Serge Muller

A New Quartz Monolithic Differential Vibrating Beam Accelerometer

This paper deals with a new monolithic differential quartz Vibrating Beam Accelerometers (VBA), called VIASC. The concept of this accelerometer includes the three major insulation requirements of the beams in the same quartz monolithic structure: insulation of the beams against thermal stresses, insulation of the beam vibrations and insulation between the two beams. In this paper, the concept of this accelerometer and its manufacturing process by chemical etching are presented. Preliminary results, which confirm the relevance of the VIASC concept, are given and future work on the sensing element is discussed. Two VIASC developments are envisaged: an accurate VIASC version compatible with inertial navigation requirements and a miniaturized version adapted to guidance applications.

The VIA vibrating beam accelerometer: concept and performance

The micro-machined quartz vibrating beam accelerometer, VIA (Vibrating Inertial Accelerometer), has been developed in ONERA aiming at civil and military purposes. The present applications of this device are the guidance and the attitude control of tactical missiles as well as the aircraft inertial navigation. High accuracy, 10/sup -5/ to 10/sup -6/ of the measurement range, and low cost manufacturing are thus demanded. The VIA concept has been selected to meet these objectives. First, the monolithic configuration of the transducers is well suited to chemical etching process and miniaturization. Secondly, the choice of vibrating beams as sensitive elements, combined with excellent quartz mechanical properties, gives a very good stability of the scale factor. The performed optimisation of the transducer leads to a very good insulation of the active part, included a proof mass, a vibrating beam and two articulations, with respect to the mounting areas of the transducer. The insulation has been obtained by a flexible frame, inserted between the active part and the mounting areas. The VIA accelerometer is composed of two transducers and two oscillating loops. A differential arrangement is needed in order to reduce in particular the thermal sensitivity. The two beam frequencies are about 60 kHz and the accelerometer scale factor is 24 Hz/g.

A new analog oscillator electronics applied to a piezoelectric vibrating gyro

This paper deals with a new analog oscillator applied to a piezoelectric vibratory gyroscope developed at ONERA. The equivalent circuit of the gyro and the readout electronics are presented. Then, the influence of phase and amplitude drifts of the drive mode vibration on the angular velocity measurements are discussed theoretically and experimentally. Finally, simulations of the new analog oscillator electronics including phase and amplitude control loops are shown.

The VIA vibrating beam accelerometer: a new quartz micromachined sensor

ONERA, the French National Establishment for Aerospace Research, under the financial support of the DGA (The French MoD Procurement Agency), has been developing a micro-machined quartz vibrating beam accelerometer called VIA (Vibrating Inertial Accelerometer). This sensor exploits the frequency change of a quartz resonator when submitted to an acceleration. The main targeted applications are the guidance and the attitude control of tactical missiles, as well as the inertial navigation of aircraft, helicopters and ground vehicles (coupled with radio-electric positioning systems such as the GPS receiver). The VIA concept has been selected to meet these objectives. First, the monolithic configuration of the transducers is well suited to chemical etching process and miniaturization. Secondly, the choice of vibrating beams as sensitive elements, combined with excellent quartz mechanical properties, gives a very good stability of the scale factor. Third, the performed optimisation of the transducer leads to a very good insulation of the active part with respect to the mounting areas of the transducer, suitable to bias stability. In order to reduce the thermal sensitivity, the accelerometer is composed of two transducers operating in differential mode.

Design and Performances of Two Quartz Monolithic Vibrating Inertial Microsensors

For several years, ONERA has been developing inertial vibrating microsensors, for military and civil applications, such as dynamic control and navigation of vehicles (coupled with radio-electric positioning system). The object of these works is to define original and accurate MEMS devices compatible with collective micromachining technologies, in order to satisfy industrial needs. This paper presents the design and the performances of two sensors : a Vibrating Beam Accelerometer (VBA), called VIA (Vibrating Inertial Accelerometer), and a Coriolis Vibrating Gyrometer (CVG), called VIG (Vibrating Integrated Gyrometer). These devices are based on monolithic structures, which are micromachined by wet etching of crystalline α-quartz substrates. The piezoelectric properties of quartz are used to both drive and detect the mechanical vibrations. The main originality of the presented designs is their specific decoupling frames, which have been developed in order to insulate the useful vibrations and to preserve the quality factor of the resonance modes. Hence energy losses represent less than 10−8 of the total vibrating energy. Thanks to these frames, it is then possible to take full advantages of the excellent mechanical properties of quartz and to achieve high accuracies. The VIA accelerometer principle is based on the frequency shift of a vibrating microcantilever, due to the axial stress generated by a proof mass submitted to an acceleration. The working frequency is around 60 kHz and the sensitivity is 24 Hz/g. Upon a measuring range of 100 g, the scale factor error is about 10 ppm and the bias error is a few hundreds of μg. The VIG uses a tuning-fork as sensitive element, which is excited at its in-plane flexural mode (driving mode). When a rotation speed is applied to this system, a transversal vibration (sensing mode) is induced by the Coriolis forces. The amplitude of this induced vibration is proportional to the rotation speed. Piezoelectricity is used for both the excitation of the driving mode and the detection of the sensing mode. The VIG measuring range is 1000 °/s, with a resolution around 0.01 °/s/√Hz and a bandwidth of 100 Hz.Copyright