Continuous mode reversal for rejecting drift in gyroscopes

A vibratory gyroscope apparatus, comprising:

• (a) a mechanical resonator having a first mode of vibration in a first axis of motion and an associated first natural frequency, and a second mode of vibration in a second axis of motion having an associated second natural frequency, wherein angular rate of motion input couples energy between said first mode of vibration and said second mode of vibration;
• (b) sensors and actuators for each of the first mode and the second mode for transduction of an electrical signal into a mechanical vibration and transduction of a mechanical vibration into an electrical signal;
• (c) driving circuitry connected to the actuators creating mechanical forces to maintain substantially constant, non-zero velocity amplitude vibrations in the first mode at a first frequency and the second mode at a second frequency;
• (d) output circuitry to infer an angular rate of motion from the mechanical forces created by said driving circuitry to said first mode or said second mode, or both said first mode and said second mode;
• and
• (e) wherein said output circuitry is configured to provide bias error cancellation based on excitation and sensing of both resonator axes and measuring sustaining forces applied to both axes of said mechanical resonator, in response to:
• (i) modulating angular rate of motion to a frequency sufficiently above one or more bias error sources to allow filtering bias error sources out of angular rate of motion, or
• (ii) driving oscillating frequencies of said first and said second axes of motion at two different frequencies from which modulation arises that cancels error terms due to non-zero resonator bandwidth and mismatch between natural frequency and driven frequency, or
• (iii) rejecting cross-spring bias error in response to it appearing in quadrature with the rate signal, or
• (iv) rejecting cross-damping bias error in response to combining measurement of angular rate of motion from said first and second axes of motion, as contrasted to gyroscope configurations having a drive and a sense axis which do not allow cross-damping error to be separated from angular rate of motion since they only measure rate on their sense axis, or
• (v) cancelling bias error in response to any combination of approaches (i) through (iv) listed above.

A vibratory gyroscope apparatus, comprising:

• (a) a mechanical resonator having a first mode of vibration in a first axis of motion and an associated first natural frequency, and a second mode of vibration in a second axis of motion having an associated second natural frequency, wherein angular rate of motion input couples energy between said first mode of vibration and said second mode of vibration;
• (b) sensors and actuators for each of the first mode and the second mode for transduction of an electrical signal into a mechanical vibration and transduction of a mechanical vibration into an electrical signal;
• (c) driving circuitry connected to the actuators creating mechanical forces to maintain substantially constant, non-zero velocity amplitude vibrations in the first mode at a first frequency and the second mode at a second frequency;
• (d) output circuitry to infer an angular rate of motion from the mechanical forces created by said driving circuitry to said first mode or said second mode, or both said first mode and said second mode;
• and
• (e) wherein said output circuitry is configured to provide bias error cancellation based on excitation and sensing of both resonator axes and measuring sustaining forces applied to both axes of said mechanical resonator, in response to:
• (i) modulating angular rate of motion to a frequency sufficiently above one or more bias error sources to allow filtering bias error sources out of angular rate of motion,
• (ii) driving oscillating frequencies of said first and said second axes of motion at two different frequencies from which modulation arises that cancels error terms due to non-zero resonator bandwidth and mismatch between natural frequency and driven frequency,
• (iii) rejecting cross-spring bias error in response to it appearing in quadrature with the rate signal, and
• (iv) rejecting cross-damping bias error in response to combining measurement of angular rate of motion from said first and second axes of motion, as contrasted to gyroscope configurations having a drive and a sense axis which do not allow cross-damping error to be separated from angular rate of motion since they only measure rate on their sense axis.