Methods of Self-Calibration for Coriolis Vibratory Gyroscopes

Brief Description

The levels of long-term instabilities in bias and scale factor are key characteristics for the utilization of gyroscopes in many practical applications in navigation, positioning, and targeting systems. The inventors at UCI have developed two methods for gyroscope calibration: 1) Utilizing the mechanical quadrature error and 2) Utilizing the voltages of amplitude gain control (AGC) of the drive-mode. The new methods have been combined with feedback signals from a third technique, Side-Band Ratio (SBR) detection, to produce bias stability of 0.1 deg/hr after 300 seconds that is maintained for over 3 hours.

Full Description

Silicon-based MEMS vibratory gyroscopes have applications in many fields, including navigation, positioning and targeting. The main barrier to utilization is the instability of bias and scale factor, which is mainly caused by thermal sensitivity of the physical gyroscope and associated electronics. The state of the art methods to reduce instabilities utilize the linear dependence of the gyroscope bias on the drive-mode resonant frequency. However, this approach only captures the thermal drift of the system’s mechanical properties. The thermal sensitivity of the other system components, such as electronics gains, are unaccounted for.

Silicon-based MEMS vibratory gyroscopes have applications in many fields, including navigation, positioning and targeting. The main barrier to utilization is the instability of bias and scale factor, which is mainly caused by thermal sensitivity of the physical gyroscope and associated electronics. The state of the art methods to reduce instabilities utilize the linear dependence of the gyroscope bias on the drive-mode resonant frequency. However, this approach only captures the thermal drift of the system’s mechanical properties. The thermal sensitivity of the other system components, such as electronics gains, are unaccounted for. The inventors at UCI have developed a new approach that improves the long term bias stability of Coriolis vibratory gyroscopes. They have developed and implemented two new techniques, utilizing the quadrature error and voltages of the amplitude gain control (ACG). The novel methods have been combined with signals from the Side-Band Ratio (SBR) detection technique, which has never been used for stabilizing the mechanical amplitude of the gyroscope. The three techniques have been combined and applied to a silicon quadruple mass gyroscope with natural frequency of 3 kHz, frequency mismatch of <0.5 Hz, and isotropic quality factor of 950, vacuum packed without getter. The experimentally demonstrated bias stability was shown to be 0.1 deg/hr after 300 seconds, and the value was retained for over 3 hours.

Advantages

§ Combination of 3 techniques

§ Addresses electronic gains as well as mechanical parameters

§ Bias stability maintained for >3 hrs

Patent Status

State Of Development

The inventors have a working prototype system.