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Abstract: The working principles of a new kind of accelerometer that allows tilt angle to be measured separately from linear acceleration are presented here. This device could have relevant applications for creating inertial platforms and where an inertial suspension for test masses is needed, as it is the case of interferometric gravitational wave detectors. [Copyright &y& Elsevier]

This paper presents the modeling and the comparison of two acquisition systems developed at the Test Centre Division, European Space and Technology Centre, of the European Space Agency in the frame of two investigations: 1) on microelectromechanical-systems-based sensors for the detection of very low-g accelerations and 2) on the feasibility of a compact and low-power multisensor acquisition platform for environmental tests of spacecrafts or subsystems. A Simulink-based approach is proposed for fast, accurate, and reconfigurable modeling of both systems, taking into consideration the sensors and the acquisition chain. This paper aims to highlight the importance of the models as key tools to predict the distortion and noise sources, to allow fast setup of the experiments, and to manage the signal conditioning process. The validity of the proposed technique, applied to the two acquisition systems, is assessed by comparing the predicted results with tests on the real system. Finally, this paper aims to prove, by comparing the two approaches (dedicated acquisition system and multisensor acquisition platform), the importance of the characterization of the whole acquisition system when high performances need to be achieved. [ABSTRACT FROM AUTHOR]

Jerk monitoring, defined as the first derivative of acceleration, has become a major issue in computerized numeric controlled (CNC) machines. Several works highlight the necessity of measuring jerk in a reliable way for improving production processes. Nowadays, the computation of jerk is done by finite differences of the acceleration signal, computed at the Nyquist rate, which leads to low signal-to-quantization noise ratio (SQNR) during the estimation. The novelty of this work is the development of a smart sensor for jerk monitoring from a standard accelerometer, which has improved SQNR. The proposal is based on oversampling techniques that give a better estimation of jerk than that produced by a Nyquist-rate differentiator. Simulations and experimental results are presented to show the overall methodology performance. [ABSTRACT FROM AUTHOR]

The dynamic response (i.e., acceleration and displacement) of a bridge under vehicular load is an important component of design and evaluation. Field measurement of girder displacement, however, is generally nontrivial. Traditional sensors often require a stationary reference such as temporary scaffolds or a suspended cable. In either form, there are added costs, restrictions, and labor. As a result, there are both economic and practical incentives for developing methods that can use an accelerometer to measure both acceleration and displacement. One difficulty of this, however, is the presence of small low-frequency errors in the measured signal, which become sufficiently large through successive integrations and lead to a significantly distorted displacement profile. The objective of this article is to examine an analytical model based on the state-space approach for minimizing such errors and to compare results with two time domain correction methods. Field measurements from a three-span continuous bridge are used to assess the accuracy of each routine. [ABSTRACT FROM AUTHOR]

A methodology has been developed for indirect, noncontact, and dynamic sensing of angles for robotic applications. Two accelerometers are placed on the adjacent links close to the joint axis, and their outputs are processed to estimate the joint angle. In the proposed technique, the joint angles are obtained without integrating the accelerometer outputs. To ensure accuracy of accelerometer readings, two calibration procedures for the accelerometers are presented, which can easily be implemented in place. Both these methods solve a nonlinear least squares problem to adjust the offset parameters of the accelerometers. The accelerometer-based angle sensor is particularly suitable for the harsh working environment of heavy-duty manipulators, where conventional contact-type angle sensors cannot be deployed or problems are associated with their use. The performance of the new sensor is studied and compared with the performance of digital resolvers in two applications, involving the position control and dynamic payload measurement of a miniexcavator. The experimental results attest to the efficiency and accuracy of the new angle-sensing mechanism. [ABSTRACT FROM PUBLISHER]

In this paper, we describe a method to test and characterize accelerometers using an accurate position sensor and nonlinear Kalman filters. The method is designed to estimate parameters in nonlinear accelerometers and could be a simpler alternative to methods using centrifuges or vibrational testing. The method makes it possible to do real-time parameter estimation. In addition, the method can be integrated into an inertial tracking or navigation system with sufficiently accurate position measurements. The estimation filters have been implemented and successfully tested using Monte Carlo simulations. An experimental setup has been built, and its functionality has been verified. [ABSTRACT FROM AUTHOR]

Abstract: Using simulated falls performed under supervised conditions and activities of daily living (ADL) performed by elderly subjects, the ability to discriminate between falls and ADL was investigated using tri-axial accelerometer sensors, mounted on the trunk and thigh. Data analysis was performed using MATLAB to determine the peak accelerations recorded during eight different types of falls. These included; forward falls, backward falls and lateral falls left and right, performed with legs straight and flexed. Falls detection algorithms were devised using thresholding techniques. Falls could be distinguished from ADL for a total data set from 480 movements. This was accomplished using a single threshold determined by the fall-event data-set, applied to the resultant-magnitude acceleration signal from a tri-axial accelerometer located at the trunk. [Copyright &y& Elsevier]

The article focuses on a study concerning the influence of speed and step frequency during walking and running on motion sensor output. It aims to determine the relationships of triaxial accelerometry, uniaxial accelerometry, and pedometry with speed and step frequency across a range of walking and running speeds. The study was conducted to nine male runners who wears two Actigraph uniaxial accelerometers, two RT3 triaxial accelerometers, and two Yamax pedometers. It was found in the study that increasing underestimation of activity by the Actigraph as speed increases is related to frequency-dependent filtering and assessment of acceleration in the vertical plane only. Detailed information regarding the methods and analysis used in the study is discussed.

The purpose of this study was to examine whether young adults changed their physical activity (PA) behavior when wearing motion sensors. PA patterns of 119 young adults (M age = 20.82 years, SD = 1.50, M body mass index = 23.93 kg/m², SD = 4.05) were assessed during 2 consecutive weeks. In Week 1, participants wore an accelerometer! During Week 2, participants wore an accelerometer and a pedometer! Counts/day from the accelerometer were examined over the entire study period. Steps/day from the pedometer were examined during Week 2. Descriptive statistics and two-factor repeated-measures analysis of variance were calculated. There were significant differences in counts/day by study day during both weeks of the study (Week 1, p <.0001; Week 2, p <.0001), and steps/day during Week 2 (p <.0001). However! reactivity was not evident, Subsequent investigation by day of the week revealed these differences were due to changes in participants' PA behavior by weekdays and weekends. With respect to gender! men were more active than women during both weeks of monitoring, but daily PA behavior between the genders followed a similar pattern. In conclusion, reactivity to accelerometers and pedometers was not evident in this sample. [ABSTRACT FROM AUTHOR]

This paper presents a method for real-time hand motion detection in two-dimensional (2-D) space. A new input device for kinetically challenged persons that uses this method is presented. The device consists of a solid-state accelerometer that senses 2-D motion, a microcontroller that samples the data in real time, and an embedded field-programmable gate array (FPGA) device that distinguishes the types of motion from programmable motion vocabularies. The system has a quadratic capability O(n²) in detecting motions, while the hardware used has a linear-complexity O(n). The motion-detection computational model is presented, along with experimental results. The system adaptation to individual requirements and the cost versus quality tradeoff can be addressed through reconfiguration. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an innovative fiber optic accelerometer system for monitoring vibration of large-size structures. The system is composed of one (or multiple) sensor head and a control unit for driving the sensor and processing sensor data. The sensing mechanism is based on a novel integration of the moiré fringe phenomenon with fiber optics, resulting in accurate and reliable measurement. A prototype fiber optic accelerometer system has been successfully developed, including a sensor head, a low-cost control unit and a software package with a unique algorithm for processing the moiré fringe signals into accelerations with a high resolution. Finally, free vibration and shaking table tests were performed to identify the dynamic characteristics and demonstrate the high performance of the sensor system developed in this study. [Copyright &y& Elsevier]

In this paper, we propose a device for the Position and Orientation (P&O) reconstruction of human segmental locomotion tasks. It is based on three mono-axial accelerometers and three angular velocity sensors, geometrically arranged to form two orthogonal terns. The device was bench tested using step-by-step motor- based equipment. The characteristics of the six channels under bench test conditions were: crosstalk absent, non linearity < ±0, 1 % fs, hysteresis < 0, 1 % fs, accuracy 0,3% fs, overall resolution better than 0,04 deg/s, 2 * g * 10-4. The device was validated with the stereophotogrammetric body motion analyzer during the execution of three different locomotion tasks: stand-to-sit, sit-to-stand, gait-initiation. Results obtained comparing the trajectories of the two methods showed that the errors were lower than 3 *10-2 m and 2 deg during a 4s of acquisition and lower than 6*10-3 m and 0.2 deg during the effective duration of a locomotory task; showing that the wearable device hereby presented permits the 3-D reconstruction of the movement of the body segment to which it is affixed for time-limited clinical applications. [ABSTRACT FROM AUTHOR]

By integrating the methodologies of window functions and the method of image, the performance of the traditional piezoelectric point and distributed sensors, such as accelerometers, can be tailored by modifying their transfer functions in the spatial domain. The approach used in extending the sensor performance consists of developing a series of methodologies that can tailor the gain of the sensor transfer function while keeping the phase of the sensor transfer function intact. We can show that these spatially introduced design methodologies bypass the Bode gain-phase theorem, which states that gain and phase are interrelated for all minimum phase systems. The effects of adopting these sensors to flexible structure control and point sensors are examined in detail. It can also be shown that a series of low-pass filters, which exerts autonomous behavior between the gain and the phase of the sensor transfer function, can be introduced to significantly influence the performance of the sensing or controlling loops that incorporates these sensors. In addition, variables such as the power of the window functions adopted, the desired corner frequency, the length of the sensor structure, etc., all can be shown to have a decisive impact on the performance of the newly invented sensors. Both theoretical and experimental results of the underlying principles, design methodologies, and implementation process of these newly invented sensors are detailed. [ABSTRACT FROM AUTHOR]

A method for removing ship motion from wind measurements using a simple and inexpensive strap-down system of accelerometers is described and analyzed. In slight seas, error analysis indicates that mean root-mean-square uncertainties associated with the motion correction are 0.03 and 0.006 m s-1 for the horizontal and vertical wind, respectively, for all runs analyzed. The mean uncertainty in the wind stress due to motion correction is 8 × 10-4 N m-2. In a shallow coastal sea setting, ship motion appears to almost always be successfully detected and removed from the vertical component of the observed wind. The horizontal wind components appear to be successfully corrected in 86% of the runs analyzed. Motion correction is shown to have a significant influence on the covariance-calculated wind stress. In approximately half of the runs analyzed the wind stress changes by more than 15%. Motion correction has a smaller effect on the heat fluxes. [ABSTRACT FROM AUTHOR]

A vision-based approach is evaluated for its applicability as a new sensing technology for measuring earthquake- induced motions. Traditional motion sensors used in laboratory and field experiments must be physically attached to the structure and require cumbersome cabling, configurations and substantial time for setup. Moreover, for reduced scale experiments, sensors generally add substantial mass or change the response characteristics of the system. The approach evaluated in this paper is advantageous since it requires very limited physical attachment to the structure of interest, is high-speed, high-resolution, and does not introduce additional mass or otherwise modify the properties of the structure. A demonstration experiment is described in which four digital high-speed, high-resolution, charge-coupled-device cameras outfitted with red light-emitting diodes are used to track 21 reflective (nearly) mass less spherical elements discretely mounted on a scale five-story steel frame structure. The structure is mounted on a Large bi-axial shake table and subjected to different earthquake motions. A total of eleven conventional (wired) transducers [linear variable displacement transducers and accelerometers] are also discretely mounted on the structure, providing a unique comparison with the vision-based approach. Results from these experiments show that the nonintrusive vision-based approach is extremely promising in terms of its ability to capture inter-story drift, floor level velocities, and accelerations, provided proper post-processing of the dynamic data occurs. [ABSTRACT FROM AUTHOR]

The article is dedicated to the problems of developing piezoaccelerometers being the sensors for measuring the vibroacoustic fields on the surfaces of compliant media. Along with this, presence of the sensor distorts the medium's vibrations near a contact zone. A criterion, suitable for estimation of the contact sensor's efficiency accounting to its interaction with the object under the measurement, is proposed. On the basis of this criterion the sensitive elements of the piezoaccelerometers having various configurations are compared. General recommendations on the design of accelerometers for measurements conducted on the soft biotissues of humans have been elaborated. [ABSTRACT FROM AUTHOR]

Describes a low noise wideband accelerometer using an inductive displacement sensor and capable of working both in horizontal and in vertical direction. Use of a suspended mass whose displacement relative to the supporting structure is sensed by a linear variable differential transformer; Spectral sensitivity; Application of the accelerometer.

The article offers information about the 8766A series triaxial accelerometers from Kistler Instruments wherein it provides versatile performance in industrial, automotive and aerospace environments. It features a broad frequency range, extremely low sensitivity to temperature alterations and high immunity to base strain errors. Its new sensors include integral hybrid microelectronics to give better performance than the other designs. On the other hand, its cube design provides flexibleness in installation and standardization.