A systematic approach for precision electrostatic mode tuning of a MEMS gyroscope

In this paper a systematic approach to precision electrostatic frequency tuning of the operational modes of a MEMS ring vibratory gyroscope is presented. In both rate and rate integrating gyroscopes the frequency split between the two modes of vibration which detect the Coriolis acceleration is one of the principal factors in determining the sensitivity and noise floor of the sensor. In high precision applications in the defence/aerospace sector a frequency split of the order of 10 mHz or less is highly desirable. In the ground-breaking Hemispherical Resonator Gyroscope (HRG) electrostatic tuning has been employed as a tuning mechanism. However, a description of the procedure is not available in the literature. The tuning scheme described here involves assessing mode mistuning by the ratio of the in-phase and quadrature components of the response to an external force that has similar properties to the gyroscopic force resulting from Coriolis action, and choosing the tuning voltages so that independent modification of the elements of the system stiffness matrix can be achieved. Experiments on a commercially available gyroscope with a natural frequency of 14 kHz show that the frequency split can be reduced from 1.5 Hz to 6 mHz. This represents a frequency precision of better than 1 part in a million.