ERROR SIMULATION AND ADAPTIVE MODE TUNING OF MICROMADHINED . GYROSCOPES

Abstract

Micromachined gyroscopes for measuring rate or angle of rotation have attracted a lot of attention during the past few years for several applications. Conventional rotating wheel as well as precision fiber optic and ring laser gyroscopes are all too expensive and too large for use in most emerging applications. Micromachined gyroscopes are mainly attractive because of their small size (— 1 mm X 1 mm including sensing circuits) and low cost. Most microgyroscopes consist of a vibrating proof-mass which is driven into oscillation by electrostatic or other means. When placed in a rotational field, the vibrating proof-mass experiences an apparent force called the Coriolis force, which is proportional to the cross-product of the angular velocity of the rotational field and the translational velocity of the oscillating proof-mass. Fabrication of micromachined gyroscopes involves multiple processing steps including deposition, etching and patterning of materials. Every fabrication step contribute to imperfections in the gyroscope. Imperfections are reflected in asymmetry and anisoelasticity of the structure. Asymmetries result in undesirable constantly acting perturbations in the form of mechanical and electrostatic forces. Simulation of non-idealities in micromachined gyroscopes is essential to understand its behaviour in the entire range of operation and formulate control strategies to counter the same. In most MEMS gyroscopes, it is desirable to operate the drive axis vibration at the resonant frequency in order to obtain a large response and phase synchronization. Adaptive mode tuning as an alternate to phase locked loop so as to place the resonant frequency at a specified frequency is analysed and simulated to obtain better performance of gyroscope