Atlantic Inertial Systems, Inc.

Matthew Williamson

John Keith Sheard

Christopher M Gregory

Thomas Mansfield

A vibrating structure gyroscope comprises a resonant structure arranged to vibrate under stimulation from a primary drive electrode. A drive system is arranged to vibrate the vibrating structure at a resonance frequency. An automatic gain control unit varies an amplitude of a primary drive signal (P). A controller operates the gyroscope such that in a first mode of operation, the automatic gain control unit varies an amplitude of the drive signal (P) between an operating range defined by upper and lower bounds and in a second mode operation, in which the automatic gain control unit sets the amplitude of the drive signal (P) to a predetermined level outside of the operating range. In the second mode of operation an amplitude of a primary sense signal (P) is measured after a predetermined time period to determine an oscillation cycle count during said predetermined time period.

Gyroscope

A method of demodulating a MEMS sensor pickoff signal from a vibrating resonator of said sensor, the method comprising: sampling the pickoff signal with an asynchronous ADC at a sampling rate of at least 50 times the resonant frequency of the resonator to generate a stream of samples; generating a first value by combining samples from said stream of samples according to a selected operation, said operation being selected in dependence on a synchronous clock signal that is synchronous to the resonant frequency of the resonator, said synchronous clock signal having a frequency at least twice the resonant frequency of the resonator; and counting the number of samples contributing to the first value. The increased sampling rate of the pickoff signal allows a much higher number of samples to be taken into account, thereby reducing noise. However, the ADC asynchronously from the resonator of the MEMS sensor.

Signal processing

A vibrating structure gyroscope includes a permanent magnet, a structure arranged in a magnetic field of the permanent magnet and arranged to vibrate under stimulation from at least one primary drive electrode and a drive system that includes: one primary drive electrode arranged at least one primary sense electrode arranged to sense motion in the vibrating structure and a drive control loop controlling the primary drive electrode dependent on the primary sense electrode. The structure also includes a compensation unit arranged to receive a signal from the drive system representative of a gain in the drive control loop and arranged to output a scale factor correction based on that signal. As the magnet degrades (e.g. naturally over time as the material ages), the magnetic field weakens. To compensate for this, the primary drive control loop will automatically increase the gain.

A method for determining an operational characteristic of a vibrating structure gyroscope having a movable mass includes: driving the mass to oscillate along a first, predefined path; rotating the vibrating structure gyroscope so as to oscillate the mass along a second path, wherein the second path is different to the first, predefined path; sensing the oscillation of the mass along the second path so as to generate a sensing signal; converting the sensing signal into an in-phase signal and an out-of-phase signal using a demodulator, wherein the in-phase signal is in phase with the oscillation of the mass along the first path, and the out-of-phase signal is out of phase with the in-phase signal.

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Plymouth, United Kingdom

Matthew Williamson