Initial Tests Results of a Multi-Axis Vibrating Ring Gyroscope and Issues Associated with its Fabrication

摘要

Initial test results from a multi-axis vibrating ring gyroscope fabricated using MEMS principles are presented in this paper. The multi-axis vibrating ring gyroscope provides a method for making simultaneous measurements of rate of rotation about three mutually orthogonal axes. This is achieved by exploiting Coriolis coupling between in-plane and out of piane modes of vibration of a ring. With the appropriate choice of dimensions, the natural frequencies of the important modes of vibration utilised in the gyro may be made equal. Such "tuning" increases the response of the gyro to applied rates of rotation. The measured natural frequencies and Q-factors are presented here and are shown to agree with the analytical and finite element predictions. Importantly, the frequency split between the out of plane modes is less than the bandwidth, thus indicating that minimal anisotropy is introduced by the fabrication process or silicon substrate material. The fabrication issues associated with the multi-axis gyroscope are discussed. An important issue is that of particle contamination. As capacitive electrodes with air gaps of the order of 1 μm are employed to actuate and sense the in-plane and out of plane modes, particles must be minimised during fabrication and testing. The results from electrostatic deflection tests are shown and suggest in some instances that the combination of particles in the vicinity of the ring and a high electric field at the edges of the electrodes, can restrict vibration. The performance of the multi-axis gyroscope may be increased by reducing the frequency split between the modes. Also presented in this paper are results of a laser ablation fine-tuning procedure. In this method, the frequency split between the out of plane modes and the in-plane modes are reduced separately. While mass reduction is the dominant effect involved during tuning the in-plane modes, tuning of the out of plane modes is not so straightforward as stiffness changes cannot be ignored. Control over the ablation dimensions is essential for an efficient tuning procedure for the out of plane modes.