The symmetric MEMS gyroscope is a typical representative of inertial navigation sensors in recent years. It is different from the traditional mechanical rotor gyroscope in that it structurally discards the high-speed rotor and other moving parts to extend the service life and significantly improve accuracy. The highest accuracy is achieved when the ideal mode-matching state is realized. Due to the processing limitation, this index cannot be achieved, and we can only explore ways to approach this index continuously. This paper’s results of error suppression for the symmetric MEMS gyroscope are initially classified into three categories. The first category mainly introduces the processing structure and working mode of the symmetrical gyroscope. The second is mechanical tuning from the structure and the third is electrostatic tuning from the peripheral control circuit. Based on the listed results, the paper compares the two tuning modes and analyzes their advantages and disadvantages. The fourth category is the tuning means incorporating the emerging algorithm. On this basis, the elements of improvement for future high-precision symmetric MEMS gyroscopes are envisioned to provide a part of the theoretical reference for the future development direction of sensors in inertial navigation.

This paper presents a bias modulation method for the force-to-rebalanced (FTR) micro hemispherical resonator gyroscope ( $\mu $ HRG) based on the mode-rotation, which is achieved by regulating the gyroscope’s drive and sense modes revolving at an assigned rate. The $\mu $ HRG output under the mode-rotation includes the sinusoidally modulated bias and a rotation-induced DC bias. Accordingly, the alternating mode-rotation is proposed to chop the DC rate bias into square waves. By this approach, errors in the DC component from the scale factor drift are also modulated. The open-loop and closed-loop relationships between the rotation actuating force and the mode-rotation rate are investigated by theoretical analyses and numerical simulations. The lower and upper bounds of the rotation rate and the alternating frequency are discussed under the considerations of the error changing rate, the forcer capacity, the maximum voltage, the resonator momentum, and the measurement range. In addition, the controllers in the amplitude, quadrature, and inclination loops utilize the proportional-integral-resonance (PIR) regulating law to suppress the sinusoidal-varying errors introduced by the assigned rotation. The proposed bias modulation method was experimentally verified by a $\mu $ HRG with an FPGA platform. The results suggest the alternating mode-rotation improved the bias temperature coefficient by 12 times over the rotation-free FTR architecture. For a three-hour measurement at room temperature, the rate-integration of the mode alternately rotated FTR was within 50 degrees. In comparison, the rate-integration of the rotation-free FTR diverged over 600 degrees due to the bias drift. The presented bias modulation method can be utilized in axisymmetric gyroscopes, such as hemispherical, ring/disk, quad-mass gyroscopes, etc.

This paper presents the characterization of the modal frequencies and the modal orientation of the axisymmetric resonators in Coriolis vibratory gyroscopes based on the approaches of the frequency sweep and the ring down. The modal frequencies and the orientation of the stiffness axis are the key parameters for the mechanical correction of the stiffness imperfections. The frequency sweep method utilizes the zero and the poles in the magnitude-frequency responses of the two-dimensional transfer function to extract the modal orientation information within the frequency domain. The ring down method makes use of the peak and the valley values of the beat signals at the readout electrodes to obtain the modal orientation and the coefficient of the nonlinear stiffness directly within the time domain. The proposed approaches were verified via a silicon ring resonator designed for gyroscopic sensing and the modal information from the experiments exhibited a good agreement between the methods of the frequency sweep and the ring down.