Type I and Type II Micromachined Vibratory Gyroscopes

Abstract

All Micromachined Vibratory Gyroscopes (MVG) are based on the principle that the Coriolis forces produced by rotation of the gyro cause a transfer of energy between two of the gyro's modes of vibration. Vibratory Gyroscopes can be classified into two broad types, angle gyroscopes (or Type I) and rate gyroscopes (or Type II). Gyroscopes of the first type measure orientation angles directly, while gyroscopes of the second type measure rotational rate. Most MVG implementations to date are found exclusively in the angular rate measuring variety, however there are opportunities for implementation on the micro-scale angle gyroscopes. This paper introduces a unified approach for description of MVGs and emphasizes the differences between the two types of devices. We also review our recent results in development of Type I and Type II gyroscopes. I. INTRODUCTION All vibratory gyroscopes use the Coriolis acceleration that arises in rotating reference frames to measure rotation. The Coriolis forces produced by vibration of the sensing element and rotation of the system cause a transfer of energy between two of the gyro's modes of vibration. Vibratory gyros divide naturally into two classes depending on whether the two modes are of the same kind or different. In the classical tuning fork gyro (Fig. 1), for example, the two modes are different. One consists of a flexural vibration of the tines and the other a torsional vibration about the stem. Vibratory gyros utilizing similar modes include the vibrating string, the vibrating rectangular bar, the vibrating cylinder, and the hemispherical resonator gyro, Fig. 2. Vibratory gyros utilizing similar modes can be operated in the whole angle mode (direct angle measurement mode) or the open-loop mode(or force-to-rebalance modes) to measure rotational rate. Conventionally, different modes gyros are used for angular rate measurement. We introduced the classification of vibratory gyroscopes based on phenomena they measure - angle gyroscopes (or Type I) and rate gyroscopes (or Type II). Almost all reported to date Micromachined Vibratory Gy- roscopes (MVG) are of Type II. They operate on the Coriolis principle of a vibrating proof mass suspended above the substrate. The proof mass is supported by anchored flexures, which serve as the flexible suspension between the proof mass and the substrate, making the mass free to oscillate in two orthogonal directions: the drive direction and the sense direction. In Type II implementation, the overall dynamical