Electronic circuitry has been devised to compensate for variations in the resonance quality factor (Q) of a planar vibratory microgyroscope like that described in the first of the two preceding articles. That is, the circuit makes the scale factor of the gyroscope (the factor of proportionality between the rate of rotation, W, and the output signal) independent of Q.

If the Coriolis signal were to constitute the output signal, then the scale factor would be proportional to the amplitude of the input displacement and to Q. The amplitude of the input displacement is maintained constant by the technique described in the immediately preceding article, "Vibration-Regulating Circuit for a Mechanical Resonator," (NPO-20088). However, the rate of damping, and thus Q, does not remain constant; the rate of damping is very sensitive to the density and pressure of the fluid in which the resonator is immersed. Thus, there is need for further processing of the Coriolis signal through circuitry like that described below to make the scale factor remain constant despite variations in Q.

The Portion of This Circuit That Compensates for Variations in Q exploits the drive voltage generated elsewhere in the circuit. The amplitude of this drive voltage is proportional to Q, while the amplitude of the Coriolis signal is proportional to ΩQ -1. The output of the analog multiplier is proportional to the two amplitudes and thus proportional to Ω, regardless of the value of Q.

The circuitry in question is part of the overall electronic circuit shown in the figure. To maintain a constant input vibration amplitude, it is necessary to drive the resonator with a voltage proportional to Q. Other parts of the circuit generate such a drive voltage, which is applied not only to the resonator but also to the input terminal of a 90° phase shifter. The output of the phase shifter is fed to one of two input terminals of an analog multiplier. An amplified version of the Coriolis signal is applied to the other input terminal of the analog amplifier. Because the Coriolis signal is approximately 90° out of phase with the drive signal, it is approximately in phase with the output of the phase shifter. Therefore, the time-averaged output of the analog multiplier is proportional to the amplitude of the Coriolis signal (proportional to WQ) and to the amplitude of the drive signal (proportional to Q-1). Thus, the output of the analog multiplier is proportional to W only, as desired, regardless of variations in Q.

This work was done by Christopher Stell, Vatché Vorperian, Roman Gutierrez, and Tony Tang of Caltech for NASA's Jet Propulsion Laboratory.

NPO-20089


This Brief includes a Technical Support Package (TSP).
Q-Compensation Circuit for a Planar Vibratory Microgyroscope

(reference NPO20089) is currently available for download from the TSP library.

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Motion Control Tech Briefs Magazine

This article first appeared in the June, 2000 issue of Motion Control Tech Briefs Magazine.

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