jingxin; Chi, Baoyong; Liu, Yunfeng

    2016-01-01

    This paper presents a novel digital closed loop microelectromechanical system (MEMS) accelerometer with the architecture and experimental evaluation. The complicated timing diagram or complex power supply in published articles are circumvented by using a charge pump system of adjustable output voltage fabricated in a 2P4M 0.35 µm complementary metal-oxide semiconductor (CMOS) process, therefore making it possible for interface circuits of MEMS accelerometers to be integrated on a single die on a large scale. The output bitstream of the sigma delta modulator is boosted by the charge pump system and then applied on the feedback comb fingers to form electrostatic forces so that the MEMS accelerometer can operate in a closed loop state. Test results agree with the theoretical formula nicely. The nonlinearity of the accelerometer within ±1 g is 0.222% and the long-term stability is about 774 µg.

  12. A Novel Digital Closed Loop MEMS Accelerometer Utilizing a Charge Pump

    PubMed Central

    Chu, Yixing; Dong, Jingxin; Chi, Baoyong; Liu, Yunfeng

    2016-01-01

    This paper presents a novel digital closed loop microelectromechanical system (MEMS) accelerometer with the architecture and experimental evaluation. The complicated timing diagram or complex power supply in published articles are circumvented by using a charge pump system of adjustable output voltage fabricated in a 2P4M 0.35 µm complementary metal-oxide semiconductor (CMOS) process, therefore making it possible for interface circuits of MEMS accelerometers to be integrated on a single die on a large scale. The output bitstream of the sigma delta modulator is boosted by the charge pump system and then applied on the feedback comb fingers to form electrostatic forces so that the MEMS accelerometer can operate in a closed loop state. Test results agree with the theoretical formula nicely. The nonlinearity of the accelerometer within ±1 g is 0.222% and the long-term stability is about 774 µg. PMID:26999157

  13. Fault Wear and Friction Evolution: Experimental Analysis

    NASA Astrophysics Data System (ADS)

    Boneh, Y.; Chang, J. C.; Lockner, D. A.; Reches, Z.

    2011-12-01

    Wear is an inevitable product of frictional sliding of brittle rocks as evidenced by the ubiquitous occurrence of fault gouge and slickenside striations. We present here experimental observations designed to demonstrate the relationship between wear and friction and their governing mechanisms. The experiments were conducted with a rotary shear apparatus on solid, ring-shaped rock samples that slipped for displacements up to tens of meters. Stresses, wear and temperature were continuously monitored. We analyzed 86 experiments of Kasota dolomite, Sierra White granite, Pennsylvania quartzite, Karoo gabbro, and Tennessee sandstone at slip velocities ranging from 0.002 to 0.97 m/s, and normal stress from 0.25 to 6.9 MPa. We conducted two types of runs: short slip experiments (slip distance < 25 mm) primarily on fresh, surface-ground samples, designed to analyze initial wear mechanisms; and long slip experiments (slip distance > 3 m) designed to achieve mature wear conditions and to observe the evolution of wear and friction as the fault surfaces evolved. The experiments reveal three wear stages: initial, running-in, and steady-state. The initial stage is characterized by (1) discrete damage striations, the length of which is comparable to total slip , and local pits or plow features; (2) timing and magnitude of fault-normal dilation corresponds to transient changes of normal and shear stresses; and (3) surface roughness increasing with the applied normal stress. We interpret these observations as wear mechanisms of (a) plowing into the fresh rock surfaces; (b) asperity breakage; and (c) asperity climb. The running-in stage is characterized by (1) intense wear-rate over a critical wear distance of Rd = 0.3-2 m; (2) drop of friction coefficient over a weakening distance of Dc = 0.2-4 m; (3) Rd and Dc display positive, quasi-linear relation with each other. We interpret these observations as indicating the organizing of newly-created wear particles into a 'three

  14. Tooth Wear Prevalence and Sample Size Determination : A Pilot Study

    PubMed Central

    Abd. Karim, Nama Bibi Saerah; Ismail, Noorliza Mastura; Naing, Lin; Ismail, Abdul Rashid

    2008-01-01

    Tooth wear is the non-carious loss of tooth tissue, which results from three processes namely attrition, erosion and abrasion. These can occur in isolation or simultaneously. Very mild tooth wear is a physiological effect of aging. This study aims to estimate the prevalence of tooth wear among 16-year old Malay school children and determine a feasible sample size for further study. Fifty-five subjects were examined clinically, followed by the completion of self-administered questionnaires. Questionnaires consisted of socio-demographic and associated variables for tooth wear obtained from the literature. The Smith and Knight tooth wear index was used to chart tooth wear. Other oral findings were recorded using the WHO criteria. A software programme was used to determine pathological tooth wear. About equal ratio of male to female were involved. It was found that 18.2% of subjects have no tooth wear, 63.6% had very mild tooth wear, 10.9% mild tooth wear, 5.5% moderate tooth wear and 1.8 % severe tooth wear. In conclusion 18.2% of subjects were deemed to have pathological tooth wear (mild, moderate & severe). Exploration with all associated variables gave a sample size ranging from 560 – 1715. The final sample size for further study greatly depends on available time and resources. PMID:22589636

  15. Using accelerometers to remotely and automatically characterize behavior in small animals.

    PubMed

    Hammond, Talisin T; Springthorpe, Dwight; Walsh, Rachel E; Berg-Kirkpatrick, Taylor

    2016-06-01

    Activity budgets in wild animals are challenging to measure via direct observation because data collection is time consuming and observer effects are potentially confounding. Although tri-axial accelerometers are increasingly employed for this purpose, their application in small-bodied animals has been limited by weight restrictions. Additionally, accelerometers engender novel complications, as a system is needed to reliably map acceleration to behaviors. In this study, we describe newly developed, tiny acceleration-logging devices (1.5-2.5 g) and use them to characterize behavior in two chipmunk species. We collected paired accelerometer readings and behavioral observations from captive individuals. We then employed techniques from machine learning to develop an automatic system for coding accelerometer readings into behavioral categories. Finally, we deployed and recovered accelerometers from free-living, wild chipmunks. This is the first time to our knowledge that accelerometers have been used to generate behavioral data for small-bodied (<100 g), free-living mammals. PMID:26994177

  16. Dynamic-scanning-electron-microscope study of friction and wear

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1974-01-01

    A friction and wear apparatus was built into a real time scanning electron microscope (SEM). The apparatus and SEM comprise a system which provides the capability of performing dynamic friction and wear experiments in situ. When the system is used in conjunction with dispersive X-ray analysis, a wide range of information on the wearing process can be obtained. The type of wear and variation with speed, load, and time can be investigated. The source, size, and distribution of wear particles can be determined and metallic transferal observed. Some typical results obtained with aluminum, copper, and iron specimens are given.

  17. ISA accelerometer and Moon science

    NASA Astrophysics Data System (ADS)

    Iafolla, Valerio; Peron, Roberto; Santoli, Francesco; Fiorenza, Emiliano; Lefevre, Carlo; Nozzoli, Sergio; Reale, Andrea

    2010-05-01

    In recent years the Moon has become again a target for exploration activities, as shown by many performed, ongoing or foreseen missions. The reason for this new wave are manifold. The knowledge of formation and evolution of the Moon to current state is important in order to trace the overall history of Solar System. An effective driving factor is the possibility of building a human settlement on its surface, with all the related issues of environment characterization, safety, resources, communication and navigation. Our natural satellite is also an important laboratory for fundamental physics: Lunar Laser Ranging is continuing to provide important data that constrain possible theories of gravitation. All these topics are providing stimulus and inspirations for new experiments. ISA (Italian Spring Accelerometer) can provide an important tool for lunar studies. Thanks to its structure (three one-dimensional sensors assembled in a composite structure) it works both in-orbit and on-ground, with the same configuration. It therefore can be used onboard a spacecraft, as a support to a radio science mission, and on the surface of the Moon, as a seismometer. The first option has been explorated in the context of MAGIA (Missione Altimetrica Gravimetrica geochImica lunAre), a proposal for an exploration mission with a noteworthy part dedicated to gravimetry and fundamental physics. The second option is candidate to be hosted on NASA ILN (International Lunar Network) and ESA First Lunar Lander. After a description of the instrument, both of them will be described and discussed, giving emphasis on the integration of the instrument with the other components of the respective experiments.

  18. Citizen sensors for SHM: use of accelerometer data from smartphones.

    PubMed

    Feng, Maria; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekin

    2015-01-01

    Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications.

  19. Citizen sensors for SHM: use of accelerometer data from smartphones.

    PubMed

    Feng, Maria; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekin

    2015-01-01

    Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications. PMID:25643056

  20. Citizen Sensors for SHM: Use of Accelerometer Data from Smartphones

    PubMed Central

    Feng, Maria; Fukuda, Yoshio; Mizuta, Masato; Ozer, Ekin

    2015-01-01

    Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications. PMID:25643056

  1. Characterizing performance of ultra-sensitive accelerometers

    NASA Technical Reports Server (NTRS)

    Sebesta, Henry

    1990-01-01

    An overview is given of methodology and test results pertaining to the characterization of ultra sensitive accelerometers. Two issues are of primary concern. The terminology ultra sensitive accelerometer is used to imply instruments whose noise floors and resolution are at the state of the art. Hence, the typical approach of verifying an instrument's performance by measuring it with a yet higher quality instrument (or standard) is not practical. Secondly, it is difficult to find or create an environment with sufficiently low background acceleration. The typical laboratory acceleration levels will be at several orders of magnitude above the noise floor of the most sensitive accelerometers. Furthermore, this background must be treated as unknown since the best instrument available is the one to be tested. A test methodology was developed in which two or more like instruments are subjected to the same but unknown background acceleration. Appropriately selected spectral analysis techniques were used to separate the sensors' output spectra into coherent components and incoherent components. The coherent part corresponds to the background acceleration being measured by the sensors being tested. The incoherent part is attributed to sensor noise and data acquisition and processing noise. The method works well for estimating noise floors that are 40 to 50 dB below the motion applied to the test accelerometers. The accelerometers being tested are intended for use as feedback sensors in a system to actively stabilize an inertial guidance component test platform.

  2. Number of accelerometer monitoring days needed for stable group-level estimates of activity.

    PubMed

    Wolff-Hughes, Dana L; McClain, James J; Dodd, Kevin W; Berrigan, David; Troiano, Richard P

    2016-09-01

    To determine the number and distribution of days required to produce stable group-level estimates of a 7 d mean for common accelerometer-derived activity measures. Data from the 2003-2006 NHANES were used in this analysis. The sample included 986 youth (6-19 year) and 2532 adults (⩾20 year) with 7 d of  ⩾10 h of wear. Accelerometer measures included minutes of inactive, light physical activity, moderate-to-vigorous physical activity (MVPA); and total activity counts/d. Twenty-five alternative protocols were bootstrapped with 50 000 samples drawn for each protocol. Alternative protocols included: 1-6 random days, Saturday plus 1-5 random weekdays (WD), Sunday plus 1-5 random WD, 1 random weekend day (WE) plus 1-5 WD, and both WE plus 1-4 random WD. Relative difference was calculated between the 7 d mean and alternative protocol mean (((alternative protocol mean - 7 d mean)/7 d mean) (*) 100). Adult MVPA is used as an example; however, similar trends were observed across age groups and variables except adult inactive time, which was stable across protocols. The 7 d mean for adult MVPA was 44.1(0.9) min d(-1). The mean bias for any 1-6 random days ranged from  -0.0(0.3) to 0.0(0.2) min d(-1) with a relative difference of  -0.1 to 0.0%. For protocols with non-random components, bias ranged from  -1.4(0.2) to 0.6(0.1) min d(-1) with relative difference ranging from  -7.2 to 3.1%. Simulation data suggest that stable estimates of group-level means can be obtained from as few as one randomly selected monitoring day from a sampled week. On the other hand, estimates using non-random selection of weekend days may be significantly biased. Purposeful sampling that disproportionally forces inclusion of weekend data in analyses should be discouraged. PMID:27510765

  3. Wear Measurement System

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Lewis Research Center developed a tribometer for in-house wear tests. Implant Sciences Corporation (ISC), working on a NASA contract to develop coatings to enhance the wear capabilities of materials, adapted the tribometer for its own use and developed a commercial line of user-friendly systems. The ISC-200 is a pin-on-disk type of tribometer, functioning like a record player and creating a wear groove on the disk, with variables of speed and load. The system can measure the coefficient of friction, the wear behavior between materials, and the integrity of thin films or coatings. Applications include measuring wear on contact lenses and engine parts and testing disk drives.

  4. Combining global positioning system and accelerometer data to determine the locations of physical activity in children.

    PubMed

    Oreskovic, Nicolas M; Blossom, Jeff; Field, Alison E; Chiang, Sylvia R; Winickoff, Jonathan P; Kleinman, Ronald E

    2012-05-01

    National trends indicate that children and adolescents are not achieving sufficient levels of physical activity. Combining global positioning system (GPS) technology with accelerometers has the potential to provide an objective determination in locations where youth engage in physical activity. The aim of this study was to identify the optimal methods for collecting combined accelerometer and GPS data in youth, to best locate where children spend time and are physically active. A convenience sample of 24 mid-school children in Massachusetts was included. Accelerometers and GPS units were used to quantify and locate childhood physical activity over 5 weekdays and 2 weekend days. Accelerometer and GPS data were joined by time and mapped with a geographical information system (GIS) using ArcGIS software. Data were collected in winter, spring, summer in 2009-2010, collecting a total of 26,406 matched datapoints overall. Matched data yield was low (19.1% total), regardless of season (winter, 12.8%; spring, 30.1%; summer, 14.3%). Teacher-provided, pre-charged equipment yielded the most matched (30.1%; range: 10.1-52.3%) and greatest average days (6.1 days) of data. Across all seasons, children spent most of their time at home. Outdoor use patterns appeared to vary by season, with street use increasing in spring, and park and playground use increasing in summer. Children spent equal amounts of physical activity time at home and walking in the streets. Overall, the various methods for combining GPS and accelerometer data provided similarly low amounts of combined data. No combined GPS and accelerometer data collection method proved superior in every data return category, but use of GIS to map joined accelerometer and GPS data can demarcate childhood physical activity locations.

  5. Fiber optic accelerometer based on clamped beam

    NASA Astrophysics Data System (ADS)

    Zhang, Wentao; Li, Fang

    2013-01-01

    In this paper a fiber optic accelerometer (FOA) based on camped beam is proposed. The clamped beam is used as the elastic element and a mass installed on the clamped beam is used as the inertial element. The accelerometer is based on a fiber optic Michelson interferometer and has a sensing arm and a reference arm. The optical fiber of the sensing arm is wrapped on the clamped beam and the mass, which are both cylinder shaped. The sensitivity of the FOA is analyzed based on the theory of elasticity; the frequency response is analyzed based on the theory of vibration. Experiment is carried out to test the performance of the fiber optic accelerometer. The experiment results show a high sensitivity and a flat frequency response within the low frequency range of 5-250 Hz, which agrees well with the theoretical result.

  6. An accelerometer-based system for elite athlete swimming performance analysis

    NASA Astrophysics Data System (ADS)

    Davey, Neil P.; Anderson, Megan E.; James, Daniel A.

    2005-02-01

    The measurement of sport specific performance characteristics is an important part of an athletes training and preparation for competition. Thus automated measurement, extraction and analysis of performance measures is desired and addressed in this paper. A tri-axial accelerometer based system was located on the lower back or swimmers to record acceleration profiles. The accelerometer system contained two ADXL202 bi-axial accelerometers positioned perpendicular to one another, and can store over 6 hours of data at 150Hz per channel using internal flash memory. The simultaneous collection of video and electronics touch pad timing was used to validate the algorithm results. Using the tri-axial accelerometer data, algorithms have been developed to derive lap times and stroke count. Comparison against electronic touch pad timing against accelerometer lap times has produced results with a typical error of better than +/-0.5 seconds. Video comparison of the stroke count algorithm for freestyle also produced results with an average error of +/-1 stroke. The developed algorithms have a higher level of reliability compared to hand timed and counted date that is commonly used during training.

  7. Wear mechanism of diamond coated cutting tools

    SciTech Connect

    Leyendecker, T.; Lemmer, O.; Esser, S.

    1995-12-31

    Since Diamond Coatings were introduced into the market in 1989, five years experience in industrial applications of diamond coated cutting tools enables to present an overview of tool life and wear behavior of diamond coated cutting tools due to different cutting conditions and workpiece-materials. Machining reinforced plastics, presintered ceramic compacts, aluminum alloys, metal-matrix composites and graphite, different wear behavior occurs at the cutting edges of diamond coated tools. Having a good adhesion fatigue and chemical wear of Diamond coatings determines life time of the tools. By a profound pretreatment procedure CVD Diamond coated tools can compete with conventional PCD-tools.

  8. Research on the effect of wear-ring clearances to the axial and radial force of a centrifugal pump

    NASA Astrophysics Data System (ADS)

    Zhao, W. G.; Y He, M.; Qi, C. X.; Li, Y. B.

    2013-12-01

    Varying of the wear-ring clearance not only has a distinct effect on the volumetric loss of the centrifugal pump, but also on the performance of the centrifugal pump including the axial and radial forces. Comparing with the experimental studies, numerical simulation methods have some special advantages, such as the low cost, fast and high efficiency, and convenient to get the detailed structure of the internal flow characteristics, so it has been widely used in the fluid machinery study in recent years. In order to study the effect of wear-ring clearance on the force performance of the centrifugal pump, based on the Reynolds Time-Averaged N-S equations and RNG k-ε turbulence model, a centrifugal pump with three variable styles of the wear-rings was simulated: Only the clearance of the front wear-ring was changed, only the clearance of the back wear-ring was changed and both were changed. Comparing with the experiment, numerical results show a good agreement. In the three changing styles of the clearance, the variable of the clearance of front wear-ring has the most influence on the axial force of the centrifugal pump, while has tiny effect on the radial force for all the conditions.

  9. Self Diagnostic Accelerometer Ground Testing on a C-17 Aircraft Engine

    NASA Technical Reports Server (NTRS)

    Tokars, Roger P.; Lekki, John D.

    2013-01-01

    The self diagnostic accelerometer (SDA) developed by the NASA Glenn Research Center was tested for the first time in an aircraft engine environment as part of the Vehicle Integrated Propulsion Research (VIPR) program. The VIPR program includes testing multiple critical flight sensor technologies. One such sensor, the accelerometer, measures vibrations to detect faults in the engine. In order to rely upon the accelerometer, the health of the accelerometer must be ensured. Sensor system malfunction is a significant contributor to propulsion in flight shutdowns (IFSD) which can lead to aircraft accidents when the issue is compounded with an inappropriate crew response. The development of the SDA is important for both reducing the IFSD rate, and hence reducing the rate at which this component failure type can put an aircraft in jeopardy, and also as a critical enabling technology for future automated malfunction diagnostic systems. The SDA is a sensor system designed to actively determine the accelerometer structural health and attachment condition, in addition to making vibration measurements. The SDA uses a signal conditioning unit that sends an electrical chirp to the accelerometer and recognizes changes in the response due to changes in the accelerometer health and attachment condition. In an effort toward demonstrating the SDAs flight worthiness and robustness, multiple SDAs were mounted and tested on a C-17 aircraft engine. The engine test conditions varied from engine off, to idle, to maximum power. The two SDA attachment conditions used were fully tight and loose. The newly developed SDA health algorithm described herein uses cross correlation pattern recognition to discriminate a healthy from a faulty SDA. The VIPR test results demonstrate for the first time the robustness of the SDA in an engine environment characterized by high vibration levels.

  10. Self diagnostic accelerometer ground testing on a C-17 aircraft engine

    NASA Astrophysics Data System (ADS)

    Tokars, Roger P.; Lekki, John D.

    The self diagnostic accelerometer (SDA) developed by the NASA Glenn Research Center was tested for the first time in an aircraft engine environment as part of the Vehicle Integrated Propulsion Research (VIPR) program. The VIPR program includes testing multiple critical flight sensor technologies. One such sensor, the accelerometer, measures vibrations to detect faults in the engine. In order to rely upon the accelerometer, the health of the accelerometer must be ensured. Sensor system malfunction is a significant contributor to propulsion in flight shutdowns (IFSD) which can lead to aircraft accidents when the issue is compounded with an inappropriate crew response. The development of the SDA is important for both reducing the IFSD rate, and hence reducing the rate at which this component failure type can put an aircraft in jeopardy, and also as a critical enabling technology for future automated malfunction diagnostic systems. The SDA is a sensor system designed to actively determine the accelerometer structural health and attachment condition, in addition to making vibration measurements. The SDA uses a signal conditioning unit that sends an electrical chirp to the accelerometer and recognizes changes in the response due to changes in the accelerometer health and attachment condition. In an effort toward demonstrating the SDA's flight worthiness and robustness, multiple SDAs were mounted and tested on a C-17 aircraft engine. The engine test conditions varied from engine off, to idle, to maximum power. The two SDA attachment conditions used were fully tight and loose. The newly developed SDA health algorithm described herein uses cross correlation pattern recognition to discriminate a healthy from a faulty SDA. The VIPR test results demonstrate for the first time the robustness of the SDA in an engine environment characterized by high vibration levels.

  11. A Self-Diagnostic System for the M6 Accelerometer

    NASA Technical Reports Server (NTRS)

    Flanagan, Patrick M.; Lekki, John

    2001-01-01

    The design of a Self-Diagnostic (SD) accelerometer system for the Space Shuttle Main Engine is presented. This retrofit system connects diagnostic electronic hardware and software to the current M6 accelerometer system. This paper discusses the general operation of the M6 accelerometer SD system and procedures for developing and evaluating the SD system. Signal processing techniques using M6 accelerometer diagnostic data are explained. Test results include diagnostic data responding to changing ambient temperature, mounting torque and base mounting impedance.

  12. µSTAR accelerometer, a fundamental physic package for future interplanetary missions

    NASA Astrophysics Data System (ADS)

    Levy, Agnes; Christophe, Bruno; Foulon, Bernard

    In the frame of Cosmic Vision selection, one resolution from the Fundamental Physic Advisory Group of ESA was to use an accelerometer on a future Solar-System mission. This paper described such accelerometer which can be implemented in the future Laplace or Tandem mission pre-selected by ESA. Space Fundamental Physic experiments require to know if the spacecraft follows a geodesic or not. For such purpose, an accelerometer is mandatory, either to control the spacecraft for following a geodesic, as in Microscope or LISA, or to have the measurement of the nongravitational forces acting on the spacecraft, in order to reconstruct on ground the geodesic motion of the spacecraft. The verification of the General Relativity at scale of the Solar System requires also accurate acceleration measurement at low frequency. For this purpose, ONERA has designed µSTAR accelerometer with an objective of performance of 10-10 m/s2 in DC. The µSTAR electrostatic accelerometer is based on ONERA expertise in the field of accelerometry and gravimetry (CHAMP, GRACE and GOCE missions). Ready-to-fly technology is used with original improvements aimed at reducing power consumption, size and weight. µSTAR has a noise better than 10-11 m/s2 in the frequency bandwidth 1 mHz - 100 mHz, but suffers a maximal bias of 5×10-6 m/s2 due to the imperfection of manufacturing. To correct it, a bias rejection system is associated with the accelerometer so as to ensure high performance at very low frequency. This system consists of a flip mechanism which allows a 180° rotation of the accelerometer to be carried out at regularly spaced times. As a consequence, the measured acceleration is a crenel signal which can be distinguished from the accelerometer bias in the frequency domain. Then, demodulation and filtering technics can be applied on the signal leading to the recovery of the original aceleration undergone by the spacecraft. The paper will conclude on the difficulty of implementation of such

  13. Dual Accelerometer Usage Strategy for Onboard Space Navigation

    NASA Technical Reports Server (NTRS)

    Zanetti, Renato; D'Souza, Chris

    2012-01-01

    This work introduces a dual accelerometer usage strategy for onboard space navigation. In the proposed algorithm the accelerometer is used to propagate the state when its value exceeds a threshold and it is used to estimate its errors otherwise. Numerical examples and comparison to other accelerometer usage schemes are presented to validate the proposed approach.

  14. Three-axis MEMS Accelerometer for Structural Inspection

    NASA Astrophysics Data System (ADS)

    Barbin, E.; Koleda, A.; Nesterenko, T.; Vtorushin, S.

    2016-01-01

    Microelectromechanical system accelerometers are widely used for metrological measurements of acceleration, tilt, vibration, and shock in moving objects. The paper presents the analysis of MEMS accelerometer that can be used for the structural inspection. ANSYS Multiphysics platform is used to simulate the behavior of MEMS accelerometer by employing a finite element model and MATLAB/Simulink tools for modeling nonlinear dynamic systems.

  15. Low-Cost Accelerometers for Physics Experiments

    ERIC Educational Resources Information Center

    Vannoni, Maurizio; Straulino, Samuele

    2007-01-01

    The implementation of a modern game-console controller as a data acquisition interface for physics experiments is discussed. The investigated controller is equipped with three perpendicular accelerometers and a built-in infrared camera to evaluate its own relative position. A pendulum experiment is realized as a demonstration of the proposed…

  16. Smartphone MEMS accelerometers and earthquake early warning

    NASA Astrophysics Data System (ADS)

    Kong, Q.; Allen, R. M.; Schreier, L.; Kwon, Y. W.

    2015-12-01

    The low cost MEMS accelerometers in the smartphones are attracting more and more attentions from the science community due to the vast number and potential applications in various areas. We are using the accelerometers inside the smartphones to detect the earthquakes. We did shake table tests to show these accelerometers are also suitable to record large shakings caused by earthquakes. We developed an android app - MyShake, which can even distinguish earthquake movements from daily human activities from the recordings recorded by the accelerometers in personal smartphones and upload trigger information/waveform to our server for further analysis. The data from these smartphones forms a unique datasets for seismological applications, such as earthquake early warning. In this talk I will layout the method we used to recognize earthquake-like movement from single smartphone, and the overview of the whole system that harness the information from a network of smartphones for rapid earthquake detection. This type of system can be easily deployed and scaled up around the global and provides additional insights of the earthquake hazards.

  17. Micro-Accelerometers Monitor Equipment Health

    NASA Technical Reports Server (NTRS)

    2014-01-01

    Glenn Research Center awarded SBIR funding to Ann Arbor, Michigan-based Evigia Systems to develop a miniaturized accelerometer to account for gravitational effects in space experiments. The company has gone on to implement the technology in its suite of prognostic sensors, which are used to monitor the integrity of industrial machinery. As a result, five employees have been hired.

  18. Miniature piezoelectric triaxial accelerometer measures cranial accelerations

    NASA Technical Reports Server (NTRS)

    Deboo, G. J.; Rogallo, V. L.

    1966-01-01

    Tiny triaxial accelerometer whose sensing elements are piezoelectric ceramic beams measures human cranial accelerations when a subject is exposed to a centrifuge or other simulators of g environments. This device could be considered for application in dental, medical, and automotive safety research.

  19. Strong Motion Seismograph Based On MEMS Accelerometer

    NASA Astrophysics Data System (ADS)

    Teng, Y.; Hu, X.

    2013-12-01

    The MEMS strong motion seismograph we developed used the modularization method to design its software and hardware.It can fit various needs in different application situation.The hardware of the instrument is composed of a MEMS accelerometer,a control processor system,a data-storage system,a wired real-time data transmission system by IP network,a wireless data transmission module by 3G broadband,a GPS calibration module and power supply system with a large-volumn lithium battery in it. Among it,the seismograph's sensor adopted a three-axis with 14-bit high resolution and digital output MEMS accelerometer.Its noise level just reach about 99μg/√Hz and ×2g to ×8g dynamically selectable full-scale.Its output data rates from 1.56Hz to 800Hz. Its maximum current consumption is merely 165μA,and the device is so small that it is available in a 3mm×3mm×1mm QFN package. Furthermore,there is access to both low pass filtered data as well as high pass filtered data,which minimizes the data analysis required for earthquake signal detection. So,the data post-processing can be simplified. Controlling process system adopts a 32-bit low power consumption embedded ARM9 processor-S3C2440 and is based on the Linux operation system.The processor's operating clock at 400MHz.The controlling system's main memory is a 64MB SDRAM with a 256MB flash-memory.Besides,an external high-capacity SD card data memory can be easily added.So the system can meet the requirements for data acquisition,data processing,data transmission,data storage,and so on. Both wired and wireless network can satisfy remote real-time monitoring, data transmission,system maintenance,status monitoring or updating software.Linux was embedded and multi-layer designed conception was used.The code, including sensor hardware driver,the data acquisition,earthquake setting out and so on,was written on medium layer.The hardware driver consist of IIC-Bus interface driver, IO driver and asynchronous notification driver. The

  20. NASA interdisciplinary collaboration in tribology. A review of oxidational wear

    NASA Technical Reports Server (NTRS)

    Quinn, T. F. J.

    1983-01-01

    An in-depth review of oxidational wear of metals is presented. Special emphasis is given to a description of the concept of oxidational wear and the formulation of an Oxidational Wear Theory. The parallelism between the formation of an oxide film for dry contact conditions and the formation of other surface films for a lubricated contact is discussed. The description of oxidational wear is prefaced with a unification of wear modes into two major classes of mild and severe wear including both lubricated and dry contacts. Oxidational wear of metals is a class of mild wear where protective oxide films are formed at real areas of contact and during the time of contact at temperataure T sub c. When the oxide reaches a critical thickness, frequently in the range of 1 to 3 microns, the oxide breaks up and eventually appears as a wear particle. These oxides are preferentially formed on plateaux which alternately carry the load as they reach their critical thickness and are removed. If the system is operated at elevated temperatures, thick oxides can form both out of contact and between the plateaux. Temperature is important in determining the structure of the oxide film present. Spinel oxide (Fe3O4) which forms above 300 C is more protective than the lower temperature rhomobohedral (alpha-Fe2O3) oxide which is abrasive. An Oxidational Wear Theory is derived using a modified Archard wear law expressed in terms of activation energy (Qp) and Arrhenius constant (Ap).

  1. Wear Modeling: Evaluation and Categorization of Wear Models

    NASA Astrophysics Data System (ADS)

    Meng, Hsien-Chung

    The objective of this study was to evaluate progress in wear modeling and propose guidelines for future work. Such guidelines can help wear modelers to make appropriate decisions and ascertain information relevant to wear modeling. Over 5,000 papers in the literature were surveyed. 182 erosion wear and sliding wear equations proposed between 1957 and 1992 were found and studied. Two approaches were taken to analyze the surveyed models. The first approach focuses on common features and variations in each of five wear modeling steps. The second approach identifies characteristics of the overall development of wear modeling. The conclusions and recommendations of this study: (1) No single universal equation or extensively accepted theory fully explains the many types of wear behavior. (2) Wear mechanisms as typically described in research literature are not fundamental processes of material loss. Mechanical, chemical, physical and metallurgical action are the four fundamental processes: future wear models should include consideration of these four simultaneously, together with their interactions. (3) Wear models based on a single academic discipline cannot fully explain a wearing process even if for a single wear mechanism. An interdisciplinary approach should be applied to build wear models. (4) Two characteristics in past development of wear modeling are positive and should be carried into future work: (a) progressively more and more local information about the variations of working conditions has been considered in wear modeling, and (b) the approaches of different disciplines has been more frequently and extensively applied together to build wear models which explain progressively more wear phenomena in a wearing system. (5) Wear modelers should derive wear equations to concisely present research results and to complete wear modeling. Out of the 5000 papers considered in this study, only 182 presented equations as well as word descriptions to describe erosion and

  2. Application of Accelerometer Data to Mars Odyssey Aerobraking and Atmospheric Modeling

    NASA Technical Reports Server (NTRS)

    Tolson, R. H.; Keating, G. M.; George, B. E.; Escalera, P. E.; Werner, M. R.; Dwyer, A. M.; Hanna, J. L.

    2002-01-01

    Aerobraking was an enabling technology for the Mars Odyssey mission even though it involved risk due primarily to the variability of the Mars upper atmosphere. Consequently, numerous analyses based on various data types were performed during operations to reduce these risk and among these data were measurements from spacecraft accelerometers. This paper reports on the use of accelerometer data for determining atmospheric density during Odyssey aerobraking operations. Acceleration was measured along three orthogonal axes, although only data from the component along the axis nominally into the flow was used during operations. For a one second count time, the RMS noise level varied from 0.07 to 0.5 mm/s2 permitting density recovery to between 0.15 and 1.1 kg per cu km or about 2% of the mean density at periapsis during aerobraking. Accelerometer data were analyzed in near real time to provide estimates of density at periapsis, maximum density, density scale height, latitudinal gradient, longitudinal wave variations and location of the polar vortex. Summaries are given of the aerobraking phase of the mission, the accelerometer data analysis methods and operational procedures, some applications to determining thermospheric properties, and some remaining issues on interpretation of the data. Pre-flight estimates of natural variability based on Mars Global Surveyor accelerometer measurements proved reliable in the mid-latitudes, but overestimated the variability inside the polar vortex.

  3. Evaluation of MEMS-Based Wireless Accelerometer Sensors in Detecting Gear Tooth Faults in Helicopter Transmissions

    NASA Technical Reports Server (NTRS)

    Lewicki, David George; Lambert, Nicholas A.; Wagoner, Robert S.

    2015-01-01

    The diagnostics capability of micro-electro-mechanical systems (MEMS) based rotating accelerometer sensors in detecting gear tooth crack failures in helicopter main-rotor transmissions was evaluated. MEMS sensors were installed on a pre-notched OH-58C spiral-bevel pinion gear. Endurance tests were performed and the gear was run to tooth fracture failure. Results from the MEMS sensor were compared to conventional accelerometers mounted on the transmission housing. Most of the four stationary accelerometers mounted on the gear box housing and most of the CI's used gave indications of failure at the end of the test. The MEMS system performed well and lasted the entire test. All MEMS accelerometers gave an indication of failure at the end of the test. The MEMS systems performed as well, if not better, than the stationary accelerometers mounted on the gear box housing with regards to gear tooth fault detection. For both the MEMS sensors and stationary sensors, the fault detection time was not much sooner than the actual tooth fracture time. The MEMS sensor spectrum data showed large first order shaft frequency sidebands due to the measurement rotating frame of reference. The method of constructing a pseudo tach signal from periodic characteristics of the vibration data was successful in deriving a TSA signal without an actual tach and proved as an effective way to improve fault detection for the MEMS.

  4. High Shock, High Frequency Characteristics of a Mechanical Isolator for a Piezoresistive Accelerometer, the ENDEVCO 7270AM6*

    SciTech Connect

    BATEMAN,VESTA I.; BROWN,FREDERICK A.; NUSSER,MICHAEL A.

    2000-07-01

    A mechanical isolator has been developed for a piezoresistive accelerometer. The purpose of the isolator is to mitigate high frequency shocks before they reach the accelerometer because the high frequency shocks may cause the accelerometer to resonate. Since the accelerometer is undamped, it often breaks when it resonates. The mechanical isolator was developed in response to impact test requirements for a variety of structures at Sandia National Laboratories (SNL). An Extended Technical Assistance Program (ETAP) with the accelerometer manufacturer has resulted in a commercial mechanically isolated accelerometer that is available to the general public, the ENDEVCO 7270AM6*, for three shock acceleration ranges of 6,000 g, 20,000 g, and 60,000 g. The in-axis response shown in this report has acceptable frequency domain performance from DC to 10 kHz and 10(XO)over a temperature range of {minus}65 F to +185 F. Comparisons with other isolated accelerometers show that the ENDEVCO 7270AM6 has ten times the bandwidth of any other commercial isolator. ENDEVCO 7270AM6 cross-axis response is shown in this report.

  5. Microgravity accelerometer characterization on Columbia STS-32 mission

    NASA Astrophysics Data System (ADS)

    Schoess, Jeff; Thomas, Don; Dunbar, Bonnie

    1992-05-01

    The Honeywell In-Space Accelerometer (HISA) is a three-axis microgravity accelerometer instrument package recently developed by Honeywell Systems and Research Center (SRC) to monitor oscillatory and transient accelerations onboard spacecraft and spaceborne structures. The HISA was designed to be co-located with materials and life sciences experiments to record real-time accelerometer event data, sampling time, and temperature. The HISA was originally developed to monitor the microgravity disturbances associated with a polymer morphology experiment developed by 3M Company in Minneapolis, Minnesota. The HISA was first flight tested with the 3M experiment on the Space Shuttle Atlantis STS-34 in October 1989. The HISA was successfully flown on a second shuttle mission (Columbia STS-32 in January 1990) in support of the NASA JSC-sponsored Microgravity Disturbances Experiment (MDE), which focused on the effects of microgravity disturbances on the growth of high-quality Indium crystals. The primary objective of the STS-32 MDE experiment was to investigate the effects of crew-induced gravity disturbances on the microstructure (crystal defects and uniformity of impurity distribution) of float-zone-grown crystals. The float-zone technique involves establishing a suspended molten zone between two cylindrical samples a pure, single-crystal sample and an impure, polycrystalline sample. Microgravity disturbances due to crew treadmill activity and orbiter maneuvering system thruster firings were sensed and recorded by the HISA to understand their effects on the stability of the float zone. The principle of operation of the HISA, the flight configuration of the HISA supporting the MDE experiment, and the characterization of STS-32 treadmill disturbance data are summarized.

  6. Microgravity accelerometer characterization on Columbia STS-32 mission

    NASA Technical Reports Server (NTRS)

    Schoess, Jeff; Thomas, Don; Dunbar, Bonnie

    1992-01-01

    The Honeywell In-Space Accelerometer (HISA) is a three-axis microgravity accelerometer instrument package recently developed by Honeywell Systems and Research Center (SRC) to monitor oscillatory and transient accelerations onboard spacecraft and spaceborne structures. The HISA was designed to be co-located with materials and life sciences experiments to record real-time accelerometer event data, sampling time, and temperature. The HISA was originally developed to monitor the microgravity disturbances associated with a polymer morphology experiment developed by 3M Company in Minneapolis, Minnesota. The HISA was first flight tested with the 3M experiment on the Space Shuttle Atlantis STS-34 in October 1989. The HISA was successfully flown on a second shuttle mission (Columbia STS-32 in January 1990) in support of the NASA JSC-sponsored Microgravity Disturbances Experiment (MDE), which focused on the effects of microgravity disturbances on the growth of high-quality Indium crystals. The primary objective of the STS-32 MDE experiment was to investigate the effects of crew-induced gravity disturbances on the microstructure (crystal defects and uniformity of impurity distribution) of float-zone-grown crystals. The float-zone technique involves establishing a suspended molten zone between two cylindrical samples a pure, single-crystal sample and an impure, polycrystalline sample. Microgravity disturbances due to crew treadmill activity and orbiter maneuvering system thruster firings were sensed and recorded by the HISA to understand their effects on the stability of the float zone. The principle of operation of the HISA, the flight configuration of the HISA supporting the MDE experiment, and the characterization of STS-32 treadmill disturbance data are summarized.

  7. Ferrographic analysis of wear debris from full-scale bearing fatigue tests

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.; Loewenthal, S. H.

    1979-01-01

    The Ferrograph was used to determine the types and quantities of wear particles generated during full scale bearing fatigue tests. Deep-groove ball bearings made from steel were used. A tetraester lubricant was used in a recirculating lubricant system containing a 49 micrometers absolute filter. Test conditions include a maximum Hertz stress of 2.4 GPa, a shaft speed of 15,000 rpm, and a lubricant supply temperature of 74 C (165 F). Four fatigue failures were detected by accelerometers in this test set. In general, the Ferrograph was more sensitive (up to 23 hr) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis. Four particle types were observed: normal rubbing weather particles, spheres, nonferrous particles, and severe wear (spall) fragments.

  8. Validation of the Actical Accelerometer in Multiethnic Preschoolers: The Children's Healthy Living (CHL) Program.

    PubMed

    Ettienne, Reynolette; Nigg, Claudio R; Li, Fenfang; Su, Yuhua; McGlone, Katalina; Luick, Bret; Tachibana, Alvin; Carran, Christina; Mercado, Jobel; Novotny, Rachel

    2016-04-01

    This study aimed to determine the validity and reliability of the Actical accelerometer for measuring physical activity (PA) in preschool children of mixed ethnicity, compared with direct observation via a modified System for Observing Fitness Instruction Time (SOFIT) protocol and proxy parental reports (PA Logs). Fifty children in Hawai'i wore wrist-mounted accelerometers for two 7-day periods with a washout period between each week. Thirty children were concurrently observed using SOFIT. Parents completed PA Logs for three days. Reliability and validity were measured by intra-class correlation coefficient and proportions of agreement concurrently. There was slight agreement (proportion of agreement: 82%; weighted Kappa=.17, P <.001) between the accelerometer and SOFIT as well as between the accelerometer and the PA Logs (proportions of agreement: 40%; weighted Kappa=0.15, P <.001). PA logs underestimated the PA levels of the children, while the Actical was found to be valid and reliable for estimating PA levels of multiethnic, mixed ethnicity preschoolers. These findings suggest that accelerometers can be objective, valid, and accurate physical activity assessment tools compared to conventional PA logs and subjective reports of activity for preschool children of mixed ethnicity. PMID:27099804

  9. Validation of the Actical Accelerometer in Multiethnic Preschoolers: The Children's Healthy Living (CHL) Program

    PubMed Central

    Ettienne, Reynolette; Li, Fenfang; Su, Yuhua; McGlone, Katalina; Luick, Bret; Tachibana, Alvin; Carran, Christina; Mercado, Jobel; Novotny, Rachel

    2016-01-01

    This study aimed to determine the validity and reliability of the Actical accelerometer for measuring physical activity (PA) in preschool children of mixed ethnicity, compared with direct observation via a modified System for Observing Fitness Instruction Time (SOFIT) protocol and proxy parental reports (PA Logs). Fifty children in Hawai‘i wore wrist-mounted accelerometers for two 7-day periods with a washout period between each week. Thirty children were concurrently observed using SOFIT. Parents completed PA Logs for three days. Reliability and validity were measured by intra-class correlation coefficient and proportions of agreement concurrently. There was slight agreement (proportion of agreement: 82%; weighted Kappa=.17, P <.001) between the accelerometer and SOFIT as well as between the accelerometer and the PA Logs (proportions of agreement: 40%; weighted Kappa=0.15, P <.001). PA logs underestimated the PA levels of the children, while the Actical was found to be valid and reliable for estimating PA levels of multiethnic, mixed ethnicity preschoolers. These findings suggest that accelerometers can be objective, valid, and accurate physical activity assessment tools compared to conventional PA logs and subjective reports of activity for preschool children of mixed ethnicity. PMID:27099804

  10. GRACE KBR and Accelerometer Data Reduction and Calibration

    NASA Astrophysics Data System (ADS)

    Rowlands, D. D.; Luthcke, S. B.; Klosko, S. M.; Lemoine, F. G.; Williams, T. A.

    2004-12-01

    The Gravity Recovery And Climate Experiment (GRACE), launched on March 17, 2002, represents the state-of-the-art in geodetic observations of the static and time varying components of the Earth's geopotential field. The fundamental measurement used to observe gravity is the inter-satellite range and range rate between two coplanar, low altitude satellites obtained from a K-band ranging (KBR) system. In addition to the K-band ranging system, each satellite possess a SuperSTAR Accelerometer, a GPS receiver/antenna package, Star Cameras and a Laser Retro Reflector (LRR) to complete the compliment of science instruments. The GRACE project has now released two years of Level 1B data derived from the science instruments and sensors. An integral component of our time variable gravity research is the reduction, calibration and analyses of these Level 1B data. In particular we have analyzed several months of K-band ranging (KBR1B), accelerometry (ACC1B) and GPS navigation (GNAV1B) data. Accelerometer calibration and KBR data reduction methodology and results will be presented. We discuss the impact of these analyses on the recovery of time variable gravity.

  11. GRACE KBR and Accelerometer Data Reduction and Calibration

    NASA Technical Reports Server (NTRS)

    Rowlands, David D.; Lutheke, Scott B.; Klosko, Steven M.; Lemoine, Frank G.; Williams, Terry A.

    2004-01-01

    The Gravity Recovery and Climate Experiment (GRACE), launched on March 17, 2002, represents the state-of-the-art in geodetic observations of the static and time varying components of the Earth's geopotential field. The fundamental measurement used to observe gravity is the inter-satellite range and range rate between two coplanar, low altitude satellites obtained from a K-band ranging (KBR) system. In addition to the K-band ranging system, each satellite possess a Super-STAR Accelerometer, a GPS receiver/antenna package, Star Cameras and a Laser Retro Reflector (LRR) to complete the compliment of science instruments. The GRACE project has now released two years of Level 1B data derived from the science instruments and sensors. An integral component of our time variable gravity research is the reduction, calibration and analyses of these Level 1B data. In particular we have analyzed several months of K-band ranging (KBR1B), accelerometry (ACC1B) and GPS navigation (GNAV1B) data. Accelerometer calibration and KBR data reduction methodology and results will be presented. We discuss the impact of these analyses on the recovery of time variable gravity.

  12. Intelligent identification of wear mechanism via on-line ferrograph images

    NASA Astrophysics Data System (ADS)

    Wu, Tonghai; Peng, Yeping; Sheng, Chenxing; Wu, Jiaoyi

    2014-03-01

    Condition based maintenance(CBM) issues a new challenge of real-time monitoring for machine health maintenance. Wear state monitoring becomes the bottle-neck of CBM due to the lack of on-line information acquiring means. The wear mechanism judgment with characteristic wear debris has been widely adopted in off-line wear analysis; however, on-line wear mechanism characterization remains a big problem. In this paper, the wear mechanism identification via on-line ferrograph images is studied. To obtain isolated wear debris in an on-line ferrograph image, the deposition mechanism of wear debris in on-line ferrograph sensor is studied. The study result shows wear debris chain is the main morphology due to local magnetic field around the deposited wear debris. Accordingly, an improved sampling route for on-line wear debris deposition is designed with focus on the self-adjustment deposition time. As a result, isolated wear debris can be obtained in an on-line image, which facilitates the feature extraction of characteristic wear debris. By referring to the knowledge of analytical ferrograph, four dimensionless morphological features, including equivalent dimension, length-width ratio, shape factor, and contour fractal dimension of characteristic wear debris are extracted for distinguishing four typical wear mechanisms including normal, cutting, fatigue, and severe sliding wear. Furthermore, a feed-forward neural network is adopted to construct an automatic wear mechanism identification model. By training with the samples from analytical ferrograph, the model might identify some typical characteristic wear debris in an on-line ferrograph image. This paper performs a meaningful exploratory for on-line wear mechanism analysis, and the obtained results will provide a feasible way for on-line wear state monitoring.

  13. Reliability of accelerometer-determined physical activity and sedentary behavior in school-aged children: a 12-country study

    PubMed Central

    Barreira, T V; Schuna, J M; Tudor-Locke, C; Chaput, J-P; Church, T S; Fogelholm, M; Hu, G; Kuriyan, R; Kurpad, A; Lambert, E V; Maher, C; Maia, J; Matsudo, V; Olds, T; Onywera, V; Sarmiento, O L; Standage, M; Tremblay, M S; Zhao, P; Katzmarzyk, P T

    2015-01-01

    Objectives: Focused on the accelerometer-determined physical activity and sedentary time metrics in 9–11-year-old children, we sought to determine the following: (i) number of days that are necessary to achieve reliable estimates (G⩾0.8); (ii) proportion of variance attributed to different facets (participants and days) of reliability estimates; and (iii) actual reliability of data as collected in The International Study of Childhood Obesity, Lifestyle and Environment (ISCOLE). Methods: The analytical sample consisted of 6025 children (55% girls) from sites in 12 countries. Physical activity and sedentary time metrics measures were assessed for up to 7 consecutive days for 24 h per day with a waist-worn ActiGraph GT3X+. Generalizability theory using R software was used to investigate the objectives i and ii. Intra-class correlation coefficients (ICC) were computed using SAS PROC GLM to inform objective iii. Results: The estimated minimum number of days required to achieve a reliability estimate of G⩾0.8 ranged from 5 to 9 for boys and 3 to 11 for girls for light physical activity (LPA); 5 to 9 and 3 to 10, for moderate-to-vigorous physical activity (MVPA); 5 to 10 and 4 to 10 for total activity counts; and 7 to 11 and 6 to 11 for sedentary time, respectively. For all variables investigated, the ‘participant' facet accounted for 30–50% of the variability, whereas the ‘days' facet accounted for ⩽5%, and the interaction (P × D) accounted for 50–70% of the variability. The actual reliability for boys in ISCOLE ranged from ICCs of 0.78 to 0.86, 0.73 to 0.85 and 0.72 to 0.86 for LPA, MVPA and total activity counts, respectively, and 0.67 to 0.79 for sedentary time. The corresponding values for girls were 0.80–0.88, 0.70–0.89, 0.74–0.86 and 0.64–0.80. Conclusions: It was rare that only 4 days from all participants would be enough to achieve desirable reliability estimates. However, asking participants to wear the device for 7 days and requiring

  14. The MESA accelerometer for space application

    NASA Technical Reports Server (NTRS)

    Lange, William G.; Dietrich, Robert W.

    1990-01-01

    An electrostatically suspended proof mass in the Miniature Electrostatic Accelerometer (MESA) is used to measure acceleration in the submicro-g range. Since no fixed mechanical suspension (such as springs or strings) is used, the constrainment scaling can be changed electrically after being placed in orbit. A single proof mass can sense accelerations in three axes simultaneously. It can survive high-g pyrotechnic-generated shocks and launch environments while unpowered.

  15. A statistical test to determine the quality of accelerometer data.

    PubMed

    Slaven, J E; Andrew, M E; Violanti, J M; Burchfiel, C M; Vila, B J

    2006-04-01

    Accelerometer data quality can be inadequate due to data corruption or to non-compliance of the subject with regard to study protocols. We propose a simple statistical test to determine if accelerometer data are of good quality and can be used for analysis or if the data are of poor quality and should be discarded. We tested several data evaluation methods using a group of 105 subjects who wore Motionlogger actigraphs (Ambulatory Monitoring, Inc.) over a 15 day period to assess sleep quality in a study of health outcomes associated with stress among police officers. Using leave-one-out cross-validation and calibration-testing methods of discrimination statistics, error rates for the methods ranged from 0.0167 to 0.4046. We found that the best method was to use the overall average distance between consecutive time points and the overall average mean amplitude of consecutive time points. These values gave us a classification error rate of 0.0167. The average distance between points is a measure of smoothness in the data, and the average mean amplitude between points gave an average reading. Both of these values were then normed to determine a final statistic, K, which was then compared to a cut-off value, K(C), to determine data quality.

  16. High performance MEMS accelerometers for concrete SHM applications and comparison with COTS accelerometers

    NASA Astrophysics Data System (ADS)

    Kavitha, S.; Joseph Daniel, R.; Sumangala, K.

    2016-01-01

    Accelerometers used for civil and huge mechanical structural health monitoring intend to measure the shift in the natural frequency of the monitored structures (<100 Hz) and such sensors should have large sensitivity and extremely low noise floor. Sensitivity of accelerometers is inversely proportional to the frequency squared. Commercial MEMS (Micro Electro-Mechanical System) accelerometers that are generally designed for large bandwidth (e.g 25 kHz in ADXL150) have poor sensor level sensitivity and therefore uses complex signal conditioning electronics to achieve large sensitivity and low noise floor which in turn results in higher cost. In this work, an attempt has been made to design MEMS capacitive and piezoresistive accelerometers for smaller bandwidth using IntelliSuite and CoventorWare MEMS tools respectively. The various performance metrics have been obtained using simulation experiments and the results show that these sensors have excellent voltage sensitivity, noise performance and high resolution at sensor level and are even superior to commercial MEMS accelerometers.

  17. General Relativity Accuracy Test (TEPEE/GReAT): new configuration for the differential accelerometer

    NASA Astrophysics Data System (ADS)

    Iafolla, V.; Lucchesi, D.; Nozzoli, S.; Santoli, F.; Shapiro, I. I.; Lorenzioni, E. C.; Cosmo, M. L.; Ashenberg, J.; Cheimets, P. N.; Glashow, S.; GReAT

    A key component of experiments to test the Weak Equivalence Principle (WEP), or the universality of free fall, is the differential acceleration detector. The detector must have a very high accuracy in measuring the difference of acceleration, possibly caused by a violation of the Equivalence Principle, acting on a pair of proof masses of different materials. At the same time, the detector must be able to reject common-mode external accelerations and gravity gradients. In this paper, we report the progress in the development of a differential accelerometer that must be able to test the WEP with an accuracy of several parts in 10^15. The detector will be released to free fall inside an evacuated capsule (Einstein elevator) which has been previously dropped from a stratospheric balloon. In order to reach the accuracy goal of the experiment, the accelerometer must attain a sensitivity close to 10^-14 g/Hz^1/2 in a 25 s integration time. The free-fall time is determined by the time that the detector takes to span the co-falling capsule. The detector will be slowly rotated about a horizontal axis to modulate the gravity signal and then released inside the capsule, immediately after the capsule's release from the balloon. First, we describe briefly the overall experiment. Then, we present experimental results obtained with a differential accelerometer prototype, by stressing experimental tests of the sensitivity of the accelerometer read-out system with very-weak signals. Due to the fact that the accelerometer has a resonant frequency as low as 3 Hz and because of the difficulty to attenuate the external noise at such low frequencies, we have carried out acceleration measurements in the laboratory in a region of the seismic noise spectrum, i.e., at frequencies around 10^-1 Hz, where the noise is very low. In addition, we have exploited the ability of the sensor to reject common-mode noise components. Finally, we present a new configuration of the differential

  18. NASA Ultra-Sensitive Miniature Accelerometer

    NASA Technical Reports Server (NTRS)

    Zavracky, Paul M.; Hartley, Frank T.

    1994-01-01

    Using micro-machined silicon technology, an ultra-sensitive miniature acce.,rometer can be constructed which meets the requirements for microgravity experiments in the space environment.Such an accelerometer will have a full scale sensitivity of 1C2 g a resolution of lC8 g, low cross axis sensitivity, and low temperature sensitivity. Mass of the device is approximately five grams and its footprint is 2 cm x 2 cm. Innovative features of the accelerometer, which are patented, are: electrostatic caging to withstand handling shock up to 150 g, in-situ calibration, in situ performance characterization, and both static and dynamic compensation. The transducer operates on a force balance principle wherein the displacement of the proof mass is monitored by measuring tunneling electron current flow between a conductive tip, and a fixed platen. The four major parts of the accelerometer are tip die, incorporating the tunneling tip and four field plates for controlling pitch and roll of the proof mass; two proof mass dies, attached to the surrounding frame by sets of four leg" springs; and a force plate die. The four parts are fuse-bonded into a complete assembly. External electrical connections are made at bond pads on the front surface of the force plate die. Materials and processes used in the construction of the transducer are compatible with volume production.

  19. Wear analysis of disc cutters of full face rock tunnel boring machine

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaohuang; Meng, Liang; Sun, Fei

    2014-11-01

    Wear is a major factor of disc cutters' failure. No current theory offers a standard for the prediction of disc cutter wear yet. In the field the wear prediction method commonly used is based on the excavation length of tunnel boring machine(TBM) to predict the disc cutter wear and its wear law, considering the location number of each disc cutter on the cutterhead(radius for installation); in theory, there is a prediction method of using arc wear coefficient. However, the preceding two methods have their own errors, with their accuracy being 40% or so and largely relying on the technicians' experience. Therefore, radial wear coefficient, axial wear coefficient and trajectory wear coefficient are defined on the basis of the operating characteristics of TBM. With reference to the installation and characteristics of disc cutters, those coefficients are modified according to penetration, which gives rise to the presentation of comprehensive axial wear coefficient, comprehensive radial wear coefficient and comprehensive trajectory wear coefficient. Calculation and determination of wear coefficients are made with consideration of data from a segment of TBM project(excavation length 173 m). The resulting wear coefficient values, after modification, are adopted to predict the disc cutter wear in the follow-up segment of the TBM project(excavation length of 5621 m). The prediction results show that the disc cutter wear predicted with comprehensive radial wear coefficient and comprehensive trajectory wear coefficient are not only accurate(accuracy 16.12%) but also highly congruous, whereas there is a larger deviation in the prediction with comprehensive axial wear coefficient(accuracy 41%, which is in agreement with the prediction of disc cutters' life in the field). This paper puts forth a new method concerning prediction of life span and wear of TBM disc cutters as well as timing for replacing disc cutters.

  20. Cyclostationarity approach for monitoring chatter and tool wear in high speed milling

    NASA Astrophysics Data System (ADS)

    Lamraoui, M.; Thomas, M.; El Badaoui, M.

    2014-02-01

    Detection of chatter and tool wear is crucial in the machining process and their monitoring is a key issue, for: (1) insuring better surface quality, (2) increasing productivity and (3) protecting both machines and safe workpiece. This paper presents an investigation of chatter and tool wear using the cyclostationary method to process the vibrations signals acquired from high speed milling. Experimental cutting tests were achieved on slot milling operation of aluminum alloy. The experimental set-up is designed for acquisition of accelerometer signals and encoding information picked up from an encoder. The encoder signal is used for re-sampling accelerometers signals in angular domain using a specific algorithm that was developed in LASPI laboratory. The use of cyclostationary on accelerometer signals has been applied for monitoring chatter and tool wear in high speed milling. The cyclostationarity appears on average properties (first order) of signals, on the energetic properties (second order) and it generates spectral lines at cyclic frequencies in spectral correlation. Angular power and kurtosis are used to analyze chatter phenomena. The formation of chatter is characterized by unstable, chaotic motion of the tool and strong anomalous fluctuations of cutting forces. Results show that stable machining generates only very few cyclostationary components of second order while chatter is strongly correlated to cyclostationary components of second order. By machining in the unstable region, chatter results in flat angular kurtosis and flat angular power, such as a pseudo (white) random signal with flat spectrum. Results reveal that spectral correlation and Wigner Ville spectrum or integrated Wigner Ville issued from second-order cyclostationary are an efficient parameter for the early diagnosis of faults in high speed machining, such as chatter, tool wear and bearings, compared to traditional stationary methods. Wigner Ville representation of the residual signal shows

  1. Wear of seal materials used in aircraft propulsion systems

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Ludwig, L. P.

    1980-01-01

    A review of various types of seal locations in a gas turbine engine and the significance of wear for each type are presented. Material selection guidelines and the PV (contact pressure times sliding velocity) criteria for seal materials are discussed, and examples of wear mechanisms in positive contact seals are given. It is suggested that improved wear, erosion, and oxidation resistant materials will be required for improved seal durability; finally, a correlation is proposed between wear characteristics and a factor that includes material strength, ductility, specific heat and hot-working temperature to attain low porosity metallic gas path seal materials.

  2. High-Resolution Analysis and Modeling of GRACE Accelerometer Observations

    NASA Astrophysics Data System (ADS)

    Flury, J.; Bettadpur, S.; Tapley, B. D.

    2007-12-01

    A better understanding and modeling of high-resolution GRACE accelerometer data serves three purposes: (1) to ensure that the best possible data are used in the GRACE gravity field processing, (2) to obtain precise and clean non-gravitational accelerations for aeronomy research, and (3) to understand and quantify disturbances which may play a role for future space-borne accelerometry. The external non-gravitational forces acting on the twin GRACE satellites are superimposed by a complex signal pattern of satellite-induced effects, originating from switching events in electrical circuits of on-board heaters and magnetic torquers, from vibrations and thruster accelerations. For each of these processes, we compared and averaged 10 Hz acceleration signals from a large number of events from long accelerometer time series. The analysis results provide constraints, e.g., on thrust accuracy, misalignments, and vibration frequencies. These constraints may help to understand the underlying physics. We modeled and reduced acceleration signals due to thrusters and heater switching and obtained considerably smoother and cleaner signals of external non-gravitational accelerations which may be useful for applications in aeronomy research.

  3. Employees Wearing Religious Attire

    ERIC Educational Resources Information Center

    Zirkel, Perry

    2004-01-01

    While adherents to many religions can be identified by distinctive clothing or accessories, the wearing of such garb by teachers is not necessarily related to evangelism in the classroom. The following case and the accompanying question-and-answer discussion illustrate the problem of the principal caught between the rock of First Amendment…

  4. A 3-axis force balanced accelerometer using a single proof-mass

    SciTech Connect

    Lemkin, M.A.; Boser, B.E.; Auslander, D.; Smith, J.

    1997-04-01

    This paper presents a new method for wideband force balancing a proof-mass in multiple axes simultaneously. Capacitive position sense and force feedback are accomplished using the same air-gap capacitors through time multiplexing. Proof of concept is experimentally demonstrated with a single-mass monolithic surface micromachined 3-axis accelerometer.

  5. Design of a self-diagnostic beam-mode piezoelectric accelerometer

    NASA Technical Reports Server (NTRS)

    Flanagan, Patrick M.

    1992-01-01

    A technique was developed for detecting in situ real-time soft failures in a beam-mode piezoelectric accelerometer. The new technique can be used to detect changes in the piezoelectric capacitance, the equivalent mechanical stiffness of the piezoelectric element and the surface mounting impedance, and the piezoelectric efficiency.

  6. A biomimetic accelerometer inspired by the cricket's clavate hair.

    PubMed

    Droogendijk, H; de Boer, M J; Sanders, R G P; Krijnen, G J M

    2014-08-01

    Crickets use so-called clavate hairs to sense (gravitational) acceleration to obtain information on their orientation. Inspired by this clavate hair system, a one-axis biomimetic accelerometer has been developed and fabricated using surface micromachining and SU-8 lithography. An analytical model is presented for the design of the accelerometer, and guidelines are derived to reduce responsivity due to flow-induced contributions to the accelerometer's output. Measurements show that this microelectromechanical systems (MEMS) hair-based accelerometer has a resonance frequency of 320 Hz, a detection threshold of 0.10 ms(-2) and a dynamic range of more than 35 dB. The accelerometer exhibits a clear directional response to external accelerations and a low responsivity to airflow. Further, the accelerometer's physical limits with respect to noise levels are addressed and the possibility for short-term adaptation of the sensor to the environment is discussed. PMID:24920115

  7. A biomimetic accelerometer inspired by the cricket's clavate hair

    PubMed Central

    Droogendijk, H.; de Boer, M. J.; Sanders, R. G. P.; Krijnen, G. J. M.

    2014-01-01

    Crickets use so-called clavate hairs to sense (gravitational) acceleration to obtain information on their orientation. Inspired by this clavate hair system, a one-axis biomimetic accelerometer has been developed and fabricated using surface micromachining and SU-8 lithography. An analytical model is presented for the design of the accelerometer, and guidelines are derived to reduce responsivity due to flow-induced contributions to the accelerometer's output. Measurements show that this microelectromechanical systems (MEMS) hair-based accelerometer has a resonance frequency of 320 Hz, a detection threshold of 0.10 ms−2 and a dynamic range of more than 35 dB. The accelerometer exhibits a clear directional response to external accelerations and a low responsivity to airflow. Further, the accelerometer's physical limits with respect to noise levels are addressed and the possibility for short-term adaptation of the sensor to the environment is discussed. PMID:24920115

  8. A new accelerometer recording system for shuttle use

    NASA Technical Reports Server (NTRS)

    Lichtenberg, Byron

    1990-01-01

    Microgravity investigators are interested in enhancing the capabilities and improving the information return from accelerometers used in microgravity research. In addition to improving the accelerometer sensor, efforts should be directed towards using recent advances in microprocessor technology and system design techniques to improve sensor calibration and temperature compensation, online data display and analysis, and data reduction and information storage. Results from the above areas of investigation should be combined in an integrated design for a spaceflight microgravity accelerometer package.

  9. Wear of Spur Gears Having a Dithering Motion and Lubricated with a Perfluorinated Polyether Grease

    NASA Technical Reports Server (NTRS)

    Krantz, Timothy; Oswald, Fred; Handschuh, Robert

    2007-01-01

    Gear contact surface wear is one of the important failure modes for gear systems. Dedicated experiments are required to enable precise evaluations of gear wear for a particular application. The application of interest for this study required evaluation of wear of gears lubricated with a grade 2 perfluorinated polyether grease and having a dithering (rotation reversal) motion. Experiments were conducted using spur gears made from AISI 9310 steel. Wear was measured using a profilometer at test intervals encompassing 10,000 to 80,000 cycles of dithering motion. The test load level was 1.1 GPa maximum Hertz contact stress at the pitch-line. The trend of total wear as a function of test cycles was linear, and the wear depth rate was approximately 1.2 nm maximum wear depth per gear dithering cycle. The observed wear rate was about 600 times greater than the wear rate for the same gears operated at high speed and lubricated with oil.

  10. Plastic latching accelerometer based on bistable compliant mechanisms

    NASA Astrophysics Data System (ADS)

    Hansen, B. J.; Carron, C. J.; Jensen, B. D.; Hawkins, A. R.; Schultz, S. M.

    2007-10-01

    This paper presents the design, fabrication, and testing of a miniature latching accelerometer that does not require electrical power. Latching is attained by using a bistable compliant mechanism that switches from one mechanical position to another when the force on the accelerometer exceeds a threshold value. Accelerometers were fabricated by laser cutting the compliant mechanism switch out of both ABS and Delrin plastic sheets. Packaging consisted of gluing the single compliant layer to a supporting substrate. The switching thresholds of the accelerometers were varied from 10g to 800g by varying the surface area of the free moving section between 100 and 500 mm2.

  11. A three-axis ultrasensitive accelerometer for space

    NASA Astrophysics Data System (ADS)

    Bernard, A.

    A three-axis ultrasensitive accelerometer ASTRE (Accelerometre Spatial Triaxial Electrostatique) is a simplified version of the GRADIO accelerometer designed for the ARISTOTELES mission, which operates by measuring the force provided by a three-axis electrostatic suspension of the proof-mass. It covers the g-spectrum from 10 exp -8 to 10 exp -4 in the frequency range dc to 5 Hz. A dedicated test bench was developed in order to preserve the accelerometer from the seismic noise. The paper presents the performance parameters of the ASTRE accelerometer and some of the design schemes.

  12. Design and Implementation of a Micromechanical Silicon Resonant Accelerometer

    PubMed Central

    Huang, Libin; Yang, Hui; Gao, Yang; Zhao, Liye; Liang, Jinxing

    2013-01-01

    The micromechanical silicon resonant accelerometer has attracted considerable attention in the research and development of high-precision MEMS accelerometers because of its output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. Because of the mismatching thermal expansion coefficients of silicon and glass, the micromechanical silicon resonant accelerometer based on the Silicon on Glass (SOG) technique is deeply affected by the temperature during the fabrication, packaging and use processes. The thermal stress caused by temperature changes directly affects the frequency output of the accelerometer. Based on the working principle of the micromechanical resonant accelerometer, a special accelerometer structure that reduces the temperature influence on the accelerometer is designed. The accelerometer can greatly reduce the thermal stress caused by high temperatures in the process of fabrication and packaging. Currently, the closed-loop drive circuit is devised based on a phase-locked loop. The unloaded resonant frequencies of the prototype of the micromechanical silicon resonant accelerometer are approximately 31.4 kHz and 31.5 kHz. The scale factor is 66.24003 Hz/g. The scale factor stability is 14.886 ppm, the scale factor repeatability is 23 ppm, the bias stability is 23 μg, the bias repeatability is 170 μg, and the bias temperature coefficient is 0.0734 Hz/°C. PMID:24256978

  13. Measurement of sensor axis misalignment in fibre-optic accelerometers

    NASA Astrophysics Data System (ADS)

    DeFreitas, J. M.; Wooler, J. P. F.; Nash, P. J.

    2006-07-01

    A method is described for the measurement of sensor axis misalignment relative to its mounting can for a fibre-optic accelerometer. The accelerometers investigated were based on the common cylindrical compliant mandrel design and mounted accelerometers showed typical angular misalignments of 2°. The influence of the misalignment on cross-axis sensitivity is also described for accelerometers orthogonally mounted in a three-component package. This paper was presented at the 13th International Conference on Sensors and Their Applications, held in Chatham, Kent, on 6-7 September 2005.

  14. Design and implementation of a micromechanical silicon resonant accelerometer.

    PubMed

    Huang, Libin; Yang, Hui; Gao, Yang; Zhao, Liye; Liang, Jinxing

    2013-01-01

    The micromechanical silicon resonant accelerometer has attracted considerable attention in the research and development of high-precision MEMS accelerometers because of its output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. Because of the mismatching thermal expansion coefficients of silicon and glass, the micromechanical silicon resonant accelerometer based on the Silicon on Glass (SOG) technique is deeply affected by the temperature during the fabrication, packaging and use processes. The thermal stress caused by temperature changes directly affects the frequency output of the accelerometer. Based on the working principle of the micromechanical resonant accelerometer, a special accelerometer structure that reduces the temperature influence on the accelerometer is designed. The accelerometer can greatly reduce the thermal stress caused by high temperatures in the process of fabrication and packaging. Currently, the closed-loop drive circuit is devised based on a phase-locked loop. The unloaded resonant frequencies of the prototype of the micromechanical silicon resonant accelerometer are approximately 31.4 kHz and 31.5 kHz. The scale factor is 66.24003 Hz/g. The scale factor stability is 14.886 ppm, the scale factor repeatability is 23 ppm, the bias stability is 23 μg, the bias repeatability is 170 μg, and the bias temperature coefficient is 0.0734 Hz/°C.

  15. Microcantilevers with embedded accelerometers for dynamic atomic force microscopy

    SciTech Connect

    Shaik, Nurul Huda; Raman, Arvind; Reifenberger, Ronald G.

    2014-02-24

    The measurement of the intermittent interaction between an oscillating nanotip and the sample surface is a key challenge in dynamic Atomic Force Microscopy (AFM). Accelerometers integrated onto AFM cantilevers can directly measure this interaction with minimal cantilever modification but have been difficult to realize. Here, we design and fabricate high frequency bandwidth accelerometers on AFM cantilevers to directly measure the tip acceleration in commercial AFM systems. We demonstrate a simple way of calibrating such accelerometers and present experiments using amplitude modulated AFM on freshly cleaved mica samples in water to study the response of the accelerometer.

  16. A novel class of MEMS accelerometers for very high-G munitions environment

    NASA Astrophysics Data System (ADS)

    Rastegar, Jahangir; Feng, Dake

    2016-05-01

    The state of art in shock resistant MEMS accelerometer design is to reduce the size of the proof-mass, thereby reducing the generated forces and moments due to shock loading. Physical stops are also provided to limit proof-mass motion to prevent damage to various moving components. The reduction of the proof-mass size reduces the sensor sensitivity. In addition, to increase the sensor dynamic response, proof-mass motion needs to be minimally damped, resulting in a significant sensor settling time after experiencing a high shock loading such as those experienced by gun-fired munitions during firing. The settling time is particularly important for accelerometers that are used in gun-fired munitions and mortars for navigation and guidance. This paper describes the development of a novel class of accelerometers that are provided with the means of locking the sensor proof-mass in its "null" position when subjected to acceleration levels above a prescribed threshold, thereby protecting the moving parts of the accelerometer. In munitions applications, the proof-mass is thereby locked in its null position during the firing and is released during the flight to measure flight acceleration with minimal settling time. Details of the design and operation of the developed sensors and results of their prototyping and testing are presented. The application of the developed technology to other types of inertial sensors and devices is discussed.

  17. A novel class of MEMS accelerometers for very high-G munitions environment

    NASA Astrophysics Data System (ADS)

    Rastegar, Jahangir; Feng, Dake

    2016-04-01

    The state of art in shock resistant MEMS accelerometer design is to reduce the size of the proof-mass, thereby reducing the generated forces and moments due to shock loading. Physical stops are also provided to limit proof-mass motion to prevent damage to various moving components. The reduction of the proof-mass size reduces the sensor sensitivity. In addition, to increase the sensor dynamic response, proof-mass motion needs to be minimally damped, resulting in a significant sensor settling time after experiencing a high shock loading such as those experienced by gun-fired munitions during firing. The settling time is particularly important for accelerometers that are used in gun-fired munitions and mortars for navigation and guidance. This paper describes the development of a novel class of accelerometers that are provided with the means of locking the sensor proof-mass in its "null" position when subjected to acceleration levels above a prescribed threshold, thereby protecting the moving parts of the accelerometer. In munitions applications, the proof-mass is thereby locked in its null position during the firing and is released during the flight to measure flight acceleration with minimal settling time. Details of the design and operation of the developed sensors and results of their prototyping and testing are presented. The application of the developed technology to other types of inertial sensors and devices is discussed.

  18. A novel class of MEMS accelerometers for guidance and control of gun-fired munitions

    NASA Astrophysics Data System (ADS)

    Rastegar, Jahangir; Feng, Dake; Pereira, Carlos M.

    2015-05-01

    The state of art in shock resistant MEMS accelerometer design is to reduce the size of the proof-mass, thereby reducing the generated forces and moments due to shock loading. Physical stops are also provided to limit proof-mass motion to prevent damage to various moving components. The reduction of the proof-mass size reduces the sensor sensitivity. In addition, to increase the sensor dynamic response, proof-mass motion needs to be minimally damped, resulting in a significant sensor settling time after experiencing a high shock loading such as those experienced by gun-fired munitions during firing. The settling time is particularly important for accelerometers that are used in gun-fired munitions and mortars for navigation and guidance. This paper describes the development of a novel class of accelerometers that are provided with the means of locking the sensor proof-mass in its "null" position when subjected to acceleration levels above prescribed thresholds, thereby protecting the moving parts of the accelerometer. In munitions applications, the proof-mass is thereby locked in its null position during the firing and released during the flight to begin to measure flight acceleration with minimal settling time. Details of the design and operation of the developed sensors and results of their prototyping and testing are presented. The application of the developed technology to other types of inertial sensors and devices is discussed.

  19. An Accelerometer as an Alternative to a Force Plate for the Step-Up-and-Over Test.

    PubMed

    Bailey, Christopher A; Costigan, Patrick A

    2015-12-01

    The step-up-and-over test has been used successfully to examine knee function after knee injury. Knee function is quantified using the following variables extracted from force plate data: the maximal force exerted during the lift, the maximal impact force at landing, and the total time to complete the step. For various reasons, including space and cost, it is unlikely that all clinicians will have access to a force plate. The purpose of the study was to determine if the step-up-and-over test could be simplified by using an accelerometer. The step-up-and-over test was performed by 17 healthy young adults while being measured with both a force plate and a 3-axis accelerometer mounted at the low back. Results showed that the accelerometer and force plate measures were strongly correlated for all 3 variables (r = .90-.98, Ps < .001) and that the accelerometer values for the lift and impact indices were 6-7% higher (Ps < .01) and occurred 0.07-0.1 s later than the force plate (Ps < .05). The accelerometer returned values highly correlated to those from a force plate. Compared with a force plate, a wireless, 3-axis accelerometer is a less expensive and more portable system with which to measure the step-up-and-over test.

  20. Classification accuracy of a single tri-axial accelerometer for training background and experience level in runners.

    PubMed

    Kobsar, Dylan; Osis, Sean T; Hettinga, Blayne A; Ferber, Reed

    2014-07-18

    Accelerometers are increasingly used tools for gait analysis, but there remains a lack of research on their application to running and their ability to classify running patterns. The purpose of this study was to conduct an exploratory examination into the capability of a tri-axial accelerometer to classify runners of different training backgrounds and experience levels, according to their 3-dimensional (3D) accelerometer data patterns. Training background was examined with 14 competitive soccer players and 12 experienced marathon runners, and experience level was examined with 16 first-time and the same 12 experienced marathon runners. Discrete variables were extracted from 3D accelerations during a short run using root mean square, wavelet transformation, and autocorrelation procedures. A principal component analysis (PCA) was conducted on all variables, including gait speed to account for covariance. Eight PCs were retained, explaining 88% of the variance in the data. A stepwise discriminant analysis of PCs was used to determine the binary classification accuracy for training background and experience level, with and without the PC of Speed. With Speed, the accelerometer correctly classified 96% of runners for both training background and experience level. Without Speed, the accelerometer correctly classified 85% of runners based on training background, but only 68% based on experience level. These findings suggest that the accelerometer is effective in classifying athletes of different training backgrounds, but is less effective for classifying runners of different experience levels where gait speed is the primary discriminator. PMID:24837221

  1. Structural transformations, strengthening, and wear resistance of titanium nickelide upon abrasive and adhesive wear

    NASA Astrophysics Data System (ADS)

    Korshunov, L. G.; Pushin, V. G.; Chernenko, N. L.; Makarov, V. V.

    2010-07-01

    Wear resistance and structural transformations upon abrasive and adhesive wear of titanium nickelide Ti49.4Ni50.6 in microcrystalline (MC) and submicrocrystalline (SMC) states have been investigated. It has been shown that the abrasive wear resistance of this alloy exceeds that of the steel 12Kh18N9 by a factor of about 2, that of the steel 110G13 (Hadfield steel), by a factor of 1.3, and is close to that of the steel 95Kh18. Upon adhesive wear in a testing-temperature range from -50 to +300°C, the Ti49.4Ni50.6 alloy, as compared to the steel 12Kh18N9, is characterized by the wear rate that is tens of times smaller and by a reduced (1.5-2.0 times) friction coefficient. The enhanced wear resistance of the Ti49.4Ni50.6 alloy is due to the development of intense strain hardening in it and to a high fracture toughness, which is a consequence of effective relaxation of high contact stresses arising in the surface layer of the alloy. The SMC state produced in the alloy with the help of equal-channel angular pressing (ECAP) has no effect on the abrasive wear resistance of the alloy. The favorable effect of ECAP on the wear resistance of the Ti49.4Ni50.6 alloy takes place under conditions of its adhesive wear at temperatures from -25 to +70°C. The electron-microscopic investigation showed that under conditions of wear at negative and room temperatures in the surface layer (1-5 μm thick) of titanium nickelide there arises a mixed structure consisting of an amorphous phase and nanocrystals of supposedly austenite and martensite. Upon friction at 200-300°C, a nanocrystalline structure of the B2 phase arises near the alloy surface, which, as is the case with the amorphous-nanocrystalline structure, is characterized by significant effective strength and wear resistance.

  2. Wear testing of moderate activities of daily living using in vivo measured knee joint loading.

    PubMed

    Reinders, Jörn; Sonntag, Robert; Vot, Leo; Gibney, Christian; Nowack, Moritz; Kretzer, Jan Philippe

    2015-01-01

    Resumption of daily living activities is a basic expectation for patients provided with total knee replacements. However, there is a lack of knowledge regarding the impact of different activities on the wear performance. In this study the wear performance under application of different daily activities has been analyzed. In vivo load data for walking, walking downstairs/upstairs, sitting down/standing up, and cycling (50 W & 120 W) has been standardized for wear testing. Wear testing of each activity was carried out on a knee wear simulator. Additionally, ISO walking was tested for reasons of comparison. Wear was assessed gravimetrically and wear particles were analyzed. In vivo walking produced the highest overall wear rates, which were determined to be three times higher than ISO walking. Moderate wear rates were determined for walking upstairs and downstairs. Low wear rates were determined for standing up/sitting down and cycling at power levels of 50 W and 120 W. The largest wear particles were observed for cycling. Walking based on in vivo data has been shown to be the most wear-relevant activity. Highly demanding activities (stair climbing) produced considerably less wear. Taking into account the expected number of loads, low-impact activities like cycling may have a greater impact on articular wear than highly demanding activities.

  3. In Situ Wear Test on Thermal Spray Coatings in a Large Chamber Scanning Electron Microscope

    NASA Astrophysics Data System (ADS)

    Luo, Weifeng; Tillmann, Wolfgang; Selvadurai, Ursula

    2015-01-01

    Currently, the determination of the mass loss is usually used for a quantitative evaluation of wear tests, while the analysis of wear tracks is utilized for a qualitative evaluation of wear. Both evaluation methods can only be used after the wear testing process and their results only present the final outcome of the wear test. However, the changes during the wear test and the time-dependent wear mechanisms are of great interest as well. A running wear test in a large chamber scanning electron microscope (SEM) offers the first opportunity to observe the wear process in situ. Different wear mechanisms, such as the adhesive, abrasive wear, surface fatigue and tribochemical reaction, can be recorded with high magnification. Within this research, a special pin-on-disk testing device is designed for a vacuum environment. Using this device, arc-sprayed NiCrBSi coatings and high-velocity-oxygen-fuel-sprayed WC-12Co coatings were tested in a large chamber SEM with Al2O3 ceramic balls as wear counterparts. During the wear testing, different wear mechanisms were determined and the processes were recorded in short video streams.

  4. Wear Testing of Moderate Activities of Daily Living Using In Vivo Measured Knee Joint Loading

    PubMed Central

    Reinders, Jörn; Sonntag, Robert; Vot, Leo; Gibney, Christian; Nowack, Moritz; Kretzer, Jan Philippe

    2015-01-01

    Resumption of daily living activities is a basic expectation for patients provided with total knee replacements. However, there is a lack of knowledge regarding the impact of different activities on the wear performance. In this study the wear performance under application of different daily activities has been analyzed. In vivo load data for walking, walking downstairs/upstairs, sitting down/standing up, and cycling (50 W & 120 W) has been standardized for wear testing. Wear testing of each activity was carried out on a knee wear simulator. Additionally, ISO walking was tested for reasons of comparison. Wear was assessed gravimetrically and wear particles were analyzed. In vivo walking produced the highest overall wear rates, which were determined to be three times higher than ISO walking. Moderate wear rates were determined for walking upstairs and downstairs. Low wear rates were determined for standing up/sitting down and cycling at power levels of 50 W and 120 W. The largest wear particles were observed for cycling. Walking based on in vivo data has been shown to be the most wear-relevant activity. Highly demanding activities (stair climbing) produced considerably less wear. Taking into account the expected number of loads, low-impact activities like cycling may have a greater impact on articular wear than highly demanding activities. PMID:25811996

  5. Incisor wear and age in Yellowstone bison

    USGS Publications Warehouse

    Christianson, D.A.; Gogan, P.J.P.; Podruzny, K.M.; Olexa, E.M.

    2005-01-01

    Biologists commonly use tooth eruption and wear patterns or cementum annuli techniques to estimate age of ungulates. However, in some situations the accuracy or sampling procedures of either approach are undesirable. We investigated the progression of several quantitative measures of wear with age, using permanent first incisors from Yellowstone bison (Bison bison), and tested for differences between sexes and herds. We further investigated the relationship of wear and age to explore an age-estimation method. Labial-lingual width (LLW) correlated best with assigned age (r2=0.66, males; r2=0.76 females). Labial-lingual width differed between sexes, with females showing ∼0.2 mm more wear than males. Additionally, differences in rate of wear existed between bison of the northern and central Yellowstone herds (1.2 and 0.9 mm/year, respectively). We developed a regression formula to test the power of LLW as an estimator of Yellowstone bison age. Our method provided estimated ages within 1 year of the assigned age 73% and 82% of the time for female and male bison, respectively.

  6. Experiment on interface separation detection of concrete-filled steel tubular arch bridge using accelerometer array

    NASA Astrophysics Data System (ADS)

    Pan, Shengshan; Zhao, Xuefeng; Zhao, Hailiang; Mao, Jian

    2015-04-01

    Based on the vibration testing principle, and taking the local vibration of steel tube at the interface separation area as the study object, a real-time monitoring and the damage detection method of the interface separation of concrete-filled steel tube by accelerometer array through quantitative transient self-excitation is proposed. The accelerometers are arranged on the steel tube area with or without void respectively, and the signals of accelerometers are collected at the same time and compared under different transient excitation points. The results show that compared with the signal of compact area, the peak value of accelerometer signal at void area increases and attenuation speed slows down obviously, and the spectrum peaks of the void area are much more and disordered and the amplitude increases obviously. whether the input point of transient excitation is on void area or not is irrelevant with qualitative identification results. So the qualitative identification of the interface separation of concrete-filled steel tube based on the signal of acceleration transducer is feasible and valid.

  7. Estimating Physical Activity in Youth Using a Wrist Accelerometer

    PubMed Central

    Crouter, Scott E.; Flynn, Jennifer I.; Bassett, David R.

    2014-01-01

    PURPOSE The purpose of this study was to develop and validate methods for analyzing wrist accelerometer data in youth. METHODS 181 youth (mean±SD; age, 12.0±1.5 yrs) completed 30-min of supine rest and 8-min each of 2 to 7 structured activities (selected from a list of 25). Receiver Operator Characteristic (ROC) curves and regression analyses were used to develop prediction equations for energy expenditure (child-METs; measured activity VO2 divided by measured resting VO2) and cut-points for computing time spent in sedentary behaviors (SB), light (LPA), moderate (MPA), and vigorous (VPA) physical activity. Both vertical axis (VA) and vector magnitude (VM) counts per 5 seconds were used for this purpose. The validation study included 42 youth (age, 12.6±0.8 yrs) who completed approximately 2-hrs of unstructured PA. During all measurements, activity data were collected using an ActiGraph GT3X or GT3X+, positioned on the dominant wrist. Oxygen consumption was measured using a Cosmed K4b2. Repeated measures ANOVAs were used to compare measured vs predicted child-METs (regression only), and time spent in SB, LPA, MPA, and VPA. RESULTS All ROC cut-points were similar for area under the curve (≥0.825), sensitivity (≥0.756), and specificity (≥0.634) and they significantly underestimated LPA and overestimated VPA (P<0.05). The VA and VM regression models were within ±0.21 child-METs of mean measured child-METs and ±2.5 minutes of measured time spent in SB, LPA, MPA, and VPA, respectively (P>0.05). CONCLUSION Compared to measured values, the VA and VM regression models developed on wrist accelerometer data had insignificant mean bias for child-METs and time spent in SB, LPA, MPA, and VPA; however they had large individual errors. PMID:25207928

  8. Some wear studies on aircraft brake systems

    NASA Technical Reports Server (NTRS)

    Ho, T. L.

    1975-01-01

    An initial investigation of worn surfaces in friction pads and steel rotors used in current aircraft brakes was carried out using electron microprobe and X-ray diffraction analysis. It consists of the topographical study and the analysis of chemical element distribution. Based upon this initial examination, two approaches, microscopic and macroscopic have been conducted to interpret and formulate the wear mechanism of the aircraft brake materials. Microscopically, the wear particles were examined. The initiation and growth of surface cracks and the oxidation were emphasized in this investigation. Macroscopically, it has been found that, for the current copper based brake material sliding against 17-22 AS steel in a caliper brake, the surface temperature raised due to frictional heat is nonlinearly proportional to the load applied and slide time with speed at 1750 rpm. The wear of brake materials is then proportional to this temperature and is also a function of the melting temperature for copper.

  9. Analysis of walking improvement with dynamic shoe insoles, using two accelerometers

    NASA Astrophysics Data System (ADS)

    Tsuruoka, Yuriko; Tamura, Yoshiyasu; Shibasaki, Ryosuke; Tsuruoka, Masako

    2005-07-01

    The orthopedics at the rehabilitation hospital found that disorders caused by sports injuries to the feet or caused by lower-back are improved by wearing dynamic shoe insoles, these improve walking balance and stability. However, the relationship of the lower-back and knees and the rate of increase in stability were not quantitatively analyzed. In this study, using two accelerometers, we quantitatively analyzed the reciprocal spatiotemporal contributions between the lower-back and knee of patients with left lower-back pain by means of Relative Power Contribution Analysis. When the insoles were worn, the contribution of the left and right knee relative to the left lower-back pain was up to 26% ( p<0.05) greater than without the insoles. Comparing patients with and without insoles, we found that the variance in the step response analysis of the left and right knee decreased by up to 67% ( p<0.05). This shows an increase in stability.

  10. Corrosive wear principles

    SciTech Connect

    Schumacher, W.J.

    1993-12-31

    The dual effects of corrosion and wear operate together in such industries as paper and pulp, coal handling, mining, and sugar beet extraction. There is a synergistic effect that causes far greater wastage to carbon steels, alloy steels, and even much more abrasion resistant cast irons. Several laboratory and in situ studies have been conducted to better understand the contributions of corrosion and wear to the wastage process. The environmental conditions are usually set by the process. However, there are a few instances where inhibitors as sodium nitrite, sodium chromate, and sodium metasilicate have been successfully used to reduce metal wastage of carbon steels. Hardness has been found to be an unreliable guide to performance under wet sliding conditions. Heat treated alloy steels and cast irons are inferior to stainless steels. Even distilled water is too severe a corrodent for steels. While the austenitic stainlesses perform the best, cold rolling to increase hardness does not further improve their performance. The surface roughness of stainless steels gets smoother during corrosive wear testing while it gets rougher for the alloy steels. This observation substantiated the reputation of improved slideability for stainless alloys over alloy steels.

  11. Accelerometer Use in a Physical Activity Intervention Trial

    PubMed Central

    Borradaile, Kelley E.; Lewis, Beth A.; Whiteley, Jessica A.; Longval, Jaime L.; Parisi, Alfred F.; Albrecht, Anna E.; Sciamanna, Christopher N.; Jakicic, John M.; Papandonatos, George D.; Marcus, Bess H.

    2010-01-01

    This paper describes the application of best practice recommendations for using accelerometers in a physical activity (PA) intervention trial, and the concordance of different methods for measuring PA. A subsample (n=63; 26%) of the 239 healthy, sedentary adults participating in a PA trial (mean age=47.5; 82% women) wore the ActiGraph monitor at all 3 assessment time points. ActiGraph data were compared with self-report (i.e., PA weekly recall and monthly log) and fitness variables. Correlations between the PA recall and ActiGraph for moderate intensity activity ranged from 0.16–0.48 and from 0.28–0.42 for vigorous intensity activity. ActiGraph and fitness [estimated VO2(ml/kg/min)] had correlations of 0.15–0.45. The ActiGraph and weekly self-report were significantly correlated at all time points (correlations ranged from 0.23–0.44). In terms of detecting intervention effects, intervention groups recorded more minutes of at least moderate-intensity PA on the ActiGraph than the control group at 6 months (min=46.47, 95% CI=14.36–78.58), but not at 12 months. Limitations of the study include a small sample size and only 3 days of ActiGraph monitoring. To obtain optimal results with accelerometers in clinical trials, the authors recommend following best practice recommendations: detailed protocols for monitor use, calibration of monitors and validation of data quality, and use of validated equations for analysis. The ActiGraph has modest concordance with other assessment tools and is sensitive to change over time. However, until more information validating the use of accelerometry in clinical trials becomes available, properly administered self-report measures of PA should remain part of the assessment battery. PMID:20723619

  12. Accelerometer use in a physical activity intervention trial.

    PubMed

    Napolitano, Melissa A; Borradaile, Kelley E; Lewis, Beth A; Whiteley, Jessica A; Longval, Jaime L; Parisi, Alfred F; Albrecht, Anna E; Sciamanna, Christopher N; Jakicic, John M; Papandonatos, George D; Marcus, Bess H

    2010-11-01

    This paper describes the application of best practice recommendations for using accelerometers in a physical activity (PA) intervention trial, and the concordance of different methods for measuring PA. A subsample (n = 63; 26%) of the 239 healthy, sedentary adults participating in a PA trial (mean age = 47.5; 82% women) wore the ActiGraph monitor at all 3 assessment time points. ActiGraph data were compared with self-report (i.e., PA weekly recall and monthly log) and fitness variables. Correlations between the PA recall and ActiGraph for moderate intensity activity ranged from 0.16-0.48 and from 0.28-0.42 for vigorous intensity activity. ActiGraph and fitness [estimated VO(2)(ml/kg/min)] had correlations of 0.15-0.45. The ActiGraph and weekly self-report were significantly correlated at all time points (correlations ranged from 0.23 to 0.44). In terms of detecting intervention effects, intervention groups recorded more minutes of at least moderate-intensity PA on the ActiGraph than the control group at 6 months (min = 46.47, 95% CI = 14.36-78.58), but not at 12 months. Limitations of the study include a small sample size and only 3 days of ActiGraph monitoring. To obtain optimal results with accelerometers in clinical trials, the authors recommend following best practice recommendations: detailed protocols for monitor use, calibration of monitors and validation of data quality, and use of validated equations for analysis. The ActiGraph has modest concordance with other assessment tools and is sensitive to change over time. However, until more information validating the use of accelerometry in clinical trials becomes available, properly administered self-report measures of PA should remain part of the assessment battery.

  13. Calibrating Accelerometers Using an Electromagnetic Launcher

    SciTech Connect

    Erik Timpson

    2012-05-13

    A Pulse Forming Network (PFN), Helical Electromagnetic Launcher (HEML), Command Module (CM), and Calibration Table (CT) were built and evaluated for the combined ability to calibrate an accelerometer. The PFN has a maximum stored energy of 19.25 kJ bank and is fired by a silicon controlled rectifier (SCR), with appropriate safety precautions. The HEML is constructed out of G-10 fiberglass and is designed to accelerate 600 grams to 10 meters per second. The CM is microcontroller based running Arduino Software. The CM has a keypad input and 7 segment outputs of the bank voltage and desired voltage. After entering a desired bank voltage, the CM controls the charge of the PFN. When the two voltages are equal it allows the fire button to send a pulse to the SCR to fire the PFN and in turn, the HEML. The HEML projectile's tip hits a target that is held by the CT. The CT consists of a table to hold the PFN and HEML, a vacuum chuck, air bearing, velocity meter and catch pot. The Target is held with the vacuum chuck awaiting impact. After impact, the air bearing allows the target to fall freely for the velocity meter to get an accurate reading. A known acceleration is determined from the known change in velocity of the target. Thus, if an accelerometer was attached to the target, the measured value can be compared to the known value.

  14. Classification of sporting activities using smartphone accelerometers.

    PubMed

    Mitchell, Edmond; Monaghan, David; O'Connor, Noel E

    2013-04-19

    In this paper we present a framework that allows for the automatic identification of sporting activities using commonly available smartphones. We extract discriminative informational features from smartphone accelerometers using the Discrete Wavelet Transform (DWT). Despite the poor quality of their accelerometers, smartphones were used as capture devices due to their prevalence in today's society. Successful classification on this basis potentially makes the technology accessible to both elite and non-elite athletes. Extracted features are used to train different categories of classifiers. No one classifier family has a reportable direct advantage in activity classification problems to date; thus we examine classifiers from each of the most widely used classifier families. We investigate three classification approaches; a commonly used SVM-based approach, an optimized classification model and a fusion of classifiers. We also investigate the effect of changing several of the DWT input parameters, including mother wavelets, window lengths and DWT decomposition levels. During the course of this work we created a challenging sports activity analysis dataset, comprised of soccer and field-hockey activities. The average maximum F-measure accuracy of 87% was achieved using a fusion of classifiers, which was 6% better than a single classifier model and 23% better than a standard SVM approach.

  15. Classification of Sporting Activities Using Smartphone Accelerometers

    PubMed Central

    Mitchell, Edmond; Monaghan, David; O'Connor, Noel E.

    2013-01-01

    In this paper we present a framework that allows for the automatic identification of sporting activities using commonly available smartphones. We extract discriminative informational features from smartphone accelerometers using the Discrete Wavelet Transform (DWT). Despite the poor quality of their accelerometers, smartphones were used as capture devices due to their prevalence in today's society. Successful classification on this basis potentially makes the technology accessible to both elite and non-elite athletes. Extracted features are used to train different categories of classifiers. No one classifier family has a reportable direct advantage in activity classification problems to date; thus we examine classifiers from each of the most widely used classifier families. We investigate three classification approaches; a commonly used SVM-based approach, an optimized classification model and a fusion of classifiers. We also investigate the effect of changing several of the DWT input parameters, including mother wavelets, window lengths and DWT decomposition levels. During the course of this work we created a challenging sports activity analysis dataset, comprised of soccer and field-hockey activities. The average maximum F-measure accuracy of 87% was achieved using a fusion of classifiers, which was 6% better than a single classifier model and 23% better than a standard SVM approach. PMID:23604031

  16. Optimal Sensor Placement for Measuring Physical Activity with a 3D Accelerometer

    PubMed Central

    Boerema, Simone T.; van Velsen, Lex; Schaake, Leendert; Tönis, Thijs M.; Hermens, Hermie J.

    2014-01-01

    Accelerometer-based activity monitors are popular for monitoring physical activity. In this study, we investigated optimal sensor placement for increasing the quality of studies that utilize accelerometer data to assess physical activity. We performed a two-staged study, focused on sensor location and type of mounting. Ten subjects walked at various walking speeds on a treadmill, performed a deskwork protocol, and walked on level ground, while simultaneously wearing five ProMove2 sensors with a snug fit on an elastic waist belt. We found that sensor location, type of activity, and their interaction-effect affected sensor output. The most lateral positions on the waist belt were the least sensitive for interference. The effect of mounting was explored, by making two subjects repeat the experimental protocol with sensors more loosely fitted to the elastic belt. The loose fit resulted in lower sensor output, except for the deskwork protocol, where output was higher. In order to increase the reliability and to reduce the variability of sensor output, researchers should place activity sensors on the most lateral position of a participant's waist belt. If the sensor hampers free movement, it may be positioned slightly more forward on the belt. Finally, sensors should be fitted tightly to the body. PMID:24553085

  17. Technical Reliability Assessment of the Actigraph GT1M Accelerometer

    ERIC Educational Resources Information Center

    Silva, Pedro; Mota, Jorge; Esliger, Dale; Welk, Gregory

    2010-01-01

    The purpose of this study was to determine the reliability of the Actigraph GT1M (Pensacola, FL, USA) accelerometer activity count and step functions. Fifty GT1M accelerometers were initialized to collect simultaneous acceleration counts and steps data using 15-sec epochs. All reliability testing was completed using a mechanical shaker plate to…

  18. Ultralow wear of gallium nitride

    NASA Astrophysics Data System (ADS)

    Zeng, Guosong; Tan, Chee-Keong; Tansu, Nelson; Krick, Brandon A.

    2016-08-01

    Here, we reveal a remarkable (and surprising) physical property of GaN: it is extremely wear resistant. In fact, we measured the wear rate of GaN is approaching wear rates reported for diamond. Not only does GaN have an ultralow wear rate but also there are quite a few experimental factors that control the magnitude of its wear rate, further contributing to the rich and complex physics of wear of GaN. Here, we discovered several primary controlling factors that will affect the wear rate of III-Nitride materials: crystallographic orientation, sliding environment, and coating composition (GaN, InN and InGaN). Sliding in the ⟨ 1 2 ¯ 10 ⟩ is significantly lower wear than ⟨ 1 1 ¯ 00 ⟩ . Wear increases by 2 orders of magnitude with increasing humidity (from ˜0% to 50% RH). III-Nitride coatings are promising as multifunctional material systems for device design and sliding wear applications.

  19. Flight calibration assessment of HiRAP accelerometer data

    NASA Technical Reports Server (NTRS)

    Blanchard, Robert C.; Larman, Kevin T.; Moast, Christina D.

    1993-01-01

    A flight derived method of calibrating the High Resolution Accelerometer Package (HiRAP) flight data has been developed and is discussed for Shuttle Orbiter missions STS-35 and STS-40. These two mission data sets have been analyzed using ground calibration factors and flight derived calibration factors. This flight technique evolved early in the flight program when it was recognized that ground calibration factors are insufficient to determine absolute low-acceleration levels. The application of flight calibration factors to the data sets from these missions produced calibrated acceleration levels within an accuracy of less than +/- 1.5 microgravity of zero during a time in the flight when the acceleration level was known to be less than 1.0 microgravity. This analysis further confirms the theory that flight calibrations are required in order to obtain the absolute measurement of low-frequency, low-acceleration flight signals.

  20. The application of EMD in activity recognition based on a single triaxial accelerometer.

    PubMed

    Liao, Mengjia; Guo, Yi; Qin, Yajie; Wang, Yuanyuan

    2015-01-01

    Activities recognition using a wearable device is a very popular research field. Among all wearable sensors, the accelerometer is one of the most common sensors due to its versatility and relative ease of use. This paper proposes a novel method for activity recognition based on a single accelerometer. To process the activity information from accelerometer data, two kinds of signal features are extracted. Firstly, five features including the mean, the standard deviation, the entropy, the energy and the correlation are calculated. Then a method called empirical mode decomposition (EMD) is used for the feature extraction since accelerometer data are non-linear and non-stationary. Several time series named intrinsic mode functions (IMFs) can be obtained after the EMD. Additional features will be added by computing the mean and standard deviation of first three IMFs. A classifier called Adaboost is adopted for the final activities recognition. In the experiments, a single sensor is separately positioned in the waist, left thigh, right ankle and right arm. Results show that the classification accuracy is 94.69%, 86.53%, 91.84% and 92.65%, respectively. These relatively high performances demonstrate that activities can be detected irrespective of the position by reducing problems such as the movement constrain and discomfort.

  1. An integrated GPS-accelerometer data processing technique for structural deformation monitoring

    NASA Astrophysics Data System (ADS)

    Chan, W. S.; Xu, Y. L.; Ding, X. L.; Dai, W. J.

    2006-12-01

    Global Positioning System (GPS) is being actively applied to measure static and dynamic displacement responses of large civil engineering structures under winds. However, multipath effects and low sampling frequencies affect the accuracy of GPS for displacement measurement. On the other hand, accelerometers cannot reliably measure static and low-frequency structural responses, but can accurately measure high-frequency structural responses. Therefore, this paper explores the possibility of integrating GPS-measured signals with accelerometer-measured signals to enhance the measurement accuracy of total (static plus dynamic) displacement response of a structure. Integrated data processing techniques using both empirical mode decomposition (EMD) and an adaptive filter are presented. A series of motion simulation table tests are then performed at a site using three GPS receivers, one accelerometer, and one motion simulation table that can simulate various types of motion defined by input wave time histories around a pre-defined static position. The proposed data processing techniques are applied to the recorded GPS and accelerometer data to find both static and dynamic displacements. These results are compared with the actual displacement motions generated by the motion simulation table. The comparative results demonstrate that the proposed technique can significantly enhance the measurement accuracy of the total displacement of a structure.

  2. Measurement of six degree-of-freedom ground motion by using eight accelerometers

    NASA Astrophysics Data System (ADS)

    Yang, Zhenyu; Shen, Yi; Liu, Zhiyan

    2005-12-01

    A new integrated measuring system with eight force-balance accelerometers is proposed to obtain a direct measurement of six degree-of freedom (DOF) ground motions, including three rotational and three actual translational acceleration components without gyroscopes. In the proposed measuring system, the relationship between the output from eight force-balance accelerometer and the six DOF motion of the measuring system under an earthquake are described by differential equations. These equations are derived from the positions and directions of the eight force-balance accelerometers in the measuring system. The third-order Runge-Kutta algorithm is used to guarantee the accuracy of the numerical calculation. All the algorithms used to compute the six DOF components of the ground motion are implemented in a real-time in Digital Signal Processor (DSP). The distortion of the measured results caused by position and direction errors of the accelerometers in the measuring system are reduced by multiplying a compensation coefficient C to the output and subtracting static zero drift from the measured results, respectively.

  3. High sensitivity optical waveguide accelerometer based on Fano resonance.

    PubMed

    Wan, Fenghua; Qian, Guang; Li, Ruozhou; Tang, Jie; Zhang, Tong

    2016-08-20

    An optical waveguide accelerometer based on tunable asymmetrical Fano resonance in a ring-resonator-coupled Mach-Zehnder interferometer (MZI) is proposed and analyzed. A Fano resonance accelerometer has a relatively large workspace of coupling coefficients with high sensitivity, which has potential application in inertial navigation, missile guidance, and attitude control of satellites. Due to the interference between a high-Q resonance pathway and a coherent background pathway, a steep asymmetric line shape is generated, which greatly improves the sensitivity of this accelerometer. The sensitivity of the accelerometer is about 111.75 mW/g. A 393-fold increase in sensitivity is achieved compared with a conventional MZI accelerometer and is approximately equal to the single ring structure.

  4. High sensitivity optical waveguide accelerometer based on Fano resonance.

    PubMed

    Wan, Fenghua; Qian, Guang; Li, Ruozhou; Tang, Jie; Zhang, Tong

    2016-08-20

    An optical waveguide accelerometer based on tunable asymmetrical Fano resonance in a ring-resonator-coupled Mach-Zehnder interferometer (MZI) is proposed and analyzed. A Fano resonance accelerometer has a relatively large workspace of coupling coefficients with high sensitivity, which has potential application in inertial navigation, missile guidance, and attitude control of satellites. Due to the interference between a high-Q resonance pathway and a coherent background pathway, a steep asymmetric line shape is generated, which greatly improves the sensitivity of this accelerometer. The sensitivity of the accelerometer is about 111.75 mW/g. A 393-fold increase in sensitivity is achieved compared with a conventional MZI accelerometer and is approximately equal to the single ring structure. PMID:27556984

  5. Consideration of wear rates at high velocity

    NASA Astrophysics Data System (ADS)

    Hale, Chad S.

    The development of the research presented here is one in which high velocity relative sliding motion between two bodies in contact has been considered. Overall, the wear environment is truly three-dimensional. The attempt to characterize three-dimensional wear was not economically feasible because it must be analyzed at the micro-mechanical level to get results. Thus, an engineering approximation was carried out. This approximation was based on a metallographic study identifying the need to include viscoplasticity constitutive material models, coefficient of friction, relationships between the normal load and velocity, and the need to understand wave propagation. A sled test run at the Holloman High Speed Test Track (HHSTT) was considered for the determination of high velocity wear rates. In order to adequately characterize high velocity wear, it was necessary to formulate a numerical model that contained all of the physical events present. The experimental results of a VascoMax 300 maraging steel slipper sliding on an AISI 1080 steel rail during a January 2008 sled test mission were analyzed. During this rocket sled test, the slipper traveled 5,816 meters in 8.14 seconds and reached a maximum velocity of 1,530 m/s. This type of environment was never considered previously in terms of wear evaluation. Each of the features of the metallography were obtained through micro-mechanical experimental techniques. The byproduct of this analysis is that it is now possible to formulate a model that contains viscoplasticity, asperity collisions, temperature and frictional features. Based on the observations of the metallographic analysis, these necessary features have been included in the numerical model, which makes use of a time-dynamic program which follows the movement of a slipper during its experimental test run. The resulting velocity and pressure functions of time have been implemented in the explicit finite element code, ABAQUS. Two-dimensional, plane strain models

  6. The role of accelerometer data calibration within GRACE gravity field recovery: Results from ITSG-Grace2016

    NASA Astrophysics Data System (ADS)

    Klinger, Beate; Mayer-Gürr, Torsten

    2016-11-01

    For more than 14 years, the Gravity Recovery and Climate Experiment (GRACE) mission has provided information about Earth's gravity field with unprecedented accuracy. The twin satellites GRACE-A and GRACE-B are both equipped with a three-axis electrostatic accelerometer, measuring the non-gravitational forces acting on the spacecraft. In order to make use of the uncalibrated Level-1B accelerometer (ACC1B) data during gravity field recovery, bias and scale parameters have to be estimated. The proposed calibration method is a two-step approach and makes use of modeled non-conservative accelerations. The simulated non-conservative accelerations serve as reference for the a priori accelerometer calibration, i.e. for the ACC1B data. During gravity field recovery the calibration parameters are re-estimated. Several calibration parameters for the GRACE accelerometers using different methods have already been published. The aim of our study was primarily to analyze the temperature-dependent behavior of the accelerometer scale factors and biases, and the impact of the parametrization of scale factors and biases on the recovered gravity field solutions; but not to obtain calibrated accelerometer data. Within the ITSG-Grace2016 release, the accelerometer biases are estimated daily using uniform cubic basis splines (UCBS), the scale factors are also estimated daily using a fully-populated scale factor matrix. Therefore, not only the scale factors in along-track, cross-track, and radial direction are estimated, but also the non-orthogonality of the accelerometer axes (cross-talk) and the misalignment between the Accelerometer Frame (AF) and Science Reference Frame (SRF) are taken into account. The time evolution of the estimated calibration parameters over the whole GRACE period (2002-04 to 2016-01) shows a clear temperature-dependency for both scale factors and biases. Using this new approach, the estimates of the C20 coefficient significantly improve, with results now

  7. Wear Mechanisms in a Reliability Methodology

    NASA Astrophysics Data System (ADS)

    Tanner, Danelle M.; Dugger, Michael T.

    2003-01-01

    The main thrust in any reliability work is identifying failure modes and mechanisms. This is especially true for the new technology of MicroElectroMechanical Systems (MEMS). The methods are sometimes just as important as the results achieved. This paper will review some of the methods developed specifically for MEMS. Our methodology uses statistical characterization and testing of complex MEMS devices to help us identify dominant failure modes. We strive to determine the root cause of each failure mode and to gain a fundamental understanding of that mechanism. Test structures designed to be sensitive to a particular failure mechanism are typically used to gain understanding. The development of predictive models follows from this basic understanding. This paper will focus on the failure mechanism of wear and how our methodology was exercised to provide a predictive model. The MEMS device stressed in these studies was a Sandia-developed microengine with orthogonal electrostatic linear actuators connected to a gear on a hub. The dominant failure mechanism was wear in the sliding/contacting regions. A sliding beam-on-post test structure was also used to measure friction coefficients and wear morphology for different surface coatings and environments. Results show that a predictive model of failure-time as a function of drive frequency based on wear fits the functional form of the reliability data quite well, and demonstrates the benefit of a fundamental understanding of wear. The results also show that while debris of similar chemistry and morphology was created in the two types of devices, the dependence of debris generation on the operating environment was entirely different. The differences are discussed in terms of wear maps for ceramics, and the mechanical and thermal contact conditions in each device.

  8. Mars Reconnaissance Orbiter Accelerometer Experiment Results

    NASA Astrophysics Data System (ADS)

    Keating, G. M.; Bougher, S. W.; Theriot, M. E.; Zurek, R. W.; Blanchard, R. C.; Tolson, R. H.; Murphy, J. R.

    2007-05-01

    The Mars Reconnaissance Orbiter (MRO) launched on August 12, 2005, designed for aerobraking, achieved Mars Orbital Insertion (MOI), March 10, 2006. Atmospheric density decreases exponentially with increasing height. By small propulsive adjustments of the apoapsis orbital velocity, periapsis altitude is fine tuned to the density surface that safely used the atmosphere of Mars to aerobrake over 400 orbits. MRO periapsis precessed from the South Pole at 6pm LST to near the equator at 3am LST. Meanwhile, apoapsis was brought dramatically from 40,000km at MOI to 460 km at aerobraking completion (ABX) August 30, 2006. After ABX, a few small propulsive maneuvers established the Primary Science Orbit (PSO), which without aerobraking would have required an additional 400 kg of fuel. Each of the 400 plus aerobraking orbits provided a vertical structure and distribution of density, scale heights, and temperatures, along the orbital path, providing key in situ insight into various upper atmosphere (greater than 100 km) processes. One of the major questions for scientists studying Mars is: "Where did the water go?" Honeywell's substantially improved electronics package for its IMU (QA-2000 accelerometer, gyro, electronics) maximized accelerometer sensitivities at the requests of The George Washington University, JPL, and Lockheed Martin. The improved accelerometer sensitivities allowed density measurements to exceed 200km, at least 40 km higher than with Mars Odyssey (MO). This extended vertical structures from MRO into the neutral lower exosphere, a region where various processes may allow atmospheric gasses to escape. Over the eons, water may have been lost in both near the surface and in the upper atmosphere. Thus the water balance throughout the entire atmosphere from subsurface to exosphere may both be critical. Comparisons of data from Mars Global Surveyor (MGS), MO and MRO help characterize key temporal and spatial cycles including: winter polar warming, planetary scale

  9. Methodology for proximal wear evaluation in posterior resin composites.

    PubMed

    Ziemiecki, T L; Wendt, S L; Leinfelder, K F

    1992-08-01

    The purpose of this study was to utilize a methodology to measure proximal wear of posterior resin composites with respect to time. A group of 10 teeth (5 premolars and 5 molars) were restored with P-30, a posterior resin composite restorative. At placement the proximal contacts were judged to be closed visually, and with unwaxed dental floss. The patients were then recalled at intervals of 6, 12, and 36 months for indirect wear evaluations. Resin composite transfer copings were made and indexed on baseline models. A zoom stereomicroscope, at 20 microns resolution, was used to determine proximal wear. For the posterior restorative material the premolar and molar teeth wore at the same rate. The amount of wear was statistically greater for premolar teeth at 6 and 12-month evaluation periods than molar teeth. At 36 months, there was no statistical difference in wear between premolar and molar teeth.

  10. Wear mechanism based on adhesion

    NASA Technical Reports Server (NTRS)

    Yamamoto, T.; Buckley, D. H.

    1982-01-01

    Various concepts concerning wear mechanisms and deformation behavior observed in the sliding wear track are surveyed. The mechanisms for wear fragment formation is discussed on the basis of adhesion. The wear process under unlubricated sliding conditions is explained in relation to the concept of adhesion at the interface during the sliding process. The mechanism for tearing away the surface layer from the contact area and forming the sliding track contour is explained by assuming the simplified process of material removal based on the adhesion theory.

  11. Wear Behavior of Newly Developed Bainitic Wheel Steels

    NASA Astrophysics Data System (ADS)

    Sharma, S.; Sangal, S.; Mondal, K.

    2015-02-01

    The present work concentrates on the analysis of wear behavior of bainitic steels made by austempering from a microalloyed steel MAS2, meant for making railway wheel, and comparison with that of a conventional railway wheel steel, wheel-R19. Austempering of the MAS2 steel samples has been performed at different times and temperatures to obtain different morphologies of bainite. Linearly reciprocating dry sliding wear tests of these samples have been carried out at laboratory scale using five different loads. The wear behavior of the bainitic steels has been compared with that of the ferritic-pearlitic steel, wheel-R19. Mechanical properties of the bainitic MAS2 steels are found to be more than that of the wheel-R19 steel. Considerable enhancement in wear resistance of the bainitic steels is attributed to high hardness and strength of the steels. The wear mechanism has been critically analyzed by examining wear track morphology. The wear data gathered have been graphically presented in the form of wear mechanism map to understand the material behavior under different sliding conditions and subsequent morphological variations.

  12. Wear-Out Sensitivity Analysis Project Abstract

    NASA Technical Reports Server (NTRS)

    Harris, Adam

    2015-01-01

    During the course of the Summer 2015 internship session, I worked in the Reliability and Maintainability group of the ISS Safety and Mission Assurance department. My project was a statistical analysis of how sensitive ORU's (Orbital Replacement Units) are to a reliability parameter called the wear-out characteristic. The intended goal of this was to determine a worst case scenario of how many spares would be needed if multiple systems started exhibiting wear-out characteristics simultaneously. The goal was also to determine which parts would be most likely to do so. In order to do this, my duties were to take historical data of operational times and failure times of these ORU's and use them to build predictive models of failure using probability distribution functions, mainly the Weibull distribution. Then, I ran Monte Carlo Simulations to see how an entire population of these components would perform. From here, my final duty was to vary the wear-out characteristic from the intrinsic value, to extremely high wear-out values and determine how much the probability of sufficiency of the population would shift. This was done for around 30 different ORU populations on board the ISS.

  13. A high performance, variable capacitance accelerometer

    NASA Astrophysics Data System (ADS)

    Wilner, L. Bruce

    1988-12-01

    A variable capacitance acceleration sensor is described. Manufactured using silicon microfabrication techniques, the sensor uses a midplane, flat plate suspension, gas damping, and overrange stops. The sensor is assembled from three silicon wafers, using anodic bonds to inlays of borosilicate glass. Typical sensor properties are 7-pF active capacitance, 3-pF tare capacitance, a response of 0.05 pF/G, a resonance frequency of 3.4 kHz, and damping 0.7 critical. It is concluded that this sensor, with appropriate electronics, forms an accelerometer with an order-of-magnitude greater sensitivity-bandwidth product than a comparable piezoresistive acclerometer, and with extraordinary shock resistance.

  14. Elucidation of wear mechanisms by ferrographic analysis

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1981-01-01

    The use of ferrographic analysis in conjunction with light and scanning electron microscopy is described for the elucidation of wear mechanisms taking place in operating equipment. Example of adhesive wear, abrasive wear, corrosive wear, rolling element fatigue, lubricant breakdown, and other wear modes are illustrated. In addition, the use of magnetic solutions to precipitate nonmagnetic debris from aqueous and nonaqueous fluids is described.

  15. Vibration sensing in smart machine rotors using internal MEMS accelerometers

    NASA Astrophysics Data System (ADS)

    Jiménez, Samuel; Cole, Matthew O. T.; Keogh, Patrick S.

    2016-09-01

    This paper presents a novel topology for enhanced vibration sensing in which wireless MEMS accelerometers embedded within a hollow rotor measure vibration in a synchronously rotating frame of reference. Theoretical relations between rotor-embedded accelerometer signals and the vibration of the rotor in an inertial reference frame are derived. It is thereby shown that functionality as a virtual stator-mounted displacement transducer can be achieved through appropriate signal processing. Experimental tests on a prototype rotor confirm that both magnitude and phase information of synchronous vibration can be measured directly without additional stator-mounted key-phasor sensors. Displacement amplitudes calculated from accelerometer signals will become erroneous at low rotational speeds due to accelerometer zero-g offsets, hence a corrective procedure is introduced. Impact tests are also undertaken to examine the ability of the internal accelerometers to measure transient vibration. A further capability is demonstrated, whereby the accelerometer signals are used to measure rotational speed of the rotor by analysing the signal component due to gravity. The study highlights the extended functionality afforded by internal accelerometers and demonstrates the feasibility of internal sensor topologies, which can provide improved observability of rotor vibration at externally inaccessible rotor locations.

  16. Type of development and application of integrating accelerometer

    NASA Astrophysics Data System (ADS)

    Pan, Hongxia; Li, Ting; Liu, Guangpu; Yu, Hongying

    2000-05-01

    In this paper a new technique is suggested to solve the problem of measuring the vibration parameters in bad conditions with strong shock, that is, using integrating accelerometers repacked with normal inertial accelerometers to measure vibration acceleration signal of rocket launcher and then integrating velocity and displacement parameters. After the problems of integral accuracy have been solved, various vibration parameters are obtained to meet the needs of a certain project. By analysis, this integrating accelerometer has been testified to be a very practical sensor with surplus value in measuring vibration parameters in bad condition with strong shock.

  17. USML-1 microgravity glovebox experiment no. 1 Passive Accelerometer System

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.; Rogers, Melissa J. B.

    1995-01-01

    The passive accelerometer system (PAS) is a simple moving ball accelerometer capable of measuring the small magnitude steady relative acceleration that occurs in a low earth orbit spacecraft due to atmospheric drag and the earth's gravity gradient. The accelerometer can be used when the spacecraft continuously rotates during the orbit such that some line of reference in the craft always points along the vector connecting the earth's mass center with the spacecraft mass center. PAS was used successfully on the first United States Microgravity Laboratory (USML-1).

  18. Wear of metal fiber brushes

    NASA Astrophysics Data System (ADS)

    Brown, Lloyd Perryman, Jr.

    The goal of this dissertation was determining the wear mechanism of metal fiber brushes on commutators and slip rings with the goal of achieving the lowest possible wear rate. To this end, metal fiber brushes were operated, while conducting direct current, on gold-plated copper rotors with and without unfilled gaps to simulate slip rings and commutators, respectively. Wear rates on unfilled-groove commutators were found to be only modestly higher than on slip ring style rotors. Three possible causes for enhanced metal fiber brush wear on commutators were considered: (i) accelerated "adhesive" wear controlled by contact spots, (ii) fatigue induced wear and (iii) "fiber chopping". Similarly, SEM analysis of fiber tips and wear particles produced scant, if any, evidence of fiber chopping, which would occur as, again, fiber tips extend elastically into the commutator grooves and small slices of them would be "chopped" off by oncoming edges of commutator bars. Finally considered was "modified chopping", wherein fiber tips would be dragged over groove edges, resulting in tensile fracture and chopping. Only a single fiber fragment showed damage that might be compatible with that mechanism. Moreover, the fact that it was exemplified by a single tenuous case, rules it out as significant. The same conclusion also follows from comparing commutator wear rates with that on slip rings. These show good correlation in terms of effective brush pressure, which on commutators is increased because only bars conduct current and gaps do not support load. (Abstract shortened by UMI.)

  19. Risk Assessment for Tooth Wear.

    PubMed

    Kontaxopoulou, Isavella; Alam, Sonia

    2015-08-01

    Tooth wear has an increasing prevalence in the UK population. The aetiology is commonly multifactorial, and the aetiopathology is through a combination of erosion, attrition, abrasion and abfraction. Erosion is associated with intrinsic or extrinsic acids, and therefore subjects with reflux disease and eating disorders are at increased risk. Fruit juice, fruits and carbonated drink consumption, frequency of consumption and specific habits are also risk factors. Attrition is more prevalent in bruxists. Other habits need to be considered when defining the risk of tooth wear. Abrasion is usually associated with toothbrushing and toothpastes, especially in an already acidic environment. Patients with extensive lesions that affect dentin may be at higher risk, as well as those presenting with unstained lesions. Monitoring of the progress of tooth wear is recommended to identify those with active tooth wear. Indices for tooth wear are a helpful aid. PMID:26556515

  20. Risk Assessment for Tooth Wear.

    PubMed

    Kontaxopoulou, Isavella; Alam, Sonia

    2015-08-01

    Tooth wear has an increasing prevalence in the UK population. The aetiology is commonly multifactorial, and the aetiopathology is through a combination of erosion, attrition, abrasion and abfraction. Erosion is associated with intrinsic or extrinsic acids, and therefore subjects with reflux disease and eating disorders are at increased risk. Fruit juice, fruits and carbonated drink consumption, frequency of consumption and specific habits are also risk factors. Attrition is more prevalent in bruxists. Other habits need to be considered when defining the risk of tooth wear. Abrasion is usually associated with toothbrushing and toothpastes, especially in an already acidic environment. Patients with extensive lesions that affect dentin may be at higher risk, as well as those presenting with unstained lesions. Monitoring of the progress of tooth wear is recommended to identify those with active tooth wear. Indices for tooth wear are a helpful aid.

  1. Advanced Prediction of Tool Wear by Taking the Load History into Consideration

    NASA Astrophysics Data System (ADS)

    Ersoy, K.; Nuernberg, G.; Herrmann, G.; Hoffmann, H.

    2007-04-01

    A disadvantage of the conventional methods of simulating the wear occurring in deep drawing processes is that the wear coefficient, and thus wear too, is considered to be constant along loading duration, which, in case of deep drawing, corresponds to sliding distance and number of punch strokes. However, in reality, it is a known fact that wear development is not constant over time. In former studies, the authors presented a method, which makes it possible to consider the number of punch strokes in the simulation of wear. Another enhancement of this method is introduced in this paper. It is proposed to consider wear as a function of wear work instead of the number of punch strokes. Using this approach, the wear coefficients are implemented as a function of wear work and fully take into account the load history of the respective node. This enhancement makes it possible to apply the variable wear coefficients to completely different geometries, where one punch stroke involves different sliding distance or pressure values than the experiments with which the wear coefficients were determined. In this study, deep drawing experiments with a cylindrical cup geometry were carried out, in which the characteristic wear coefficient values as well as their gradients along the life cycle were determined. In this case, the die was produced via rapid tooling techniques. The prediction of tool wear is carried out with REDSY, a wear simulation software which was developed at the Institute of Metal Forming and Casting, TU-Muenchen. The wear predictions made by this software are based on the results of a conventional deep drawing simulation. For the wear modelling a modified Archard model was used.

  2. Steady-state wear and friction in boundary lubrication studies

    NASA Technical Reports Server (NTRS)

    Loomis, W. R.; Jones, W. R., Jr.

    1980-01-01

    A friction and wear study was made at 20 C to obtain improved reproducibility and reliability in boundary lubrication testing. Ester-base and C-ether-base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a friction and wear apparatus. Conditions included loads of 1/2 and 1 kg and sliding velocities of 3.6 to 18.2 m/min in a dry air atmosphere and stepwise time intervals from 1 to 250 min for wear measurements. The wear rate results were compared with those from previous studies where a single 25 min test period was used. Satisfactory test conditions for studying friction and wear in boundary lubrication for this apparatus were found to be 1 kg load; sliding velocities of 7.1 to 9.1 m/min (50 rpm disk speed); and use of a time stepwise test procedure. Highly reproducible steady-state wear rates and steady-state friction coefficients were determined under boundary conditions. Wear rates and coefficients of friction were constant following initially high values during run-in periods.

  3. Switch wear leveling

    SciTech Connect

    Wu, Hunter; Sealy, Kylee; Gilchrist, Aaron

    2015-09-01

    An apparatus for switch wear leveling includes a switching module that controls switching for two or more pairs of switches in a switching power converter. The switching module controls switches based on a duty cycle control technique and closes and opens each switch in a switching sequence. The pairs of switches connect to a positive and negative terminal of a DC voltage source. For a first switching sequence a first switch of a pair of switches has a higher switching power loss than a second switch of the pair of switches. The apparatus includes a switch rotation module that changes the switching sequence of the two or more pairs of switches from the first switching sequence to a second switching sequence. The second switch of a pair of switches has a higher switching power loss than the first switch of the pair of switches during the second switching sequence.

  4. Decrease in the visibility of the interference fringes in a cold-atom accelerometer

    SciTech Connect

    Stickney, James A.; Zozulya, Alex A.

    2004-06-01

    We analyze operation of a cold-atom accelerometer, an interferometric device which measures linear accelerations. We develop an analytic model that predicts a decrease in the visibility of the interference fringes and also their shift caused by the acceleration of the device. This effect places an upper limit on the maximum value of acceleration that can be measured for given parameters of the confining potential and the measurement cycle time.

  5. Fabrication and assembly of MEMS accelerometer-based heart monitoring device with simplified, one step placement.

    PubMed

    Tjulkins, Fjodors; Nguyen, Anh-Tuan Thai; Andreassen, Erik; Aasmundtveit, Knut; Hoivik, Nils; Hoff, Lars; Halvorsen, Per Steinar; Grymyr, Ole-Johannes; Imenes, Kristin

    2015-01-01

    An accelerometer-based heart monitoring system has been developed for real-time evaluation of heart wall movement. In this paper, assembly and fabrication of an improved device is presented along with system characterization and test data from an animal experiment. The new device is smaller and has simplified the implantation procedure compared to earlier prototypes. Leakage current recordings were well below those set by the corresponding standards. PMID:25429874

  6. The vertical accelerometer, a new instrument for air navigation

    NASA Technical Reports Server (NTRS)

    Laboccetta, Letterio

    1923-01-01

    This report endeavors to show the possibility of determining the rate of acceleration and the advantage of having such an accelerometer in addition to other aviation instruments. Most of the discussions concern balloons.

  7. SEMICONDUCTOR DEVICES: Characteristics of a novel biaxial capacitive MEMS accelerometer

    NASA Astrophysics Data System (ADS)

    Linxi, Dong; Yongjie, Li; Haixia, Yan; Lingling, Sun

    2010-05-01

    A novel MEMS accelerometer with grid strip capacitors is developed. The mechanical and electrical noise can be reduced greatly for the novel structure design. ANSOFT-Maxwell software was used to analyze the fringing electric field of the grid strip structure and its effects on the designed accelerometer. The effects of the width, thickness and overlapping width of the grid strip on the sensing capacitance are analyzed by using the ANSOFT-Maxwell software. The results show that the parameters have little effect on the characteristics of the presented accelerometer. The designed accelerometer was fabricated based on deep RIE and silicon-glass bonding processes. The preliminary tested sensitivities are 0.53 pF/g and 0.49 pF/g in the x and y axis directions, respectively. A resonator with grid strip structure was also fabricated whose tested quality factor is 514 in air, which proves that the grid strip structure can reduce mechanical noise.

  8. Development of an accelerometer-based underwater acoustic intensity sensor.

    PubMed

    Kim, Kang; Gabrielson, Thomas B; Lauchle, Gerald C

    2004-12-01

    An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.

  9. Child activity recognition based on cooperative fusion model of a triaxial accelerometer and a barometric pressure sensor.

    PubMed

    Nam, Yunyoung; Park, Jung Wook

    2013-03-01

    This paper presents a child activity recognition approach using a single 3-axis accelerometer and a barometric pressure sensor worn on a waist of the body to prevent child accidents such as unintentional injuries at home. Labeled accelerometer data are collected from children of both sexes up to the age of 16 to 29 months. To recognize daily activities, mean, standard deviation, and slope of time-domain features are calculated over sliding windows. In addition, the FFT analysis is adopted to extract frequency-domain features of the aggregated data, and then energy and correlation of acceleration data are calculated. Child activities are classified into 11 daily activities which are wiggling, rolling, standing still, standing up, sitting down, walking, toddling, crawling, climbing up, climbing down, and stopping. The overall accuracy of activity recognition was 98.43% using only a single- wearable triaxial accelerometer sensor and a barometric pressure sensor with a support vector machine.

  10. A three-axis micromachined accelerometer with a CMOS position-sense interface and digital offset-trim electronics

    SciTech Connect

    Lemkin, M.; Boser, B.E.

    1999-04-01

    This paper describes a three-axis accelerometer implemented in a surface-micromachining technology with integrated CMOS. The accelerometer measures changes in a capacitive half-bridge to detect deflections of a proof mass, which result from acceleration input. The half-bridge is connected to a fully differential position-sense interface, the output of which is used for one-bit force feedback. By enclosing the proof mass in a one-bit feedback loop, simultaneous force balancing and analog-to-digital conversion are achieved. On-chip digital offset-trim electronics enable compensation of random offset in the electronic interface. Analytical performance calculations are shown to accurately model device behavior. The fabricated single-chip accelerometer measures 4 {times} 4 mm{sup 2}, draws 27 mA from a 5-V supply, and has a dynamic range of 84, 81, and 70 dB along the x-, y-, and z-axes, respectively.

  11. Input-output stability for accelerometer control systems

    NASA Technical Reports Server (NTRS)

    Banks, H. T.; Morris, K. A.

    1991-01-01

    It is shown that, although accelerometer control systems are not well-posed in the sense of Salamon, a well-defined input-output relation exists. It is established that the output of an accelerometer control system can be described by the convolution of the input and a distribution. This distribution is Laplace transformable, and the Laplace transform of the distribution is the transfer function of the system.

  12. Design, Simulation and Fabrication of Triaxial MEMS High Shock Accelerometer.

    PubMed

    Zhang, Zhenhai; Shi, Zhiguo; Yang, Zhan; Xie, Zhihong; Zhang, Donghong; Cai, De; Li, Kejie; Shen, Yajing

    2015-04-01

    On the basis of analyzing the disadvantage of other structural accelerometer, three-axis high g MEMS piezoresistive accelerometer was put forward in order to apply to the high-shock test field. The accelerometer's structure and working principle were discussed in details. The simulation results show that three-axis high shock MEMS accelerometer can bear high shock. After bearing high shock impact in high-shock shooting test, three-axis high shock MEMS accelerometer can obtain the intact metrical information of the penetration process and still guarantee the accurate precision of measurement in high shock load range, so we can not only analyze the law of stress wave spreading and the penetration rule of the penetration process of the body of the missile, but also furnish the testing technology of the burst point controlling. The accelerometer has far-ranging application in recording the typical data that projectile penetrating hard target and furnish both technology guarantees for penetration rule and defend engineering.

  13. High-G accelerometer for earth-penetrator weapons applications. LDRD final report

    SciTech Connect

    Davies, B.R.; Montague, S.; Bateman, V.I.; Brown, F.A.; Chanchani, R.; Christenson, T.; Murray, J.R.; Rey, D.; Ryerson, D.

    1998-03-01

    Micromachining technologies, or Micro-Electro-Mechanical Systems (MEMS), enable the develop of low-cost devices capable of sensing motion in a reliable and accurate manner. Sandia has developed a MEMS fabrication process for integrating both the micromechanical structures and microelectronics circuitry of surface micromachined sensors, such as silicon accelerometers, on the same chip. Integration of the micromechanical sensor elements with microelectronics provides substantial performance and reliability advantages for MEMS accelerometers. A design team at Sandia was assembled to develop a micromachined silicon accelerometer capable of surviving and measuring very high accelerations (up to 50,000 times the acceleration due to gravity). The Sandia integrated surface micromachining process was selected for fabrication of the sensor due to the extreme measurement sensitivity potential associated with integrated microelectronics. Very fine measurement sensitivity was required due to the very small accelerometer proof mass (< 200 {times} 10{sup {minus}9} gram) obtainable with this surface micromachining process. The small proof mass corresponded to small sensor deflections which required very sensitive electronics to enable accurate acceleration measurement over a range of 1,000 to 50,000 times the acceleration due to gravity. Several prototype sensors, based on a suspended plate mass configuration, were developed and the details of the design, modeling, fabrication and validation of the device will be presented in this paper. The device was analyzed using both conventional lumped parameter modeling techniques and finite element analysis tools. The device was tested and performed well over its design range (the device was tested over a range of a few thousand G to 46,000 G, where 1 G equals the acceleration due to gravity).

  14. Performance of several low-cost accelerometers

    USGS Publications Warehouse

    Evans, J.R.; Allen, R.M.; Chung, A. I.; Cochran, E.S.; Guy, R.; Hellweg, M.; Lawrence, J. F.

    2014-01-01

    Several groups are implementing low‐cost host‐operated systems of strong‐motion accelerographs to support the somewhat divergent needs of seismologists and earthquake engineers. The Advanced National Seismic System Technical Implementation Committee (ANSS TIC, 2002), managed by the U.S. Geological Survey (USGS) in cooperation with other network operators, is exploring the efficacy of such systems if used in ANSS networks. To this end, ANSS convened a working group to explore available Class C strong‐motion accelerometers (defined later), and to consider operational and quality control issues, and the means of annotating, storing, and using such data in ANSS networks. The working group members are largely coincident with our author list, and this report informs instrument‐performance matters in the working group’s report to ANSS. Present examples of operational networks of such devices are the Community Seismic Network (CSN; csn.caltech.edu), operated by the California Institute of Technology, and Quake‐Catcher Network (QCN; Cochran et al., 2009; qcn.stanford.edu; November 2013), jointly operated by Stanford University and the USGS. Several similar efforts are in development at other institutions. The overarching goals of such efforts are to add spatial density to existing Class‐A and Class‐B (see next paragraph) networks at low cost, and to include many additional people so they become invested in the issues of earthquakes, their measurement, and the damage they cause.

  15. Pendulous assembly for use in an accelerometer

    SciTech Connect

    Hanson, R.A.

    1991-08-27

    This patent describes a pendulous assembly for use in an accelerometer or other such device which senses forces acting on the device in a particular direction. It comprises a proofmass; and means supporting one end of the proofmass for pivotal movement about a given axis back and forth through a resting plane which contains the proofmass when the proofmass is at rest in the absence of any of the forces, the supporting means including: a frame and means for mounting the frame to a main support forming part of the force sensing device, an isolation bridge; isolation bridge flexure means connecting the isolation bridge with a section of the frame for pivotal movement of the isolation bridge back and forth about the given axis; and proofmass flexure means separate from and substantially unconnected with the isolation bridge flexure means, the proofmass flexure means comprising a pair of proofmass flexures connecting the proofmass with the isolation bridge for pivotal movement of the proofmass back and forth about the given axis; the isolation bridge flexure means and the proofmass flexure means being aligned along the given axis with the isolation bridge flexure means positioned between the proofmass flexures.

  16. Quantitative evaluation of gait ataxia by accelerometers.

    PubMed

    Shirai, Shinichi; Yabe, Ichiro; Matsushima, Masaaki; Ito, Yoichi M; Yoneyama, Mitsuru; Sasaki, Hidenao

    2015-11-15

    An appropriate biomarker for spinocerebellar degeneration (SCD) has not been identified. Here, we performed gait analysis on patients with pure cerebellar type SCD and assessed whether the obtained data could be used as a neurophysiological biomarker for cerebellar ataxia. We analyzed 25 SCD patients, 25 patients with Parkinson's disease as a disease control, and 25 healthy control individuals. Acceleration signals during 6 min of walking and 1 min of standing were measured by two sets of triaxial accelerometers that were secured with a fixation vest to the middle of the lower and upper back of each subject. We extracted two gait parameters, the average and the coefficient of variation of motion trajectory amplitude, from each acceleration component. Then, each component was analyzed by correlation with the Scale for the Assessment and Rating of Ataxia (SARA) and the Berg Balance Scale (BBS). Compared with the gait control of healthy subjects and concerning correlation with severity and disease specificity, our results suggest that the average amplitude of medial-lateral (upper back) of straight gait is a physiological biomarker for cerebellar ataxia. Our results suggest that gait analysis is a quantitative and concise evaluation scale for the severity of cerebellar ataxia.

  17. Friction and wear of nickel in sulfuric acid

    NASA Technical Reports Server (NTRS)

    Rengstorff, G. W. P.; Miyoshi, K.; Buckley, D. H.

    1984-01-01

    Experiments were conducted with elemental nickel sliding on aluminum oxide in aerated sulfuric acid in concentrations ranging from very dilute (10 -4 N, i.e., 5 ppm) to very concentrated (96 percent) acid. Load and reciprocating sliding speeds were kept constant. With the most dilute concentration (10 -4 N) no observable corrosion occurred in or outside the wear area. This was used as the base condition to determine the high contribution of corrosion to total wear loss at acid concentrations between 0.5 percent (0.1 N) and 75 percent. Corrosion reached a maximum rate of 100 millimeters per year at 30 percent acid. At the same time, general corrosion outside the wear area was very low, in agreement with published information. It is clear that friction and wear greatly accelerated corrosion in the wear area. At dilute concentrations of 0.001 and 0.01 N, corrosion in the wear area was low, and general corrosion outside was also low, but local outside regions in the direction of the wear motion experienced some enhanced corrosion, apparently due to fluid motion of the acid.

  18. Test-Retest Reliability and Concurrent Validity of a Single Tri-Axial Accelerometer-Based Gait Analysis in Older Adults with Normal Cognition

    PubMed Central

    Byun, Seonjeong; Han, Ji Won; Kim, Tae Hui; Kim, Ki Woong

    2016-01-01

    Objective We investigated the concurrent validity and test-retest reliability of spatio-temporal gait parameters measured with a single tri-axial accelerometer (TAA), determined the optimal number of steps required for obtaining acceptable levels of reliability, and compared the validity and reliability of the estimated gait parameters across the three reference axes of the TAA. Methods A total of 82 cognitively normal elderly participants walked around a 40-m long round walkway twice wearing a TAA at their center of body mass. Gait parameters such as cadence, gait velocity, step time, step length, step time variability, and step time asymmetry were estimated from the low pass-filtered signal of the TAA. The test-retest reliability and concurrent validity with the GAITRite® system were evaluated for the estimated gait parameters. Results Gait parameters using signals from the vertical axis showed excellent reliability for all gait parameters; the intraclass correlation coefficient (ICC) was 0.79–0.90. A minimum of 26 steps and 14 steps were needed to achieve excellent reliability in step time variability and step time asymmetry, respectively. A strong level of agreement was seen for the basic gait parameters between the TAA and GAITRiteⓇ (ICC = 0.91–0.96). Conclusions The measurement of gait parameters of elderly individuals with normal cognition using a TAA placed on the body’s center of mass was reliable and showed superiority over the GAITRiteⓇ with regard to gait variability and asymmetry. The TAA system was a valid tool for measuring basic gait parameters. Considering its wearability and low price, the TAA system may be a promising alternative to the pressure sensor walkway system for measuring gait parameters. PMID:27427965

  19. Temporal feature estimation during walking using miniature accelerometers: an analysis of gait improvement after hip arthroplasty.

    PubMed

    Aminian, K; Rezakhanlou, K; De Andres, E; Fritsch, C; Leyvraz, P F; Robert, P

    1999-11-01

    A new method for the detection of gait cycle phases using only two miniature accelerometers together with a light, portable digital recorder is proposed. Each subject is asked to walk on a walkway at his/her own preferred speed. Gait analysis was performed using an original method of computing the values of temporal parameters from accelerometer signals. First, to validate the accelerometric method, measurements are taken on a group of healthy subjects. No significant differences are observed between the results thus obtained and those from pressure sensors attached under the foot. Then, measurements using only accelerometers are performed on a group of 12 patients with unilateral hip osteo-arthritis. The gait analysis is carried out just before hip arthroplasty and again, three, six and nine months afterwards. A mean decrease of 88% of asymmetry of stance time and especially a mean decrease of 250% of asymmetry of double support time are observed, nine months after the operation. These results confirm the validity of the proposed method for healthy subjects and its efficiency for functional evaluation of gait improvement after arthroplasty.

  20. A modified Hopkinson pressure bar experiment to evaluate a damped piezoresistive MEMS accelerometer.

    SciTech Connect

    Frew, Danny Joe; Duong, Henry

    2009-03-01

    We conducted a series of modified Hopkinson pressure bar (HPB) experiments to evaluate a new, damped, high-shock accelerometer that has recently been developed by PCB Piezotronics Inc. Pulse shapers were used to create a long duration, non-dispersive stress pulse in an aluminum bar that interacted with a tungsten disk at the end of the incident bar. We measured stress at the aluminum bar-disk interface with a quartz gage and measured acceleration at the free-end of the disk with an Endevco brand 7270A and the new PCB 3991 accelerometers. The rise-time of the incident stress pulse in the aluminum bar was long enough and the disk length short enough so that the response of the disk can be approximated closely as rigid-body motion; an experimentally verified analytical model has been shown previously to support this assumption. Since the cross-sectional area and mass of the disk were known, we calculated acceleration of the rigid-disk from the quartz-gage force measurement and Newton's Second Law of Motion. Comparisons of accelerations calculated from the quartz-gage data and measured acceleration data show excellent agreement for acceleration pulses with the PCB accelerometer for peak amplitudes between 4,000 and 40,000 Gs , rise times as short as 40 microsec, and pulse durations between 150 and 320 microsec.

  1. Application of MAVEN Accelerometer and Attitude Control Data to Mars Atmospheric Characterization

    NASA Astrophysics Data System (ADS)

    Zurek, Richard W.; Tolson, Robert H.; Baird, Darren; Johnson, Mark Z.; Bougher, Stephen W.

    2015-12-01

    The structure of the upper atmosphere of Mars (above ˜100 km) has been probed in situ mainly using spacecraft accelerometers during the aerobraking phases of 3 Mars orbiters. In a similar manner, the Mars Atmosphere and Volatile Evolution (MAVEN) Accelerometer Experiment (ACC) will also use atmospheric drag accelerations sensed by inertial measurement units (IMU) onboard the spacecraft to recover atmospheric density along the orbiter path. These densities are used to estimate hydrostatic `vertical' density and temperature profiles, along track and altitudinal density waves, and latitudinal and longitudinal density variations. The IMU accelerometer signal-to-noise should permit profile reconstructions from spacecraft periapsis, nominally at 150 km altitude, to ˜170 km, an altitude range nominally spanning densities of 0.05-0.15 kg/km3. However, in situ measurements over a much greater altitude range, down to ˜125 km (reaching densities of ˜2-3.5 kg/km3), can be made during each of five week-long "Deep Dip" (DD) campaigns, and these are the prime focus of the Accelerometer Experiment. Judicious choice of the timing of these Deep-Dip campaigns during the MAVEN periapsis progression through local time, latitude and longitude in both hemispheres and in different seasons will add significantly to the existing data base of lower thermospheric densities. Other IMU and attitude control data may be used to estimate torques in order to improve the atmospheric density analysis, especially in the higher altitudes of the nominal science orbit, and, more challengingly, to estimate cross-track winds during the Deep-Dips.

  2. Italian spring accelerometer (ISA) a high sensitive accelerometer for ``BepiColombo'' ESA CORNERSTONE

    NASA Astrophysics Data System (ADS)

    Iafolla, V.; Nozzoli, S.

    2001-12-01

    The targets of the ESA CORNERSTONE mission to Mercury "BepiColombo" are concerned with both planetary and magnetospheric physics and to test some aspects of the general relativity. A payload devoted to a set of experiments named radio science is located within one of the three proposed modules, the Mercury Planetary Orbiter (MPO). In particular, a high sensitivity accelerometer ( a min<10 -9√g/ Hz in the range 10 -4- 10 -1 Hz) will measure the inertial acceleration acting on the MPO. Such data, together with tracking data are used to evaluate the purely gravitational trajectory of the MPO, transforming it to a virtual drag-free satellite system. The ISA accelerometer, considered for this mission, is a well-studied instrument developed at the Istituto di Fisica dello Spazio Interplanetario (IFSI), with the financial support of the Agenzia Spaziale Italiana (ASI). A prototype of such an instrument was constructed, matching the requirements of the radio science experiment. Results of the study concerning the use of ISA in the BepiColombo mission are reported here, particular care being devoted to the description of the instrument and to its sensitivity and thermal stabilisation.

  3. BepiColombo ISA accelerometer: ready for launch

    NASA Astrophysics Data System (ADS)

    Francesco, Santoli; Valerio, Iafolla; Emiliano, Fiorenza; Carlo, Lefevre; Lucchesi David, M.; Marco, Lucente; Carmelo, Magnafico; Sergio, Nozzoli; Roberto, Peron

    2016-04-01

    To be launched in 2017, ESA mission BepiColombo will perform a thorough study of the planet Mercury and its environment. Among the wide range of its scientific objectives, an important set is constituted by the so-called Radio Science Experiments (RSE), which will study the gravitational field and rotation of the planet, and will perform very precise tests of general relativity theory. The fulfilment of these scientific objectives will be made possible by a precise orbit determination of the Mercury Planetary Orbiter (MPO), at the same time estimating a number of relevant parameters. In order to reach the required level of accuracy in recovering these parameters, the data coming from the high-sensitivity ISA (Italian Spring Accelerometer) instrument onboard the MPO probe will be used: the first time for a deep-space probe. After a long path of design and development, the instrument is now ready for integration into MPO. Following a brief description of the RSE in the context of the mission, the instrument and its capabilities will be reviewed. Emphasis will be given to the foreseen strategies for its operation in the various phases of the mission, along with the manifold calibration possibilities.

  4. Modelling of the MEA float zone using accelerometer data

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.

    1993-01-01

    During a floating zone experiment involving the growth of indium on a recent orbiter mission, (STS 32) oscillation of the zone shapes were observed to occur in response to the background acceleration. An understanding of the nature of the response of the zone shape to forced (g-jitter) oscillations and predictions of its impact on future experiments is of great interest not only to the PI's but to other commercial and academic investigators who plan to fly similar experiments in the orbiter and on space station. Motivated by this, a 15 month study was undertaken to analyze the nature of the g-sensitivity of the STS 32 floating zone crystal growth experiment. Numerical models were used to describe the time-dependent free surface motion of the zone as it responds to the spacecraft residual acceleration. Relevant experimental data concerning the acceleration environment was obtained from the Honeywell in Space Accelerometer (HISA) investigators through MSFC's ACAP program and processed and analyzed. For the indium floating zone experiment, a series of calculations were made using time-dependent axial accelerations g(t). The form of g(t) included simple sinusoidal disturbances as well as actual data (subject to appropriate filtering) measured on the STS 32 mission. Focus was on the calculation of the response of the free surface of the zone as well as the internal flows and internal heat transfer. The influence of solidification on the response of the zone shape was also examined but found to be negligible.

  5. Relative performance of several inexpensive accelerometers

    USGS Publications Warehouse

    Evans, John R.; Rogers, John A.

    1995-01-01

    We examined the performance of several low-cost accelerometers for highly cost-driven applications in recording earthquake strong motion. We anticipate applications for such sensors in providing the lifeline and emergency-response communities with an immediate, comprehensive picture of the extent and characteristics of likely damage. We also foresee their use as 'filler' instruments sited between research-grade instruments to provide spatially detailed and near-field records of large earthquakes (on the order of 1000 stations at 600-m intervals in San Fernando Valley, population 1.2 million, for example). The latter applications would provide greatly improved attenuation relationships for building codes and design, the first examples of mainshock information (that is, potentially nonlinear regime) for microzonation, and a suite of records for structural engineers. We also foresee possible applications in monitoring structural inter-story drift during earthquakes, possibly leading to local and remote alarm functions as well as design criteria. This effort appears to be the first of its type at the USGS. It is spurred by rapid advances in sensor technology and the recognition of potential non-classical applications. In this report, we estimate sensor noise spectra, relative transfer functions and cross-axis sensitivity of six inexpensive sensors. We tested three micromachined ('silicon-chip') sensors in addition to classical force-balance and piezoelectric examples. This sample of devices is meant to be representative, not comprehensive. Sensor noise spectra were estimated by recording system output with the sensor mounted on a pneumatically supported 545-kg optical-bench isolation table. This isolation table appears to limit ground motion to below our system noise level. These noise estimates include noise introduced by signal-conditioning circuitry, the analog-to-digital converter (ADC), and noise induced in connecting wiring by ambient electromagnetic fields in

  6. Update on slip and wear in multi-layer azimuth track systems

    NASA Astrophysics Data System (ADS)

    Juneja, Gunjeet; Kan, Frank W.; Antebi, Joseph

    2006-06-01

    Many antennas, such as the 100-m Green Bank Telescope, use a wheel-on-track systems in which the track segments consist of wear plates mounted on base plates. The wear plates are typically 2 to 3 inches thick and are case hardened or through hardened. The base plates are usually 3 to 4 times thicker than the wear plates and are not hardened. The wear plates are typically connected to the base plates using bolts. The base plates are supported on grout and anchored to the underlying concrete foundation. For some antennas, slip has been observed between the wear plate and base plate, and between the base plate and the grout, with the migration in the wheel rolling direction. In addition, there has been wear at the wear plate/base plate interface. This paper is an update on the evaluation of GBT track retrofit. The paper describes the use of three-dimensional non-linear finite element analyses to understand and evaluate the behavior of (1) the existing GBT wheel-on-track system with mitered joints, and (2) the various proposed modifications. The modifications include welding of the base plate joints, staggering of the wear plate joints from the base plate joints, changing thickness of the wear plate, and increasing bolt diameter and length. Parameters included in the evaluation were contact pressure, relative slip, wear at the wear plate/base plate interface, and bolt shears and moments.

  7. Assessment of the MyWellness Key accelerometer in people with type 2 diabetes.

    PubMed

    McGinley, Samantha Kate; Armstrong, Marni J; Khandwala, Farah; Zanuso, Silvano; Sigal, Ronald J

    2015-11-01

    Accelerometers are designed to measure physical activity (PA) objectively. The MyWellness Key (MWK) accelerometer has been validated primarily in younger, normal-weight populations. The aims of this study were to examine the accuracy of the MWK against directly measured lab-based exercise and free-living PA in people with type 2 diabetes, many of whom are older and overweight or obese. Thirty-five participants with type 2 diabetes completed the protocol, which included a laboratory-based session and a free-living phase. In the laboratory visit, participants completed a structured treadmill protocol wearing MWKs on each hip (all subjects) and bra cup (women only). The speed where each MWK switched from recording light- to moderate-intensity activity was determined for each MWK worn. In the free-living phase, participants wore the MWK for all waking hours for 2 weeks, and recorded exercise in PA diaries immediately after each exercise session. The mean cut-points between low ("Free") and moderate ("Play") intensity for the right and left waist-worn MWKs were 4.1 ± 0.5 km/h and 5.0 ± 0.9 km/h for the bra-mounted MWK; ideal cut-point would be 4.0 km/h. In the free-living phase, the Spearman correlation between PA according to PA diary and the waist-worn MWK was 0.81 (95% confidence interval (CI): 0.76, 0.85; P < 0.001), but only 0.66 (95% CI: 0.53, 0.77; P < 0.001) when on the bra. In conclusion, the waist-worn MWK measured PA volume accurately, and was acceptably accurate at discriminating between low- and moderate-intensity PA in people with type 2 diabetes. The MWK underestimated PA volume and intensity when worn on a bra.

  8. Calorimetric validation of the Caltrac accelerometer during level walking.

    PubMed

    Balogun, J A; Martin, D A; Clendenin, M A

    1989-06-01

    The primary purpose of this study was to compare the Caltrac accelerometer output with measured energy expenditure (Ee). Twenty-five volunteers (10 men, 15 women) walked on a level motor-driven treadmill at four different speeds (54, 81, 104, and 130 m.min-1) with the Caltrac device affixed to the waistline. Each of the four experimental trials lasted eight minutes, and the testing was completed within an hour. During the test, oxygen consumption (VO2) (in L.min-1 and in mL.kg-1.min-1) and nonprotein respiratory exchange ratio were monitored by the Beckman Horizon metabolic cart. The accelerometer output at the end of each exercise bout was also monitored and subsequently divided by 8 to convert the readings to counts.min-1. The mean VO2 (L.min-1) at steady state (ie, 6th-8th minutes of exercise) was converted to a caloric value. We obtained a moderate correlation coefficient (r) of .76 between the accelerometer output and the VO2 (mL.kg-1.min-1) and a high correlation coefficient of .92 between the Ee and the accelerometer readings. The Caltrac accelerometer output (counts.min-1) was significantly higher (p less than .01) than the Ee (kcal.min-1) at the four walking speeds. The difference between the accelerometer output and the Ee ranged from 13.3% to 52.9%. The data were further analyzed with linear, polynomial, multiple, and stepwise regression models. The results of the analyses revealed that the Caltrac accelerometer output is a valid predictor of Ee during level walking when the appropriate regression equation is used to adjust the values.(ABSTRACT TRUNCATED AT 250 WORDS)

  9. Polyethylene Wear in Knee Arthroplasty.

    PubMed

    Chakravarty, Rajit; Elmallah, Randa D K; Cherian, Jeffrey Jai; Kurtz, Steven M; Mont, Michael A

    2015-10-01

    Polyethylene (PE) wear and osteolysis are common causes for late revisions of knee arthroplasties. Several implant and surgical factors have been implicated in contributing to the development of wear, such as type of bearing surface used, inaccurate articular geometry, and poor knee kinematics. In addition, patient-related factors, such as younger age and higher activity levels, may also contribute to wear. Our purpose was to evaluate and compare the effect of these variables on wear rates following knee arthroplasty. Recently, technological advancements have been aimed at reducing the incidence of wear by improving the PE manufacturing process, creating implants that minimize contact stresses, and refining our surgical techniques. Furthermore, the development of newer highly cross-linked PEs (HXLPEs) and the introduction of additives, such as vitamin E, to the PEs may improve overall implant survivorship. As a result, with the advent of newer implant and PE designs, wear is no longer the most common cause of early failure, though it remains an important factor in limiting long-term implant survivorship. However, there are a few clinical studies evaluating the long-term outcomes of newer HXLPEs and implant designs, with further evaluations necessary to determine the best implant-PE combination for improved knee arthroplasty survivorship. PMID:26030263

  10. Surgery to improve contact lens wear in keratoconus.

    PubMed

    Moodaley, L; Buckley, R J; Woodward, E G

    1991-04-01

    Contact lens intolerance in keratoconus may be due to the formation of a proud nebula at or near the apex of the cone that gives rise to contact lens related abrasions. These nebulae do not flatten when contact lens wear is discontinued. We describe a simple technique of superficial keratectomy to remove proud nebulae in which the resulting defect healed quickly under a therapeutic hydrogel lens. In all of the six cases described patients were able to resume contact lens wear within one month of the procedure. One case was lost to follow-up. Of the remaining five (follow-up 3-9 months), all achieved comfortable wearing times of 8 hours or more and visual acuities of 20/40 or better. One patient developed a recurrent epithelial defect that resolved on discontinuing lens wear for one week. Corneal transplantation was thus avoided. PMID:2049822

  11. Quality of GOCE accelerometer data and analysis with ionospheric dynamics during geomagnetically active days

    NASA Astrophysics Data System (ADS)

    Sinem Ince, Elmas; Fomichev, Victor; Floberghagen, Rune; Schlicht, Anja; Martynenko, Oleg; Pagiatakis, Spiros

    2016-07-01

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was launched in March, 2009 and completed its mission with great success in November, 2011. GOCE data processing is challenging and not all the disturbances are removed from the gravitational field observations. The disturbances observed in GOCE Vyy gradients around magnetic poles are investigated by using external datasets. It is found that the amplitude of these disturbances increase during geomagnetically active days and can reach up to 5 times the expected noise level of the gradiometer. ACE (Advanced Composition Explorer) and Wind satellites measured electric field and interplanetary magnetic field components have shown that the disturbances observed in the polar regions agree with the increased solar activity. Moreover, equivalent ionospheric currents computed along ascending satellite tracks over North America and Greenland have shown a noticeable correlation with the cross-track and vertical currents and the pointing flux (ExB) components in the satellite cross track direction. Lastly, Canadian Ionosphere and Atmosphere Model (C-IAM) electric field and neutral wind simulations have shown a strong correlation of the enhancement in the ionospheric dynamics during geomagnetically active days and disturbances measured by the GOCE accelerometers over high latitudes. This may be a result of imperfect instrumentation and in-flight calibration of the GOCE accelerometers for an increased geomagnetic activity or a real disturbance on the accelerometers. We use above listed external datasets to understand the causes of the disturbances observed in gravity gradients and reduce/ eliminate them by using response analyses in frequency domain. Based on our test transfer functions, improvement is possible in the quality of the gradients. Moreover, this research also confirms that the accelerometer measurements can be useful to understand the ionospheric dynamics and space weather forecasting.

  12. Should We Believe Atmospheric Temperatures Measured by Entry Accelerometers Traveling at "Slow" Near-Sonic Speeds?

    NASA Technical Reports Server (NTRS)

    Withers, Paul

    2005-01-01

    Mars Pathfinder's Accelerometer instrument measured an unexpected and large temperature inversion between 10 and 20 kilometer altitude. Other instruments have failed to detect similar temperature inversions. I test whether this inversion is real or not by examining what changes have to be made to the assumptions in the accelerometer data processing to obtain a more "expected" temperature profile. Changes in derived temperature of up to 30K, or 15%, are necessary, which correspond to changes in derived density of up to 25% and changes in derived pressure of up to 10%. If the drag coefficient is changed to satisfy this, then instead of decreasing from 1.6 to 1.4 from 20 kilometers to 10 kilometers, the drag coefficient must increase from 1.6 to 1.8 instead. If winds are invoked, then speeds of 60 meters per second are necessary, four times greater than those predicted. Refinements to the equation of hydrostatic equilibrium modify the temperature profile by an order of magnitude less than the desired amount. Unrealistically large instrument drifts of 0.5-1.0 meters per square second are needed to adjust the temperature profile as desired. However, rotational contributions to the accelerations may have the necessary magnitude and direction to make this correction. Determining whether this hypothesis is true will require further study of the rigid body equations of motion, with detailed knowledge of the positions of all six accelerometers. The paradox concerning this inversion is not yet resolved. It is important to resolve it because the paradox has some startling implications. At one extreme, are temperature profiles derived from accelerometers inherently inaccurate by 20K or more? At the other extreme, are RS temperature profiles inaccurate by this same amount?

  13. Accelerometer and Gyroscope Based Gait Analysis Using Spectral Analysis of Patients with Osteoarthritis of the Knee

    PubMed Central

    Staab, Wieland; Hottowitz, Ralf; Sohns, Christian; Sohns, Jan Martin; Gilbert, Fabian; Menke, Jan; Niklas, Andree; Lotz, Joachim

    2014-01-01

    [Purpose] A wide variety of accelerometer tools are used to estimate human movement, but there are no adequate data relating to gait symmetry parameters in the context of knee osteoarthritis. This study’s purpose was to evaluate a 3D-kinematic system using body-mounted sensors (gyroscopes and accelerometers) on the trunk and limbs. This is the first study to use spectral analysis for data post processing. [Subjects] Twelve patients with unilateral knee osteoarthritis (OA) (10 male) and seven age-matched controls (6 male) were studied. [Methods] Measurements with 3-D accelerometers and gyroscopes were compared to video analysis with marker positions tracked by a six-camera optoelectronic system (VICON 460, Oxford Metrics). Data were recorded using the 3D-kinematic system. [Results] The results of both gait analysis systems were significantly correlated. Five parameters were significantly different between the knee OA and control groups. To overcome time spent in expensive post-processing routines, spectral analysis was performed for fast differentiation between normal gait and pathological gait signals using the 3D-kinematic system. [Conclusions] The 3D-kinematic system is objective, inexpensive, accurate and portable, and allows long-term recordings in clinical, sport as well as ergonomic or functional capacity evaluation (FCE) settings. For fast post-processing, spectral analysis of the recorded data is recommended. PMID:25140082

  14. Automatic compensation for the errors of a gyroscopic linear integrating accelerometer

    SciTech Connect

    Bezvesil`naya, E.N.

    1995-10-01

    The method of least squares and the Kalman filter are the basis for developing algorithms and studying the errors of estimation of the state of a gyroscopic linear integrating accelerometer with digital processing of the data. The article considers the development of algorithms for self-compensation of the errors of a gyroscopic linear integrating accelerometer (GLIA). One of the promising applications of a gyroscopic linear integrating accelerometer is its use as a sensing element for an aviration gravimetric system. At the same time, a GLIA has errors due to nonlinear distortions of the path of the sensing element or gyroscope, the nonzero damping factor of precessional oscillations due to viscous friction moments acting frequency of the precessional oscillations used in the estimation algorithms and the frequency of the precessional oscillations of the gyroscope, and the disturbances that affect the law of motion of the gyroscope. These errors may have an unacceptably large effect (roughly 0.5 g) if not taken into account. The goal here, therefore, is to obtain an algorithm of automatic compensation for the indicated errors. Such a problem has not hitherto been formulated and solved in the theory and practice of gravimetric measurements.

  15. Accelerometer and gyroscope based gait analysis using spectral analysis of patients with osteoarthritis of the knee.

    PubMed

    Staab, Wieland; Hottowitz, Ralf; Sohns, Christian; Sohns, Jan Martin; Gilbert, Fabian; Menke, Jan; Niklas, Andree; Lotz, Joachim

    2014-07-01

    [Purpose] A wide variety of accelerometer tools are used to estimate human movement, but there are no adequate data relating to gait symmetry parameters in the context of knee osteoarthritis. This study's purpose was to evaluate a 3D-kinematic system using body-mounted sensors (gyroscopes and accelerometers) on the trunk and limbs. This is the first study to use spectral analysis for data post processing. [Subjects] Twelve patients with unilateral knee osteoarthritis (OA) (10 male) and seven age-matched controls (6 male) were studied. [Methods] Measurements with 3-D accelerometers and gyroscopes were compared to video analysis with marker positions tracked by a six-camera optoelectronic system (VICON 460, Oxford Metrics). Data were recorded using the 3D-kinematic system. [Results] The results of both gait analysis systems were significantly correlated. Five parameters were significantly different between the knee OA and control groups. To overcome time spent in expensive post-processing routines, spectral analysis was performed for fast differentiation between normal gait and pathological gait signals using the 3D-kinematic system. [Conclusions] The 3D-kinematic system is objective, inexpensive, accurate and portable, and allows long-term recordings in clinical, sport as well as ergonomic or functional capacity evaluation (FCE) settings. For fast post-processing, spectral analysis of the recorded data is recommended.

  16. Application of MEMS Accelerometers and Gyroscopes in Fast Steering Mirror Control Systems.

    PubMed

    Tian, Jing; Yang, Wenshu; Peng, Zhenming; Tang, Tao; Li, Zhijun

    2016-01-01

    In a charge-coupled device (CCD)-based fast steering mirror (FSM) tracking control system, high control bandwidth is the most effective way to enhance the closed-loop performance. However, the control system usually suffers a great deal from mechanical resonances and time delays induced by the low sampling rate of CCDs. To meet the requirements of high precision and load restriction, fiber-optic gyroscopes (FOGs) are usually used in traditional FSM tracking control systems. In recent years, the MEMS accelerometer and gyroscope are becoming smaller and lighter and their performance have improved gradually, so that they can be used in a fast steering mirror (FSM) to realize the stabilization of the line-of-sight (LOS) of the control system. Therefore, a tentative approach to implement a CCD-based FSM tracking control system, which uses MEMS accelerometers and gyroscopes as feedback components and contains an acceleration loop, a velocity loop and a position loop, is proposed. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop and the position loop. Extensive experimental results show that the MEMS accelerometers and gyroscopes can act the similar role as the FOG with lower cost for stabilizing the LOS of the FSM tracking control system. PMID:27023557

  17. Application of MEMS Accelerometers and Gyroscopes in Fast Steering Mirror Control Systems.

    PubMed

    Tian, Jing; Yang, Wenshu; Peng, Zhenming; Tang, Tao; Li, Zhijun

    2016-01-01

    In a charge-coupled device (CCD)-based fast steering mirror (FSM) tracking control system, high control bandwidth is the most effective way to enhance the closed-loop performance. However, the control system usually suffers a great deal from mechanical resonances and time delays induced by the low sampling rate of CCDs. To meet the requirements of high precision and load restriction, fiber-optic gyroscopes (FOGs) are usually used in traditional FSM tracking control systems. In recent years, the MEMS accelerometer and gyroscope are becoming smaller and lighter and their performance have improved gradually, so that they can be used in a fast steering mirror (FSM) to realize the stabilization of the line-of-sight (LOS) of the control system. Therefore, a tentative approach to implement a CCD-based FSM tracking control system, which uses MEMS accelerometers and gyroscopes as feedback components and contains an acceleration loop, a velocity loop and a position loop, is proposed. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop and the position loop. Extensive experimental results show that the MEMS accelerometers and gyroscopes can act the similar role as the FOG with lower cost for stabilizing the LOS of the FSM tracking control system.

  18. Using accelerometers to determine the calling behavior of tagged baleen whales.

    PubMed

    Goldbogen, J A; Stimpert, A K; DeRuiter, S L; Calambokidis, J; Friedlaender, A S; Schorr, G S; Moretti, D J; Tyack, P L; Southall, B L

    2014-07-15

    Low-frequency acoustic signals generated by baleen whales can propagate over vast distances, making the assignment of calls to specific individuals problematic. Here, we report the novel use of acoustic recording tags equipped with high-resolution accelerometers to detect vibrations from the surface of two tagged fin whales that directly match the timing of recorded acoustic signals. A tag deployed on a buoy in the vicinity of calling fin whales and a recording from a tag that had just fallen off a whale were able to detect calls acoustically but did not record corresponding accelerometer signals that were measured on calling individuals. Across the hundreds of calls measured on two tagged fin whales, the accelerometer response was generally anisotropic across all three axes, appeared to depend on tag placement and increased with the level of received sound. These data demonstrate that high-sample rate accelerometry can provide important insights into the acoustic behavior of baleen whales that communicate at low frequencies. This method helps identify vocalizing whales, which in turn enables the quantification of call rates, a fundamental component of models used to estimate baleen whale abundance and distribution from passive acoustic monitoring.

  19. Lumped parameter analytic modeling and behavioral simulation of a 3-DOF MEMS gyro-accelerometer

    NASA Astrophysics Data System (ADS)

    Verma, Payal; Arya, Sandeep K.; Gopal, Ram

    2015-12-01

    A new analytical model of a 3-degree-of-freedom (3-DOF) gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with each DOF of the system by vector analysis. The coupled differential equations thus established are solved analytically for their responses in both the time and frequency domains. Considering these frequency response equations, novel device design concepts are derived by forcing the sense phase to zero, which leads to a certain relationship between the structural frequencies, thereby causing minimization of the damping effect on the performance of the system. Furthermore, the feasibility of the present gyro-accelerometer structure is studied using a unique discriminatory scheme for the detection of both gyro action and linear acceleration at their events. This scheme combines the formulated settled transient solution of the gyro-accelerometer with the processes of synchronous demodulation and filtration, which leads to the in-phase and quadrature components of the system's output signal. These two components can be utilized in the detection of angular motion and linear acceleration. The obtained analytical results are validated by simulation in a MATLAB/Simulink environment, and it is found that the results are in excellent agreement with each other.

  20. Automatic Stress Detection in Working Environments From Smartphones' Accelerometer Data: A First Step.

    PubMed

    Garcia-Ceja, Enrique; Osmani, Venet; Mayora, Oscar

    2016-07-01

    Increase in workload across many organizations and consequent increase in occupational stress are negatively affecting the health of the workforce. Measuring stress and other human psychological dynamics is difficult due to subjective nature of selfreporting and variability between and within individuals. With the advent of smartphones, it is now possible to monitor diverse aspects of human behavior, including objectively measured behavior related to psychological state and consequently stress. We have used data from the smartphone's built-in accelerometer to detect behavior that correlates with subjects stress levels. Accelerometer sensor was chosen because it raises fewer privacy concerns (e.g., in comparison to location, video, or audio recording), and because its low-power consumption makes it suitable to be embedded in smaller wearable devices, such as fitness trackers. About 30 subjects from two different organizations were provided with smartphones. The study lasted for eight weeks and was conducted in real working environments, with no constraints whatsoever placed upon smartphone usage. The subjects reported their perceived stress levels three times during their working hours. Using combination of statistical models to classify selfreported stress levels, we achieved a maximum overall accuracy of 71% for user-specific models and an accuracy of 60% for the use of similar-users models, relying solely on data from a single accelerometer.

  1. Using accelerometers to determine the calling behavior of tagged baleen whales.

    PubMed

    Goldbogen, J A; Stimpert, A K; DeRuiter, S L; Calambokidis, J; Friedlaender, A S; Schorr, G S; Moretti, D J; Tyack, P L; Southall, B L

    2014-07-15

    Low-frequency acoustic signals generated by baleen whales can propagate over vast distances, making the assignment of calls to specific individuals problematic. Here, we report the novel use of acoustic recording tags equipped with high-resolution accelerometers to detect vibrations from the surface of two tagged fin whales that directly match the timing of recorded acoustic signals. A tag deployed on a buoy in the vicinity of calling fin whales and a recording from a tag that had just fallen off a whale were able to detect calls acoustically but did not record corresponding accelerometer signals that were measured on calling individuals. Across the hundreds of calls measured on two tagged fin whales, the accelerometer response was generally anisotropic across all three axes, appeared to depend on tag placement and increased with the level of received sound. These data demonstrate that high-sample rate accelerometry can provide important insights into the acoustic behavior of baleen whales that communicate at low frequencies. This method helps identify vocalizing whales, which in turn enables the quantification of call rates, a fundamental component of models used to estimate baleen whale abundance and distribution from passive acoustic monitoring. PMID:24803468

  2. Differences in V1 and V2 ski skating techniques described by accelerometers.

    PubMed

    Myklebust, H; Losnegard, T; Hallén, J

    2014-12-01

    The aims of the study were to describe the differences between the ski skating techniques V1 and V2 and evaluate reproducibility in complex cyclic hip movements measured by accelerometers. Fourteen elite senior male cross-country skiers rollerskied twice for 1 min (V1 and V2) at 4° inclination and 3 m/s. Tests were repeated after 20 min and again 4 months later. Five triaxial accelerometers were attached to the subject's hip (os sacrum), poles, and ski boots. Post-processing included transforming to an approximately global coordinate system, normalization for cycle time, double integration for displacement, and revealing temporal patterns. Different acceleration patterns between techniques and large correlation coefficients (Pearson's r = 0.6-0.9) between repeated trials were seen for most parameters. In V2, the hip was lowered [-10.9 (1.2) cm], whereas in V1, the hip was elevated [4.8 (1.5) cm] during the pole thrust. In conclusion, V2 but not V1 showed similarities to double poling in the way that potential energy is gained between poling strokes and transferred to propulsion during the poling action. Elite skiers reproduce their own individual patterns. One triaxial accelerometer on the lower back can distinguish techniques and might be useful in field research as well as in providing individual feedback on daily technique training.

  3. Application of MEMS Accelerometers and Gyroscopes in Fast Steering Mirror Control Systems

    PubMed Central

    Tian, Jing; Yang, Wenshu; Peng, Zhenming; Tang, Tao; Li, Zhijun

    2016-01-01

    In a charge-coupled device (CCD)-based fast steering mirror (FSM) tracking control system, high control bandwidth is the most effective way to enhance the closed-loop performance. However, the control system usually suffers a great deal from mechanical resonances and time delays induced by the low sampling rate of CCDs. To meet the requirements of high precision and load restriction, fiber-optic gyroscopes (FOGs) are usually used in traditional FSM tracking control systems. In recent years, the MEMS accelerometer and gyroscope are becoming smaller and lighter and their performance have improved gradually, so that they can be used in a fast steering mirror (FSM) to realize the stabilization of the line-of-sight (LOS) of the control system. Therefore, a tentative approach to implement a CCD-based FSM tracking control system, which uses MEMS accelerometers and gyroscopes as feedback components and contains an acceleration loop, a velocity loop and a position loop, is proposed. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop and the position loop. Extensive experimental results show that the MEMS accelerometers and gyroscopes can act the similar role as the FOG with lower cost for stabilizing the LOS of the FSM tracking control system. PMID:27023557

  4. Design and implementation of an intelligent belt system using accelerometer.

    PubMed

    Liu, Botong; Wang, Duo; Li, Sha; Nie, Xuhui; Xu, Shan; Jiao, Bingli; Duan, Xiaohui; Huang, Anpeng

    2015-01-01

    Activity monitor systems are increasing used recently. They are important for athletes and casual users to manage physical activity during daily exercises. In this paper, we use a triaxial accelerometer to design and implement an intelligent belt system, which can detect the user's step and flapping motion. In our system, a wearable intelligent belt is worn on the user's waist to collect activity acceleration signals. We present a step detection algorithm to detect real-time human step, which has high accuracy and low complexity. In our system, an Android App is developed to manage the intelligent belt. We also propose a protocol, which can guarantee data transmission between smartphones and wearable belt effectively and efficiently. In addition, when users flap the belt in emergency, the smartphone will receive alarm signal sending by the belt, and then notifies the emergency contact person, which can be really helpful for users in danger. Our experiment results show our system can detect physical activities with high accuracy (overall accuracy of our algorithm is above 95%) and has an effective alarm subsystem, which is significant for the practical use.

  5. Can accelerometers detect mass variations in Amazonian trees?

    NASA Astrophysics Data System (ADS)

    van Emmerik, Tim; Steele-Dunne, Susan; Gentine, Pierre; Guerin, Marceau; Hut, Rolf; Oliveira, Rafael; van de Giesen, Nick

    2016-04-01

    The mass of trees is influenced by physiological processes within the tree (e.g. transpiration and root water uptake), as well as external loads (e.g. intercepted precipitation). Recent studies have found diurnal variations in radar backscatter over vegetated areas, which might be attributed to mass changes of the vegetation layer. Field measurements are required to study the driving processes. This study aims to use measured three-dimensional displacement and acceleration of trees, to detect and quantify their diurnal (bio)mass variations. Accelerometers and dendrometers were installed on seven different tree species in the Amazon rainforest. Trees were selected to cover a broad range of wood density. Using spectral analysis, the governing frequencies in the acceleration time series were found. The governing frequencies showed a diurnal pattern, as well as a change during precipitation events. Our results suggest that we can separate and potentially quantify tree mass changes due to (1) internal water redistribution and (2) intercepted precipitation. This will allow further investigation of the effect of precipitation and water stress on tree dynamics in forest canopies.

  6. Wear Assessment of Conical Pick used in Coal Cutting Operation

    NASA Astrophysics Data System (ADS)

    Dewangan, Saurabh; Chattopadhyaya, Somnath; Hloch, Sergej

    2015-09-01

    Conical pick is a widely used tool for cutting coal in mines. It has a cemented carbide tip inserted in a steel body. Cemented carbide has been in use for many years for coal/rock cutting because it has the optimum combination of hardness, toughness and resistance against abrasive wear. As coal/rock is a heterogeneous substance, the cutting tool has to undergo various obstructions at the time of excavation that cause the tool to wear out. The cracks and fractures developing in the cemented carbide limit the life of the tool. For a long time, different wear mechanisms have been studied to develop improved grades of cemented carbide with high wear resistance properties. The research is still continuing. Moreover, due to the highly unpredictable nature of coal/rock, it is not easy to understand the wear mechanisms. In the present work, an attempt has been made to understand the wear mechanisms in four conical picks, which were used in a continuous miner machine for underground mining of coal. The wearing pattern of the conical pick indicates damage in its cemented carbide tip as well as the steel body. The worn out parts of the tools have been critically examined using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) point analysis. Mainly four types of wear mechanisms, namely, coal/rock intermixing, plastic deformation, rock channel formation and crushing and cracking, have been detected. The presence of coal/rock material and their respective concentrations in the selected area of worn out surface were observed using the spectra generated by EDX analysis.

  7. In vivo measurements of tooth wear over 12 months.

    PubMed

    Rodriguez, J M; Austin, R S; Bartlett, D W

    2012-01-01

    The aim of this study was to measure the progression of tooth wear in a cohort of 63 patients, 43 males and 20 females with a mean age of 39.1 years. Recruitment followed referral from general practice to Guy's Hospital for advice/management of tooth wear. Addition silicone impressions were taken at 6-month intervals for a total of 12 months; impressions were subsequently poured in type IV gypsum. Casts were scanned using a non-contacting laser profilometer and then superimposed using Geomagic® Qualify 11. Wear was measured in μm by tooth per time interval. A questionnaire highlighting dietary, parafunctional and gastric risk factors was obtained from each participant. Clustered multiple regression analysis was used to determine the relationship between tooth wear progression and risk factors. Maximum follow-up times were 6 months for 63 participants and 12 months for 30 participants. The measurement error was 15 μm. At the tooth level, 72.2% of 1,078 teeth wore <15 μm over a 6-month period. At the subject level, 77.7% of 63 participants showed median wear <15 μm over a 6-month period. There was a statistical trend towards tooth wear progression being associated with gastric risk factors (p < 0.05). The lower molars and the upper anterior teeth were the most commonly affected teeth; the lower molars and the upper central incisors were the most severely affected teeth. Tooth wear progression was slow in this cohort, suggesting that tooth wear may be cyclical and inactive in the majority of participants.

  8. Evaluation of shock isolation techniques for a piezoresistive accelerometer

    SciTech Connect

    Bateman, V.I.; Bell, R.G.; Davie, N.T. )

    1989-06-01

    Sandia conducts impact testing for a variety of structures. In this slapdown test, one end of the cask impacts the hard concrete target, then the structure rotates so that the other end of the cask impacts the target. During an impact test, metal to metal contact may occur within the structure and produce high frequency, high amplitude shock inputs. The high frequency portion of this transient vibration has been observed to excite the accelerometer resonance even though this resonance exceeds 350 kHz. The amplitude of the resonating accelerometer response can be so large that the data are clipped and are rendered useless. If the data are not clipped, a digital filter must be applied to eliminate the undesired accelerometer resonant response. If possible, it is more desirable to prevent excitation of the accelerometer resonance, This may be accomplished by mechanically isolating the accelerometer from the high frequency excitation without degrading the transducer response in the bandwidth of interest which is usually 10 kHz or less. To achieve this desirable isolation, two mounting configurations were designed and characterized. The objective of this paper is to describe the evaluation technique and to discuss the shock isolation properties of each mounting configuration. One configuration was actually used in a field test of bomb impacting a target. 4 figs.

  9. Characterization of a MEMS Accelerometer for Inertial Navigating Applications

    SciTech Connect

    Kinney, R.D.

    1999-02-12

    Inertial MEMS sensors such as accelerometers and angular rotation sensing devices continue to improve in performance as advances in design and processing are made. Present state-of-the-art accelerometers have achieved performance levels in the laboratory that are consistent with requirements for successful application in tactical weapon navigation systems. However, sensor performance parameters that are of interest to the designer of inertial navigation systems are frequently not adequately addressed by the MEMS manufacturer. This paper addresses the testing and characterization of a MEMS accelerometer from an inertial navigation perspective. The paper discusses test objectives, data reduction techniques and presents results from the test of a three-axis MEMS accelerometer conducted at Sandia National Laboratories during 1997. The test was structured to achieve visibility and characterization of the accelerometer bias and scale factor stability overtime and temperature. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy under contract DE-AC04-94AL85000.

  10. One testing method of dynamic linearity of an accelerometer

    NASA Astrophysics Data System (ADS)

    Lei, Jing-Yu; Guo, Wei-Guo; Tan, Xue-Ming; Shi, Yun-Bo

    2015-09-01

    To effectively test dynamic linearity of an accelerometer over a wide rang of 104 g to about 20 × 104g, one published patent technology is first experimentally verified and analysed, and its deficient is presented, then based on stress wave propagation theory on the thin long bar, the relation between the strain signal and the corresponding acceleration signal is obtained, one special link of two coaxial projectile is developed. These two coaxial metal cylinders (inner cylinder and circular tube) are used as projectiles, to prevent their mutual slip inside the gun barrel during movement, the one end of two projectiles is always fastened by small screws. Ti6-AL4-V bar with diameter of 30 mm is used to propagate loading stress pulse. The resultant compression wave can be measured by the strain gauges on the bar, and a half -sine strain pulse is obtained. The measuring accelerometer is attached on the other end of the bar by a vacuum clamp. In this clamp, the accelerometer only bear compression wave, the reflected tension pulse make the accelerometer off the bar. Using this system, dynamic linearity measurement of accelerometer can be easily tested in wider range of acceleration values. And a really measuring results are presented.

  11. Optimal Placement of Accelerometers for the Detection of Everyday Activities

    PubMed Central

    Cleland, Ian; Kikhia, Basel; Nugent, Chris; Boytsov, Andrey; Hallberg, Josef; Synnes, Kåre; McClean, Sally; Finlay, Dewar

    2013-01-01

    This article describes an investigation to determine the optimal placement of accelerometers for the purpose of detecting a range of everyday activities. The paper investigates the effect of combining data from accelerometers placed at various bodily locations on the accuracy of activity detection. Eight healthy males participated within the study. Data were collected from six wireless tri-axial accelerometers placed at the chest, wrist, lower back, hip, thigh and foot. Activities included walking, running on a motorized treadmill, sitting, lying, standing and walking up and down stairs. The Support Vector Machine provided the most accurate detection of activities of all the machine learning algorithms investigated. Although data from all locations provided similar levels of accuracy, the hip was the best single location to record data for activity detection using a Support Vector Machine, providing small but significantly better accuracy than the other investigated locations. Increasing the number of sensing locations from one to two or more statistically increased the accuracy of classification. There was no significant difference in accuracy when using two or more sensors. It was noted, however, that the difference in activity detection using single or multiple accelerometers may be more pronounced when trying to detect finer grain activities. Future work shall therefore investigate the effects of accelerometer placement on a larger range of these activities. PMID:23867744

  12. Fretting Wear Mechanisms in A216 Plain Carbon Steel

    NASA Astrophysics Data System (ADS)

    Maich, Alyssa Anne

    The subsurface and surface microstructures during pin-on-disk fretting wear of A216 steel disks under various loading conditions and times are investigated. The corresponding pins are fabricated from 410 stainless steel to simulate in-service conditions found in such engineering components as the Siemens W501FD engine row-2 diaphragm of a Siemens turbine engine, which is known to be prone to failure by fretting wear. Loading conditions range from 2N to 15N and times from 1 hour to a maximum of 69 hours, when steady state is confirmed. Wear track depth is quantitatively determined by optical profilometry, and found to range from 3 to 11 microns dependent upon load. Wear depth increases from 2N to 10N load, but decreases when increased to 15N load, due to heavier transfer of pin material to disk, as can be seen by EDS images of chromium transfer on A216 disk. Microstructures are evaluated by transmission electron microscopy of samples prepared by focused ion beam machining to pinpoint wear tracks and expose them in cross-section. EDS is used, in conjunction with TEM, to elucidate primary wear mechanisms at each stage of fretting wear. Microstructures in the subsurface of wear tracks are found to be heavily dislocated and layered, features that vary with both applied load and time. The microstructure eventually evolves into stable dislocation cells with cell walls aligned parallel to the surface. Penetration depth of the damaged layers increases with applied load, associated with a non-uniform maximum shear stress distribution that varies with depth. Primary oxide appears to evolve from Fe2O3 to Fe3O4, with increasing fretting time, leading to a uniform oxide on the surface of the A216 disk. Oxidation rate may be increased with the evolution of this subsurface dislocation cell structure. It is concluded that fretting wear failure is likely associated with a synergy between oxidative wear and crack initiation and propagation along dislocation cell walls under high

  13. Industrial Noise and Tooth Wear - Experimental Study

    PubMed Central

    Cavacas, Maria Alzira; Tavares, Vitor; Borrecho, Gonçalo; Oliveira, Maria João; Oliveira, Pedro; Brito, José; Águas, Artur; dos Santos, José Martins

    2015-01-01

    Tooth wear is a complex multifactorial process that involves the loss of hard dental tissue. Parafunctional habits have been mentioned as a self-destructive process caused by stress, which results in hyperactivity of masticatory muscles. Stress manifests itself through teeth grinding, leading to progressive teeth wear. The effects of continuous exposure to industrial noise, a “stressor” agent, cannot be ignored and its effects on the teeth must be evaluated. Aims: The aim of this study was to ascertain the effects of industrial noise on dental wear over time, by identifying and quantifying crown area loss. Material and Methods: 39 Wistar rats were used. Thirty rats were divided in 3 experimental groups of 10 animals each. Animals were exposed to industrial noise, rich in LFN components, for 1, 4 and 7 months, with an average weekly exposure of 40 hours (8h/day, 5 days/week with the weekends in silence). The remaining 9 animals were kept in silence. The areas of the three main cusps of the molars were measured under light microscopy. Statistical analysis used: A two-way ANOVA model was applied at significance level of 5%. Results: The average area of the molar cusps was significantly different between exposed and non-exposed animals. The most remarkable differences occurred between month 1 and 4. The total crown loss from month 1 to month 7 was 17.3% in the control group, and 46.5% in the exposed group, and the differences between these variations were significant (p<0.001). Conclusions: Our data suggest that industrial noise is an important factor in the pathogenesis of tooth wear. PMID:25798052

  14. Gaze Tracking System for User Wearing Glasses

    PubMed Central

    Gwon, Su Yeong; Cho, Chul Woo; Lee, Hyeon Chang; Lee, Won Oh; Park, Kang Ryoung

    2014-01-01

    Conventional gaze tracking systems are limited in cases where the user is wearing glasses because the glasses usually produce noise due to reflections caused by the gaze tracker's lights. This makes it difficult to locate the pupil and the specular reflections (SRs) from the cornea of the user's eye. These difficulties increase the likelihood of gaze detection errors because the gaze position is estimated based on the location of the pupil center and the positions of the corneal SRs. In order to overcome these problems, we propose a new gaze tracking method that can be used by subjects who are wearing glasses. Our research is novel in the following four ways: first, we construct a new control device for the illuminator, which includes four illuminators that are positioned at the four corners of a monitor. Second, our system automatically determines whether a user is wearing glasses or not in the initial stage by counting the number of white pixels in an image that is captured using the low exposure setting on the camera. Third, if it is determined that the user is wearing glasses, the four illuminators are turned on and off sequentially in order to obtain an image that has a minimal amount of noise due to reflections from the glasses. As a result, it is possible to avoid the reflections and accurately locate the pupil center and the positions of the four corneal SRs. Fourth, by turning off one of the four illuminators, only three corneal SRs exist in the captured image. Since the proposed gaze detection method requires four corneal SRs for calculating the gaze position, the unseen SR position is estimated based on the parallelogram shape that is defined by the three SR positions and the gaze position is calculated. Experimental results showed that the average gaze detection error with 20 persons was about 0.70° and the processing time is 63.72 ms per each frame. PMID:24473283

  15. Terrestrial Applications of a Nano-g Accelerometer

    NASA Technical Reports Server (NTRS)

    Hartley, Frank T.

    1996-01-01

    The ultra-sensitive accelerometer, developed for NASA to monitor the microgravity environments of Space Shuttle, five orbiters and Space Station, needed to measure accelerations up to 10 mg with an absolute accuracy of 10 nano-g (10(exp -8)g) for at least two orbits (10(exp 4) seconds) to resolve accelerations associated with orbital drag. Also, the accelerometers needed to have less than 10(exp -9) F.S. off-axis sensitivity; to be thermally and magnetically inert; to be immune to quiescent shock, and to have an in-situ calibration capability. Multi-axis compact seismometers, designs that have twelve decades of dynamic range will be described. Density profilometers, precision gradiometers, gyros and vibration isolation designs and applications will be discussed. Finally, examples of transformations of the accelerometer into sensitive anemometers and imaging spectrometers will be presented.

  16. Description of the three axis low-g accelerometer package

    NASA Technical Reports Server (NTRS)

    Amalavage, A. J.; Fikes, E. H.; Berry, E. H.

    1978-01-01

    The three axis low-g accelerometer package designed for use on the Space Processing Application Rocket (SPAR) Program is described. The package consists of the following major sections: (1) three Kearfott model 2412 accelerometers mounted in an orthogonal triad configuration on a temperature controlled, thermally isolated cube, (2) the accelerometer servoelectronics (printed circuit cards PC-6 through PC-12), and (3) the signal conditioner (printed circuit cards PC-15 and PC-16). The measurement range is 0 + or - 0.031 g with a quantization of 1.1 x 10 to the 7th power g. The package was flown successfully on six SPAR launches with the Black Brant booster. These flights provide approximately 300 s of free fall or zero-g environment.

  17. The ISA accelerometer for BepiColombo mission .

    NASA Astrophysics Data System (ADS)

    Iafolla, V.; Fiorenza, E.; Lefevre, C.; Nozzoli, S.; Peron, R.; Reale, A.; Santoli, F.

    The Italian Spring Accelerometer (ISA) will give a fundamental contribution to the Radio Science Experiments of BepiColombo mission, enabling substantial improvement of the knowledge of Mercury's orbit and rotation, and of the relativistic dynamics in the solar system. ISA is a three-axis accelerometer devoted to the measurement of the non-gravitational acceleration of Mercury Planetary Orbiter (MPO), whose knowledge is important in order to fully exploit the quality of the tracking data. ISA shall have an intrinsic noise level of (10^{-9} m/s^2/&sqrt;{Hz}) in the (3 \\cdot 10^{-5}) Hz to (10^{-1}) Hz frequency range, to guarantee the fulfilment of the RSE scientific goals. A comprehensive presentation of ISA accelerometer is given, including details about its scientific and technological features, the updated measurement error budget, the ongoing experimental activities and foreseen calibration and science operations strategies.

  18. Design and Process Considerations for a Tunneling Tip Accelerometer

    NASA Technical Reports Server (NTRS)

    Paul M. Zavracky, Bob McClelland, Keith Warner, Neil Sherman, Frank Hartley

    1995-01-01

    In this paper, we discuss issues related to the fabrication of a bulk micromachined single axis accelerometer. The accelerometer is designed to have a full scale range of ten millig and a sensitivity of tens of nanog. During the process, three distinctly different die are fabricated. These are subsequently assembled using an ally bonding technique. During the bonding operation, electrical contacts are made between layers. The accelerometer is controlled by electrostatic force plates above and below the proof mass. The lower electrode has a dual role. In operation, it provides a necessary control electrode. When not in operation, it is used to clamp the proof mass and prevents its motion. Results of the fabrication process and initial testing of the clamping function are reported.

  19. Adapting MCM-D technology to a piezoresistive accelerometer packaging

    NASA Astrophysics Data System (ADS)

    Collado, A.; Plaza, J. A.; Cabruja, E.; Esteve, J.

    2003-07-01

    A silicon-on-silicon multichip module for a piezoresistive accelerometer is presented in this paper. This packaging technology, a type of wafer level packaging, offers fully complementary metal-oxide semiconductor compatible silicon substrates, so a pre-amplification stage can be included at substrate level. The electrical contacts and a partial sealing of the sensor mobile structures are performed at the same step using flip-chip technology, so the cost is reduced. As accelerometers are stress-sensitive devices, great care must be taken in the fabrication process and materials. Thus, test structures have been included to study the packaging effects. In this paper we report on the compatibility of accelerometer and wafer level packaging technologies.

  20. Micromachined force-balance feedback accelerometer with optical displacement detection

    SciTech Connect

    Nielson, Gregory N.; Langlois, Eric; Baker, Michael; Okandan, Murat; Anderson, Robert

    2014-07-22

    An accelerometer includes a proof mass and a frame that are formed in a handle layer of a silicon-on-an-insulator (SOI). The proof mass is separated from the frame by a back-side trench that defines a boundary of the proof mass. The accelerometer also includes a reflector coupled to a top surface of the proof mass. An optical detector is located above the reflector at the device side. The accelerometer further includes at least one suspension spring. The suspension spring has a handle anchor that extends downwards from the device side to the handle layer to mechanically support upward and downward movement of the proof mass relative to a top surface of the proof mass.

  1. Optical accelerometer design based on laser self-mixing interference

    NASA Astrophysics Data System (ADS)

    Yang, Ying; Li, Xingfei; Kou, Ke; Zhang, Limin

    2015-03-01

    A novel optical accelerometer based on laser self-mixing effect is presented and experimentally demonstrated, which consists of a mass-loaded elastic-beam assembly and laser self-mixing interferometer. Under external acceleration, an inertial force is applied to the mass, flexible beams deflect from their equilibrium position. The deflection can be read out by the self-mixing interferometer. In order to reduce the impact of higher harmonic, wavelet analysis is introduced to remove singular points. Preliminary results indicate that the resolution is 0.19μg/Hz1/2 within a bandwidth of 100Hz. The optical accelerometer has the potential to achieve high-precision, compact accelerometers.

  2. The development of a bearing spectral analyzer and algorithms to detect turbopump bearing wear from deflectometer and strain gage data

    NASA Astrophysics Data System (ADS)

    Martinez, Carol L.

    1992-07-01

    Over the last several years, Rocketdyne has actively developed condition and health monitoring techniques and their elements for rocket engine components, specifically high pressure turbopumps. Of key interest is the development of bearing signature analysis systems for real-time monitoring of the cryogen-cooled turbopump shaft bearings, which spin at speeds up to 36,000 RPM. These system elements include advanced bearing vibration sensors, signal processing techniques, wear mode algorithms, and integrated control software. Results of development efforts in the areas of signal processing and wear mode identification and quantification algorithms based on strain gage and deflectometer data are presented. Wear modes investigated include: inner race wear, cage pocket wear, outer race wear, differential ball wear, cracked inner race, and nominal wear.

  3. [Wear and periprosthetic osteolysis of modular, hemispheric acetabular cups].

    PubMed

    Blacha, Jan; Bogacz, Alina

    2006-01-01

    Osteolysis associated with polyethylene wear has become one of the most prevalent complications associated with uncemented modular, hemispherical cups. Sixty-five consecutive total hip arthroplasties (ABG i, Howmedica, Stryker) were followed 6-12 years. Cumulative survivorship for the cup was 55.7% after 10 years. There were 20 cups revisions because of polyethylene wear and periprosthetic osteolysis (14 cups) or cup loosening (6 cups). Stability was assessed intraoperatively, 14 cups were revised, whereas 6 new polyethylene cups were cemented into stable metal-back of acetabular component. The average annual wear of revised cups was 0.32 mm. The annual wear of not revised cups was 0.12 mm. The differences were statistically significant (p = 0.002). The mean area of osteolysis was 472 mm2 (SD 257 mm2). There was no significant correlation between wear and area of osteolysis. There was significant correlation R = 0.54, p = 0.014) between time to revision and area of osteolysis. There were no significant differences of wear of polyethylene inlay or area of osteolysis between stable and unstable acetabular cups.

  4. Evaluation Of Saltstone Mixer Paddle Configuration For Improved Wear Resistance

    SciTech Connect

    Reigel, M. M.; Fowley, M. D.; Pickenheim, B. R.

    2012-09-27

    A soft metal with low wear resistance (6000 series aluminum), was used to minimize run time while maximizing wear rate. Two paddle configurations were tested, with the first four paddles after the augers replaced by the wear paddles. The first configuration was all flat paddles, with the first paddle not aligned with the augers and is consistent with present SPF mixer. The second configuration had helical paddles for the first three stages after the augers and a flat paddle at the fourth stage. The first helical paddle was aligned with the auger flight for the second configuration. The all flat paddle configuration wear rate was approximately double the wear rate of the helical paddles for the first two sets of paddles after the augers. For both configurations, there was little or no wear on the third and fourth paddle sets based on mass change, indicating that the fully wetted premix materials are much less abrasive than the un-wetted or partially wetted premix. Additionally, inspection of the wear surface of the paddles at higher magnification showed the flat paddles were worn much more than the helical and is consistent with the wear rates. Aligning the auger discharge flight with the first set of helical paddles was effective in reducing the wear rate as compared to the flat paddle configuration. Changing the paddle configuration from flat to helical resulted in a slight increase in rheological properties. Although, both tests produced grout-like material that is within the processing rage of the SPF, it should be noted that cement is not included in the premix and water was used rather than salt solution, which does affect the rheology of the fresh grout. The higher rheological properties from the helical wear test are most likely due to the reduced number of shearing paddles in the mixer. In addition, there is variation in the rheological data for each wear test. This is most likely due to the way that the dry feeds enter the mixer from the dry feeder. The

  5. A bimorph flexural-disk accelerometer for underwater use

    SciTech Connect

    Moffett, M.B.; Powers, J.M.

    1996-04-01

    Design equations, based on Ralph Woollett{close_quote}s 1960 report [{open_quote}{open_quote}The Flexural Disk Transducer,{close_quote}{close_quote} U.S. Navy Underwater Sound Laboratory Research Report No. 490], are presented for a bimorph accelerometer. Figures-of-merit are compared for PZT-4, PZT-5A, PZT-5H, PZT-8 piezoceramics, and PVDF-TrFE copolymer. Neutrally buoyant, spherical and cylindrical accelerometer configurations can be designed to meet bandwidth, sensitivity, and depth requirements. Experimental results for PZT-8 bimorphs indicate that simply-supported edge conditions are easily achievable. {copyright} {ital 1996 American Institute of Physics.}

  6. Monitoring the Dynamic Deformation of the Bridge Structures by Accelerometers

    NASA Astrophysics Data System (ADS)

    Lipták, Imrich

    2013-10-01

    The paper presents current trends in determining the dynamic deformations of bridge structures through the exploitation of geodetic measurements by accelerometers. The main aim of the paper is to demonstrate the practical application of these measurements on the cycling bridge over the river Morava in Devínska Nová Ves. Possibilities for the processing and analysis of accelerometer measurements by spectral analysis are described. An evaluation of the results is realized based on the modal characteristics from a numerical model designed by the finite element method.

  7. Validity of two brief physical activity questionnaires with accelerometers among African-American women

    PubMed Central

    Joseph, Rodney P.; Keller, Colleen; Adams, Marc A.; Ainsworth, Barbara E.

    2015-01-01

    Aim To evaluate the validity of the Stanford Brief Activity Survey (SBAS) and Exercise Vital Sign (EVS) questionnaire against accelerometer-determined time in moderate-to-vigorous physical activity (MVPA) among African-American (AA) women. Background Limited research has evaluated the validity of brief physical activity (PA) questionnaires among AA women. Since the validity of PA questionnaires may differ among members of varying racial/ethnic groups, research is needed to explore the validity of self-report PA measures among AA women. Methods A total of 30 AA women [M age = 35.5 ± 5.3; M body mass index (BMI) = 31.1 ± 7.8] wore ActiGraph GT3X + accelerometers (ActiGraph, LLC, Pensacola FL, USA) for seven days and completed both the SBAS and EVS at two different assessment periods (T1 and T2). Criterion validity was calculated using Spearman's rank order correlations between each questionnaire score and accelerometer-measured MVPA. Sensitivity, specificity, and positive and negative predictive values were calculated using accelerometer-measured MVPA as the criterion to determine the ability of each questionnaire to predict whether or not a participant was meeting the 2008 US PA Guidelines Findings Spearman correlation coefficients between questionnaire scores and minutes of accelerometer-measured MVPA were low (EVS, r = 0.27 at T1 and r = 0.26 at T2; SBAS, r = 0.10 at T1 and r = 0.28 at T2) and not statistically significant (P's > 0.05). The EVS had sensitivity, specificity, and negative and positive predictive values of 27, 89, 59, and 68% at T1 and 33, 74, 38, and 70% at T2, respectively. The SBAS had sensitivity, specificity, and negative and positive predictive values were 18, 79, 33, and 62% at T1 and 67, 58, 43, and 79% at T2. While both questionnaires may be useful in identifying AA women who do not meet the 2008 PA Guidelines, using the questionnaires to identify AA women meeting the PA Guidelines should be done with caution. PMID:26178779

  8. Total hip wear assessment: a comparison between computational and in vitro wear assessment techniques using ISO 14242 loading and kinematics.

    PubMed

    Matsoukas, George; Willing, Ryan; Kim, Il Yong

    2009-04-01

    In the present study a direct comparison was made between in vitro total hip wear testing and a computational analysis considering the effects of time and a nonlinear stress-strain relationship for ultrahigh molecular weight polyethylene (UHMWPE) at 37 degrees C. The computational simulation was made correct through calibration to experimental volumetric wear results, and the predicted damage layout on the acetabular liner surface was compared with results estimated from laser scanning of the actual worn specimens. The wear rates for the testing specimens were found to be 17.14+/-1.23 mg/10(6) cycles and 19.39+/-0.79 mg/10(6) cycles, and the cumulative volumetric wear values after 3x10(6) cycles were 63.70 mm(3) and 64.02 mm(3) for specimens 1 and 2, respectively. The value of the calibrated wear coefficient was found to be 5.32(10(-10)) mm(3)/N mm for both specimens. The major difference between the computational and experimental wear results was the existence of two damage vectors in the experimental case. The actual location of damage was virtually the same in both cases, and the maximum damage depth of the computational model agreed well with the experiment. The existence of multiple wear vectors may indicate the need for computational approaches to account for multidirectional sliding or strain hardening of UHMWPE. Despite the limitation in terms of describing the overall damage layout, the present computational model shows that simulation can mimic some of the behavior of in vitro wear. PMID:19275440

  9. Total hip wear assessment: a comparison between computational and in vitro wear assessment techniques using ISO 14242 loading and kinematics.

    PubMed

    Matsoukas, George; Willing, Ryan; Kim, Il Yong

    2009-04-01

    In the present study a direct comparison was made between in vitro total hip wear testing and a computational analysis considering the effects of time and a nonlinear stress-strain relationship for ultrahigh molecular weight polyethylene (UHMWPE) at 37 degrees C. The computational simulation was made correct through calibration to experimental volumetric wear results, and the predicted damage layout on the acetabular liner surface was compared with results estimated from laser scanning of the actual worn specimens. The wear rates for the testing specimens were found to be 17.14+/-1.23 mg/10(6) cycles and 19.39+/-0.79 mg/10(6) cycles, and the cumulative volumetric wear values after 3x10(6) cycles were 63.70 mm(3) and 64.02 mm(3) for specimens 1 and 2, respectively. The value of the calibrated wear coefficient was found to be 5.32(10(-10)) mm(3)/N mm for both specimens. The major difference between the computational and experimental wear results was the existence of two damage vectors in the experimental case. The actual location of damage was virtually the same in both cases, and the maximum damage depth of the computational model agreed well with the experiment. The existence of multiple wear vectors may indicate the need for computational approaches to account for multidirectional sliding or strain hardening of UHMWPE. Despite the limitation in terms of describing the overall damage layout, the present computational model shows that simulation can mimic some of the behavior of in vitro wear.

  10. Analysis of Accelerometer Data from a Woven Inflatable Creep Burst Test

    NASA Technical Reports Server (NTRS)

    James, George H.; Grygier, Michael; Selig, Molly M.

    2015-01-01

    Accelerometers were used to montor an inflatable test article during a creep test to failure. The test article experienced impulse events that were classified based on the response of the sensors and their time-dependent manifestation. These impulse events required specialized techniques to process the structural dynamics data. However, certain phenomena were defined as worthy of additional study. An assessment of one phenomena (a frequency near 1000Hz) showed a time dependent frequency and an amplitude that increased significantly near the end of the test. Hence, these observations are expected to drive future understanding of and utility in inflatable space structures.

  11. Fabrication of a Miniaturized ZnO Nanowire Accelerometer and Its Performance Tests.

    PubMed

    Kim, Hyun Chan; Song, Sangho; Kim, Jaehwan

    2016-01-01

    This paper reports a miniaturized piezoelectric accelerometer suitable for a small haptic actuator array. The accelerometer is made with zinc oxide (ZnO) nanowire (NW) grown on a copper wafer by a hydrothermal process. The size of the accelerometer is 1.5 × 1.5 mm², thus fitting the 1.8 × 1.8 mm² haptic actuator array cell. The detailed fabrication process of the miniaturized accelerometer is illustrated. Performance evaluation of the fabricated accelerometer is conducted by comparing it with a commercial piezoelectric accelerometer. The output current of the fabricated accelerometer increases linearly with the acceleration. The miniaturized ZnO NW accelerometer is feasible for acceleration measurement of small and lightweight devices. PMID:27649184

  12. Fabrication of a Miniaturized ZnO Nanowire Accelerometer and Its Performance Tests

    PubMed Central

    Kim, Hyun Chan; Song, Sangho; Kim, Jaehwan

    2016-01-01

    This paper reports a miniaturized piezoelectric accelerometer suitable for a small haptic actuator array. The accelerometer is made with zinc oxide (ZnO) nanowire (NW) grown on a copper wafer by a hydrothermal process. The size of the accelerometer is 1.5 × 1.5 mm2, thus fitting the 1.8 × 1.8 mm2 haptic actuator array cell. The detailed fabrication process of the miniaturized accelerometer is illustrated. Performance evaluation of the fabricated accelerometer is conducted by comparing it with a commercial piezoelectric accelerometer. The output current of the fabricated accelerometer increases linearly with the acceleration. The miniaturized ZnO NW accelerometer is feasible for acceleration measurement of small and lightweight devices. PMID:27649184

  13. Fabrication of a Miniaturized ZnO Nanowire Accelerometer and Its Performance Tests.

    PubMed

    Kim, Hyun Chan; Song, Sangho; Kim, Jaehwan

    2016-01-01

    This paper reports a miniaturized piezoelectric accelerometer suitable for a small haptic actuator array. The accelerometer is made with zinc oxide (ZnO) nanowire (NW) grown on a copper wafer by a hydrothermal process. The size of the accelerometer is 1.5 × 1.5 mm², thus fitting the 1.8 × 1.8 mm² haptic actuator array cell. The detailed fabrication process of the miniaturized accelerometer is illustrated. Performance evaluation of the fabricated accelerometer is conducted by comparing it with a commercial piezoelectric accelerometer. The output current of the fabricated accelerometer increases linearly with the acceleration. The miniaturized ZnO NW accelerometer is feasible for acceleration measurement of small and lightweight devices.

  14. Design and Fabrication of a Differential Electrostatic Accelerometer for Space-Station Testing of the Equivalence Principle

    PubMed Central

    Han, Fengtian; Liu, Tianyi; Li, Linlin; Wu, Qiuping

    2016-01-01

    The differential electrostatic space accelerometer is an equivalence principle (EP) experiment instrument proposed to operate onboard China’s space station in the 2020s. It is designed to compare the spin-spin interaction between two rotating extended bodies and the Earth to a precision of 10−12, which is five orders of magnitude better than terrestrial experiment results to date. To achieve the targeted test accuracy, the sensitive space accelerometer will use the very soft space environment provided by a quasi-drag-free floating capsule and long-time observation of the free-fall mass motion for integration of the measurements over 20 orbits. In this work, we describe the design and capability of the differential accelerometer to test weak space acceleration. Modeling and simulation results of the electrostatic suspension and electrostatic motor are presented based on attainable space microgravity condition. Noise evaluation shows that the electrostatic actuation and residual non-gravitational acceleration are two major noise sources. The evaluated differential acceleration noise is 1.01 × 10−9 m/s2/Hz1/2 at the NEP signal frequency of 0.182 mHz, by neglecting small acceleration disturbances. The preliminary work on development of the first instrument prototype is introduced for on-ground technological assessments. This development has already confirmed several crucial fabrication processes and measurement techniques and it will open the way to the construction of the final differential space accelerometer. PMID:27517927

  15. Design and Fabrication of a Differential Electrostatic Accelerometer for Space-Station Testing of the Equivalence Principle.

    PubMed

    Han, Fengtian; Liu, Tianyi; Li, Linlin; Wu, Qiuping

    2016-08-10

    The differential electrostatic space accelerometer is an equivalence principle (EP) experiment instrument proposed to operate onboard China's space station in the 2020s. It is designed to compare the spin-spin interaction between two rotating extended bodies and the Earth to a precision of 10(-12), which is five orders of magnitude better than terrestrial experiment results to date. To achieve the targeted test accuracy, the sensitive space accelerometer will use the very soft space environment provided by a quasi-drag-free floating capsule and long-time observation of the free-fall mass motion for integration of the measurements over 20 orbits. In this work, we describe the design and capability of the differential accelerometer to test weak space acceleration. Modeling and simulation results of the electrostatic suspension and electrostatic motor are presented based on attainable space microgravity condition. Noise evaluation shows that the electrostatic actuation and residual non-gravitational acceleration are two major noise sources. The evaluated differential acceleration noise is 1.01 × 10(-9) m/s²/Hz(1/2) at the NEP signal frequency of 0.182 mHz, by neglecting small acceleration disturbances. The preliminary work on development of the first instrument prototype is introduced for on-ground technological assessments. This development has already confirmed several crucial fabrication processes and measurement techniques and it will open the way to the construction of the final differential space accelerometer.

  16. Design and Fabrication of a Differential Electrostatic Accelerometer for Space-Station Testing of the Equivalence Principle.

    PubMed

    Han, Fengtian; Liu, Tianyi; Li, Linlin; Wu, Qiuping

    2016-01-01

    The differential electrostatic space accelerometer is an equivalence principle (EP) experiment instrument proposed to operate onboard China's space station in the 2020s. It is designed to compare the spin-spin interaction between two rotating extended bodies and the Earth to a precision of 10(-12), which is five orders of magnitude better than terrestrial experiment results to date. To achieve the targeted test accuracy, the sensitive space accelerometer will use the very soft space environment provided by a quasi-drag-free floating capsule and long-time observation of the free-fall mass motion for integration of the measurements over 20 orbits. In this work, we describe the design and capability of the differential accelerometer to test weak space acceleration. Modeling and simulation results of the electrostatic suspension and electrostatic motor are presented based on attainable space microgravity condition. Noise evaluation shows that the electrostatic actuation and residual non-gravitational acceleration are two major noise sources. The evaluated differential acceleration noise is 1.01 × 10(-9) m/s²/Hz(1/2) at the NEP signal frequency of 0.182 mHz, by neglecting small acceleration disturbances. The preliminary work on development of the first instrument prototype is introduced for on-ground technological assessments. This development has already confirmed several crucial fabrication processes and measurement techniques and it will open the way to the construction of the final differential space accelerometer. PMID:27517927

  17. Clinical measurement of tooth wear: Tooth wear indices

    PubMed Central

    López-Frías, Francisco J.; Castellanos-Cosano, Lizett; Martín-González, Jenifer; Llamas-Carreras, José M.

    2012-01-01

    Attrition, erosion, and abrasion result in alterations to the tooth and manifest as tooth wear. Each classification corresponds to a different process with specific clinical features. Classifications made so far have no accurate prevalence data because the indexes do not necessarily measure a specific etiology, or because the study populations can be diverse in age and characteristics. Tooth wears (attrition, erosion and abrasion) is perceived internationally as a growing problem. However, the interpretation and comparison of clinical and epidemiological studies, it is increasingly difficult because of differences in terminology and the large number of indicators/indices that have been developed for the diagnosis, classification and monitoring of the loss of dental hard tissue. These indices have been designed to identify increasing severity and are usually numerical, none have universal acceptance, complicating the evaluation of the true increase in prevalence reported. This article considers the ideal requirements for an erosion index. A literature review is conducted with the aim of analyzing the evolution of the indices used today and discuss whether they meet the clinical needs and research in dentistry. Key words:Tooth wear, tooth wear indices, attrition, erosion, abrasion, abfraction. PMID:24558525

  18. Steam generator fretting-wear damage: A summary of recent findings

    SciTech Connect

    Guerout, F.M.; Fisher, N.J.

    1999-08-01

    Flow-induced vibration of steam generator (SG) tubes may sometimes result in fretting-wear damage at the tube-to-support locations. Fretting-wear damage predictions are largely based on experimental data obtained at representative test conditions. Fretting-wear of SG materials has been studied at the Chalk River Laboratories for two decades. Tests are conducted in fretting-wear test machines that simulate SG environmental conditions and tube-to-support dynamic interactions. A new high-temperature force and displacement measuring system was developed to monitor tube-to-support interaction (i.e., work-rate) at operating conditions. This improvement in experimental fretting-wear technology was used to perform a comprehensive study of the effect of various environment and design parameters on SG tube wear damage. This paper summarizes the results of tests performed over the past 4 yr to study the effect of temperature, water chemistry, support geometry, and tube material on fretting-wear. The results show a significant effect of temperature on tube wear damage. Therefore, fretting-wear tests must be performed at operating temperatures in order to be relevant. No significant effect of the type of water treatment on tube wear damage was observed. For predominantly impacting motion, the wear of SG tubes in contact with 410 stainless steel is similar regardless of whether Alloy 690 or Alloy 800 is used as tubing material or whether lattice bars or broached hole supports are used. Based on results presented in this paper, an average wear coefficient value is recommended that is used for the prediction of SG tube wear depth versus time.

  19. Self-noise models of five commercial strong-motion accelerometers

    USGS Publications Warehouse

    Ringler, Adam; Evans, John R.; Hutt, Charles R.

    2015-01-01

    To better characterize the noise of a number of commonly deployed accelerometers in a standardized way, we conducted noise measurements on five different models of strong‐motion accelerometers. Our study was limited to traditional accelerometers (Fig. 1) and is in no way exhaustive.

  20. Numerical modelling of tool wear in turning with cemented carbide cutting tools

    SciTech Connect

    Franco, P.; Estrems, M.; Faura, F.

    2007-04-07

    A numerical model is proposed for analysing the flank and crater wear resulting from the loss of material on cutting tool surface in turning processes due to wear mechanisms of adhesion, abrasion and fracture. By means of this model, the material loss along cutting tool surface can be analysed, and the worn surface shape during the workpiece machining can be determined. The proposed model analyses the gradual degradation of cutting tool during turning operation, and tool wear can be estimated as a function of cutting time. Wear-land width (VB) and crater depth (KT) can be obtained for description of material loss on cutting tool surface, and the effects of the distinct wear mechanisms on surface shape can be studied. The parameters required for the tool wear model are obtained from bibliography and experimental observation for AISI 4340 steel turning with WC-Co cutting tools.

  1. Improved assembly processes for the Quartz Digital Accelerometer cantilever

    SciTech Connect

    Romero, A.M.; Gebert, C.T.

    1990-07-01

    This report covers the development of improved assembly processes for the Quartz Digital Accelerometer cantilever. In this report we discuss improved single-assembly tooling, the development of tooling and processes for precision application of polyimide adhesive, the development of the wafer scale assembly procedure, and the application of eutectic bonding to cantilever assembly. 2 refs., 17 figs.

  2. Silicon-micromachined accelerometers for space inertial systems

    NASA Astrophysics Data System (ADS)

    Saha, I.; Islam, R.; Kanakaraju, K.; Jain, Yashwant K.; Alex, T. K.

    1999-11-01

    Accelerometers are key components of various motion control systems ranging in use from inertial guidance of rockets and satellite launch vehicles to safety applications in the automotive industry. The accelerometers that are used for spare inertial systems are characterized by high resolution, small bandwidth, large working range and excellent linearity. Current advances in this field are based on silicon micromachining. Silicon bulk and surface micromachined accelerometers offer advantages of reduced size and weight, less power consumption and the use of a fabrication process derived form an already well established semiconductor fab technology. Of the various approaches to silicon micromachined accelerometers, two are in a well advanced state of development. The first is the capacitive force balanced type and the second the piezoresistive type. The capacitive approach has the advantage of higher stability and resolution and lower temperature coefficients. But it requires proximal detection circuitry to prevent parasitics to overwhelm the circuit. A new approach reported recently uses a silicon micromachined cantilever beam which acts as a Fabry Perot interferometer when light form an optical fiber is impinged on it. In this paper we overview all the approaches and try to select a suitable candidate for use in space borne inertial systems.

  3. Standardizing accelerometer-based activity monitor calibration and output reporting.

    PubMed

    Coolbaugh, Crystal L; Hawkins, David A

    2014-08-01

    Wearable accelerometer-based activity monitors (AMs) are used to estimate energy expenditure and ground reaction forces in free-living environments, but a lack of standardized calibration and data reporting methods limits their utility. The objectives of this study were to (1) design an inexpensive and easily reproducible AM testing system, (2) develop a standardized calibration method for accelerometer-based AMs, and (3) evaluate the utility of the system and accuracy of the calibration method. A centrifuge-type device was constructed to apply known accelerations (0-8g) to each sensitive axis of 30 custom and two commercial AMs. Accelerometer data were recorded and matrix algebra and a least squares solution were then used to determine a calibration matrix for the custom AMs to convert raw accelerometer output to units of g's. Accuracy was tested by comparing applied and calculated accelerations for custom and commercial AMs. AMs were accurate to within 4% of applied accelerations. The relatively inexpensive AM testing system (< $100) and calibration method has the potential to improve the sharing of AM data, the ability to compare data from different studies, and the accuracy of AM-based models to estimate various physiological and biomechanical quantities of interest in field-based assessments of physical activity.

  4. Estimating Energy Expenditure with the RT3 Triaxial Accelerometer

    ERIC Educational Resources Information Center

    Maddison, Ralph; Jiang, Yannan; Vander Hoorn, Stephen; Mhurchu, Cliona Ni; Lawes, Carlene M. M.; Rodgers, Anthony; Rush, Elaine

    2009-01-01

    The RT3 is a relatively new triaxial accelerometer that has replaced the TriTrac. The aim of this study was to validate the RT3 against doubly labeled water (DLW) in a free-living, mixed weight sample of adults. Total energy expenditure (TEE) was measured over a 15-day period using DLW. Activity-related energy expenditure (AEE) was estimated by…

  5. Joint angle estimation with accelerometers for dynamic postural analysis.

    PubMed

    Ma, Jianting; Kharboutly, Haissam; Benali, Abderraouf; Benamar, Faïz; Bouzit, Mourad

    2015-10-15

    This paper presents a new accelerometer based method for estimating the posture of a subject standing on a dynamic perturbation platform. The induced perturbation is used to study the control mechanisms as well as the balance requirements that regulate the upright standing. These perturbations are translated into different intensity levels of speed and acceleration along longitudinal and lateral directions of motion. In our method, the human posture is modeled by a tridimensional, three-segment inverted pendulum which simultaneously takes into account both the anterior-posterior and medio-lateral strategies of hip and ankle. Four tri-axial accelerometers are used her, one accelerometer is placed on the platform, and the other three are attached to a human subject. Based on the results, the joint angle estimated compare closely to measurements from magnetic encoders placed on an articulated arm joint. The results were also comparable to those found when using a high-end optical motion capture system coupled with advanced biomechanical simulation software. This paper presents the comparisons of our accelerometer-based method with encoder and optical marker based method of the estimated joint angles under different dynamics perturbations. PMID:26338097

  6. Integrated smart actuator containing a monolithic coformed accelerometer

    NASA Astrophysics Data System (ADS)

    Corsaro, Robert D.; Houston, Brian H.; Klunder, Joseph D.

    1997-05-01

    A general need exists for inexpensive finite-area transducer arrays which intrinsically combine acoustic or vibration sensing with area actuation. Such combination transducers are particularly needed in active sound and vibration control and smart-materials applications. Commercial areas of interest include advanced underwater, aerospace or robotic-sensing applications. To be economically attractive they must be relatively simple to manufacture from reasonable cost materials. One promising new technology for such applications is injection-molded 1-3 composite piezo- ceramics, pioneered by Material Systems Inc. This transducer material is well suited for use as the low-cost actuator component of such a smart actuator. The challenge of this study was to design an inexpensive accelerometer which could be injection molded along with the actuator as an interspersed array. This paper describes a monolithic accelerometer which is suitable for fabrication by injection-molding as an integrated co-formed actuator component. Experimental results are presented for actuator/accelerometer arrays and issues related to the design and use of accelerometers in close proximity to an actuator are discussed.

  7. Joint angle estimation with accelerometers for dynamic postural analysis.

    PubMed

    Ma, Jianting; Kharboutly, Haissam; Benali, Abderraouf; Benamar, Faïz; Bouzit, Mourad

    2015-10-15

    This paper presents a new accelerometer based method for estimating the posture of a subject standing on a dynamic perturbation platform. The induced perturbation is used to study the control mechanisms as well as the balance requirements that regulate the upright standing. These perturbations are translated into different intensity levels of speed and acceleration along longitudinal and lateral directions of motion. In our method, the human posture is modeled by a tridimensional, three-segment inverted pendulum which simultaneously takes into account both the anterior-posterior and medio-lateral strategies of hip and ankle. Four tri-axial accelerometers are used her, one accelerometer is placed on the platform, and the other three are attached to a human subject. Based on the results, the joint angle estimated compare closely to measurements from magnetic encoders placed on an articulated arm joint. The results were also comparable to those found when using a high-end optical motion capture system coupled with advanced biomechanical simulation software. This paper presents the comparisons of our accelerometer-based method with encoder and optical marker based method of the estimated joint angles under different dynamics perturbations.

  8. Critical length scale controls adhesive wear mechanisms.

    PubMed

    Aghababaei, Ramin; Warner, Derek H; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  9. Critical length scale controls adhesive wear mechanisms

    PubMed Central

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  10. Critical length scale controls adhesive wear mechanisms

    NASA Astrophysics Data System (ADS)

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-06-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients.

  11. Elastomer Compound Developed for High Wear Applications

    NASA Technical Reports Server (NTRS)

    Crawford, D.; Feuer, H.; Flanagan, D.; Rodriguez, G.; Teets, A.; Touchet, P.

    1993-01-01

    The U.S. Army is currently spending 300 million dollars per year replacing rubber track pads. An experimental rubber compound has been developed which exhibits 2 to 3 times greater service life than standard production pad compounds. To improve the service life of the tank track pads various aspects of rubber chemistry were explored including polymer, curing and reinforcing systems. Compounds that exhibited superior physical properties based on laboratory data were then fabricated into tank pads and field tested. This paper will discuss the compounding studies, laboratory data and field testing that led to the high wear elastomer compound.

  12. GPS-Based Reduced Dynamic Orbit Determination Using Accelerometer Data

    NASA Technical Reports Server (NTRS)

    VanHelleputte, Tom; Visser, Pieter

    2007-01-01

    Currently two gravity field satellite missions, CHAMP and GRACE, are equipped with high sensitivity electrostatic accelerometers, measuring the non-conservative forces acting on the spacecraft in three orthogonal directions. During the gravity field recovery these measurements help to separate gravitational and non-gravitational contributions in the observed orbit perturbations. For precise orbit determination purposes all these missions have a dual-frequency GPS receiver on board. The reduced dynamic technique combines the dense and accurate GPS observations with physical models of the forces acting on the spacecraft, complemented by empirical accelerations, which are stochastic parameters adjusted in the orbit determination process. When the spacecraft carries an accelerometer, these measured accelerations can be used to replace the models of the non-conservative forces, such as air drag and solar radiation pressure. This approach is implemented in a batch least-squares estimator of the GPS High Precision Orbit Determination Software Tools (GHOST), developed at DLR/GSOC and DEOS. It is extensively tested with data of the CHAMP and GRACE satellites. As accelerometer observations typically can be affected by an unknown scale factor and bias in each measurement direction, they require calibration during processing. Therefore the estimated state vector is augmented with six parameters: a scale and bias factor for the three axes. In order to converge efficiently to a good solution, reasonable a priori values for the bias factor are necessary. These are calculated by combining the mean value of the accelerometer observations with the mean value of the non-conservative force models and empirical accelerations, estimated when using these models. When replacing the non-conservative force models with accelerometer observations and still estimating empirical accelerations, a good orbit precision is achieved. 100 days of GRACE B data processing results in a mean orbit fit of

  13. Comparison of estimated energy intake using Web-based Dietary Assessment Software with accelerometer-determined energy expenditure in children

    PubMed Central

    Biltoft-Jensen, Anja; Hjorth, Mads F.; Trolle, Ellen; Christensen, Tue; Brockhoff, Per B.; Andersen, Lene F.; Tetens, Inge; Matthiessen, Jeppe

    2013-01-01

    Background The OPUS (Optimal well-being, development and health for Danish children through a healthy New Nordic Diet) project carried out a school meal study to assess the impact of a New Nordic Diet (NND). The random controlled trial involved 834 children aged 8–11 in nine local authority schools in Denmark. Dietary assessment was carried out using a program known as WebDASC (Web-based Dietary Assessment Software for Children) to collect data from the children. Objective To compare the energy intake (EI) of schoolchildren aged 8–11 estimated using the WebDASC system against the total energy expenditure (TEE) as derived from accelerometers worn by the children during the same period. A second objective was to evaluate the WebDASC's usability. Design Eighty-one schoolchildren took part in what was the pilot study for the OPUS project, and they recorded their total diet using WebDASC and wore an accelerometer for two periods of seven consecutive days: at baseline, when they ate their usual packed lunches and at intervention when they were served the NND. EI was estimated using WebDASC, and TEE was calculated from accelerometer-derived activity energy expenditure, basal metabolic rate, and diet-induced thermogenesis. WebDASC's usability was assessed using a questionnaire. Parents could help their children record their diet and answer the questionnaire. Results Evaluated against TEE as derived from the accelerometers worn at the same time, the WebDASC performed just as well as other traditional methods of collecting dietary data and proved both effective and acceptable with children aged 8–11, even with perhaps less familiar foods of the NND. Conclusions WebDASC is a useful method that provided a reasonably accurate measure of EI at group level when compared to TEE derived from accelerometer-determined physical activity in children. WebDASC will benefit future research in this area. PMID:24358037

  14. Structurally Integrated Coatings for Wear and Corrosion

    SciTech Connect

    Beardsley, M. Brad; Sebright, Jason L.

    2008-11-18

    Wear and corrosion of structures cuts across industries and continues to challenge materials scientists and engineers to develop cost effective solutions. Industries typically seek mature technologies that can be implemented for production with rapid or minimal development and have little appetite for the longer-term materials research and development required to solve complex problems. The collaborative work performed in this project addressed the complexity of this problem in a multi-year program that industries would be reluctant to undertake without government partnership. This effort built upon the prior development of Advanced Abrasion Resistant Materials conduct by Caterpillar Inc. under DOE Cooperative Agreement No. DE-FC26-01NT41054. In this referenced work, coatings were developed that exhibited significant wear life improvements over standard carburized heat treated steel in abrasive wear applications. The technology used in this referenced work, arc lamp fusing of thermal spray coatings, was one of the primary technical paths in this work effort. In addition to extending the capability of the coating technology to address corrosion issues, additional competitive coating technologies were evaluated to insure that the best technology was developed to meet the goals of the program. From this, plasma transferred arc (PTA) welding was selected as the second primary technology that was investigated. Specifically, this project developed improved, cost effective surfacing materials and processes for wear and corrosion resistance in both sliding and abrasive wear applications. Materials with wear and corrosion performance improvements that are 4 to 5 times greater than heat treated steels were developed. The materials developed were based on low cost material systems utilizing ferrous substrates and stainless steel type matrix with hard particulates formed from borides and carbides. Affordability was assessed against other competing hard surfacing or coating

  15. Microstructure and elevated temperature wear behavior of induction melted Fe-based composite coating

    NASA Astrophysics Data System (ADS)

    Hu, Ge; Meng, Huimin; Liu, Junyou

    2014-10-01

    Fe-based composite coating prepared onto the component of guide wheel using ultrasonic frequency inductive cladding (UFIC) technique has been investigated in terms of microstructure, phase constitutions, microhardness and elevated temperature wear behavior by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), Vickers microhardness tester and ball-on-disc wear tester. The results indicated that the primary phase in the coating contained austenite γ-Fe, eutectic γ-Fe/(Cr,Fe)2B, boride (Cr,Fe)2B and precipitation enriched in Mo. The average microhardness of the coating was 760 ± 10 HV0.2, which was three times higher than that of the substrate. With increasing temperature, the friction coefficients of the coating and high-chromium cast iron decreased gradually while the wear rates increased during dry sliding wear condition. The relative wear resistance of the coating was 1.63 times higher than that of the high-chromium cast iron at 500 °C, which was ascribed to the hard borides with high thermal stability uniformly embedded in the coating and the formation of dense transfer layer formed onto the worn surface. The high temperature wear mechanism of the coating was dominated by mild abrasive wear. The study revealed that Fe-based composite coating had excellent high temperature wear resistance under dry sliding wear condition.

  16. Needs and challenges in precision wear measurement

    SciTech Connect

    Blau, P.J.

    1996-01-10

    Accurate, precise wear measurements are a key element in solving both current wear problems and in basic wear research. Applications range from assessing durability of micro-scale components to accurate screening of surface treatments and thin solid films. Need to distinguish small differences in wear tate presents formidable problems to those who are developing new materials and surface treatments. Methods for measuring wear in ASTM standard test methods are discussed. Errors in using alterate methods of wear measurement on the same test specimen are also described. Human judgemental factors are a concern in common methods for wear measurement, and an experiment involving measurement of a wear scar by ten different people is described. Precision in wear measurement is limited both by the capabilities of the measuring instruments and by the nonuniformity of the wear process. A method of measuring wear using nano-scale indentations is discussed. Current and future prospects for incorporating advanced, higher-precision wear measurement methods into standards are considered.

  17. Wear particle analysis using the ferrograph

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1983-01-01

    The use of the Ferrograph in analyzing wear particles from a variety of different sources is reported. Examples of wear particles from gas turbine engines, bearing tests, friction and wear tests, hydraulic systems, and human joints are illustrated. In addition, the separation of bacteria and human cells is described.

  18. Testing of a Fiber Optic Wear, Erosion and Regression Sensor

    NASA Technical Reports Server (NTRS)

    Korman, Valentin; Polzin, Kurt A.

    2011-01-01

    The nature of the physical processes and harsh environments associated with erosion and wear in propulsion environments makes their measurement and real-time rate quantification difficult. A fiber optic sensor capable of determining the wear (regression, erosion, ablation) associated with these environments has been developed and tested in a number of different applications to validate the technique. The sensor consists of two fiber optics that have differing attenuation coefficients and transmit light to detectors. The ratio of the two measured intensities can be correlated to the lengths of the fiber optic lines, and if the fibers and the host parent material in which they are embedded wear at the same rate the remaining length of fiber provides a real-time measure of the wear process. Testing in several disparate situations has been performed, with the data exhibiting excellent qualitative agreement with the theoretical description of the process and when a separate calibrated regression measurement is available good quantitative agreement is obtained as well. The light collected by the fibers can also be used to optically obtain the spectra and measure the internal temperature of the wear layer.

  19. Rig for testing the relative wear resistance of materials

    SciTech Connect

    Berdikov, V.F.; Diulin, A.I.; Efimchuk, V.P.; Pushkarev, O.I.; Finogenov, G.P.

    1987-01-01

    The authors have developed a simple and compact rig for studying the relative wear resistance of materials subjected to mechanical abrasion and friction. The rig has an electronic control system. It was used to test the relative wear resistance of a wide range of superhard and brittle materials under mechanical abrasion against a counterbody. The counterbody was made of modified iron and the test medium was a diamond suspension in oil. The results showed that specimen wear exhibits a linear relationship with abrasion time (in the range of 0.5-20 min.) at unit pressure from 0.01 to 0.10 MPa. That a standard wear pattern exists within a wide range of parameters indicates that abrasive conditions are highly stable and makes it possible to control conditions. The rig was used to establish the relative wear resistance of several abrasives, minerals, and refractory compounds. The very large difference (15.2 times) between the most and least-resistant materials (tungsten carbide and fluoride) illustrates the sensitivity of the methodology.

  20. Lameness detection via leg-mounted accelerometers on dairy cows on four commercial farms.

    PubMed

    Thorup, V M; Munksgaard, L; Robert, P-E; Erhard, H W; Thomsen, P T; Friggens, N C

    2015-10-01

    Lameness in dairy herds is traditionally detected by visual inspection, which is time-consuming and subjective. Compared with healthy cows, lame cows often spend longer time lying down, walk less and change behaviour around feeding time. Accelerometers measuring cow leg activity may assist farmers in detecting lame cows. On four commercial farms, accelerometer data were derived from hind leg-mounted accelerometers on 348 Holstein cows, 53 of them during two lactations. The cows were milked twice daily and had no access to pasture. During a lactation, locomotion score (LS) was assessed on average 2.4 times (s.d. 1.3). Based on daily lying duration, standing duration, walking duration, total number of steps, step frequency, motion index (MI, i.e. total acceleration) for lying, standing and walking, eight accelerometer means and their corresponding coefficient of variation (CV) were calculated for each week immediately before an LS. A principal component analysis was performed to evaluate the relationship between the variables. The effects of LS and farm on the principal components (PC) and on the variables were analysed in a mixed model. The first four PC accounted for 27%, 18%, 12% and 10% of the total variation, respectively. PC1 corresponded to Activity variability due to heavy loading by five CV variables related to standing and walking. PC2 corresponded to Activity level due to heavy loading by MI walking, MI standing and walking duration. PC3 corresponded to Recumbency due to heavy loading by four variables related to lying. PC4 corresponded mainly to Stepping due to heavy loading by step frequency. Activity variability at LS4 was significantly higher than at the lower LS levels. Activity level was significantly higher at LS1 than at LS2, which was significantly higher than at LS4. Recumbency was unaffected by LS. Stepping at LS1 and LS2 was significantly higher than at LS3 and LS4. Activity level was significantly lower on farm 3 compared with farms 1 and 2

  1. Ultra-Low Power Event-Driven Wireless Sensor Node Using Piezoelectric Accelerometer for Health Monitoring

    NASA Astrophysics Data System (ADS)

    Okada, Hironao; Kobayashi, Takeshi; Masuda, Takashi; Itoh, Toshihiro

    2009-07-01

    We describe a low power consumption wireless sensor node designed for monitoring the conditions of animals, especially of chickens. The node detects variations in 24-h behavior patterns by acquiring the number of the movement of an animal whose acceleration exceeds a threshold measured in per unit time. Wireless sensor nodes when operated intermittently are likely to miss necessary data during their sleep mode state and waste the power in the case of acquiring useless data. We design the node worked only when required acceleration is detected using a piezoelectric accelerometer and a comparator for wake-up source of micro controller unit.

  2. Wear patterns of, and wear volume formulae for, cylindrically elongated acetabular cup liners.

    PubMed

    Wu, James Shih-Shyn; Hsu, Shu-Ling; Chen, Jian-Horng

    2010-07-01

    This study analyzed the wear patterns of, and wear volume formulae for, cylindrically elongated acetabular cup liners. The geometric patterns of the wear surface were first classified, then wear volume formulae were derived by integral calculus. SolidWorks((R)) software or published formulae were used to verify the accuracy of the proposed formulae. The analytical results showed that the wear shape of the liner can be categorized into seven wear patterns, including the special case of wear at 90 degrees , and the seven corresponding wear formulae were derived. In addition, wear of the cylindrical elongation might add considerably to the volume loss of the liner, depending on the height and shape of the elongation and the depth and direction of the linear penetration, being maximally 21% in the investigated model. The proposed wear formulae and patterns will be useful for more accurate performance evaluation of existing hip components implanted in patients and for the designing of new hip components.

  3. Assessing head and trunk symmetry during sleep using tri-axial accelerometers.

    PubMed

    Sato, Haruhiko; Ikura, Daiki; Tsunoda, Masahiro

    2015-03-01

    Using two types of small, lightweight tri-axial accelerometers, we obtained evidence for the effectiveness of an approach for assessing head-trunk symmetrical or asymmetrical positions during sleep. First, we assessed the accuracy of our monitoring system in five healthy young adults (age range, 22-24 years). The participants wore acceleration monitors on the sternum and forehead; then spent 5 min in six different positions. Once accuracy was confirmed, we assessed head-trunk symmetry during night-time sleep in 10 healthy children (age range, 3-13 years) and 10 young adults (age range, 21-26 years) in their home environments. All participants wore the monitors during one night's sleep in their homes. After computing head-trunk positions using the orientation data obtained by the accelerometers, head and trunk symmetry were evaluated. The head and trunk positions were correctly detected: the positional data from the trunk had 99% agreement, and the data from the head had 96% agreement. Both the young adults and children were observed to spend time with the head-trunk in asymmetric positions; however, the subjects changed position frequently so the asymmetrical postures were mobile. We concluded that the proposed monitoring system is a reliable and valid approach for assessing head-trunk symmetry during sleep at home. Implications for Rehabilitation We propose a head and trunk symmetry monitoring system using accelerometers. The proposed system could accurately identify head and trunk position. Asymmetrical positioning was seen in healthy participants but it was not immobile. PMID:24274623

  4. Traveling Atmospheric Disturbances (TADs) in the thermosphere inferred from accelerometer data at three altitudes

    NASA Astrophysics Data System (ADS)

    Bruinsma, Sean; Forbes, Jeffrey

    2010-05-01

    Densities derived from accelerometer measurements on the GRACE, CHAMP and Air Force/SETA satellites near 490, 390, and 220 km, respectively, are used to elucidate global-scale characteristics of traveling atmospheric disturbances. The accelerometers on the CHAMP and GRACE satellites have made it possible to accumulate near-continuous records of thermosphere density between about 320 and 490 km since May 2001, and July 2002, respectively. They have recorded the response to virtually every significant geomagnetic storm during this period. CHAMP and GRACE are in (near) polar and quasi-circular orbits, sampling 24 hr local time approximately every 4 and 5 months, respectively. These capabilities offer unique opportunities to study the temporal and latitudinal responses of the thermosphere to geomagnetic disturbances. The Air Force/SETA accelerometer data have also been processed, but the analysis is more complicated due to data gaps. Significant and unambiguous TAD activity in the observed response of the thermosphere was detected for about 25 events with CHAMP and GRACE, and less than 10 with SETA. The atmospheric variability is evaluated by de-trending the data, allowing the extraction of specific ranges in horizontal scale, and analyzing density "residuals". The scale of the perturbation is decisive for its lifetime and relative amplitude. Sometimes the disturbances represent wave-like structures propagating far from the source, and these so-called ‘TADs' were detected and described for the May 2003 storm for the first time. Some TADs traveled over the pole into the opposite hemisphere; this was found in both CHAMP and GRACE data. Most TADs propagate equatorward, but poleward propagating TADs have on occasion been detected too. The estimated speeds and amplitudes of the observed TADs, and their dependence on altitude and solar and geomagnetic activity in particular, will be presented in this poster.

  5. Assessing head and trunk symmetry during sleep using tri-axial accelerometers.

    PubMed

    Sato, Haruhiko; Ikura, Daiki; Tsunoda, Masahiro

    2015-03-01

    Using two types of small, lightweight tri-axial accelerometers, we obtained evidence for the effectiveness of an approach for assessing head-trunk symmetrical or asymmetrical positions during sleep. First, we assessed the accuracy of our monitoring system in five healthy young adults (age range, 22-24 years). The participants wore acceleration monitors on the sternum and forehead; then spent 5 min in six different positions. Once accuracy was confirmed, we assessed head-trunk symmetry during night-time sleep in 10 healthy children (age range, 3-13 years) and 10 young adults (age range, 21-26 years) in their home environments. All participants wore the monitors during one night's sleep in their homes. After computing head-trunk positions using the orientation data obtained by the accelerometers, head and trunk symmetry were evaluated. The head and trunk positions were correctly detected: the positional data from the trunk had 99% agreement, and the data from the head had 96% agreement. Both the young adults and children were observed to spend time with the head-trunk in asymmetric positions; however, the subjects changed position frequently so the asymmetrical postures were mobile. We concluded that the proposed monitoring system is a reliable and valid approach for assessing head-trunk symmetry during sleep at home. Implications for Rehabilitation We propose a head and trunk symmetry monitoring system using accelerometers. The proposed system could accurately identify head and trunk position. Asymmetrical positioning was seen in healthy participants but it was not immobile.

  6. The influence of nominal stress on wear factors of carbon fibre-reinforced polyetheretherketone (PEEK-OPTIMA® Wear Performance) against zirconia toughened alumina (Biolox® delta ceramic).

    PubMed

    Evans, Andrew; Horton, Henrietta; Unsworth, Anthony; Briscoe, Adam

    2014-06-01

    Carbon fibre-reinforced polyetheretherketone is an attractive alternative to ultra-high-molecular-weight polyethylene in artificial joints, but little has been published on the influence of stress on the wear factor. We know that in ultra-high-molecular-weight polyethylene, the wear factor reduces as the normal stress increases, which is counter-intuitive but very helpful in the case of non-conforming contacts. In this study, carbon fibre-reinforced polyetheretherketone (PEEK-OPTIMA(®) Wear Performance) has been investigated in a pin-on-plate machine under steady loads and under stresses typical of hip and knee joints. At stresses below about 6 MPa, wear factors are between 10 and a 100 times lower than for ultra-high-molecular-weight polyethylene but at higher stresses the wear factors increase substantially.

  7. Backside Wear Analysis of Retrieved Acetabular Liners with a Press-Fit Locking Mechanism in Comparison to Wear Simulation In Vitro

    PubMed Central

    Jäger, Marcus; Floerkemeier, Thilo; Frecher, Sven; Delank, Karl-Stefan

    2016-01-01

    Backside wear due to micromotion and poor conformity between the liner and its titanium alloy shell may contribute to the high rates of retroacetabular osteolysis and consequent aseptic loosening. The purpose of our study was to understand the wear process on the backside of polyethylene liners from two acetabular cup systems, whose locking mechanism is based on a press-fit cone in combination with a rough titanium conical inner surface on the fixation area. A direct comparison between in vitro wear simulator tests (equivalent to 3 years of use) and retrieved liners (average 13.1 months in situ) was done in order to evaluate the backside wear characteristics and behavior of these systems. Similar wear scores between in vitro tested and retrieved liners were observed. The results showed that this locking mechanism did not significantly produce wear marks at the backside of the polyethylene liners due to micromotion. In all the analyzed liners, the most common wear modes observed were small scratches at the cranial fixation zone directly below the rough titanium inner surface of the shell. It was concluded that most of the wear marks were produced during the insertion and removal of the liner, rather than during its time in situ. PMID:27722174

  8. Inhibition of erosive wear by fluoride varnish.

    PubMed

    Vieira, A; Jager, D H J; Ruben, J L; Huysmans, M C D N J M

    2007-01-01

    It has been suggested that fluoride products with a protective mechanical component are advantageous in the prevention of erosive wear. The aim of this study was to evaluate in situ the effect of fluoride varnish (FV) in the prevention of wear due to erosion and combined erosion and toothbrush abrasion. Eleven volunteers wore for 3 weeks, during working hours, appliances containing 2 control and 2 FV-treated human enamel samples. Erosion took place extraorally 3 times a day (5 min) in the soft drink Sprite. At the end of each experimental day one control and one FV sample (C-er+abr and FV-er+abr) were brushed (5 s) with fluoridated dentrifice. The remaining control and FV sample (C-er and FV-er) were left unbrushed. Enamel volume loss was quantified by optical profilometry at day 5, 10 and 15. A statistically significant progression in enamel loss was found for the C-er, C-er+abr and FV-er+abr groups (p < 0.001, p < 0.001 and p = 0.001, respectively) but not for the FV-er group (p = 0.053). The values of cumulative normalized volume loss (x10(8) mum) at day 15 were: C-er 5.53 +/- 2.14, C-er+abr 5.70 +/- 2.07, FV-er 0.79 +/- 0.67 and FV-er+abr 2.76 +/- 1.35. The FV-er and FV-er+abr groups showed significant lower volume loss than the C-er group (p < 0.001 and p = 0.005, respectively) and the C-er+abr group (p < 0.001 and p = 0.002, respectively). The results indicate that fluoride varnish is effective in the reduction of erosive wear. PMID:17167261

  9. A high and low noise model for strong motion accelerometers

    NASA Astrophysics Data System (ADS)

    Clinton, J. F.; Cauzzi, C.; Olivieri, M.

    2010-12-01

    We present reference noise models for high-quality strong motion accelerometer installations. We use continuous accelerometer data acquired by the Swiss Seismological Service (SED) since 2006 and other international high-quality accelerometer network data to derive very broadband (50Hz-100s) high and low noise models. The proposed noise models are compared to the Peterson (1993) low and high noise models designed for broadband seismometers; the datalogger self-noise; background noise levels at existing Swiss strong motion stations; and typical earthquake signals recorded in Switzerland and worldwide. The standard strong motion station operated by the SED consists of a Kinemetrics Episensor (2g clip level; flat acceleration response from 200 Hz to DC; <155dB dynamic range) coupled with a 24-bit Nanometrics Taurus datalogger. The proposed noise models are based on power spectral density (PSD) noise levels for each strong motion station computed via PQLX (McNamara and Buland, 2004) from several years of continuous recording. The 'Accelerometer Low Noise Model', ALNM, is dominated by instrument noise from the sensor and datalogger. The 'Accelerometer High Noise Model', AHNM, reflects 1) at high frequencies the acceptable site noise in urban areas, 2) at mid-periods the peak microseismal energy, as determined by the Peterson High Noise Model and 3) at long periods the maximum noise observed from well insulated sensor / datalogger systems placed in vault quality sites. At all frequencies, there is at least one order of magnitude between the ALNM and the AHNM; at high frequencies (> 1Hz) this extends to 2 orders of magnitude. This study provides remarkable confirmation of the capability of modern strong motion accelerometers to record low-amplitude ground motions with seismic observation quality. In particular, an accelerometric station operating at the ALNM is capable of recording the full spectrum of near source earthquakes, out to 100 km, down to M2. Of particular

  10. 3D Simulation Modeling of the Tooth Wear Process

    PubMed Central

    Dai, Ning; Hu, Jian; Liu, Hao

    2015-01-01

    Severe tooth wear is the most common non-caries dental disease, and it can seriously affect oral health. Studying the tooth wear process is time-consuming and difficult, and technological tools are frequently lacking. This paper presents a novel method of digital simulation modeling that represents a new way to study tooth wear. First, a feature extraction algorithm is used to obtain anatomical feature points of the tooth without attrition. Second, after the alignment of non-attrition areas, the initial homogeneous surface is generated by means of the RBF (Radial Basic Function) implicit surface and then deformed to the final homogeneous by the contraction and bounding algorithm. Finally, the method of bilinear interpolation based on Laplacian coordinates between tooth with attrition and without attrition is used to inversely reconstruct the sequence of changes of the 3D tooth morphology during gradual tooth wear process. This method can also be used to generate a process simulation of nonlinear tooth wear by means of fitting an attrition curve to the statistical data of attrition index in a certain region. The effectiveness and efficiency of the attrition simulation algorithm are verified through experimental simulation. PMID:26241942

  11. 3D Simulation Modeling of the Tooth Wear Process.

    PubMed

    Dai, Ning; Hu, Jian; Liu, Hao

    2015-01-01

    Severe tooth wear is the most common non-caries dental disease, and it can seriously affect oral health. Studying the tooth wear process is time-consuming and difficult, and technological tools are frequently lacking. This paper presents a novel method of digital simulation modeling that represents a new way to study tooth wear. First, a feature extraction algorithm is used to obtain anatomical feature points of the tooth without attrition. Second, after the alignment of non-attrition areas, the initial homogeneous surface is generated by means of the RBF (Radial Basic Function) implicit surface and then deformed to the final homogeneous by the contraction and bounding algorithm. Finally, the method of bilinear interpolation based on Laplacian coordinates between tooth with attrition and without attrition is used to inversely reconstruct the sequence of changes of the 3D tooth morphology during gradual tooth wear process. This method can also be used to generate a process simulation of nonlinear tooth wear by means of fitting an attrition curve to the statistical data of attrition index in a certain region. The effectiveness and efficiency of the attrition simulation algorithm are verified through experimental simulation.

  12. Technical note: Accuracy of an ear tag-attached accelerometer to monitor rumination and feeding behavior in feedlot cattle.

    PubMed

    Wolfger, B; Timsit, E; Pajor, E A; Cook, N; Barkema, H W; Orsel, K

    2015-06-01

    Early identification of sick cattle increases treatment success and decreases mortality. Continuous automated records of behavior can be used to identify sick cattle early in the disease process. The objective was to evaluate accuracy of an ear-attached accelerometer (SensOor) that quantified ear movements and estimated feeding and rumination time through a proprietary algorithm. Accelerometers were attached to the ear tag of 18 steers with an initial mean BW of 326 ± 46 kg. The manufacturer's proprietary software was used to determine time spent "feeding," "ruminating," "active," and "resting." Direct visual observation was used to validate the accelerometer. Sensitivity, specificity, and predictive values were calculated for rumination and feeding separately. Repeated measures were accounted for using mixed model logistic regression. Single minutes of either feeding or rumination in a run of other behavior minutes were changed to the preceding behavior. Accuracy and precision of hourly recorded feeding and rumination times were assessed using the concordance correlation coefficient adjusted for repeated measurements. Sensitivity and specificity were 95 and 76% for feeding and 49 and 96% for rumination, respectively. Concordance correlation between observations and the sensor were 0.79 (95% CI: 0.61 to 0.85) and 0.44 (95% CI: 0.23 to 0.60) for feeding and rumination, respectively. There was large variability among steers, with concordance correlations ranging from 0.09 to 0.98 for rumination time and from 0.58 to 0.96 for feeding time. We conclude that the accelerometer is a promising monitoring system for feeding behavior. PMID:26115302

  13. Wear study under plastic deformation conditions

    NASA Astrophysics Data System (ADS)

    Shukla, B. M.; Singhal, S.; Singh, D. V.

    1994-03-01

    Lubrication in metalworking processes is characterized by plastic deformation conditions resulting in generation of a large amount of virgin surface and of heat of deformation. The study of wear under these conditions is important from the point of view of product quality and tool/die wear. A laboratory study of wear under simulated plastic deformation conditions using pairs of mild steel and EN31 discs on an Amsler friction and wear testing machine was carried out. The worn surfaces and wear particles were examined by scanning electron microscopy. It was observed that wear with a mineral oil was greater than that with a vegetable oil. This paper analyzes the phenomenon through an examination of the surfaces and the wear particles.

  14. Using Accelerometer and Gyroscopic Measures to Quantify Postural Stability

    PubMed Central

    Alberts, Jay L.; Hirsch, Joshua R.; Koop, Mandy Miller; Schindler, David D.; Kana, Daniel E.; Linder, Susan M.; Campbell, Scott; Thota, Anil K.

    2015-01-01

    Context Force platforms and 3-dimensional motion-capture systems provide an accurate method of quantifying postural stability. Substantial cost, space, time to administer, and need for trained personnel limit widespread use of biomechanical techniques in the assessment of postural stability in clinical or field environments. Objective To determine whether accelerometer and gyroscope data sampled from a consumer electronics device (iPad2) provide sufficient resolution of center-of-gravity (COG) movements to accurately quantify postural stability in healthy young people. Design Controlled laboratory study. Setting Research laboratory in an academic medical center. Patients or Other Participants A total of 49 healthy individuals (age = 19.5 ± 3.1 years, height = 167.7 ± 13.2 cm, mass = 68.5 ± 17.5 kg). Intervention(s) Participants completed the NeuroCom Sensory Organization Test (SOT) with an iPad2 affixed at the sacral level. Main Outcome Measure(s) Primary outcomes were equilibrium scores from both systems and the time series of the angular displacement of the anteroposterior COG sway during each trial. A Bland-Altman assessment for agreement was used to compare equilibrium scores produced by the NeuroCom and iPad2 devices. Limits of agreement was defined as the mean bias (NeuroCom − iPad) ± 2 standard deviations. Mean absolute percentage error and median difference between the NeuroCom and iPad2 measurements were used to evaluate how closely the real-time COG sway measured by the 2 systems tracked each other. Results The limits between the 2 devices ranged from −0.5° to 0.5° in SOT condition 1 to −2.9° to 1.3° in SOT condition 5. The largest absolute value of the measurement error within the 95% confidence intervals for all conditions was 2.9°. The mean absolute percentage error analysis indicated that the iPad2 tracked NeuroCom COG with an average error ranging from 5.87% to 10.42% of the NeuroCom measurement across SOT conditions. Conclusions The i

  15. Research on novel MEMS shear beam strain gauge and PZT accelerometer based on deep RIE process

    NASA Astrophysics Data System (ADS)

    Wang, Yu

    2000-10-01

    In this thesis research, the design and processing of a shear beam strain gauge and a PZT accelerometer MEMS device have been investigated in order to understand the effects of chip geometry and processing methods on the performance of these two kinds of MEMS chips. The thesis provides a theoretical analysis using an area-moment method coupled with silicon piezoresistance characteristics to analyze the stresses and the strain state and the piezoresistance effect on the resistors that formed a Wheatstone bridge in the shear beam; the analysis also demonstrates the relation between the dimensions of key chip structures and the device sensitivity. A processing including ion implantation plus drive-in and metalization was investigated in order to attain high sensitivity and good ohmic contact characteristics for a single-step implantation process. A photolithography process, using photo resists of about 30 mum thickness, was developed and investigated for Deep RIE etching in order to form the microstructure. As a result of the design and processing work, the strain gauge device showed good linearity over a +/-300 mum/m range, good temperature characteristics over 13--54°C, low transverse sensitivity and a gauge factor 10 times larger than the foil gauge cousin. The thesis presents the processing research on PZT accelerometer. The research involved compatible process development in order to integrate a PZT capacitor structure (with thick PZT film) into the silicon microstructure. The thesis also presents investigation of wet bulk micromachining processes and Deep RIE process. The thesis discusses the process and behavior of different mask layers for different approaches. The factors that affect the aspect ratio of Si during the DRIE process are also discussed. Accelerometers showed good sensitivities (2.04 PC/g) with a bandwidth of 8kHz. Future work based on these investigations has been proposed to improve the devices performance.

  16. Validation of triaxial accelerometers to measure the lying behaviour of adult domestic horses.

    PubMed

    DuBois, C; Zakrajsek, E; Haley, D B; Merkies, K

    2015-01-01

    Examining the characteristics of an animal's lying behaviour, such as frequency and duration of lying bouts, has become increasingly relevant for animal welfare research. Triaxial accelerometers have the advantage of being able to continuously monitor an animal's standing and lying behaviour without relying on live observations or video recordings. Multiple models of accelerometers have been validated for use in monitoring dairy cattle; however, no units have been validated for use in equines. This study tested Onset Pendant G data loggers attached to the hind limb of each of two mature Standardbred horses for a period of 5 days. Data loggers were set to record their position every 20 s. Horses were monitored via live observations during the day and by video recordings during the night to compare activity against accelerometer data. All lying events occurred overnight (three to five lying bouts per horse per night). Data collected from the loggers was converted and edited using a macro program to calculate the number of bouts and the length of time each animal spent lying down by hour and by day. A paired t-test showed no significant difference between the video observations and the output from the data loggers (P=0.301). The data loggers did not distinguish standing hipshot from standing square. Predictability, sensitivity, and specificity were all >99%. This study has validated the use of Onset Pendant G data loggers to determine the frequency and duration of standing and lying bouts in adult horses when set to sample and register readings at 20 s intervals.

  17. Validation of triaxial accelerometers to measure the lying behaviour of adult domestic horses.

    PubMed

    DuBois, C; Zakrajsek, E; Haley, D B; Merkies, K

    2015-01-01

    Examining the characteristics of an animal's lying behaviour, such as frequency and duration of lying bouts, has become increasingly relevant for animal welfare research. Triaxial accelerometers have the advantage of being able to continuously monitor an animal's standing and lying behaviour without relying on live observations or video recordings. Multiple models of accelerometers have been validated for use in monitoring dairy cattle; however, no units have been validated for use in equines. This study tested Onset Pendant G data loggers attached to the hind limb of each of two mature Standardbred horses for a period of 5 days. Data loggers were set to record their position every 20 s. Horses were monitored via live observations during the day and by video recordings during the night to compare activity against accelerometer data. All lying events occurred overnight (three to five lying bouts per horse per night). Data collected from the loggers was converted and edited using a macro program to calculate the number of bouts and the length of time each animal spent lying down by hour and by day. A paired t-test showed no significant difference between the video observations and the output from the data loggers (P=0.301). The data loggers did not distinguish standing hipshot from standing square. Predictability, sensitivity, and specificity were all >99%. This study has validated the use of Onset Pendant G data loggers to determine the frequency and duration of standing and lying bouts in adult horses when set to sample and register readings at 20 s intervals. PMID:25273864

  18. Low wear partially fluorinated polyimides

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.; Hady, W. F.

    1984-01-01

    Tribological studies were conducted on five different polyimide solid bodies formulated from the diamine 2,2-bis 4-(4-aminophenoxy)phenyl hexafluoropropane (4-BDAF) and the dianhydrides pyromellitic acid (PMDS) and benzophenonetetracarboxylic acid (BTDA). The following polyimides were evaluated 4-BDAF/PMDA, 4-BDAF/BTDA, 4-BDAF/80 mole percent PMDA, 20 mole percent BTDA, 4-BDAF/60 mole percent BTDA. Friction coefficients, polyimide wear rates, polyimide surface morphology and transfer films were evaluated at sliding speeds of 0.31 to 11.6 m/s and at temperatures of 25 C to 300 C. The results indicate that the tribological properties are highly dependent on the composition of the polyimide and on the experimental conditions. Two polyimides were found which produced very low wear rates but very high friction coefficients (greater than 0.85) under ambient conditions. They offer considerable potential for high traction types of application such as brakes.

  19. Coatings for wear and lubrication

    NASA Technical Reports Server (NTRS)

    Spalvins, T.

    1978-01-01

    Recent advances in the tribological uses of rf-sputtered and ion plated films of solid film lubricants (laminar solids, soft metals, organic polymers) and wear resistant refractory compounds (carbides, nitrides, silicides) are reviewed. The sputtering and ion plating potentials and the corresponding coatings formed were evaluated relative to the friction coefficient, wear endurance life and mechanical properties. The tribological and mechanical properties for each kind of film are discussed in terms of film adherence, coherence, density, grain size, morphology, internal stresses, thickness, and substrate conditions such as temperature, topography, chemistry and dc-biasing. The ion plated metallic films in addition to improved tribological properties also have better mechanical properties such as tensile strength and fatigue life.

  20. Nuclear fuel assembly wear sleeve

    SciTech Connect

    Cadwell, D.J.; Kmonk, S.

    1983-03-08

    An improved control rod guide tube for use in a fuel assembly in a nuclear reactor. The guide tube extends the complete length of the fuel assembly and has its upper end fastened in a cylindrical housing by swaging the guide tube material into grooves formed in the housing walls. To eliminate wear on the guide tube inner walls caused by hydraulic induced vibratory forces on a control rod adapted to move therein, a thin-walled chrome plated sleeve is threaded into the top end of the guide thimble and extends downwardly a distance sufficient to be engaged by the control rod during reactor operation. The sleeve serves as a highly resistant wear surface between the control rod and walls on the guide tube in the fuel assembly.

  1. Multiple Hollow Cathode Wear Testing

    NASA Technical Reports Server (NTRS)

    Soulas, George C.

    1994-01-01

    A hollow cathode-based plasma contactor has been baselined for use on the Space Station to reduce station charging. The plasma contactor provides a low impedance connection to space plasma via a plasma produced by an arc discharge. The hollow cathode of the plasma contactor is a refractory metal tube, through which xenon gas flows, which has a disk-shaped plate with a centered orifice at the downstream end of the tube. Within the cathode, arc attachment occurs primarily on a Type S low work function insert that is next to the orifice plate. This low work function insert is used to reduce cathode operating temperatures and energy requirements and, therefore, achieve increased efficiency and longevity. The operating characteristics and lifetime capabilities of this hollow cathode, however, are greatly reduced by oxygen bearing contaminants in the xenon gas. Furthermore, an optimized activation process, where the cathode is heated prior to ignition by an external heater to drive contaminants such as oxygen and moisture from the insert absorbed during exposure to ambient air, is necessary both for cathode longevity and a simplified power processor. In order to achieve the two year (approximately 17,500 hours) continuous operating lifetime requirement for the plasma contactor, a test program was initiated at NASA Lewis Research Center to demonstrate the extended lifetime capabilities of the hollow cathode. To date, xenon hollow cathodes have demonstrated extended lifetimes with one test having operated in excess of 8000 hours in an ongoing test utilizing contamination control protocols developed by Sarver-Verhey. The objectives of this study were to verify the transportability of the contamination control protocols developed by Sarver-Verhey and to evaluate cathode contamination control procedures, activation processes, and cathode-to-cathode dispersions in operating characteristics with time. These were accomplished by conducting a 2000 hour wear test of four hollow

  2. Friction and wear behavior of aluminum and composite airplane skins

    NASA Technical Reports Server (NTRS)

    Jackson, K. E.

    1984-01-01

    Friction and wear behavior was determined for small skin specimens under abrasive loading conditions typical of those occurring on the underside of a transport airplane during emergency belly landing. A test apparatus consisting of a standard belt sander provided the sliding surface. Small test specimens constructed of aluminum, standard graphite-epoxy composite, aramid-epoxy composite, and toughened-resin composites were tested undar a range of pressures, belt velocities, and belt-surface textures. The effects of these test variables on the wear rate and the coefficient of friction are discussed and comparisons are made between the composite materials and aluminum. The effect of fiber orientation in the composite materials on wear rate was also investigated. In addition, tests were performed in which thermocouples were imbedded into the various test specimens to obtain temperature-time histories during abrasion.

  3. Wear of steel by rubber

    NASA Technical Reports Server (NTRS)

    Gent, A. N.; Pulford, C. T. R.

    1978-01-01

    Wear of a steel blade used as a scraper to abrade rubber surfaces has been found to take place much more rapidly on a cis-polyisoprene (natural rubber) surface than on a cis-polybutadiene surface, and much more rapidly in an inert atmosphere than in air. These observations are attributed to the direct attack upon steel of free-radical species generated by mechanical rupture of elastomer molecules during abrasion.

  4. Optical accelerometer based on grating interferometer with phase modulation technique.

    PubMed

    Zhao, Shuangshuang; Zhang, Juan; Hou, Changlun; Bai, Jian; Yang, Guoguang

    2012-10-10

    In this paper, an optical accelerometer based on grating interferometer with phase modulation technique is proposed. This device architecture consists of a laser diode, a sensing chip and an optoelectronic processing circuit. The sensing chip is a sandwich structure, which is composed of a grating, a piezoelectric translator and a micromachined silicon structure consisting of a proof mass and four cantilevers. The detected signal is intensity-modulated with phase modulation technique and processed with a lock-in amplifier for demodulation. Experimental results show that this optical accelerometer has acceleration sensitivity of 619 V/g and high-resolution acceleration detection of 3 μg in the linear region. PMID:23052079

  5. Guidelines for Standardized Testing of Broadband Seismometers and Accelerometers

    USGS Publications Warehouse

    Hutt, Charles R.; Evans, John R.; Followill, Fred; Nigbor, Robert L.; Wielandt, Erhard

    2010-01-01

    Testing and specification of seismic and earthquake-engineering sensors and recorders has been marked by significant variations in procedures and selected parameters. These variations cause difficulty in comparing such specifications and test results. In July 1989, and again in May 2005, the U.S. Geological Survey hosted international pub-lic/private workshops with the goal of defining widely accepted guidelines for the testing of seismological inertial sensors, seismometers, and accelerometers. The Proceedings of the 2005 workshop have been published and include as appendix 6 the report of the 1989 workshop. This document represents a collation and rationalization of a single set of formal guidelines for testing and specifying broadband seismometers and accelerometers.

  6. A simple intensity modulation based fiber-optic accelerometer

    NASA Astrophysics Data System (ADS)

    Guozhen, Yao; Yongqian, Li; Zhi, Yang

    2016-05-01

    A fiber-optic accelerometer with simple structure and high performance based on intensity modulation is proposed. Using only a length of single mode fiber compressed by a cantilever, the intensity of reflected light is modulated by the vibration acceleration applied to it. The effects of the fiber location, the dimension parameters of the cantilever on frequency response and sensitivity are investigated. The experimental results demonstrate that the accelerometer has a flat frequency response over a 4700 Hz bandwidth and a sensitivity of 21.24 mV/g with a cantilever dimension of 30 × 8 × 1.6 mm3 and a distance of 5 mm between the fiber location and the suspended cantilever end; the coefficient of determination is better than 0.999. In addition, the effect of temperature and the stability of the sensing system are investigated.

  7. A New Force Balanced Accelerometer Using Tunneling Tip Position Sensing

    NASA Technical Reports Server (NTRS)

    Zavracky, P.; Hartley, F.; Sherman, N.; Warner, K.

    1993-01-01

    In this paper, we report the initial development of a single-axis bulk micromachined accelerometer. The device employs an electron tunneling tip as a position detector in a force feedback control system. Control electrodes are placed above and below the proof mass and act as electrostatic force plates. Using the force plates, the position of the proof mass relative to the tunneling tip can be controlled.

  8. Teaching elementary mechanics using a simple 'bubble tube' accelerometer

    NASA Astrophysics Data System (ADS)

    Bunker, C. A.

    1986-09-01

    Most people would probably like a direct-reading accelerometer which will give acceleration immediately and which may be used to confirm Newton's second law quickly and simply without the need for the excessive use of ticker timers. The article describes such an instrument for use in these experiments and in many others too: in particular, it enables what might be thought of as a revolutionary approach to circular motion.

  9. The use of a heel-mounted accelerometer as an adjunct measure of slip distance.

    PubMed

    McGorry, Raymond W; DiDomenico, Angela; Chang, Chien-Chi

    2007-05-01

    A human-centered measure of floor slipperiness could be useful as an adjunct to conventional tribologic measures. This paper reports on the development and evaluation of a measure of slip distance based on variables derived from the signal of a heel-mounted accelerometer. Twenty-one participants walked on a laboratory runway under several surface slipperiness conditions at three walking speeds during a protocol designed to produce a wide range of slip distances at heel strike. Analysis of variance showed significant effects of slip distance (no-slip, micro-slip and slide), walking speed (1.52, 1.78 and 2.13 m/s) and their interactions on peak forward acceleration, peak vertical acceleration and deceleration time of the heel following heel strike in 704 trials. Regression analysis of slip distance and deceleration time showed the strongest relationship with R2=0.511. Large individual variation in the strength of this relationship was observed. The heel-mounted accelerometer may have utility as an adjunct measure in the evaluation of floor slipperiness, particularly for field applications where direct measurement may not be feasible.

  10. Determination of gait events using an externally mounted shank accelerometer.

    PubMed

    Sinclair, Jonathan; Hobbs, Sarah J; Protheroe, Laurence; Edmundson, Christopher J; Greenhalgh, Andrew

    2013-02-01

    Biomechanical analysis requires the determination of specific foot contact events. This is typically achieved using force platform information; however, when force platforms are unavailable, alternative methods are necessary. A method was developed for the determination of gait events using an accelerometer mounted to the distal tibia, measuring axial accelerations. The aim of the investigation was to determine the efficacy of this method. Sixteen participants ran at 4.0 m/s ± 5%. Synchronized tibial accelerations and vertical ground reaction forces were sampled at 1000 Hz as participants struck a force platform with their dominant foot. Events determined using the accelerometer, were compared with the corresponding events determined using the force platform. Mean errors of 1.68 and 5.46 ms for average and absolute errors were observed for heel strike and of -3.59 and 5.00 ms for toe-off. Mean and absolute errors of 5.18 and 11.47 ms were also found for the duration of the stance phase. Strong correlations (r = .96) were also observed between duration of stance obtained using the two different methods. The error values compare favorably to other alternative methods of predicting gait events. This suggests that shank-mounted accelerometers can be used to accurately and reliably detect gait events.

  11. Huygens HASI servo accelerometer: A review and lessons learned

    NASA Astrophysics Data System (ADS)

    Hathi, B.; Ball, A. J.; Colombatti, G.; Ferri, F.; Leese, M. R.; Towner, M. C.; Withers, P.; Fulchigioni, M.; Zarnecki, J. C.

    2009-10-01

    The servo accelerometer constituted a vital part of the Huygens Atmospheric Structure Instrument (HASI): flown aboard the Huygens probe, it operated successfully during the probe's entry, descent, and landing on Titan, on 14th January 2005. This paper reviews the Servo accelerometer, starting from its development/assembly in the mid-1990s, to monitoring its technical performance through its seven-year long in-flight (or cruise) journey, and finally its performance in measuring acceleration (or deceleration) upon encountering Titan's atmosphere. The aim of this article is to review the design, ground tests, in-flight tests and operational performance of the Huygens servo accelerometer. Techniques used for data analysis and lessons learned that may be useful for accelerometry payloads on future planetary missions are also addressed. The main finding of this review is that the conventional approach of having multiple channels to cover a very broad measurement range: from 10 -6g to the order of 10 g (where g=Earth's surface gravity, 9.8 m/s 2), with on-board software deciding which of the channels to telemeter depending on the magnitude of the measured acceleration, works well. However, improvements in understanding the potential effects of the sensor drifts and ageing on the measurements can be achieved in future missions by monitoring the 'scale factor' - a measure of such sensors' sensitivity, along with the already implemented monitoring of the sensor's offset during the in-flight phase.

  12. Determination of gait events using an externally mounted shank accelerometer.

    PubMed

    Sinclair, Jonathan; Hobbs, Sarah J; Protheroe, Laurence; Edmundson, Christopher J; Greenhalgh, Andrew

    2013-02-01

    Biomechanical analysis requires the determination of specific foot contact events. This is typically achieved using force platform information; however, when force platforms are unavailable, alternative methods are necessary. A method was developed for the determination of gait events using an accelerometer mounted to the distal tibia, measuring axial accelerations. The aim of the investigation was to determine the efficacy of this method. Sixteen participants ran at 4.0 m/s ± 5%. Synchronized tibial accelerations and vertical ground reaction forces were sampled at 1000 Hz as participants struck a force platform with their dominant foot. Events determined using the accelerometer, were compared with the corresponding events determined using the force platform. Mean errors of 1.68 and 5.46 ms for average and absolute errors were observed for heel strike and of -3.59 and 5.00 ms for toe-off. Mean and absolute errors of 5.18 and 11.47 ms were also found for the duration of the stance phase. Strong correlations (r = .96) were also observed between duration of stance obtained using the two different methods. The error values compare favorably to other alternative methods of predicting gait events. This suggests that shank-mounted accelerometers can be used to accurately and reliably detect gait events. PMID:23462448

  13. Optical Readout of Micro-Accelerometer Code Features

    SciTech Connect

    Dickey, Fred M.; Holswade, Scott C.; Polosky, Marc A.; Shagam, Richard N.; Sullivan, Charles T.

    1999-07-08

    Micromachine accelerometers offer a way to enable critical functions only when a system encounters a particular acceleration environment. This paper describes the optical readout of a surface micromachine accelerometer containing a unique 24-bit code. The readout uses waveguide-based optics, which are implemented as a photonic integrated circuit (PIC). The PIC is flip-chip bonded over the micromachine, for a compact package. The shuttle moves 500 {micro}m during readout, and each code element is 17 {micro}m wide. The particular readout scheme makes use of backscattered radiation from etched features in the accelerometer shuttle. The features are etched to create corner reflectors that return radiation back toward the source for a one bit. For a zero bit, the shuttle is not etched, and the radiation scatters forward, away from the detector. This arrangement provides a large signal difference between a one and zero signal, since the zero signal returns virtually no signal to the detector. It is thus superior to schemes that interrogate the code vertically, which have a limited contrast between a one and a zero. Experimental results are presented for mock shuttle features etched into a silicon substrate. To simulate the shuttle moving under a fixed PIC, a commercially available waveguide source was scanned over the mock code.

  14. Validation of mercury tip-switch and accelerometer activity sensors for identifying resting and active behavior in bears

    USGS Publications Warehouse

    Jasmine Ware,; Rode, Karyn D.; Pagano, Anthony M.; Bromaghin, Jeffrey; Charles T Robbins,; Joy Erlenbach,; Shannon Jensen,; Amy Cutting,; Nicole Nicassio-Hiskey,; Amy Hash,; Owen, Megan A.; Heiko Jansen,

    2015-01-01

    Activity sensors are often included in wildlife transmitters and can provide information on the behavior and activity patterns of animals remotely. However, interpreting activity-sensor data relative to animal behavior can be difficult if animals cannot be continuously observed. In this study, we examined the performance of a mercury tip-switch and a tri-axial accelerometer housed in collars to determine whether sensor data can be accurately classified as resting and active behaviors and whether data are comparable for the 2 sensor types. Five captive bears (3 polar [Ursus maritimus] and 2 brown [U. arctos horribilis]) were fitted with a collar specially designed to internally house the sensors. The bears’ behaviors were recorded, classified, and then compared with sensor readings. A separate tri-axial accelerometer that sampled continuously at a higher frequency and provided raw acceleration values from 3 axes was also mounted on the collar to compare with the lower resolution sensors. Both accelerometers more accurately identified resting and active behaviors at time intervals ranging from 1 minute to 1 hour (≥91.1% accuracy) compared with the mercury tip-switch (range = 75.5–86.3%). However, mercury tip-switch accuracy improved when sampled at longer intervals (e.g., 30–60 min). Data from the lower resolution accelerometer, but not the mercury tip-switch, accurately predicted the percentage of time spent resting during an hour. Although the number of bears available for this study was small, our results suggest that these activity sensors can remotely identify resting versus active behaviors across most time intervals. We recommend that investigators consider both study objectives and the variation in accuracy of classifying resting and active behaviors reported here when determining sampling interval.

  15. Development of a gear vibration indicator and its application in gear wear monitoring

    NASA Astrophysics Data System (ADS)

    Hu, Chongqing; Smith, Wade A.; Randall, Robert B.; Peng, Zhongxiao

    2016-08-01

    Gear tooth wear is an inevitable phenomenon and has a significant influence on gear dynamic features. Although vibration analysis has been widely used to diagnose localised gear tooth faults, its techniques for gear wear monitoring have not been well-established. This paper aims at developing a vibration indicator to evaluate the effects of wear on gear performance. For this purpose, a gear state vector is extracted from time synchronous averaged gear signals to describe the gear state. This gear state vector consists of the sideband ratios obtained from a number of tooth meshing harmonics and their sidebands. Then, two averaged logarithmic ratios, ALR and mALR, are defined with fixed and moving references, respectively, to provide complementary information for gear wear monitoring. Since a fixed reference is utilised in the definition of ALR, it reflects the cumulated wear effects on the gear state. An increase in the ALR value indicates that the gear state deviates further from its reference condition. With the use of a moving reference, the indicator mALR shows changes in the gear state within short time intervals, making it suitable for wear process monitoring. The efficiency of these vibration indicators is demonstrated using experimental results from two sets of tests, in which the gears experienced different wear processes. In addition to gear wear monitoring, the proposed indicators can be used as general parameters to detect the occurrence of other faults, such as a tooth crack or shaft misalignment, because these faults would also change the gear vibrations.

  16. Assessment of wear coefficients of nuclear zirconium claddings without and with pre-oxidation

    DOE PAGES

    Qu, Jun; Cooley, Kevin M.; Shaw, Austin H.; Lu, Roger Y.; Blau, Peter J.

    2016-03-16

    In the cores of pressurized water nuclear reactors, water-flow induced vibration is known to cause claddings on the fuel rods to rub against their supporting grids. Such grid-to-rod-fretting (GTRF) may lead to fretting wear-through and the leakage of radioactive species. The surfaces of actual zirconium alloy claddings in a reactor are inevitably oxidized in the high-temperature pressurized water, and some claddings are even pre-oxidized. As a result, the wear process of the surface oxide film is expected to be quite different from the zirconium alloy substrate. In this paper, we attempt to measure the wear coefficients of zirconium claddings withoutmore » and with pre-oxidation rubbing against grid samples using a bench-scale fretting tribometer. Results suggest that the volumetric wear coefficient of the pre-oxidized cladding is 50 to 200 times lower than that of the untreated cladding. In terms of the linear rate of wear depth, the pre-oxidized alloy wears about 15 times more slowly than the untreated cladding. Finally, fitted with the experimentally-determined wear rates, a stage-wise GTRF engineering wear model demonstrates good agreement with in-reactor experience in predicting the trend of cladding lives.« less

  17. A new methodology for predictive tool wear

    NASA Astrophysics Data System (ADS)

    Kim, Won-Sik

    An empirical approach to tool wear, which requires a series of machining tests for each combination of insert and work material, has been a standard practice for industries since early part of the twentieth century. With many varieties of inserts and work materials available for machining, the empirical approach is too experiment-intensive that the demand for the development of a model-based approach is increasing. With a model-based approach, the developed wear equation can be extended without additional machining experiments. The main idea is that the temperatures on the primary wear areas are increasing such that the physical properties of the tool material degrade substantially and consequently tool wear increases. Dissolution and abrasion are identified to be the main mechanisms for tool wear. Flank wear is predominantly a phenomenon of abrasion as evident by the presence of a scoring mark on the flank surface. Based on this statement, it is reasonable to expect that the flank-wear rate would increase with the content of hard inclusions. However, experimental flank wear results did not necessary correspond to the content of cementite phase present in the steels. Hence, other phenomena are believed to significantly affect wear behavior under certain conditions. When the cutting temperature in the flank interface is subjected to high enough temperatures, pearlitic structure austenizes. During the formation of a new austenitic phase, the existing carbon is dissolved into the ferrite matrix, which will reduce the abrasive action. To verify the austenitic transformation, turning tests were conducted with plain carbon steels. The machined surface areas are imaged using X-ray diffraction the Scanning Electron Microscope (SEM) and the Transmission Electron Microscope (TEM). On the other hand, crater wear occurs as a result of dissolution wear and abrasive wear. To verify the wear mechanisms of crater wear, various coating inserts as well as uncoated inserts were

  18. Wear mechanism and wear prevention in coal-fueled diesel engines. Task 3, Traditional approaches to wear prevention

    SciTech Connect

    Schwalb, J.A.

    1991-06-01

    Contamination of the lube-oil with hard abrasive particles leads to a three-body abrasive wear mechanism that highly accelerates piston ring/cylinder liner wear in coal-fueled diesel engines. One approach to reducing that wear is to modify the size and orientation of surface asperities on the cylinder to enhance the formation of a hydrodynamic film, and to provide avenues of escape for particles that would otherwise be trapped in the wear zone. Another approach is to introduce additives into the contaminated lube-oil that further enhance hydrodynamic film formation, form chemical films on the wearing surfaces, or form films on the contaminant particles. This work focuses on defining the effects of cylinder liner surface finish, various configurations of slots in the cylinder liner surface, and various additives in the contaminated lube-oil on the wear process. Wear tests were initiated in a bench apparatus using coal-ash contaminated lube-oil to test the various wear configurations. The results of these tests indicate that the formation of a hydrodynamic film between the ring and cylinder specimens is enhanced by increasing surface roughness, and by orienting the surface asperities normal to the direction of ring travel but modifications to the cylinder liner surface did not greatly reduce the wear rate. Additives to the lubricant seemed to have a much more significant effect on wear, with a dispersant additive highly accelerating the wear, while a detergent additive was able to reduce the wear almost to the rate achieved where there was no contaminant.

  19. Alternate paddle configuration for improved wear resistance in the saltstone mixer

    SciTech Connect

    Reigel, M.; Fowley, M.

    2013-09-23

    The Saltstone Production Facility has a 10-inch Readco-Kurimoto continuous mixer that mixes the premix dry feeds and low-level waste salt solution to make fresh (uncured) saltstone. Inspection of the mixer in January 2013 showed significant wear on the third, fourth and fifth paddle pairs after the conveying augers. A 2-inch Readco-Kurimoto continuous mixer was used to test alternate paddle configurations for use in the 10-inch mixer to decrease the wear rate on the paddles. Two wear tests were conducted to investigate a method of reducing wear on the mixer paddles. The first test (wear test 2a) had a paddle configuration similar to the currently installed 10-inch mixer in the SPF. This test established baseline wear. The second test (wear test 2b) had a reconfigured paddle arrangement that replaced the flat paddles with helical paddles for paddle pairs 2 - 6 and aligned paddle pair 1 with the augers. The intent of the reconfiguration was to more effectively convey the partially wetted dry feeds through the transition region and into the liquid feed where paddle wear is reduced due to dry feeds and salt solution being mixed at the intended water to premix ratio. The design of the helical paddles provides conveyance through the transition region to the liquid feed inlet. The alignment with the auger is aimed to provide a smoother transition (minimizing the discontinuity between the auger and paddle pair 1) into the downstream paddles. A soft metal with low wear resistance (6000 series aluminum) was used for the wear testing paddles to determine wear patterns while minimizing run time and maximizing wear rate. For the two paddle configurations tested using the scaled 2-inch Readco-Kurimoto continuous mixer, with the first six paddles after the augers replaced by the wear paddles and the remaining paddles were stainless steel. Since the 10-inch SPF mixer is designed with the liquid inlet centered over paddle pairs 5 and 6, the scaled 2-inch mixer was configured the

  20. Vehicle Unpaved Road Response Spectrum Acquisition Based on Accelerometer and GPS Data

    PubMed Central

    Cong, Nan; Shang, Jianzhong; Ren, Yanxi; Guo, Yao

    2012-01-01

    This paper describes a response acquisition system composed of some spindle accelerometers and a time synchronized on-board GPS receiver developed in order to collect the dynamic response of vehicle riding on an unpaved road. A method of time-space conversion for calculating the response spectrum is proposed to eliminate the adverse effect of time-varying speed, based on the transform from the equitime sampled spindle acceleration responses to equidistance sampling. By using two groups of independent distance histories acquired from GPS, a method called long-range error correction is proposed to improve the accuracy of the vehicle's distance information, which is critical for the time-space conversion. The accuracy and limitations of the system have been analyzed, and its validity has been verified by implementing the system on a wheel loader for road response spectrum measuring. This paper offers a practical approach to obtaining unpaved road response spectra for durability road simulation. PMID:23112581

  1. Vehicle unpaved road response spectrum acquisition based on accelerometer and GPS data.

    PubMed

    Cong, Nan; Shang, Jianzhong; Ren, Yanxi; Guo, Yao

    2012-01-01

    This paper describes a response acquisition system composed of some spindle accelerometers and a time synchronized on-board GPS receiver developed in order to collect the dynamic response of vehicle riding on an unpaved road. A method of time-space conversion for calculating the response spectrum is proposed to eliminate the adverse effect of time-varying speed, based on the transform from the equitime sampled spindle acceleration responses to equidistance sampling. By using two groups of independent distance histories acquired from GPS, a method called long-range error correction is proposed to improve the accuracy of the vehicle's distance information, which is critical for the time-space conversion. The accuracy and limitations of the system have been analyzed, and its validity has been verified by implementing the system on a wheel loader for road response spectrum measuring. This paper offers a practical approach to obtaining unpaved road response spectra for durability road simulation.

  2. Vehicle unpaved road response spectrum acquisition based on accelerometer and GPS data.

    PubMed

    Cong, Nan; Shang, Jianzhong; Ren, Yanxi; Guo, Yao

    2012-01-01

    This paper describes a response acquisition system composed of some spindle accelerometers and a time synchronized on-board GPS receiver developed in order to collect the dynamic response of vehicle riding on an unpaved road. A method of time-space conversion for calculating the response spectrum is proposed to eliminate the adverse effect of time-varying speed, based on the transform from the equitime sampled spindle acceleration responses to equidistance sampling. By using two groups of independent distance histories acquired from GPS, a method called long-range error correction is proposed to improve the accuracy of the vehicle's distance information, which is critical for the time-space conversion. The accuracy and limitations of the system have been analyzed, and its validity has been verified by implementing the system on a wheel loader for road response spectrum measuring. This paper offers a practical approach to obtaining unpaved road response spectra for durability road simulation. PMID:23112581

  3. Computational analysis of polyethylene wear in anatomical and reverse shoulder prostheses.

    PubMed

    Quental, C; Folgado, J; Fernandes, P R; Monteiro, J

    2015-02-01

    The wear of ultra-high molecular weight polyethylene, UHMWPE, components has been associated with the failure of joint prostheses in the hip, knee, and shoulder. Considering that in vitro experiments are generally too expensive and time-consuming, computational models are an attractive alternative to study the wear behavior of UHMWPE components. The objective of the present study was to develop a computational wear model to evaluate the wear resistance of anatomical and reverse shoulder prostheses. The effects of the wear law and the updating of the UHMWPE surface on the prediction of wear were also considered. Apart from Archard's law, a new wear law, so-called second generation law, which includes the concept of cross-shear and a pressure-independent wear factor, was considered. The wear analyses were performed considering three shoulder joint motions. The muscle and joint reaction forces applied were estimated by an inverse biomechanical model of the upper limb. The results show that abrasive wear is as important for the reverse components as it is for the anatomical. Nevertheless, the volumetric wears estimated over 1 year are within the range considered clinically desirable to reduce the risk of osteolysis. For the anatomical components, the predictions from Archard's law compare better, than those of the second generation law, to the experimental and clinical data available in the literature. Yet, the opposite result is obtained for the reverse components. From the numerical point of view, an updating procedure for the UHMWPE surface is mandatory to improve the numerical predictions. PMID:25362522

  4. Oscillatory wear tests of dental composites.

    PubMed

    Pilliar, R M; Smith, D C; Maric, B

    1984-09-01

    The wear behavior of 12 commercial restorative composites (conventional and microfilled) and an unfilled restorative material was evaluated using an in vitro wear test referred to as an oscillatory wear test. The effect of varying test conditions was evaluated in a series of preliminary experiments in order to define test conditions for material evaluation. The materials were tested after being aged in water at 37 degrees C for periods of from seven days to one year. The results indicated consistently lower wear rates for the microfilled materials as compared with those of the conventional composites. Aging did not result in significant differences in wear rates measured by this method. Scanning electron micrography of worn surfaces suggested a possible effect of filler particle shape and bonding to the matrix to explain this difference. Although the relevance of the results to clinical behavior is not yet known, the study indicated the importance of material variables on wear.

  5. A Multi-Stage Wear Model for Grid-to-Rod Fretting of Nuclear Fuel Rods

    SciTech Connect

    Blau, Peter Julian

    2014-01-01

    The wear of fuel rod cladding against the supporting structures in the cores of pressurized water nuclear reactors (PWRs) is an important and potentially costly tribological issue. Grid-to-rod fretting (GTRF), as it is known, involves not only time-varying contact conditions, but also elevated temperatures, flowing hot water, aqueous tribo-corrosion, and the embrittling effects of neutron fluences. The multi-stage, closed-form analytical model described in this paper relies on published out-of-reactor wear and corrosion data and a set of simplifying assumptions to portray the conversion of frictional work into wear depth. The cladding material of interest is a zirconium-based alloy called Zircaloy-4, and the grid support is made of a harder and more wear-resistant material. Focus is on the wear of the cladding. The model involves an incubation stage, a surface oxide wear stage, and a base alloy wear stage. The wear coefficient, which is a measure of the efficiency of conversion of frictional work into wear damage, can change to reflect the evolving metallurgical condition of the alloy. Wear coefficients for Zircaloy-4 and for a polyphase zirconia layer were back-calculated for a range of times required to wear to a critical depth. Inputs for the model, like the friction coefficient, are taken from the tribology literature in lieu of in-reactor tribological data. Concepts of classical fretting were used as a basis, but are modified to enable the model to accommodate the complexities of the PWR environment. Factors like grid spring relaxation, pre-oxidation of the cladding, multiple oxide phases, gap formation, impact, and hydrogen embrittlement are part of the problem definition but uncertainties in their relative roles limits the ability to validate the model. Sample calculations of wear depth versus time in the cladding illustrate how GTRF wear might occur in a discontinuous fashion during months-long reactor operating cycles. A means to account for grid/rod gaps

  6. Globally averaged exospheric temperatures derived from CHAMP and GRACE accelerometer measurements

    NASA Astrophysics Data System (ADS)

    Wise, J. O.; Burke, W. J.; Sutton, E. K.

    2012-04-01

    Neutral densities (ρ) inferred from accelerometer measurements on the polar-orbiting Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites are used to compile exospheric temperatures (T∞) during extended periods in 2003 and 2004 when their orbital planes were nearly parallel and at quadrature, respectively. Exospheric temperatures were first estimated using ρ-h-T∞ relationships implicit within the Jacchia models, then averaged over individual orbits. We found good agreement between the orbital-averaged T∞ obtained from CHAMP and GRACE accelerometer data as well as with globally averaged exospheric temperatures derived from drag measurements from the constellation of satellites used in the High-Accuracy Satellite Drag Model. Our analysis corrects a critical conjecture by Burke (2008) that globally averaged T∞ is essentially the same as orbit-averaged values obtained by polar-orbiting satellites, independent of the local time of their orbital planes. Unlike the symmetric 0200-1400 LT distribution of T∞ minima and maxima found in early Jacchia models, presented data indicate that the minima are located closer to the dawn meridian. We also demonstrate that the averaging technique used to estimate T∞ affects the outcomes. Statistical analyses provide an empirical basis for improving estimates of the thermosphere's total energy budget.

  7. Spend Less, Get More? Using Low-Cost Accelerometers to Calculate Building Responses

    NASA Astrophysics Data System (ADS)

    Chung, A. I.; Lawrence, J. F.; Prieto, G.; Kohler, M. D.; Cochran, E. S.

    2009-12-01

    We present a new technique for predicting the earthquake responses of various structures, and we demonstrate its effectiveness by applying the method to several buildings, including several newly instrumented buildings around the Stanford University campus. While the use of ambient noise recordings to determine structural qualities of buildings is not new, our technique produces robust results that are independent of the noise sources. The process of averaging 10-minute inter-station transfer functions for a long duration (approximately 14 days) generates robust building responses comparable to those generated with earthquake data. The method allows us to employ large volumes of data recorded from low-gain accelerometers such as those currently used by the Quake-Catcher Network. Furthermore, as we can obtain the phase information, we can Fourier transform the transfer functions into the time domain to calculate the Impulse Response Function (IRF). The IRF can then be used to approximate a building’s response to a moderate earthquake. Using small, inexpensive accelerometers means that there is the exciting potential of being able to perform minimally invasive campaign-style state-of-health monitoring for many buildings at low cost. The increased data volume will provide useful and dependable results for many structures, thereby improving our understanding of building responses.

  8. Using commodity accelerometers and gyroscopes to improve speed and accuracy of JanusVF

    NASA Astrophysics Data System (ADS)

    Hutson, Malcolm; Reiners, Dirk

    2010-01-01

    Several critical limitations exist in the currently available commercial tracking technologies for fully-enclosed virtual reality (VR) systems. While several 6DOF solutions can be adapted to work in fully-enclosed spaces, they still include elements of hardware that can interfere with the user's visual experience. JanusVF introduced a tracking solution for fully-enclosed VR displays that achieves comparable performance to available commercial solutions but without artifacts that can obscure the user's view. JanusVF employs a small, high-resolution camera that is worn on the user's head, but faces backwards. The VR rendering software draws specific fiducial markers with known size and absolute position inside the VR scene behind the user but in view of the camera. These fiducials are tracked by ARToolkitPlus and integrated by a single-constraint-at-a-time (SCAAT) filter to update the head pose. In this paper we investigate the addition of low-cost accelerometers and gyroscopes such as those in Nintendo Wii remotes, the Wii Motion Plus, and the Sony Sixaxis controller to improve the precision and accuracy of JanusVF. Several enthusiast projects have implemented these units as basic trackers or for gesture recognition, but none so far have created true 6DOF trackers using only the accelerometers and gyroscopes. Our original experiments were repeated after adding the low-cost inertial sensors, showing considerable improvements and noise reduction.

  9. Investigation of wear phenomena by microscopy

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1982-01-01

    The various wear mechanisms involved in the loss of material from metallic and nonmetallic surfaces are discussed. The results presented indicate how various microscopy techniques used in conjunction with other analytical tools can assist in the elucidation of a wear mechanism. Without question, microscopy is the single most important tool for the study of the wear of surfaces, to assess and address inherent mechanisms of the material removal process.

  10. Surface Wear Measurement Using Optical Correlation Technique

    NASA Astrophysics Data System (ADS)

    Acinger, Kresimir

    1983-12-01

    The coherent optical correlation technique was applied for measuring the surface wear of a tappet (part of car engine), worn by friction with the camshaft. It was found that maximum correlation intensity decays exponentially with the number of wear cycles (i.e. camshaft revolutions). Tappets of the same make have an identical rate of correlation decay. Tappets of different makes have different rates of correlation decay which are in agreement with observed long term wear.

  11. In-Axis and Cross-Axid Accelerometer Response in Shock Environments

    SciTech Connect

    Bateman, V.I.; Brown, F.A.

    1999-03-10

    The characteristics of a piezoresistive accelerometer in shock environments have been studied at Sandia National Laboratories (SNL) in the Mechanical Shock Testing Laboratory for ten years The SNL Shock Laboratory has developed a capability to characterize accelerometers and other transducers with shocks aligned with the transducer's sensing axis and perpendicular to the transducer's sensing axis. This unique capability includes Hopkinson bars made of aluminum, steel, titanium, and beryllium. The bars are configured as both single and split Hopkinson bars. Four different areas that conclude this study are summarized in this paper: characterization of the cross-axis response of the accelerometer in the four environments of static compression, static strain on a beam, dynamic strain, and mechanical shock, the accelerometer's response on a titanium Hopkinson bar with two 45{degree} flats on the end of the bar; failure analysis of the accelerometer; and measurement of the accelerometer's self-generating cable response in a shock environment.

  12. Abrasive Wear Study of NiCrFeSiB Flame Sprayed Coating

    NASA Astrophysics Data System (ADS)

    Sharma, Satpal

    2013-10-01

    In the present study, abrasive wear behavior of NiCrFeSiB alloy coating on carbon steel was investigated. The NiCrFeSiB coating powder was deposited by flame spraying process. The microstructure, porosity and hardness of the coatings were evaluated. Elemental mapping was carried out in order to study the distribution of various elements in the coating. The abrasive wear behavior of these coatings was investigated under three normal loads (5, 10 and 15 N) and two abrasive grit sizes (120 and 320 grit). The abrasive wear rate was found to increase with the increase of load and abrasive size. The abrasive wear resistance of coating was found to be 2-3 times as compared to the substrate. Analysis of the scanning electron microscope images revealed cutting and plowing as the material removal mechanisms in these coatings under abrasive wear conditions used in this investigation.

  13. High Temperature Erosive Wear Study of NiCrFeSiB Flame Sprayed Coatings

    NASA Astrophysics Data System (ADS)

    Sharma, S.

    2012-04-01

    In the present work erosive wear behavior of NiCrFeSiB coating deposited by flame spraying process was studied. The microstructure, porosity and hardness of the coatings have been evaluated. The high temperature (150, 300 and 450 °C) erosive wear behavior of these coatings was studied under 30, 60 and 90° impact angles against 30, 45 and 60 m/s velocity. The erosive wear was found to increase with the increase in velocity of the erodent and decrease with the increase of impact angle. The erosive wear resistance of the coating is higher than the substrate. The erosive wear of the coating was 4-5 times lower than the substrate. Scanning Electron Microscopy (SEM) analysis was carried out to determine the material removal mechanisms. The ductile fracture and platelets were revealed as the material removal mechanisms in these coatings.

  14. CCLRU standards for success of daily and extended wear contact lenses.

    PubMed

    Terry, R L; Schnider, C M; Holden, B A; Cornish, R; Grant, T; Sweeney, D; La Hood, D; Back, A

    1993-03-01

    Success in contact lens wear is often judged on the basis of patient "survival" rather than the achievement of satisfactory performance based on specific criteria. In 1971, Sarver and Harris defined a series of standards for successful polymethyl methacrylate (PMMA) lens wear which incorporated criteria for wearing time, comfort, vision, ocular tissue changes, and patient appearance. In this paper we propose a revision of these criteria based on current understanding of the ocular response to contact lens wear. These revised CCLRU (Cornea and Contact Lens Research Unit) standards for success are intended as realistic performance objectives, and can be applied in clinical trials to evaluate and compare the clinical performance of present and future rigid and soft contact lenses, worn for daily and extended wear. PMID:8483586

  15. Surface chemical modification for exceptional wear life of MEMS materials

    NASA Astrophysics Data System (ADS)

    Singh, R. Arvind; Satyanarayana, N.; Sinha, Sujeet Kumar

    2011-12-01

    Micro-Electro-Mechanical-Systems (MEMS) are built at micro/nano-scales. At these scales, the interfacial forces are extremely strong. These forces adversely affect the smooth operation and cause wear resulting in the drastic reduction in wear life (useful operating lifetime) of actuator-based devices. In this paper, we present a surface chemical modification method that reduces friction and significantly extends the wear life of the two most popular MEMS structural materials namely, silicon and SU-8 polymer. The method includes surface chemical treatment using ethanolamine-sodium phosphate buffer, followed by coating of perfluoropolyether (PFPE) nanolubricant on (i) silicon coated with SU-8 thin films (500 nm) and (ii) MEMS process treated SU-8 thick films (50 μm). After the surface chemical modification, it was observed that the steady-state coefficient of friction of the materials reduced by 4 to 5 times and simultaneously their wear durability increased by more than three orders of magnitude (> 1000 times). The significant reduction in the friction coefficients is due to the lubrication effect of PFPE nanolubricant, while the exceptional increase in their wear life is attributed to the bonding between the -OH functional group of ethanolamine treated SU-8 thin/thick films and the -OH functional group of PFPE. The surface chemical modification method acts as a common route to enhance the performance of both silicon and SU-8 polymer. It is time-effective (process time ≤ 11 min), cost-effective and can be readily integrated into MEMS fabrication/assembly processes. It can also work for any kind of structural material from which the miniaturized devices are/can be made.

  16. Volumetric wear of various orthotic appliance materials.

    PubMed

    Issar-Grill, Noana; Roberts, Howard W; Wright, Edward F; Dixon, Sara A; Vandewalle, Kraig S

    2013-10-01

    The purpose of this study was to compare the resistance to wear of six commonly used orthotic appliance materials. These materials were: SR Ivocap (Ivoclar Vivadent, Inc., Amherst, NY), Eclipse (Dentsply International, York, PA), ProBase (Ivoclar Vivadent), Valplast (Valplast International Corp., Oceanside, NY), Impak (CMP Industries LLC, Albany, NY), and Clearsplint (Astron Dental Corp., Lake Zurich, IL). Twelve cylindrical specimens of each material were fabricated per manufacturer instructions. Occlusal wear was simulated in a custom-made wear simulator with each specimen receiving four wear scars in a two-body wear simulation using a 1.5 mm tungsten-carbide tipped stylus at 40 newtons for 2500 cycles at 1 Hz, while immersed in 37 degrees C distilled water (n = 48). The specimens were evaluated before and after wear testing using a three-dimensional (3D) noncontact profilometer (Proscan 2000, Scantron Corp., Eagan, MN). A mean change in volume was determined for each orthotic material. Results found that Clearsplint material displayed the greatest amount of volume loss/wear, while SR Ivocap, Eclipse, and ProBase materials had the least amount of wear. Valplast and Impak performed more moderately. Based upon this wear knowledge, practitioners are able to more reliably choose the appliance material necessary for their various patients. PMID:24308100

  17. Wear Performance of Laser Processed Tantalum Coatings

    PubMed Central

    Dittrick, Stanley; Balla, Vamsi Krishna; Bose, Susmita; Bandyopadhyay, Amit

    2011-01-01

    This first generation investigation evaluates the in vitro tribological performance of laser-processed Ta coatings on Ti for load-bearing implant applications. Linear reciprocating wear tests in simulated body fluid showed one order of magnitude less wear rate, of the order of 10−4mm3(N.m)−1, for Ta coatings compared to Ti. Our results demonstrate that Ta coatings can potentially minimize the early-stage bone-implant interface micro-motion induced wear debris generation due to their excellent bioactivity comparable to that of hydroxyapatite (HA), high wear resistance and toughness compared to popular HA coatings. PMID:22058608

  18. Predicting and preventing casing wear while drilling

    SciTech Connect

    Perdue, J.M.

    1998-06-01

    Drillpipe rotating inside a well`s intermediate string of casing has long been recognized as the principal cause of internal casing wear. Because today`s wells are longer and deeper than ever, prolonged contact can cause sufficient wear to either breach the casing or weaken it to the extent that it will rupture when the casing is pressure tested, delaying the project while an unplanned tieback casing string is installed. Based on more than 300 casing wear experiments, a computer program was developed to calculate the potential for casing wear during drilling operations. Taking proper precautions can save operators more than $1 million per well.

  19. Comparative gravimetric wear analysis in mobile versus fixed-bearing posterior stabilized total knee prostheses.

    PubMed

    Delport, Hendrik P; Sloten, Jos Vander; Bellemans, Johan

    2010-06-01

    Polyethylene (PE) wear is the limiting factor for the longevity of a conventional total knee arthroplasty (TKA). Excessive wear leads to loosening and eventual implant failure. The aim of our in vitro study was to investigate wear of a PE tibial insert on a rotating platform as compared to the same insert fixed to the tibial baseplate and articulating with a similar femoral component. All tests were performed at Endolab Laboratories, Rosenheim, Germany using a knee joint simulator following ISO 14243-1. Three specific configurations were tested and compared to a loaded soak control: (1) the rotating platform using machined polyethylene (PE), (2) fixed bearing using machined PE, (3) fixed bearing using compression-moulded PE. Calf serum with a high protein concentration of 30 g/l was chosen as test lubricant. PE wear was measured gravimetrically using the ISO 14243-2 protocol. The total wear rates found for all systems tested were low. The mean wear rate was 1.40 mg per million cycles for the moulded fixed bearing, 4.07 mg per million cycles for the machined fixed bearing type and 0.82 mg per million cycles for the machined rotating platform bearing type. We conclude that the TKA system we tested (Performance, Biomet, Warsaw, IND, USA) demonstrated very low gravimetric wear. The wear rate of the same implant in the fixed mode compared to the rotating platform mode was four times higher.

  20. Fault sensitivity and wear-out analysis of VLSI systems

    NASA Astrophysics Data System (ADS)

    Choi, Gwan Seung

    1994-07-01

    This thesis describes simulation approaches to conduct fault sensitivity and wear-out failure analysis of VLSI systems. A fault-injection approach to study transient impact in VLSI systems is developed. Through simulated fault injection at the device level and, subsequent fault propagation at the gate functional and software levels, it is possible to identify critical bottlenecks in dependability. Techniques to speed up the fault simulation and to perform statistical analysis of fault-impact are developed. A wear-out simulation environment is also developed to closely mimic dynamic sequences of wear-out events in a device through time, to localize weak location/aspect of target chip and to allow generation of TTF (Time-to-failure) distribution of VLSI chip as a whole. First, an accurate simulation of a target chip and its application code is performed to acquire trace data (real workload) on switch activity. Then, using this switch activity information, wear-out of the each component in the entire chip is simulated using Monte Carlo techniques.

  1. Development of a quartz digital accelerometer for environmental sensing and navigation applications

    SciTech Connect

    Kass, W.J.; Vianco, P.T.

    1993-03-01

    A quartz digital accelerometer has been developed which uses double ended tuning forks as the active sensing elements. The authors have demonstrated the ability of this accelerometer to be capable of acceleration measurements between {+-}150G with {+-}0.5G accuracy. They have further refined the original design and assembly processes to produce accelerometers with < 1mG stability in inertial measurement applications. This report covers the development, design, processing, assembly, and testing of these devices.

  2. Acquisition and analysis of accelerometer data

    NASA Technical Reports Server (NTRS)

    Verges, Keith R.

    1990-01-01

    Acceleration data reduction must be undertaken with a complete understanding of the physical process, the means by which the data are acquired, and finally, the calculations necessary to put the data into a meaningful format. Discussed here are the acceleration sensor requirements dictated by the measurements desired. Sensor noise, dynamic range, and linearity will be determined from the physical parameters of the experiment. The digitizer requirements are discussed. Here the system from sensor to digital storage medium will be integrated, and rules of thumb for experiment duration, filter response, and number of bits are explained. Data reduction techniques after storage are also discussed. Time domain operations including decimating, digital filtering, and averaging are covered, as well as frequency domain methods, including windowing and the difference between power and amplitude spectra, and simple noise determination via coherence analysis. Finally, an example experiment using the Teledyne Geotech Model 44000 Seismometer to measure from 1 Hz to 10(exp -6) Hz is discussed. The sensor, data acquisition system, and example spectra are presented.

  3. Calibration and Validation of a Wrist- and Hip-Worn Actigraph Accelerometer in 4-Year-Old Children

    PubMed Central

    Johansson, Elin; Larisch, Lisa-Marie; Marcus, Claude; Hagströmer, Maria

    2016-01-01

    Introduction To determine time spent at different physical activity intensities, accelerometers need calibration. The aim of this study was to develop and cross-validate intensity thresholds for the Actigraph GT3X+ accelerometer for wrist and hip placement in four-year-old children. Methods In total 30 children (49 months, SD 3.7) were recruited from five preschools in Stockholm. Equipped with an accelerometer on the wrist and another on the hip, children performed three indoor activities and one free-play session while being video recorded. Subsequently, physical activity intensity levels were coded every 5th second according to the Children’s Activity Rating Scale. Receiver Operating Characteristic (ROC) curves was used to develop wrist and hip intensity thresholds, the upper threshold for sedentary, and lower threshold for moderate-to-vigorous physical activity (MVPA), for the vertical axis (VA) and for the vector magnitude (VM). A leave-one-out method was used to cross-validate the thresholds. Results Intensity thresholds for wrist placement were ≤ 178 (VA) and ≤ 328 (VM) for sedentary and ≥ 871 (VA) and ≥ 1393 (VM) counts/5 seconds for MVPA. The corresponding thresholds for hip placement were ≤ 43 (VA) and ≤ 105 (VM) for sedentary and ≥ 290 (VA) and ≥ 512 (VM) for MVPA. The quadratic weighted Kappa was 0.92 (95% CI 0.91–0.93) (VA) and 0.95 (95% CI 0.94–0.96) (VM) for the wrist-worn accelerometer and 0.76 (98% CI 0.74–0.77) and 0.86 (95% CI 0.85–0.87) for the hip-worn. Conclusion Using wrist placement and the VM when measuring physical activity with accelerometry in 4-year-old children is recommended. PMID:27617962

  4. A method for extracting human gait series from accelerometer signals based on the ensemble empirical mode decomposition

    NASA Astrophysics Data System (ADS)

    Fu, Mao-Jing; Zhuang, Jian-Jun; Hou, Feng-Zhen; Zhan, Qing-Bo; Shao, Yi; Ning, Xin-Bao

    2010-05-01

    In this paper, the ensemble empirical mode decomposition (EEMD) is applied to analyse accelerometer signals collected during normal human walking. First, the self-adaptive feature of EEMD is utilised to decompose the accelerometer signals, thus sifting out several intrinsic mode functions (IMFs) at disparate scales. Then, gait series can be extracted through peak detection from the eigen IMF that best represents gait rhythmicity. Compared with the method based on the empirical mode decomposition (EMD), the EEMD-based method has the following advantages: it remarkably improves the detection rate of peak values hidden in the original accelerometer signal, even when the signal is severely contaminated by the intermittent noises; this method effectively prevents the phenomenon of mode mixing found in the process of EMD. And a reasonable selection of parameters for the stop-filtering criteria can improve the calculation speed of the EEMD-based method. Meanwhile, the endpoint effect can be suppressed by using the auto regressive and moving average model to extend a short-time series in dual directions. The results suggest that EEMD is a powerful tool for extraction of gait rhythmicity and it also provides valuable clues for extracting eigen rhythm of other physiological signals.

  5. Relationships between vocal function measures derived from an acoustic microphone and a subglottal neck-surface accelerometer

    PubMed Central

    Mehta, Daryush D.; Van Stan, Jarrad H.; Hillman, Robert E.

    2016-01-01

    Monitoring subglottal neck-surface acceleration has received renewed attention due to the ability of low-profile accelerometers to confidentially and noninvasively track properties related to normal and disordered voice characteristics and behavior. This study investigated the ability of subglottal neck-surface acceleration to yield vocal function measures traditionally derived from the acoustic voice signal and help guide the development of clinically functional accelerometer-based measures from a physiological perspective. Results are reported for 82 adult speakers with voice disorders and 52 adult speakers with normal voices who produced the sustained vowels /a/, /i/, and /u/ at a comfortable pitch and loudness during the simultaneous recording of radiated acoustic pressure and subglottal neck-surface acceleration. As expected, timing-related measures of jitter exhibited the strongest correlation between acoustic and neck-surface acceleration waveforms (r ≤ 0.99), whereas amplitude-based measures of shimmer correlated less strongly (r ≤ 0.74). Additionally, weaker correlations were exhibited by spectral measures of harmonics-to-noise ratio (r ≤ 0.69) and tilt (r ≤ 0.57), whereas the cepstral peak prominence correlated more strongly (r ≤ 0.90). These empirical relationships provide evidence to support the use of accelerometers as effective complements to acoustic recordings in the assessment and monitoring of vocal function in the laboratory, clinic, and during an individual’s daily activities. PMID:27066520

  6. Heat stress while wearing long pants or shorts under firefighting protective clothing.

    PubMed

    McLellan, T M; Selkirk, G A

    2004-01-15

    It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8 km x h(-1), 5% grade), moderate (M, 4.5 km x h(-1), 2.5% grade), light (L, 4.5 km x h(-1)) or very light (VL, 2.5 km x h(-1)) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35 degrees C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (Tre) or heart rate response during heavy or moderate exercise where exposure times were less than 1 h (40.8 +/- 5.8 and 53.5 +/- 9.2 min for H and M, respectively while wearing P, and 43.5 +/- 5.3 and 54.2 +/- 8.4 min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise Tre was reduced by as much as 0.4 degrees C after 80 min of exercise while wearing S. Exposure times were significantly increased from 65.8 +/- 9.6 and 83.5 +/- 11.6 min during L and VL, respectively while wearing P to 73.3 +/- 8.4 and 97.0 +/- 12.5 min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10 - 15% during light exercise. However, during heavier exercise where exposure times were less than 1 h replacing P with S was of little benefit.

  7. Wear of highly crosslinked polyethylene acetabular components

    PubMed Central

    Callary, Stuart A; Solomon, Lucian B; Holubowycz, Oksana T; Campbell, David G; Munn, Zachary; Howie, Donald W

    2015-01-01

    Background and purpose Wear rates of highly crosslinked polyethylene (XLPE) acetabular components have varied considerably between different published studies. This variation is in part due to the different techniques used to measure wear and to the errors inherent in measuring the relatively low amounts of wear in XLPE bearings. We undertook a scoping review of studies that have examined the in vivo wear of XLPE acetabular components using the most sensitive method available, radiostereometric analysis (RSA). Methods A systematic search of the PubMed, Scopus, and Cochrane databases was performed to identify published studies in which RSA was used to measure wear of XLPE components in primary total hip arthroplasty (THA). Results 18 publications examined 12 primary THA cohorts, comprising only 260 THAs at 2–10 years of follow-up. The mean or median proximal wear rate reported ranged from 0.00 to 0.06 mm/year. However, differences in the manner in which wear was determined made it difficult to compare some studies. Furthermore, differences in RSA methodology between studies, such as the use of supine or standing radiographs and the use of beaded or unbeaded reference segments, may limit future meta-analyses examining the effect of patient and implant variables on wear rates. Interpretation This scoping review confirmed the low wear rates of XLPE in THA, as measured by RSA. We make recommendations to enhance the standardization of reporting of RSA wear results, which will facilitate early identification of poorly performing implants and enable a better understanding of the effects of surgical and patient factors on wear. PMID:25301435

  8. Interest of the MICROSTAR Accelerometer to improve the GRASP Mission.

    NASA Astrophysics Data System (ADS)

    Perrot, E.; Lebat, V.; Foulon, B.; Christophe, B.; Liorzou, F.; Huynh, P. A.

    2015-12-01

    The Geodetic Reference Antenna in Space (GRASP) is a micro satellite mission concept proposed by JPL to improve the definition of the Terrestrial Reference Frame (TRF). GRASP collocates GPS, SLR, VLBI, and DORIS sensors on a dedicated spacecraft in order to establish precise and stable ties between the key geodetic techniques used to define and disseminate the TRF. GRASP also offers a space-based reference antenna for the present and future Global Navigation Satellite Systems (GNSS). By taking advantage of the new testing possibilities offer by the catapult facility at the ZARM drop tower, the ONERA's space accelerometer team proposes an up-dated version, called MICROSTAR, of its ultra sensitive electrostatic accelerometers which have contributed to the success of the last Earth's gravity missions GRACE and GOCE. Built around a cubic proof-mass, it provides the 3 linear accelerations with a resolution better than 10-11 ms-2/Hz1/2 into a measurement bandwidth between 10-3 Hz and 0.1 Hz and the 3 angular accelerations about its 3 orthogonal axes with 5´10-10 rad.s-2/Hz1/2 resolution. Integrated at the centre of mass of the satellite, MICROSTAR improves the Precise Orbit Determination (POD) by accurate measurement of the non-gravitational force acting on the satellite. It offers also the possibility to calibrate the change in the position of the satellite center of mass with an accuracy better than 100 μm as demonstrated in the GRACE mission. Assuming a sufficiently rigid structure between the antennas and the accelerometer, its data can participate to reach the mission objective of 1 mm precision for the TRF position.

  9. MEMS capacitive accelerometer-based middle ear microphone.

    PubMed

    Young, Darrin J; Zurcher, Mark A; Semaan, Maroun; Megerian, Cliff A; Ko, Wen H

    2012-12-01

    The design, implementation, and characterization of a microelectromechanical systems (MEMS) capacitive accelerometer-based middle ear microphone are presented in this paper. The microphone is intended for middle ear hearing aids as well as future fully implantable cochlear prosthesis. Human temporal bones acoustic response characterization results are used to derive the accelerometer design requirements. The prototype accelerometer is fabricated in a commercial silicon-on-insulator (SOI) MEMS process. The sensor occupies a sensing area of 1 mm × 1 mm with a chip area of 2 mm × 2.4 mm and is interfaced with a custom-designed low-noise electronic IC chip over a flexible substrate. The packaged sensor unit occupies an area of 2.5 mm × 6.2 mm with a weight of 25 mg. The sensor unit attached to umbo can detect a sound pressure level (SPL) of 60 dB at 500 Hz, 35 dB at 2 kHz, and 57 dB at 8 kHz. An improved sound detection limit of 34-dB SPL at 150 Hz and 24-dB SPL at 500 Hz can be expected by employing start-of-the-art MEMS fabrication technology, which results in an articulation index of approximately 0.76. Further micro/nanofabrication technology advancement is needed to enhance the microphone sensitivity for improved understanding of normal conversational speech.

  10. Distributed Computing and MEMS Accelerometers: The Quake Catcher Network

    NASA Astrophysics Data System (ADS)

    Lawrence, J. F.; Cochran, E. S.; Christensen, C.; Jakka, R. S.

    2008-12-01

    Recent advances in distributed computing provide exciting opportunities for seismic data collection. We are in the early stages of implementing a high density, low cost strong-motion network for rapid response and early warning by placing accelerometers in schools, homes, offices, government buildings, fire houses and more. The Quake Catcher Network (QCN) employs existing networked laptops and desktops to form a dense, distributed computing seismic network. Costs for this network are minimal because the QCN uses 1) strong motion sensors (accelerometers) already internal to many laptops and 2) low-cost universal serial bus (USB) accelerometers for use with desktops. The Berkeley Open Infrastructure for Network Computing (BOINC!) provides a free, proven paradigm for involving the public in large-scale computational research projects. The QCN leverages public participation to fully implement the seismic network. As such engaging the public to participate in seismic data collection is not only an integral part of the project, but an added value to the QCN. The software provides the client-user with a screen-saver displaying seismic data recorded on their laptop or recently detected earthquakes. Furthermore, this project installs sensors in K-12 classrooms as an educational tool for teaching science. Through a variety of interactive experiments students can learn about earthquakes and the hazards earthquakes pose. In the first six months of limited release of the QCN software, we successfully received triggers and waveforms from laptops near the M 4.7 April 25, 2008 earthquake in Reno, Nevada and the M 5.4 July 29, 2008 earthquake in Chino, California (as well as a few 3.6 and higher events). This fall we continued to expand the network further by installing seismometers in K-12 schools, museums, and government buildings in the greater Los Angeles basin and the San Francisco Bay Area. By summer 2009 we expect to have 1000 USB sensors deployed in California, in addition

  11. Piezoelectric Shaker Development for High Frequency Calibration of Accelerometers

    SciTech Connect

    Payne, Bev; Harper, Kari K.; Vogl, Gregory W.

    2010-05-28

    Calibration of vibration transducers requires sinusoidal motion over a wide frequency range with low distortion and low cross-axial motion. Piezoelectric shakers are well suited to generate such motion and are suitable for use with laser interferometric methods at frequencies of 3 kHz and above. An advantage of piezoelectric shakers is the higher achievable accelerations and displacement amplitudes as compared to electro-dynamic (ED) shakers. Typical commercial ED calibration shakers produce maximum accelerations from 100 m/s{sup 2} to 500 m/s{sup 2}. Very large ED shakers may produce somewhat higher accelerations but require large amplifiers and expensive cooling systems to dissipate heat. Due to the limitations in maximum accelerations by ED shakers at frequencies above 5 kHz, the amplitudes of the generated sinusoidal displacement are frequently below the resolution of laser interferometers used in primary calibration methods. This limits the usefulness of ED shakers in interferometric based calibrations at higher frequencies.Small piezoelectric shakers provide much higher acceleration and displacement amplitudes for frequencies above 5 kHz, making these shakers very useful for accelerometer calibrations employing laser interferometric measurements, as will be shown in this paper. These piezoelectric shakers have been developed and used at NIST for many years for high frequency calibration of accelerometers. This paper documents the construction and performance of a new version of these shakers developed at NIST for the calibration of accelerometers over the range of 3 kHz to 30 kHz and possibly higher. Examples of typical calibration results are also given.

  12. ISA accelerometer onboard the Mercury Planetary Orbiter: error budget

    NASA Astrophysics Data System (ADS)

    Iafolla, Valerio; Lucchesi, David M.; Nozzoli, Sergio; Santoli, Francesco

    2007-03-01

    We have estimated a preliminary error budget for the Italian Spring Accelerometer (ISA) that will be allocated onboard the Mercury Planetary Orbiter (MPO) of the European Space Agency (ESA) space mission to Mercury named BepiColombo. The role of the accelerometer is to remove from the list of unknowns the non-gravitational accelerations that perturb the gravitational trajectory followed by the MPO in the strong radiation environment that characterises the orbit of Mercury around the Sun. Such a role is of fundamental importance in the context of the very ambitious goals of the Radio Science Experiments (RSE) of the BepiColombo mission. We have subdivided the errors on the accelerometer measurements into two main families: (i) the pseudo-sinusoidal errors and (ii) the random errors. The former are characterised by a periodic behaviour with the frequency of the satellite mean anomaly and its higher order harmonic components, i.e., they are deterministic errors. The latter are characterised by an unknown frequency distribution and we assumed for them a noise-like spectrum, i.e., they are stochastic errors. Among the pseudo-sinusoidal errors, the main contribution is due to the effects of the gravity gradients and the inertial forces, while among the random-like errors the main disturbing effect is due to the MPO centre-of-mass displacements produced by the onboard High Gain Antenna (HGA) movements and by the fuel consumption and sloshing. Very subtle to be considered are also the random errors produced by the MPO attitude corrections necessary to guarantee the nadir pointing of the spacecraft. We have therefore formulated the ISA error budget and the requirements for the satellite in order to guarantee an orbit reconstruction for the MPO spacecraft with an along-track accuracy of about 1 m over the orbital period of the satellite around Mercury in such a way to satisfy the RSE requirements.

  13. Effects of dielectric charging on the output voltage of a capacitive accelerometer

    NASA Astrophysics Data System (ADS)

    Qu, Hao; Yu, Huijun; Zhou, Wu; Peng, Bei; Peng, Peng; He, Xiaoping

    2016-11-01

    Output voltage drifting observed in one typical capacitive microelectromechanical system (MEMS) accelerometer is discussed in this paper. Dielectric charging effect is located as one of the major determinants of this phenomenon through a combination of experimental and theoretical studies. A theoretical model for the electromechanical effects of the dielectric surface charges within the electrode gap is established to analyze the dielectric charge effect on the output voltage. Observations of output voltage drift against time are fitted to this model in order to estimate the possible dielectric layer thickness. Meanwhile, Auger electron spectroscopy is carried out to analyze the electrode surface material composition and confirms a mixture layer of dielectric SiO2 and Si with a thickness about 5 nm, which is very close to the model estimation. In addition, observation of time-varing output drift in the variable bias voltage experiment indicates the movement of dielectric charge can be controlled by the applied electric field.

  14. Speed estimation from a tri-axial accelerometer using neural networks.

    PubMed

    Song, Yoonseon; Shin, Seungchul; Kim, Seunghwan; Lee, Doheon; Lee, Kwang H

    2007-01-01

    We propose a speed estimation method with human body accelerations measured on the chest by a tri-axial accelerometer. To estimate the speed we segmented the acceleration signal into strides measuring stride time, and applied two neural networks into the patterns parameterized from each stride calculating stride length. The first neural network determines whether the subject walks or runs, and the second neural network with different node interactions according to the subject's status estimates stride length. Walking or running speed is calculated with the estimated stride length divided by the measured stride time. The neural networks were trained by patterns obtained from 15 subjects and then validated by 2 untrained subjects' patterns. The result shows good agreement between actual and estimated speeds presenting the linear correlation coefficient r=0.9874. We also applied the method to the real field and track data.

  15. Rapid tremor frequency assessment with the iPhone accelerometer.

    PubMed

    Joundi, Raed A; Brittain, John-Stuart; Jenkinson, Ned; Green, Alexander L; Aziz, Tipu

    2011-05-01

    The physician is often seeking more efficient ways of performing patient assessments. Currently, measuring tremor frequency requires expensive and bulky equipment. We propose the use of the in-built accelerometer of the iPhone via the iSeismo application for rapid measurement of tremor frequency. We use this device in a series of 7 different tremor cases, and show that the frequency measurements on the iSeismo graph closely match the more sophisticated EMG analysis during tremor. This is a preliminary confirmation of the usefulness of this device in the clinical setting for quick assessment of the dominant frequency component in a variety of tremors. PMID:21300563

  16. Accelerometer Placement for the International Space Station Node Modal Test

    NASA Technical Reports Server (NTRS)

    Tinker, Michael L.

    1998-01-01

    Accelerometer location analysis for the modal survey test of the International Space Station Node is described. Three different approaches were utilized: (1) Guyan reduction; (2) Iterative Guyan reduction; and (3) The average driving point residue (ADPR) method. Both Guyan approaches worked well, but poor results were observed for the ADPR method. Although the iterative Guyan approach appears to provide the best set of sensor locations, it is intensive computationally, becoming impractical for large initial location sets. While this is computer dependent, it appears that initial sets larger than about 1500 degrees of freedom are impractical for the iterative technique.

  17. Macro- to nanoscale wear prevention via molecular adsorption.

    PubMed

    Asay, David B; Dugger, Michael T; Ohlhausen, James A; Kim, Seong H

    2008-01-01

    As the size of mechanical systems shrinks from macro- to nanoscales, surface phenomena such as adhesion, friction, and wear become increasingly significant. This paper demonstrates the use of alcohol adsorption as a means of continuously replenishing the lubricating layer on the working device surfaces and elucidates the tribochemical reaction products formed in the sliding contact region. Friction and wear of native silicon oxide were studied over a wide range of length scales from macro- to nanoscales using a ball-on-flat tribometer (millimeter scale), sidewall microelectromechanical system (MEMS) tribometer (micrometer scale), and atomic force microscopy (nanometer scale). In all cases, the alcohol vapor adsorption successfully lubricated and prevented wear. Imaging time-of-flight secondary ion mass spectrometry analysis of the sliding contact region revealed that high molecular weight oligomeric species were formed via tribochemical reactions of the adsorbed linear alcohol molecules. These tribochemical products seemed to enhance the lubrication and wear prevention. In the case of sidewall MEMS tests, the lifetime of the MEMS device was radically increased via vapor-phase lubrication with alcohol.

  18. Macro- to nanoscale wear prevention via molecular adsorption.

    SciTech Connect

    Kim, Seong H.; Asay, David B.; Dugger, Michael Thomas; Ohlhausen, James Anthony

    2007-04-01

    As the size of mechanical systems shrinks from macro- to nanoscales, surface phenomena such as adhesion, friction, and wear become increasingly significant. This paper demonstrates the use of alcohol adsorption as a means of continuously replenishing the lubricating layer on the working device surfaces and elucidates the tribochemical reaction products formed in the sliding contact region. Friction and wear of native silicon oxide were studied over a wide range of length scales from macro- to nanoscales using a ball-on-flat tribometer (millimeter scale), sidewall microelectromechanical system (MEMS) tribometer (micrometer scale), and atomic force microscopy (nanometer scale). In all cases, the alcohol vapor adsorption successfully lubricated and prevented wear. Imaging time-of-flight secondary ion mass spectrometry analysis of the sliding contact region revealed that high molecular weight oligomeric species were formed via tribochemical reactions of the adsorbed linear alcohol molecules. These tribochemical products seemed to enhance the lubrication and wear prevention. In the case of sidewall MEMS tests, the lifetime of the MEMS device was radically increased via vapor-phase lubrication with alcohol.

  19. Development of wear resistant ceramic coatings for diesel engine components

    SciTech Connect

    Haselkorn, M.H. )

    1992-04-01

    Improved fuel economy and a reduction of emissions can be achieved by insulation of the combustion chamber components to reduce heat rejection. However, insulating the combustion chamber components will also increase the operating temperature of the piston ring/cylinder liner interface from approximately 150{degree}C to over 300{degree}C. Existing ring/liner materials can not withstand these higher operating temperatures and for this reason, new materials need to be developed for this critical tribological interface. The overall goal of this program is the development of piston ring/cylinder liner material pairs which would be able to provide the required friction and wear properties at these more severe operating conditions. More specifically, this program first selected, and then evaluated, potential d/wear resistant coatings which could be applied to either piston rings an or cylinder liners and provide, at 350{degree}C under lubricated conditions, coefficients of friction below 0.1 and wear rates of less than 25 {times} lO{sup {minus}6} mm/hour. The processes selected for applying the candidate wear resistant coatings to piston rings and/or cylinder liners were plasma spraying, chemical vapor, physical vapor and low temperature arc vapor deposition techniques as well as enameling techniques.

  20. Factors influencing PM 10 emissions from road pavement wear

    NASA Astrophysics Data System (ADS)

    Gustafsson, Mats; Blomqvist, Göran; Gudmundsson, Anders; Dahl, Andreas; Jonsson, Per; Swietlicki, Erik

    Accelerated pavement wear is one of the major environmental disadvantages of studded tyres in northern regions and results in increased levels of PM 10. Measurements of PM 10 in a road simulator hall have been used to study the influence of pavement properties, tyre type and vehicle speed on pavement wear. The test set-up included three different pavements (one granite and two quartzite with different aggregate sizes), three different tyre types (studded, non-studded, and summer tyres) and different speeds (30-70 km h -1). The results show that the granite pavement was more prone to PM 10 production compared to the quartzite pavements. Studded winter tyres yield tens of times higher PM 10 concentrations compared to non-studded winter tyres. Wear from summer tyres was negligible in comparison. It was also shown that wear is strongly dependent on speed; every 10 km h -1 increase yielded an increase of the PM 10 concentration of 680 μg m -3 in one of the simulator experiments.

  1. The effect of insert conformity and material on total knee replacement wear

    PubMed Central

    Brockett, Claire L; Liu, Feng; Jennings, Louise M; Jin, Zhongmin; Fisher, John

    2014-01-01

    The mean average life is increasing; therefore, there is a need to increase the lifetime of the prostheses. To fulfil this requirement, new prosthetic designs and materials are being introduced. Two of the design parameters that may affect wear of total knee replacements, and hence the expected lifetime, are the insert conformity and material. Computational models have been used extensively for wear prediction and optimisation of artificial knee designs. The objective of the present study was to use a previously validated non-dimensional wear coefficient-based computational wear model to investigate the effect of insert conformity and material on the predicted wear in total knee replacements. Four different inserts (curved, lipped, partial flat and custom flat), with different conformity levels, were tested against the same femoral and under two different kinematic inputs (intermediate and high), with different levels of cross-shear. The insert bearing materials were either conventional or moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE). Wear predictions were validated against the experimental data from Leeds knee simulation tests. The predicted wear rates for the curved insert (most conformed) were more than three times those for the flat insert (least conformed). In addition, the computationally predicted average volumetric wear rates for moderately cross-linked UHMWPE bearings were less than half of their corresponding conventional UHMWPE bearings. Moreover, the wear of the moderately cross-linked UHMWPE was shown to be less dependent on the degree of cross-shear, compared to conventional UHMWPE. These results along with supporting experimental studies provide insight into the design variables, which may reduce wear in knee replacements. PMID:24297773

  2. The effect of insert conformity and material on total knee replacement wear.

    PubMed

    Abdelgaied, Abdellatif; Brockett, Claire L; Liu, Feng; Jennings, Louise M; Jin, Zhongmin; Fisher, John

    2014-01-01

    The mean average life is increasing; therefore, there is a need to increase the lifetime of the prostheses. To fulfil this requirement, new prosthetic designs and materials are being introduced. Two of the design parameters that may affect wear of total knee replacements, and hence the expected lifetime, are the insert conformity and material. Computational models have been used extensively for wear prediction and optimisation of artificial knee designs. The objective of the present study was to use a previously validated non-dimensional wear coefficient-based computational wear model to investigate the effect of insert conformity and material on the predicted wear in total knee replacements. Four different inserts (curved, lipped, partial flat and custom flat), with different conformity levels, were tested against the same femoral and under two different kinematic inputs (intermediate and high), with different levels of cross-shear. The insert bearing materials were either conventional or moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE). Wear predictions were validated against the experimental data from Leeds knee simulation tests. The predicted wear rates for the curved insert (most conformed) were more than three times those for the flat insert (least conformed). In addition, the computationally predicted average volumetric wear rates for moderately cross-linked UHMWPE bearings were less than half of their corresponding conventional UHMWPE bearings. Moreover, the wear of the moderately cross-linked UHMWPE was shown to be less dependent on the degree of cross-shear, compared to conventional UHMWPE. These results along with supporting experimental studies provide insight into the design variables, which may reduce wear in knee replacements.

  3. Teenagers' attitudes towards bicycle helmets three years after the introduction of mandatory wearing.

    PubMed Central

    Finch, C. F.

    1996-01-01

    OBJECTIVES AND SETTING: To address helmet wearing by 13-17 year olds this study posed the following research questions: 'Do education programs continue to be necessary even after the community wearing rate has increased?' and 'Are helmet laws more effective in encouraging wearing among certain age groups?' Victoria was the first place in the world to introduce bicycle helmet legislation. Experiences in Victoria therefore provide a good model for the introduction of similar legislation in other areas. This study is the first to examine teenagers' attitudes towards helmet wearing after the introduction of compulsory helmet wearing legislation. METHODS: A survey of 1240 year 9 and year 10 students, aged 13-17 years, from 14 secondary schools in the outer south eastern suburbs of Melbourne, was conducted in September 1993. Information about bicycle use, helmet wearing, and attitudes towards helmets was obtained by a self report questionnaire. RESULTS: Bicycles are a popular form of wheeled recreation/self transport among teenagers. 65% of teenagers reported that they owned a helmet but only one third wore a helmet the last time they rode a bicycle. Fewer than 25% of students always wore a helmet when they rode a bicycle, despite compulsory helmet wearing legislation. Major factors leading to teenagers not wanting to wear a helmet were appearance and comfort. Both safety considerations and parental pressures were factors that influenced a teenager to wear a helmet. CONCLUSIONS: The major areas that need to be addressed are low helmet wearing rates; the low priority given to safety issues compared with comfort and peer acceptance; an ignorance of the need for helmets in all riding situations; and a perception that the legislation would not be enforced. PMID:9346076

  4. Astronaut James Buchli wearing extravehicular mobility unit

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Astronaut James F. Buchli, wearing an extravehicular mobility unit (EMU), is about to be submerged in the weightless environment training facility (WETF) to simulate a contingency extravehicular activity (EVA) for STS 61-A. In this portrait view, Buchli is wearing a communications carrier assembly (CCA).

  5. Friction, wear, and lubrication in vacuum

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1971-01-01

    A review of studies and observations on the friction, wear, and lubrication behavior of materials in a vacuum environment is presented. The factors that determine and influence friction and wear are discussed. They include topographical, physical, mechanical, and the chemical nature of the surface. The effects of bulk properties such as deformation characteristics, fracture behavior, and structure are included.

  6. A Novel, Open Access Method to Assess Sleep Duration Using a Wrist-Worn Accelerometer

    PubMed Central

    Anderson, Kirstie N.; Denton, Sarah J.; Oliver, James; Catt, Michael; Abell, Jessica G.; Kivimäki, Mika; Trenell, Michael I.; Singh-Manoux, Archana

    2015-01-01

    Wrist-worn accelerometers are increasingly being used for the assessment of physical activity in population studies, but little is known about their value for sleep assessment. We developed a novel method of assessing sleep duration using data from 4,094 Whitehall II Study (United Kingdom, 2012–2013) participants aged 60–83 who wore the accelerometer for 9 consecutive days, filled in a sleep log and reported sleep duration via questionnaire. Our sleep detection algorithm defined (nocturnal) sleep as a period of sustained inactivity, itself detected as the absence of change in arm angle greater than 5 degrees for 5 minutes or more, during a period recorded as sleep by the participant in their sleep log. The resulting estimate of sleep duration had a moderate (but similar to previous findings) agreement with questionnaire based measures for time in bed, defined as the difference between sleep onset and waking time (kappa = 0.32, 95%CI:0.29,0.34) and total sleep duration (kappa = 0.39, 0.36,0.42). This estimate was lower for time in bed for women, depressed participants, those reporting more insomnia symptoms, and on weekend days. No such group differences were found for total sleep duration. Our algorithm was validated against data from a polysomnography study on 28 persons which found a longer time window and lower angle threshold to have better sensitivity to wakefulness, while the reverse was true for sensitivity to sleep. The novelty of our method is the use of a generic algorithm that will allow comparison between studies rather than a “count” based, device specific method. PMID:26569414

  7. Characteristics of satellite accelerometer measurements of thermospheric neutral winds at high latitudes

    NASA Astrophysics Data System (ADS)

    Doornbos, E.; Ridley, A. J.; Cnossen, I.; Aruliah, A. L.; Foerster, M.

    2015-12-01

    Thermospheric neutral winds play an important part in the coupled thermosphere-ionosphere system at high latitudes. Neutral wind speeds have been derived from the CHAMP and GOCE satellites, which carried precise accelerometers in low Earth orbits. Due to the need to simultaneously determine thermosphere neutral density from the accelerometer in-track measurements, only information on the wind component in the cross-track direction, perpendicular to the flight direction can be derived. However, contrary to ground-based Fabry-Perot interferometer and scanning Doppler imager observations of the thermosphere wind, these satellite-based measurements provide equally distributed coverage over both hemispheres. The sampling of seasonal and local time variations depend on the precession rate of the satellite's orbital plane, with CHAMP covering about 28 cycles of 24-hour local solar time coverage, during its 10 year mission (2000-2010), while the near sun-synchronous orbit of GOCE resulted in a much more limited local time coverage ranging from 6:20 to 8:00 (am and pm), during a science mission duration of 4 years (2009-2013). For this study, the wind data from both CHAMP and GOCE have been analysed in terms of seasonal variations and geographic and geomagnetic local solar time and latitude coordinates, in order to make statistical comparisons for both the Northern and Southern polar areas. The wind data from both satellites were studied independently and in combination, in order to investigate how the strengths and weaknesses of the instruments and orbit parameters of these missions affect investigations of interhemispheric differences. Finally, the data have been compared with results from coupled ionosphere-thermosphere models and from ground-based FPI and SDI measurements.

  8. Number of Days Required to Estimate Habitual Activity Using Wrist-Worn GENEActiv Accelerometer: A Cross-Sectional Study

    PubMed Central

    Dillon, Christina B.; Fitzgerald, Anthony P.; Kearney, Patricia M.; Perry, Ivan J.; Rennie, Kirsten L.; Kozarski, Robert; Phillips, Catherine M.

    2016-01-01

    Introduction Objective methods like accelerometers are feasible for large studies and may quantify variability in day-to-day physical activity better than self-report. The variability between days suggests that day of the week cannot be ignored in the design and analysis of physical activity studies. The purpose of this paper is to investigate the optimal number of days needed to obtain reliable estimates of weekly habitual physical activity using the wrist-worn GENEActiv accelerometer. Methods Data are from a subsample of the Mitchelstown cohort; 475 (44.6% males; mean aged 59.6±5.5 years) middle-aged Irish adults. Participants wore the wrist GENEActiv accelerometer for 7-consecutive days. Data were collected at 100Hz and summarised into a signal magnitude vector using 60s epochs. Each time interval was categorised according to intensity based on validated cut-offs. Spearman pairwise correlations determined the association between days of the week. Repeated measures ANOVA examined differences in average minutes across days. Intraclass correlations examined the proportion of variability between days, and Spearman-Brown formula estimated intra-class reliability coefficient associated with combinations of 1–7 days. Results Three hundred and ninety-seven adults (59.7±5.5yrs) had valid accelerometer data. Overall, men were most sedentary on weekends while women spent more time in sedentary behaviour on Sunday through Tuesday. Post hoc analysis found sedentary behaviour and light activity levels on Sunday to differ to all other days in the week. Analysis revealed greater than 1 day monitoring is necessary to achieve acceptable reliability. Monitoring frame duration for reliable estimates varied across intensity categories, (sedentary (3 days), light (2 days), moderate (2 days) and vigorous activity (6 days) and MVPA (2 days)). Conclusion These findings provide knowledge into the behavioural variability in weekly activity patterns of middle-aged adults. Since Sunday

  9. Wear mechanisms of partially stabilized zirconia

    SciTech Connect

    Aronov, V.

    1987-01-01

    This paper is devoted to an investigation of the wear mechanisms of magnesia and yttria partially-stabilized zirconia in ceramic/ceramic and ceramic/metal sliding-contact tribological systems at high temperature. It was found that the wear of ceramics rubbed against ceramics at room temperature may be attributed to intensive plastic deformation of surfaces resulting in low cycle fatigue. The wear mechanism of ceramics rubbed against metals was by polishing and surface fracture, while that of metals was adhesive transfer of material on to ceramic surfaces. Investigation of the wear behavior of magnesia partially-stabilized zirconia rubbed against itself showed that up to three orders of magnitude increase in wear resistance can be achieved in a particular temperature range, depending on both sliding speed and the ambient temperature. XRD analysis revealed that a thermally-induced phase transformation takes place on the frictional interface.

  10. Modeling wear of cast Ti alloys

    PubMed Central

    Chan, Kwai S.; Koike, Marie; Okabe, Toru

    2007-01-01

    The wear behavior of Ti-based alloys was analyzed by considering the elastic–plastic fracture of individual alloys in response to the relevant contact stress field. Using the contact stresses as the process driving force, wear was computed as the wear rate or volume loss as a function of hardness and tensile ductility for Ti-based cast alloys containing an α, α+β or β microstructure with or without the intermetallic precipitates. Model predictions indicated that wear of Ti alloys increases with increasing hardness but with decreasing fracture toughness or tensile ductility. The theoretical results are compared with experimental data to elucidate the roles of microstructure in wear and contrasted against those in grindability. PMID:17224314

  11. Wear simulation effects on overdenture stud attachments.

    PubMed

    Rutkunas, Vygandas; Mizutani, Hiroshi; Takahashi, Hidekazu; Iwasaki, Naohiko

    2011-01-01

    The aim of this study was to evaluate wear effects on overdenture resilient attachments. Six commercially available attachments were investigated: ERA orange and white (EO and EW), Locator pink, white and blue (LRP, LRW and LRB) and OP anchor (OP). Five specimens were used for wear simulation while other two specimens served as controls. Fifteen thousands insertion-removal cycles were simulated. Dimensional changes and surface characteristics were evaluated using light microscopy and SEM, respectively. Sudden decrease of retentive force was characteristic for EO and EW attachments. Retentive force of Locator attachments fluctuated throughout the wear simulation period. Dimensional changes and surface wear was more expressed on plastic cores than on plastic rings of attachment males. Based on SEM analysis, some of the specimens obtained smoother surface after wear simulation. Mechanism of retention loss of resilient overdenture attachments can be only partially explained by dimensional changes and surface alterations.

  12. Biologically Based Restorative Management of Tooth Wear

    PubMed Central

    Kelleher, Martin G. D.; Bomfim, Deborah I.; Austin, Rupert S.

    2012-01-01

    The prevalence and severity of tooth wear is increasing in industrialised nations. Yet, there is no high-level evidence to support or refute any therapeutic intervention. In the absence of such evidence, many currently prevailing management strategies for tooth wear may be failing in their duty of care to first and foremost improve the oral health of patients with this disease. This paper promotes biologically sound approaches to the management of tooth wear on the basis of current best evidence of the aetiology and clinical features of this disease. The relative risks and benefits of the varying approaches to managing tooth wear are discussed with reference to long-term follow-up studies. Using reference to ethical standards such as “The Daughter Test”, this paper presents case reports of patients with moderate-to-severe levels of tooth wear managed in line with these biologically sound principles. PMID:22315608

  13. Assessment of variations in wear test methodology.

    PubMed

    Gouvêa, Cresus V D; Weig, Karin; Filho, Thales R M; Barros, Renata N

    2010-01-01

    The properties of composite resin for dental fillings were improved by development, but its weakness continues to be its wear strength. Several tests have been proposed to evaluate wear in composite resin materials. The aim of this study was to verify how polishing and the type of abrasive can influence the wear rate of composite resin. The test was carried out on two groups. In one group we employed an ormocer and a hybrid composite that was polished group the composite was polished with the same abrasive paper plus a 1 microm and 0.25 microm grit diamond paste. A three-body wear test was performed using the metal sphere of the wear test machine, the composite and an abrasive. A diamond paste and aluminum oxide dispersion were used as abrasive. Analysis of the results showed that there was no difference between polishing techniques, but revealed a difference between abrasives.

  14. Friction, wear, transfer and wear surface morphology of ultra-high-molecular-weight polyethylene

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1983-01-01

    Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

  15. Friction, wear, transfer, and wear surface morphology of ultrahigh-molecular-weight polyethylene

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1985-01-01

    Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

  16. Dynamic SEM wear studies of tungsten carbide cermets. [friction and wear experiments

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1975-01-01

    Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined, and etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the tungsten carbide (WC) and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation, and the wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation, and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

  17. Adhesive Wear of Rollers in Vacuum

    NASA Technical Reports Server (NTRS)

    Shaeef, Iqbal; Krantz, Timothy L.

    2012-01-01

    This work was done to support NASA's James Webb Space Telescope that is equipped with a Near Infrared Camera and Spectrograph and Micro Shutter Assembly (MSA). A MSA mechanism's qualification test in cryogenic vacuum at 30deg K for 96K cycles resulted in roller wear and formation of some debris. Lab tests in vacuum were conducted at NASA Glenn Research Center (GRC) to understand the wear of Ti6Al4V mated with 440F steel rollers. Misalignment angle was found to have the most significant effect on debris formation. At misalignment angle of 1.4deg, significant amount of wear debris were formed within 50,000 cycles. Very few wear particles were found for a zero misalignment angle, and the total wear was small even after 367,000 cycles. The mode of wear in all the tests was attributed to adhesion, which was clearly evident from video records as well as the plate-like amalgamated debris material from both rollers. The adhesive wear rate was found to be approximately proportional to the misalignment angle. The wear is a two-way phenomenon, and the mixing of both roller materials in wear debris was confirmed by x-ray fluorescence (XRF) and EDX spectra. While there was a net loss of mass from the steel rollers, XRF and energy dispersive x-ray (EDX) spectra showed peaks of Ti on steel rollers, and peaks of Fe on Ti rollers. These results are useful for designers in terms of maintaining appropriate tolerances to avoid misalignment of rolling elements and the resulting severe wear

  18. The application of counter immunoelectrophoresis (CIE) in ocular protein studies Part II: Kinin activity in the lens wearing eye.

    PubMed

    Mann, Aisling M; Tighe, Brian J

    2002-06-01

    The kinin family are a group of bioactive peptides that are closely involved in the modulation of vascular inflammation and local injury. We have demonstrated here, for the first time, a link between kinin activity and contact lens wear. Protein extracts from daily and extended wear etafilcon A, Group IV, Acuvue lenses (Vistakon), were analysed by counter immunoelectrophoresis. In this way, kinin activity associated with contact lens wear was detected. High molecular weight kininogen was used as the marker protein. In contrast, no kinin activity was detected in the non-lens wearing normal eye.

  19. Airbag accelerometer with a simple switched-capacitor readout ASIC

    NASA Astrophysics Data System (ADS)

    Tsugai, Masahiro; Hirata, Yoshiaki; Tanimoto, Koji; Usami, Teruo; Araki, Toru; Otani, Hiroshi

    1997-09-01

    A bulk micromachined capacitive accelerometer for airbag applications based on (110) silicon anisotropic KOH etching is presented. The sensor is a two-chip accelerometer that consists of a glass-silicon-glass stacked sense element and an interface ASIC containing an impedance converter for capacitance detection, an EPROM and DACs for digital trimming, and a self-test feature for diagnosis. A simple switched-capacitor readout circuit with DC offset error cancellation scheme is proposed as the impedance converter. The dependence of narrow gap etching, surface roughness, and uniformity of the groove depth on the KOH concentration are also investigated for the fabrication of the device, and it is shown that the etch rate of the plane intrinsically controls the depth of the narrow gap with a KOH concentration of over 30 wt. percent, and smooth surface and uniformity of groove depth are obtained at 40 wt. percent KOH. The nonlinearity of the output is about 1.5 percent FS. The temperature coefficient of sensitivity and the off-axis sensitivity are 150 ppm/degree C and 2 percent respectively. The dimensions of the sensor are 10.3 X 10.3 X 3 mm.

  20. Microelectromechanical Resonant Accelerometer Designed with a High Sensitivity.

    PubMed

    Zhang, Jing; Su, Yan; Shi, Qin; Qiu, An-Ping

    2015-01-01

    This paper describes the design and experimental evaluation of a silicon micro-machined resonant accelerometer (SMRA). This type of accelerometer works on the principle that a proof mass under acceleration applies force to two double-ended tuning fork (DETF) resonators, and the frequency output of two DETFs exhibits a differential shift. The dies of an SMRA are fabricated using silicon-on-insulator (SOI) processing and wafer-level vacuum packaging. This research aims to design a high-sensitivity SMRA because a high sensitivity allows for the acceleration signal to be easily demodulated by frequency counting techniques and decreases the noise level. This study applies the energy-consumed concept and the Nelder-Mead algorithm in the SMRA to address the design issues and further increase its sensitivity. Using this novel method, the sensitivity of the SMRA has been increased by 66.1%, which attributes to both the re-designed DETF and the reduced energy loss on the micro-lever. The results of both the closed-form and finite-element analyses are described and are in agreement with one another. A resonant frequency of approximately 22 kHz, a frequency sensitivity of over 250 Hz per g, a one-hour bias stability of 55 μg, a bias repeatability (1σ) of 48 μg and the bias-instability of 4.8 μg have been achieved. PMID:26633425

  1. Evolution of accelerometer methods for physical activity research.

    PubMed

    Troiano, Richard P; McClain, James J; Brychta, Robert J; Chen, Kong Y

    2014-07-01

    The technology and application of current accelerometer-based devices in physical activity (PA) research allow the capture and storage or transmission of large volumes of raw acceleration signal data. These rich data not only provide opportunities to improve PA characterisation, but also bring logistical and analytic challenges. We discuss how researchers and developers from multiple disciplines are responding to the analytic challenges and how advances in data storage, transmission and big data computing will minimise logistical challenges. These new approaches also bring the need for several paradigm shifts for PA researchers, including a shift from count-based approaches and regression calibrations for PA energy expenditure (PAEE) estimation to activity characterisation and EE estimation based on features extracted from raw acceleration signals. Furthermore, a collaborative approach towards analytic methods is proposed to facilitate PA research, which requires a shift away from multiple independent calibration studies. Finally, we make the case for a distinction between PA represented by accelerometer-based devices and PA assessed by self-report.

  2. Applications of the ISA accelerometer for Moon exploration

    NASA Astrophysics Data System (ADS)

    Iafolla, Valerio; Peron, Roberto; Carmisciano, Cosmo

    2012-07-01

    The recent years have seen again the Moon as a target for exploration activities. The reasons for this new wave are manifold, from the knowledge of formation and evolution of the Moon towards its current state to the possibility of building a human settlement on its surface, with all the related issues of environment characterization, safety, resources, communication and navigation. The space agencies are planning future missions for Moon exploration, in particular they are defining the main science objectives and the core instruments to be used in the nodes intended for a future lunar network. The International Lunar Network (ILN) Core Instruments Working Group identified these core instruments, recommending a broadband seismometer as one of the most important. It will be presented a broadband seismometer that can be a suitable candidate for this purpose. The seismometer is based on the heritage experience from IAPS made in the ongoing development of the ISA (Italian Spring Accelerometer) accelerometer, for the ESA BepiColombo mission to Mercury, and in the know-how in the production of geophysical instrument owned by AGI srl, plus the experience of the INGV in the use of such instruments. The proposed instrument can be considered a possible candidate to be hosted both in NASA ILN and in ESA First Lunar Lander. The concept underlying this new instrument and its principal characteristics will be described, giving emphasis on the possible science return and operational scenarios.

  3. Technique for Determining Bridge Displacement Response Using MEMS Accelerometers.

    PubMed

    Sekiya, Hidehiko; Kimura, Kentaro; Miki, Chitoshi

    2016-01-01

    In bridge maintenance, particularly with regard to fatigue damage in steel bridges, it is important to determine the displacement response of the entire bridge under a live load as well as that of each member. Knowing the displacement response enables the identification of dynamic deformations that can cause stresses and ultimately lead to damage and thus also allows the undertaking of appropriate countermeasures. In theory, the displacement response can be calculated from the double integration of the measured acceleration. However, data measured by an accelerometer include measurement errors caused by the limitations of the analog-to-digital conversion process and sensor noise. These errors distort the double integration results. Furthermore, as bridges in service are constantly vibrating because of passing vehicles, estimating the boundary conditions for the numerical integration is difficult. To address these problems, this paper proposes a method for determining the displacement of a bridge in service from its acceleration based on its free vibration. To verify the effectiveness of the proposed method, field measurements were conducted using nine different accelerometers. Based on the results of these measurements, the proposed method was found to be highly accurate in comparison with the reference displacement obtained using a contact displacement gauge. PMID:26907287

  4. Surface Micromachined Silicon Carbide Accelerometers for Gas Turbine Applications

    NASA Technical Reports Server (NTRS)

    DeAnna, Russell G.

    1998-01-01

    A finite-element analysis of possible silicon carbide (SIC) folded-beam, lateral-resonating accelerometers is presented. Results include stiffness coefficients, acceleration sensitivities, resonant frequency versus temperature, and proof-mass displacements due to centripetal acceleration of a blade-mounted sensor. The surface micromachined devices, which are similar to the Analog Devices Inc., (Norwood, MA) air-bag crash detector, are etched from 2-pm thick, 3C-SiC films grown at 1600 K using atmospheric pressure chemical vapor deposition (APCVD). The substrate is a 500 gm-thick, (100) silicon wafer. Polysilicon or silicon dioxide is used as a sacrificial layer. The finite element analysis includes temperature-dependent properties, shape change due to volume expansion, and thermal stress caused by differential thermal expansion of the materials. The finite-element results are compared to experimental results for a SiC device of similar, but not identical, geometry. Along with changes in mechanical design, blade-mounted sensors would require on-chip circuitry to cancel displacements due to centripetal acceleration and improve sensitivity and bandwidth. These findings may result in better accelerometer designs for this application.

  5. Noise power spectral density of the Sundstrand QA-2000 accelerometer

    NASA Technical Reports Server (NTRS)

    Peters, Rex; Grindeland, David; Baugher, Charles R. (Editor)

    1990-01-01

    There are no good data on low frequency (less than 0.1 Hz) power spectral density (PSD) for the Q-Flex accelerometer. However, some preliminary stability measurements were made over periods of 12 to 24 hours and demonstrated stability less than 0.5 micro-g over greater than 12 hours. The test data appear to contain significant contributions from temperature variations at that level, so the true sensor contribution may be less than that. If what was seen could be construed as a true random process, it would correspond to about 0.1 micro-g rms over a bandwidth from 10(exp -5) Hz to about 1 Hz. Other studies of low frequency PSD in flexure accelerometers have indicated that material aging effects tend to approximate a first order Markhov process. If we combine such a model with the spectrum obtained at higher frequencies, it suggests the spectrum shown here as a conservative estimate of Q-Flex noise performance.

  6. A miniature high-resolution accelerometer utilizing electron tunneling

    NASA Technical Reports Server (NTRS)

    Rockstad, Howard K.; Kenny, T. W.; Reynolds, J. K.; Kaiser, W. J.; Vanzandt, T. R.; Gabrielson, Thomas B.

    1992-01-01

    New methods have been developed to implement high-resolution position sensors based on electron tunneling. These methods allow miniaturization while utilizing the position sensitivity of electron tunneling to give high resolution. A single-element tunneling accelerometer giving a displacement resolution of 0.002 A/sq rt Hz at 10 Hz, corresponding to an acceleration resolution of 5 x 10 exp -8 g/sq rt Hz, is described. A new dual-element tunneling structure which overcomes the narrow bandwidth limitations of a single-element structure is described. A sensor with an operating range of 5 Hz to 10 kHz, which can have applications as an acoustic sensor, is discussed. Noise is analyzed for fundamental thermal vibration of the suspended masses and is compared to electronic noise. It is shown that miniature tunnel accelerometers can achieve resolution such that thermal noise in the suspended masses is the dominant cause of the resolution limit. With a proof mass of order 100 mg, noise analysis predicts limiting resolutions approaching 10 exp -9 g/sq rt Hz in a 300 Hz band and 10 exp -8 g/sq rt Hz at 1 kHz.

  7. Use of accelerometers to measure stress levels in shelter dogs.

    PubMed

    Jones, Sarah; Dowling-Guyer, Seana; Patronek, Gary J; Marder, Amy R; Segurson D'Arpino, Sheila; McCobb, Emily

    2014-01-01

    Stress can compromise welfare in any confined group of nonhuman animals, including those in shelters. However, an objective and practical method for assessing the stress levels of individual dogs housed in a shelter does not exist. Such a method would be useful for monitoring animal welfare and would allow shelters to measure the effectiveness of specific interventions for stress reduction. In this pilot study, activity levels were studied in 13 dogs using accelerometers attached to their collars. Behavioral stress scores as well as urinary and salivary cortisol levels were measured to determine if the dogs' activity levels while confined in the kennel correlated with behavioral and physiological indicators of stress in this population. The results indicated that the accelerometer could be a useful tool to study stress-related activity levels in dogs. Specific findings included a correlation between the salivary cortisol and maximum activity level (r = .62, p = .025) and a correlation between the urine cortisol-to-creatinine ratio and average activity level (r = .61, p = .028) among the study dogs. Further research is needed to better understand the complex relationship between stress and activity level among dogs in a kennel environment. PMID:24484308

  8. Microelectromechanical Resonant Accelerometer Designed with a High Sensitivity

    PubMed Central

    Zhang, Jing; Su, Yan; Shi, Qin; Qiu, An-Ping

    2015-01-01

    This paper describes the design and experimental evaluation of a silicon micro-machined resonant accelerometer (SMRA). This type of accelerometer works on the principle that a proof mass under acceleration applies force to two double-ended tuning fork (DETF) resonators, and the frequency output of two DETFs exhibits a differential shift. The dies of an SMRA are fabricated using silicon-on-insulator (SOI) processing and wafer-level vacuum packaging. This research aims to design a high-sensitivity SMRA because a high sensitivity allows for the acceleration signal to be easily demodulated by frequency counting techniques and decreases the noise level. This study applies the energy-consumed concept and the Nelder-Mead algorithm in the SMRA to address the design issues and further increase its sensitivity. Using this novel method, the sensitivity of the SMRA has been increased by 66.1%, which attributes to both the re-designed DETF and the reduced energy loss on the micro-lever. The results of both the closed-form and finite-element analyses are described and are in agreement with one another. A resonant frequency of approximately 22 kHz, a frequency sensitivity of over 250 Hz per g, a one-hour bias stability of 55 μg, a bias repeatability (1σ) of 48 μg and the bias-instability of 4.8 μg have been achieved. PMID:26633425

  9. Shock margin testing of a one-axis MEMS accelerometer.

    SciTech Connect

    Parson, Ted Blair; Tanner, Danelle Mary; Buchheit, Thomas Edward

    2008-07-01

    Shock testing was performed on a selected commercial-off-the-shelf - MicroElectroMechanical System (COTS-MEMS) accelerometer to determine the margin between the published absolute maximum rating for shock and the 'measured' level where failures are observed. The purpose of this testing is to provide baseline data for isolating failure mechanisms under shock and environmental loading in a representative device used or under consideration for use within systems and assemblies of the DOD/DOE weapons complex. The specific device chosen for this study was the AD22280 model of the ADXL78 MEMS Accelerometer manufactured by Analog Devices Inc. This study focuses only on the shock loading response of the device and provides the necessary data for adding influence of environmental exposure to the reliability of this class of devices. The published absolute maximum rating for acceleration in any axis was 4000 G for this device powered or unpowered. Results from this study showed first failures at 8000 G indicating a margin of error of two. Higher shock level testing indicated that an in-plane, but off-axis acceleration was more damaging than one in the sense direction.

  10. Applying macro design tools to the design of MEMS accelerometers

    SciTech Connect

    Davies, B.R.; Rodgers, M.S.; Montague, S.

    1998-02-01

    This paper describes the design of two different surface micromachined (MEMS) accelerometers and the use of design and analysis tools intended for macro sized devices. This work leverages a process for integrating both the micromechanical structures and microelectronics circuitry of a MEMS accelerometer on the same chip. In this process, the mechanical components of the sensor are first fabricated at the bottom of a trench etched into the wafer substrate. The trench is then filled with oxide and sealed to protect the mechanical components during subsequent microelectronics processing. The wafer surface is then planarized in preparation for CMOS processing. Next, the CMOS electronics are fabricated and the mechanical structures are released. The mechanical structure of each sensor consists of two polysilicon plate masses suspended by multiple springs (cantilevered beam structures) over corresponding polysilicon plates fixed to the substrate to form two parallel plate capacitors. One polysilicon plate mass is suspended using compliant springs forming a variable capacitor. The other polysilicon plate mass is suspended using very stiff springs acting as a fixed capacitor. Acceleration is measured by comparing the variable capacitance with the fixed capacitance during acceleration.

  11. Technique for Determining Bridge Displacement Response Using MEMS Accelerometers

    PubMed Central

    Sekiya, Hidehiko; Kimura, Kentaro; Miki, Chitoshi

    2016-01-01

    In bridge maintenance, particularly with regard to fatigue damage in steel bridges, it is important to determine the displacement response of the entire bridge under a live load as well as that of each member. Knowing the displacement response enables the identification of dynamic deformations that can cause stresses and ultimately lead to damage and thus also allows the undertaking of appropriate countermeasures. In theory, the displacement response can be calculated from the double integration of the measured acceleration. However, data measured by an accelerometer include measurement errors caused by the limitations of the analog-to-digital conversion process and sensor noise. These errors distort the double integration results. Furthermore, as bridges in service are constantly vibrating because of passing vehicles, estimating the boundary conditions for the numerical integration is difficult. To address these problems, this paper proposes a method for determining the displacement of a bridge in service from its acceleration based on its free vibration. To verify the effectiveness of the proposed method, field measurements were conducted using nine different accelerometers. Based on the results of these measurements, the proposed method was found to be highly accurate in comparison with the reference displacement obtained using a contact displacement gauge. PMID:26907287

  12. Technique for Determining Bridge Displacement Response Using MEMS Accelerometers.

    PubMed

    Sekiya, Hidehiko; Kimura, Kentaro; Miki, Chitoshi

    2016-02-19

    In bridge maintenance, particularly with regard to fatigue damage in steel bridges, it is important to determine the displacement response of the entire bridge under a live load as well as that of each member. Knowing the displacement response enables the identification of dynamic deformations that can cause stresses and ultimately lead to damage and thus also allows the undertaking of appropriate countermeasures. In theory, the displacement response can be calculated from the double integration of the measured acceleration. However, data measured by an accelerometer include measurement errors caused by the limitations of the analog-to-digital conversion process and sensor noise. These errors distort the double integration results. Furthermore, as bridges in service are constantly vibrating because of passing vehicles, estimating the boundary conditions for the numerical integration is difficult. To address these problems, this paper proposes a method for determining the displacement of a bridge in service from its acceleration based on its free vibration. To verify the effectiveness of the proposed method, field measurements were conducted using nine different accelerometers. Based on the results of these measurements, the proposed method was found to be highly accurate in comparison with the reference displacement obtained using a contact displacement gauge.

  13. Free fall tests of the accelerometers of the MICROSCOPE mission

    NASA Astrophysics Data System (ADS)

    Liorzou, F.; Boulanger, D.; Rodrigues, M.; Touboul, P.; Selig, H.

    2014-09-01

    The MICROSCOPE mission is fully dedicated to the in-orbit test of the Universality of free fall, the so-called Weak Equivalence Principle (WEP), with an expected accuracy better than 10-15. The test principle consists in comparing the accelerations of two proof masses of different composition in the Earth gravitational field. The payload embarks two pairs of test-masses made of Platinum Rhodium and Titanium alloys at the core of two dedicated coaxial electrostatic accelerometers. These instruments are under qualification for a launch in 2016. Their operations are only possible in microgravity environment which makes its validation on ground a real issue. In Europe, only the drop tower of the ZARM Institute provides a facility for experiments under conditions of weightlessness and offers the experimental conditions to verify the correct functioning of the MICROSCOPE payload. The height of the tower limits the “free fall” experiment period to 4.72 s. Under this strong constraint, the demonstration of the capability to control the test masses of the two coaxial electrostatic accelerometers is challenging. This paper describes the complete experimental set up and in which condition the test has been performed, then an analysis of a drop result is given with its interpretations.

  14. Mechanisms for fatigue and wear of polysilicon structural thinfilms

    SciTech Connect

    Alsem, Daniel Henricus

    2006-01-01

    extreme temperature increases are found, ruling out plasticity and temperature-assisted mechanisms. The COF reaches a steady-state value of ~0.20±0.05 after a short time at an initial value of ~0.11±0.01. Plowing tracks are found before the steady-state value of the COF is reached, suggesting only a short adhesive wear regime. This suggests a predominantly abrasive wear mechanism, controlled by fracture, which commences by the first particles created by adhesive wear.

  15. Stick-slip friction and wear of articular joints

    PubMed Central

    Lee, Dong Woog; Banquy, Xavier; Israelachvili, Jacob N.

    2013-01-01

    Stick-slip friction was observed in articular cartilage under certain loading and sliding conditions and systematically studied. Using the Surface Forces Apparatus, we show that stick-slip friction can induce permanent morphological changes (a change in the roughness indicative of wear/damage) in cartilage surfaces, even under mild loading and sliding conditions. The different load and speed regimes can be represented by friction maps—separating regimes of smooth and stick-slip sliding; damage generally occurs within the stick-slip regimes. Prolonged exposure of cartilage surfaces to stick-slip sliding resulted in a significant increase of surface roughness, indicative of severe morphological changes of the cartilage superficial zone. To further investigate the factors that are conducive to stick-slip and wear, we selectively digested essential components of cartilage: type II collagen, hyaluronic acid (HA), and glycosaminoglycans (GAGs). Compared with the normal cartilage, HA and GAG digestions modified the stick-slip behavior and increased surface roughness (wear) during sliding, whereas collagen digestion decreased the surface roughness. Importantly, friction forces increased up to 2, 10, and 5 times after HA, GAGs, and collagen digestion, respectively. Also, each digestion altered the friction map in different ways. Our results show that (i) wear is not directly related to the friction coefficient but (ii) more directly related to stick-slip sliding, even when present at small amplitudes, and that (iii) the different molecular components of joints work synergistically to prevent wear. Our results also suggest potential noninvasive diagnostic tools for sensing stick-slip in joints. PMID:23359687

  16. Stick-slip friction and wear of articular joints.

    PubMed

    Lee, Dong Woog; Banquy, Xavier; Israelachvili, Jacob N

    2013-02-12

    Stick-slip friction was observed in articular cartilage under certain loading and sliding conditions and systematically studied. Using the Surface Forces Apparatus, we show that stick-slip friction can induce permanent morphological changes (a change in the roughness indicative of wear/damage) in cartilage surfaces, even under mild loading and sliding conditions. The different load and speed regimes can be represented by friction maps--separating regimes of smooth and stick-slip sliding; damage generally occurs within the stick-slip regimes. Prolonged exposure of cartilage surfaces to stick-slip sliding resulted in a significant increase of surface roughness, indicative of severe morphological changes of the cartilage superficial zone. To further investigate the factors that are conducive to stick-slip and wear, we selectively digested essential components of cartilage: type II collagen, hyaluronic acid (HA), and glycosaminoglycans (GAGs). Compared with the normal cartilage, HA and GAG digestions modified the stick-slip behavior and increased surface roughness (wear) during sliding, whereas collagen digestion decreased the surface roughness. Importantly, friction forces increased up to 2, 10, and 5 times after HA, GAGs, and collagen digestion, respectively. Also, each digestion altered the friction map in different ways. Our results show that (i) wear is not directly related to the friction coefficient but (ii) more directly related to stick-slip sliding, even when present at small amplitudes, and that (iii) the different molecular components of joints work synergistically to prevent wear. Our results also suggest potential noninvasive diagnostic tools for sensing stick-slip in joints.

  17. Single-asperity contributions to multi-asperity wear simulated with molecular dynamics

    NASA Astrophysics Data System (ADS)

    Eder, S. J.; Cihak-Bayr, U.; Bianchi, D.

    2016-03-01

    We use a molecular dynamics approach to simulate the wear of a rough ferrite surface due to multiple hard, abrasive particles under variation of normal pressure, grinding direction, and particle geometry. By employing a clustering algorithm that incorporates some knowledge about the grinding process such as the main grinding direction, we can break down the total wear volume into contributions from the individual abrasive particles in a time-resolved fashion. The resulting analysis of the simulated grinding process allows statements on wear particle generation, distribution, and stability depending on the initial topography, the grinding angle, the normal pressure, as well as the abrasive shape and orientation with respect to the surface.

  18. Friction and wear of selected metals and of carbons in liquid natural gas

    NASA Technical Reports Server (NTRS)

    Wisander, D. W.

    1971-01-01

    Friction and wear experiments were conducted with hemispherically tipped (4.76-mm radius) rider specimens in sliding contact with a rotating disk submerged in liquid natural gas (LNG). The program included metal combinations and carbon-metal combinations. These experiments revealed that the metal combinations were not lubricated by the LNG. Carbons had much lower wear in LNG than in liquid hydrogen or in liquid nitrogen. (Wear of carbon in liquid hydrogen was 100 times that in LNG.) The friction coefficients obtained in LNG (0.6 for metal-metal and 0.2 for carbon-metal) are similar to those obtained in liquid hydrogen.

  19. Determining the functional and material properties needed for abrasive wear prediction

    NASA Astrophysics Data System (ADS)

    Petre, I.

    2016-08-01

    Abrassive wear is a complex mechanical process with specific characteristics, dependent on the bodies velocities and load, the quality of contact surfaces, the mechanical properties of the superficial layers, lubrication etc. During the friction of the bodies in contact, the mechanical properties and the micro-topography of superficial layers change, most of the time irrecoverable, leading to the shut-down of the technical system they are part of. The present paper proposes a theoretical and experimental analysis of the abrassive wear behaviour of a coupling made of steel/cast iron as well as the detection of the wear trace dependent on the inclination angle of the harder material asperities (penetrator).

  20. Wear behavior of AISI 1090 steel modified by pulse plasma technique

    SciTech Connect

    Ayday, Aysun; Durman, Mehmet

    2012-09-06

    AISI 1090 steel was pulse plasma treated (PPT) using a Molybdenum electrode. Two different pulse numbers were chosen to obtain modified layers of 20{+-}5 {mu}m thickness. The dry sliding wear studies performed on this steel with and without PPT against an alumina ball counterpart showed that the PPT improved the wear resistance. The pulse number of the PPT modified layer was found to be highly influential in imparting the wear resistance to this steel, due to enhancement of surface hardness depending on treatment time.