Littérature scientifique sur le sujet « Pendulous triaxial accelerometer »

In engineering practice, instruments, such as accelerometer and laser interferometer, are widely used in vibration measurement of structural parts. A method for using a triaxial fluxgate magnetometer as a microvibration sensor to measure low-frequency pendulum microvibration (not translational vibration) is proposed in this paper, so as to detect vibration from low-frequency vibration sources, such as large rotating machine, large engineering structure, earthquake, and microtremor. This method provides vibration detection based on the environmental magnetic field signal to avoid increased measurement difficulty and error due to different relative positions of permanent magnet and magnetometer on the device under test (DUT) when using the original magnetic measurement method. After fixedly connecting the fluxgate probe with the DUT during the test, the angular displacement due to vibration can be deduced by measuring the geomagnetic field’s magnetic induction intensity change on the orthogonal three components during the vibration. The test shows that the microvibration sensor has angular resolution of over 0.05° and maximum measuring frequency of 64 Hz. As an exploring test aimed to detect the microvibration of earth-orbiting satellite in the in-orbit process, the simulation experiment successfully provides the real-time microvibration information for attitude and orbit control subsystem.

Abstract A new class-A force-balance accelerometer (FBA) is designed, simulated, and evaluated. The focus of this work was to design a low-cost but high-performance instrument. The FBA has output voltage proportional to ground acceleration, flat response from direct current to 200 Hz, output range ± 10 V differential (40Vpp, peak-to-peak) and sensitivity 2.5 V/g, which provides a ± 4g range. Unlike other well-established designs with rotational pendulum systems and single-coil actuators that present partially nonlinear performance, the proposed design is based on a linear motion spring-mass mechanism with two parallel leaf springs and a double symmetrical magnet-coil force actuator. This architecture ensures that the displacement transducer’s response is linear and that an acting force on the seismic mass is not disturbed by any cross-axial motion. This force depends on displacement only, as imposed by the electronic control circuit, which is implemented on a small high-density printed circuit board (PCB) mounted on top of the mechanical construction. The plates of the variable capacitance displacement transducer consist of ordinary PCBs for cost efficiency. The coils of the force actuator are placed on each side of the moving plate of the capacitive transducer and the magnets are placed on the aluminum rigid frame of the device. The central moving plate of the variable capacitor and the attached force actuator coils, along with some extra aluminum mass, consist the accelerometer’s seismic mass. The performance of the accelerometer is evaluated in terms of earthquake data records and in comparison of its response with that of a commercial FBA with corresponding specifications. The instrument’s self-noise was also measured over a long period of operation and proved to comply with typical FBA application requirements and commercial product standards.

This paper presents the results obtained during an experimental campaign on blast resistant wheels designed for a low-cost demining machine, derived from an agricultural tractor. Such wheels must fulfil two requirements: first, they have to be able to retain their mechanical integrity in case of blast and still work after one or more explosions, in order to be able to drive the machine out of the minefield without human intervention; second, they must reduce as much as possible the amount of energy transferred to the vehicle, to protect the on-board equipment from the effect of the detonation of a landmine. One of the goals of the experimental activity was to compare two wheels characterized by different designs. Mechanical performance and capacity of the wheels to reduce the energy transferred to the vehicle have been assessed to verify whether the wheels were suitable for the task and to identify which wheel performs best. Physical integrity of both wheels was assessed by visual inspection after each explosion. To evaluate the energy transferred to the vehicle, a measurement of the potential energy transferred, by means of a ballistic pendulum, equipped with an encoder, was performed together with a triaxial acceleration measurement in correspondence of the wheel hub. The triaxial accelerometer measurement was then also used to assess the behaviour of the wheels mounted on the vehicle after tests on the ballistic pendulum. Wheel performances have been quantified using specific features and frequency domain functions, related to the damage induced by the vibration at the interface between the hub and the demining machine. The obtained results suggest that the heaviest wheel performs better both in terms of mechanical integrity and of shock response.

Cette thèse est une contribution à la métrologie des faibles forces qui s'inscrit dans la continuité des activités de recherche menées au département AS2M de l'institut FEMTO-ST. Ce manuscrit présente la conception et la mise en œuvre expérimentale d'un accéléromètre pendulaire triaxial qui mesure les composantes non filtrées du régime sismique, puisque ces dernières sont susceptibles de perturber le fonctionnement d'une balance de micro-nanoforce électromagnétique actuellement en développement. Une méthodologie alternative de calcul est également proposée dans ce manuscrit afin d'estimer spécifiquement la valeur et l'incertitude associée à une ou plusieurs grandeurs d'intérêt inconnues, par l'intermédiaire d'un système dynamique SISO dont le comportement est incertain et perturbé. Cette approche repose sur la représentation exacte de ce système grâce à une entrée correctrice virtuelle qui contient les grandeurs d'intérêt. Cette entrée est estimée puis mise en forme afin de déterminer l'incertitude associée à ces grandeurs d'intérêt, en utilisant les outils de l'analyse par intervalles. La méthodologie proposée est validée à partir de simulations de l'accéléromètre en modes actif et passif, puis illustrée sur le dispositif expérimental. Une étude en simulation du fonctionnement couplé de la future balance de micro-nanoforce électromagnétique avec l'accéléromètre triaxial est également réalisée. L'approche proposée est mise en œuvre lors d'un essai simulé visant à caractériser la raideur mécanique d'un levier élastique
This PhD thesis is a contribution to small force metrology, in line with the research activities carried out in the AS2M department of the FEMTO-ST institute. This manuscript presents the design and experimental implementation of a triaxial pendulous accelerometer, which measures the unfiltered seismic activity, since the latter is likely to interfere with the operation of an electromagnetic micro-nanoforce balance currently under development. An alternative methodology is also proposed in this manuscript to specifically estimate the value and uncertainty associated with one or more unknown quantities of interest, using a dynamical SISO system whose behavior is uncertain and disturbed. This approach is based on the exact representation of this system by means of a virtual corrective input containing the quantities of interest. This input is estimated and then shaped to determine the uncertainty associated with these quantities of interest, using the tools of interval analysis. The proposed methodology is validated on the basis of simulated accelerometer responses in active and passive modes, then illustrated on the experimental setup. A simulation study of the coupled operation of the future electromagnetic micro-nanoforce balance with the triaxial accelerometer is also carried out. The proposed approach is implemented in a simulated test aiming at characterizing the mechanical stiffness of an elastic cantilever

Abstract The objective of the study was to determine the biomechanics of the human head-neck complex secondary to whiplash loading. Intact human cadaver head-neck complexes were prepared by maintaining the integrity of the skin and musculature around the ligamentous column. Retroreflective targets were inserted into the bony articulations of the cervical spine at all levels. The specimens were rigidly fixed to a six-axis load cell at the distal end. Instrumentation consisted of triaxial angular velocity sensors and accelerometers on the cranium. A linear accelerometer was attached to the distal end of the preparation. The specimens were subjected to dynamic loading at speeds ranging from 1.6 to 4.2 m/s. They were placed on the slider of the mini-sled pendulum which applied the whiplash loading pulse from the posterior to the anterior direction. The input pulse was measured in terms of acceleration-time histories. Principles of continuous motion analysis were used to determine the kinematics of the head-neck complex as a function of time. The specimens were radiographed pre- and post-test. Results indicated that the structure undergoes continuous change in the head-neck curvature. Initially, the cranium lags the cervical spine resulting in a reverse curvature, the upper cervical spine undergoes flexion with a concomitant extension of the lower cervical spine, and finally, the head catches-up with the lower cervical spine resulting in a single curvature. Increasing velocities/accelerations produced nonlinear increases in extension moment, axial and shear forces, and head-neck kinematics. These strength and kinematic information add to our knowledge of the understanding of the biomechanics of the human head-neck under whiplash.