CONTINUOUS MODE REVERSAL FOR REJECTING DRIFT IN GYROSCOPES

• US 20160109258A1
• Filed: 10/15/2015
• Published: 04/21/2016
• Est. Priority Date: 04/16/2013
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Boser, Bernhard E., Kline, Mitchell H., Izyumin, Igor, Yeh, Yu-Ching, Eminoglu, Burak
• Granted Patent: US 9,846,055 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5705 using masses driven in reciprocating rotary motion about an axis
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A vibratory gyroscope system is described which utilizes a mechanical resonator having a first mode of vibration and an associated first natural frequency, and a second mode of vibration having an associated second natural frequency. The angular rate of motion input couples energy between the first and second modes of vibration. The gyroscope has driver circuits, sensors and actuators for the first and second modes. The invention utilizes a bias error shifting method which provides for shifting the bias error away from DC to a higher frequency, where it can be removed by low pass filtering. As a result of the inventive method, gyroscope systems can be produced with significantly lower bias error.

Claims

1. A vibratory gyroscope apparatus, comprising:

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;

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;

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; and

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;

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.

2. The apparatus recited in claim 1, wherein said bias error cancelation is achieved in response to angular rate of motion being modulated to a frequency above one or more bias error sources, whereby bias error is cancelled by filtering it out, since the rate signal is at a higher frequency than the bias error.

3. The apparatus recited in claim 2, wherein said modulating of frequency above the bias error sources is in contrast to techniques in which certain bias error sources are added to angular rate of motion.

4. The apparatus recited in claim 1, wherein said bias error cancelation is performed in the apparatus without interrupting the ordinary rate measurement process and without the need for a known, or reference, angular rate input.

5. The apparatus recited in claim 1, wherein modulation that arises because said first and second axes of motion are oscillating at two different frequencies cancels error terms due to the non-zero resonator bandwidth and mismatch between natural frequency and driven frequency.

6. The apparatus recited in claim 1, wherein cross-spring bias error is rejected as it appears in quadrature with the rate signal.

7. The apparatus recited in claim 1, wherein cross-damping bias error is cancelled in response to combining rate measurements 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.

8. The apparatus recited in claim 1, wherein said apparatus performs sensing of both said first and second axes of motion for said mechanical resonator, as distinct from approaches which drive a first axis and sense on a second axis.

9. The apparatus recited in claim 1, wherein said natural frequencies on said first axis and said second axis of motion are not equal resulting in a finite frequency difference between the axes, as a split frequency.

10. The apparatus recited in claim 1, further comprising at least one synchronous demodulator within said output circuitry, wherein said synchronous demodulator is configured for generating in-phase components, quadrature component, or a combination of in phase and quadrature components, of mechanical force applied to a mode with a phase reference being determined by displacement or velocity of the mode.

11. The apparatus recited in claim 1, further comprising amplitude control circuitry connected to said sensors for controlling said driving circuitry, wherein said amplitude control circuitry adjusts the magnitude of applied driving voltage in order to maintain a constant displacement amplitude or velocity amplitude of the said first mode or said second mode, or both said first mode and said second mode.

12. The apparatus recited in claim 11, wherein the displacement or velocity amplitudes of the first mode and the second mode are constant and substantially equal.

13. The apparatus recited in claim 11, further comprising a rate reference detector in said output circuitry, wherein said rate reference detector generates one or more of the phase difference signals between first mode and second mode vibrations.

14. The apparatus recited in claim 13, wherein said one or more of the phase difference signals comprise a sine of said phase difference, or a cosine of said phase difference, or both a sine and a cosine of said phase difference.

15. The apparatus recited in claim 13, wherein the output circuitry further comprises a rate demodulator connected to a synchronous demodulator and rate reference detector, wherein said rate demodulator produces one or both of the in-phase and quadrature components of at least one of the demodulated mechanical forces or at least one of a linear combination of demodulated forces with a phase reference being defined by the rate reference detector.

16. The apparatus recited in claim 1, wherein said variable gain amplifier (VGA) and phase shifter comprises a Pierce oscillator circuit.

17. The apparatus recited in claim 1, wherein said vibratory gyroscope comprises a high-bandwidth gyroscope configured with oscillation frequencies determined by external oscillation references, instead of utilizing self-referenced oscillation in which frequencies are determined by natural resonant frequencies of both axes, whereby utilizing the external oscillation references additional information is obtained from said vibratory gyroscope to extend bandwidth.

18. The apparatus recited in claim 1, wherein said mechanical resonator is suspended for movement along two orthogonal axes simultaneously.

19. The apparatus recited in claim 1, wherein said vibratory gyroscope is configured to follow a Lissajous trajectory.

20. The apparatus recited in claim 1, wherein said vibratory gyroscope is configured for application to inertial navigation, stabilization, or maintaining direction.

21. 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.

22. The apparatus recited in claim 21, wherein said bias error cancelation is performed in the apparatus without interrupting the ordinary rate measurement process and without the need for a known, or reference, angular rate input.

23. The apparatus recited in claim 21, wherein said apparatus performs sensing of both said first and second axes of motion for said mechanical resonator, as distinct from approaches which drive a first axis and sense on a second axis.

24. The apparatus recited in claim 21, wherein said natural frequencies on said first axis and said second axis of motion are not equal resulting in a finite frequency difference between the axes, as a split frequency.

25. The apparatus recited in claim 21, further comprising at least one synchronous demodulator within said output circuitry, wherein said synchronous demodulator is configured for generating in-phase components, quadrature component, or a combination of in phase and quadrature components, of mechanical force applied to a mode with a phase reference being determined by displacement or velocity of the mode.

26. The apparatus recited in claim 21, further comprising amplitude control circuitry connected to said sensors for controlling said driving circuitry, wherein said amplitude control circuitry adjusts the magnitude of applied driving voltage in order to maintain a constant displacement amplitude or velocity amplitude of the said first mode or said second mode, or both said first mode and said second mode.

27. The apparatus recited in claim 26, wherein the displacement or velocity amplitudes of the first mode and the second mode are constant and substantially equal.

28. The apparatus recited in claim 26, further comprising a rate reference detector in said output circuitry, wherein said rate reference detector generates one or more of the phase difference signals between first mode and second mode vibrations.

29. The apparatus recited in claim 28, wherein said one or more of the phase difference signals comprise a sine of said phase difference, or a cosine of the said phase difference, or both a sine and a cosine of said phase difference.

30. The apparatus recited in claim 28, wherein the output circuitry further comprises a rate demodulator connected to a synchronous demodulator and rate reference detector, wherein said rate demodulator produces one or both of the in-phase and quadrature components of at least one of the demodulated mechanical forces or at least one of a linear combination of demodulated forces with a phase reference being defined by the rate reference detector.

31. The apparatus recited in claim 21, wherein said variable gain amplifier (VGA) and phase shifter comprises a Pierce oscillator circuit.

32. The apparatus recited in claim 21, wherein said vibratory gyroscope comprises a high-bandwidth gyroscope configured with oscillation frequencies determined by external oscillation references, instead of utilizing self-referenced oscillation in which frequencies are determined by natural resonant frequencies of both axes, whereby utilizing the external oscillation references additional information is obtained from said vibratory gyroscope to extend bandwidth.

33. 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.