Development of a MEMS gyroscope for absolute angle measurement.

摘要

MEMS gyroscopes are typically designed to measure angular rate of rotation. A measurement of the angle itself is useful in many applications but cannot be obtained by integrating the angular rate due to the presence of bias errors which cause a drift. This thesis presents an innovative design for a vibrating gyroscope that can directly measure both angle and angular rate. The design is based on the principle of measuring the angle of free vibration of a suspended mass with respect to the casing of the device. Several critical challenges have to be handled before the theoretical sensing concept can be converted into a reliable practical sensor. These include compensating for the presence of dissipative forces, mismatched springs, cross-axis stiffness and transmission of rotary torque. These challenges are addressed by the development of a composite nonlinear feedback control system that compensates for each of the above effects and ensures that the mass continues to behave as a freely vibrating structure. Theoretical analysis and simulation results presented in this thesis show that the gyroscope can accurately measure both angle and angular rate for low bandwidth applications.; A MEMS device is designed and fabricated to evaluate the real-world experimental performance of the sensor. It utilizes electrostatic comb actuators and capacitive sensing along both vibration axes fabricated by using Deep Reactive Ion Etching (DRIE) technique. Sensor noise is found to be a major impediment to successful implementation of the controller. The use of a Kalman filter enables some mitigation of noise and successful implementation of control, but the Kalman filter gain cannot be selected too high due to system stability limitations.; In summary, the developed sensor provides a slightly improved measurement of angle compared to that obtained from integrating a commercially available rate gyroscope. However, due to noisy position measurements, it is unable to provide the drift free performance predicted by theory. Several lines of investigation are suggested in the thesis to study and solve the noise problem associated with the capacitive sensors. Simulations show that reducing the noise in the capacitive sensors will enable significantly superior angle measurement.