A new operational mode for axisymmetric Coriolis vibrating gyroscopes: Force Angle Tracking (FAT)

Coriolis Vibrating Gyroscopes (CVGs) are becoming increasingly popular because of their small size, low cost and low power consumption [1–7]. Axisymmetric CVGs, like the macro [7] and micro [8] Hemispherical Resonator Gyroscope (HRG), are operated in either the Force To Rebalance (FTR) or Whole Angle (WA) modes [9]. In the first case, the vibrating wave is maintained at a specific position and the force applied to hold the wave is proportional to the input angular rate. In the second case, for angular velocities greater than the lock-in rate [10–11], the wave rotates and the output is proportional to the input angular position. For angular rates smaller than the lock-in rate, the wave will precess until it locks at a determined angular position [10–11]. The FTR mode is capable of overcoming this limitation, but its dynamic range is usually restricted by the rebalance force.The aim of this work is to present a new operational mode for axisymmetric CVGs which overcomes the lock-in effect of the WA mode and, at the same time, the force limitation of the FTR mode. We call this mechanization Force Angle Tracking, or simply FAT. The new approach is based on the idea of operating the gyroscope in the FTR and WA modes “simultaneously” by closing the FTR control loop to a “non-constant” setpoint value. This allows us to integrate the FTR and WA modes in a “single” mechanization permitting a robust gyroscope output, without dead zones and dynamic range limitations. Finally, we have implemented the FAT mode in a macro HRG and performed several experiments to demonstrate the operation of this new mechanization.