Method for reducing bias error in a vibrating structure gyroscope

Abstract

A method for reducing bias error in a Vibrating Structure Gyroscope having a vibrating structure, a primary drive for putting the vibrating structure into carrier mode resonance, a primary pick-off device for sensing carrier mode motion, a secondary pick-off for sensing response mode vibration of the vibrating structure in response to applied rotation rate, a secondary drive for applying a force to control the response mode motion, closed loop primary control loops for maintaining a fixed amplitude of motion at the primary pick-off device, for maintaining the drive frequency at the resonance maximum, and secondary control loops for maintaining a null at the secondary pick-off device. In the method the ratio SFover SFis measured from the secondary control loop to provide a direct measurement of Sin (φ+φ), according to the relationship SF=SF×Sin (φ+) where SFis the quadrature scalefactor SFis the in-phase scalefactor, φis the phase error in the secondary drive and φis the phase error in the primary pick-off device. The total phase error φis obtained directly from the measured Sin (φ+φ) according to the relationship; φ=φ+φand phase corrections applied to the secondary drive and/or primary pick-off device to reduce the phase error φ, and hence the quadrature bias error, to enhance the performance of the gyroscope.