Precision mode tuning towards a low angle drift MEMS rate integrating gyroscope

Abstract

This paper describes a high precision mode tuning scheme for a MEMS vibratory gyroscope operating in the rate integrating mode (RIG). The tuning scheme minimizes both the cross and diagonal imperfection components in the stiffness matrix. It consists of “coarse” and “fine” tuning stages respectively conducted in rate mode and rate integrating mode. The first stage of mode tuning in the rate mode is automated and can be completed within a few minutes with an accuracy of a few tens of mHz. The tuning accuracy at this stage is restricted by the damping imperfections that distort the phase response as the stiffness imperfections are reduced. Further improvement to the tuning accuracy is achieved at the second stage by switching the gyro to operate in the rate integrating mode, where the influence of damping imperfections on the tracked resonance frequency is negligible when the amplitude of the minor axis of the elliptical trajectory of the vibration is minimized. Accurate assessments of the stiffness imperfections are made by deliberate angle precession and examining the tracked resonant frequency variation from the average resonance frequency at certain angular locations. A tuning accuracy of 10 mHz is achieved while the gyroscope is operated in whole angle mode. Minimum frequency mismatch is a great advantage for the closed-loop control of the rate integrating gyroscope, such as quadrature nulling and phase locked loop based frequency tracking, it also reduces angle error.