Breaking the 1 deg/h Bias Instability Limit With Frequency Modulated Gyroscopes: Adaptive Notch Filters for Enhanced Bandwidth and Control

Compared with amplitude modulated (AM) gyroscopes, Lissajous frequency modulated (LFM) gyroscopes have demonstrated excellent temperature and scale factor stability, but typically angle random walk (ARW) is elevated and bias instability (BI) is above 1 deg/hr. Symmetric resonators should improve stability as theoretically LFM gyroscope bias is limited by cross-axis damping differences. Based on modeling, it is claimed that simple amplitude control methods introduce trade-offs between BI and bandwidth. This effort documents means to reduce BI below 1 deg/hr. Central to the improvements is the large displacement linear drive quadruple mass gyroscope (QMG). To both increase the amplitude control bandwidth and the available sensor bandwidth, adaptive notch filters are added to the digital signal processing. During periods of low temperature variation, excellent stability of 0.19 deg/hr at 100 sec is possible. For longer tests, it is suspected that temperature effects are present, but can be well modeled using autoregressive methods.