A Low-Complexity In-Run Modal Frequency Tuning Method for MEMS Disk Gyroscopes Without Gain Calibration and Phase Shifting

The approach of obtaining modal frequency split information using conventional sideband excitation signals requires gain calibration and compensation, and sense mode output signals as the frequency split decreases produce a phase shifting, which increases the complexity of the in-run modal frequency tuning (MFT) method for MEMS gyroscope. In this article, an in-run MFT system based on multiple frequency sideband excitation (MFSE) signals and preset stiffness regulation voltages (quadrature stiffness correction and frequency tuning voltages) is designed and implemented. The frequencies of MFSE signals are proportional to the drive modal frequency and eliminating the need for gain calibration of the MFT system. The preset stiffness regulation voltages are adopted to control the initial frequency split within 0.1 Hz, so that the phase of demodulation reference signals for sense mode remains fixed during the frequency tuning processing. First, the conditions of modal frequency matching are analyzed based on the stiffness regulation electrodes. Second, the necessity of modal frequency matching is investigated from the perspectives of signal acquisition and mechanical sensitivity. Third, the in-run MFT system is designed. Finally, the static performance of the disk gyroscope before and after modal frequency matching is compared. Bias instability (BI) is reduced from 3.543 to 0.902°/h, and angular random walk is reduced from 0.646 to $0.049^{\circ} /\sqrt {\text {h}}$ , achieving the static performance of the tactical-grade gyroscope.

I. Introduction

MEMS gyroscope, as a sensor that utilizes the Coriolis principle for angular motion measurement, has a low cost, size, weight, and power (CSWaP) [1], [2], [3], [4], [5], [6], [7], as shown in Fig. 1. MEMS gyroscopes utilize the energy transfer between operational modes induced by Coriolis force to achieve rate integrating or rate measurement and have the following three measurement modes: rate mode, rate-integrated mode, and frequency-modulated mode [8], [9]. Compared with the rate integrated mode, the rate mode does not require complex calculations [10] and has the highest measurement accuracy among the three measurement modes [10], [11], [12]. In addition, Fig. 1 shows the optimal static performance of three types of MEMS gyroscopes, where all gyroscopes adopt rate mode and operate in modal frequency matching case [13], [14], [15]. Fig. 1.

CSWaP and working principle of MEMS gyroscope.