Bias and quadrature reduction in class II coriolis vibratory gyros

• US 20070039386A1
• Filed: 08/07/2006
• Published: 02/22/2007
• Est. Priority Date: 08/08/2005
• Status: Active Grant

• Current Assignee: Litton Systems Incorporated, Northrop Grumman Corporation
• Original Assignee: Litton Systems Incorporated
• Inventors: Stewart, Robert, Wyse, Stanley
• Granted Patent: US 7,565,839 B2
• Time in Patent Office: Days
• US Class Current: 73/504.140
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5649 Signal processing
• CPC Class Codes: G01C 19/5691 of essentially three-dimensional vibrators, e.g. wine glass-type vibrators

Abstract

The method and apparartus in one embodiment may have the steps of: providing a two-dimensional axisymmetric oscillator having a beam containing two principal elastic axes and two principal damping axes; driving the beam with drive components to oscillate; driving, during a first period, the beam along a drive axis of the beam in a direction normal to one pair of faces of the beam while Coriolis coupled vibration is sensed along a sense axis of the beam normal to an orthogonal pair of faces of the beam; reversing, during a second period, drive and sense axes driving the beam; reducing a bias of the beam to zero; and reducing a quadrature of the beam to zero.

Claims

1. An apparatus, comprising:

class II coriolis vibratory gyro (CVG);

a bias that is equal to sin 2θ

_τ

(1/τ

₁−

1/τ

₂)/2k rad/sec;

a quadrature that is equal to sin 2θ

_ω

(ω

₁−

ω

₂)/2k rad/sec;

where;

θ

_τ

=angle between vibration drive axis and principal damping axis;

θ

_ω

=angle between vibration drive axis and principal elastic axis;

τ

₁ and τ

₂=damping time constant in each of the principal damping axes;

ω

₁ and ω

₂=resonant frequency in each of the principal elastic axes; and

k=geometry dependant scaling constant; and

means for reducing a bias to substantially zero; and

means for reducing a quadrature to substantially zero.

2. The apparatus according to claim 1, wherein a magnitude of gyro bias and quadrature of the gyro has a continuous reduction in real time.

3. A method, comprising:

providing a class II coriolis vibratory gyro (CVG), a bias of the gyro being equal to sin 2θ

_τ

(1/τ

₁−

1/τ

₂)/2k rad/sec, and a quadrature of the gyro being equal to sin 2θ

_ω

(ω

₁−

ω

₂)/2k rad/sec;

where;

θ

_τ

=angle between vibration drive axis and principal damping axis;

θ

_ω

=angle between vibration drive axis and principal elastic axis;

T₁ and T₂=damping time constant in each of the principal damping axes;

ω

₁ and ω

₂=resonant frequency in each of the principal elastic axes; and

k=geometry dependant scaling constant; and

reducing a bias to zero; and

reducing a quadrature to zero.

4. The method according to claim 3, wherein a servo is operatively coupled to the gyro, and wherein the method further comprises controlling proportioning of a drive signal to gyro by the servo that nulls a bias that is being estimated.

5. The method according to claim 3, wherein the gyro is driven by drive and sense electrodes that are operatively coupled to the gyro, and

wherein in the step of reducing a quadrature of the gyro to zero, the method further comprises:

applying DC voltages to the drive and sense electrodes;

introducing, via the DC voltages, beam, a negative electrostatic spring which alters orientation of the principal elastic axes of the gyro.

6. The method according to claim 5, wherein a rate servo is operatively coupled to the gyro, and wherein magnitude and ratio of the DC voltages are servoed to align the principal elastic axes to a drive axis and reduce a quadrature portion of the rate servo to zero.

7. An apparatus, comprising:

a beam in a vibrating beam gyro;

drive components operatively coupled to the beam, the drive components driving the beam to oscillate;

a Coriolis induced vibration in two orthogonal faces of the beam;

means for reducing a bias of the beam to zero; and

means for reducing a quadrature of the beam to zero.

8. The apparatus according to claim 7, wherein the drive components drive the beam to oscillate across corners of the beam at approximately 45 degrees to sides of the beam, wherein resulting 45°

drive orientation closely matches an orientation of a principal elastic axis of the beam when small dimensional tolerances cause resonant frequencies along the principal elastic axes to be different.

9. The apparatus according to claim 7, wherein the drive components drive the beam to oscillate across corners of the beam at approximately 45 degrees to sides of the beam, wherein small tolerance variations of the beam cause principal damping axes to be oriented substantially 45°

to faces of the beam.

10. The apparatus according to claim 7, wherein a magnitude of gyro bias and quadrature of the gyro has a continuous reduction in real time.

11. The apparatus according to claim 7, wherein the vibrating beam comprises a rectangular, triangular, hexagonal, octagonal, or circular prism substantially symmetric for oscillation in first and second directions.

12. The apparatus according to claim 11, wherein the first direction is substantially perpendicular to the second direction.

13. The apparatus according to claim 12, wherein the apparatus further comprises a frame that supports the vibrating beam in a plane, wherein the first direction comprises an in-plane direction, and wherein the second direction comprises an out-of-plane direction.

14. A method, comprising:

providing a two-dimensional axisymmetric oscillator having a beam containing two principal elastic axes and two principal damping axes;

driving the beam with drive components to oscillate;

reducing a bias of the beam to zero; and

reducing a quadrature of the beam to zero.

15. The method according to claim 14, wherein the method further comprises reducing, by increasing a drive signal on one face of the beam and decreasing a signal of the orthogonal face of the beam, an angle, between a drive axis of the beam and a principal damping axis of the beam, to zero while maintaining a constant drive amplitude.

16. The method according to claim 15, wherein a servo is operatively coupled to the beam, and wherein the method further comprises controlling proportioning of a drive signal to two orthogonal faces of the beam by the servo that nulls a bias that is being estimated.

17. The method according to claim 14, wherein the beam is driven by drive and sense electrodes that are operatively coupled to the beam, and

wherein in the step of reducing a quadrature of the beam to zero, the method further comprises:

applying DC voltages to the drive and sense electrodes;

proportioning, via the DC voltages, between orthogonal faces of the beam, to thereby introduce a negative electrostatic spring which alters orientation of the principal elastic axes of the beam.

18. The method according to claim 17, wherein a rate servo is operatively coupled to the gyro, and wherein magnitude and ratio of the DC voltages are servoed to align the principal elastic axes to a drive axis and reduce a quadrature portion of the rate servo to zero.

19. A method, comprising:

providing a two-dimensional axisymmetric oscillator having a beam containing two principal elastic axes and two principal damping axes;

driving the beam with drive components to oscillate across corners of the beam at approximately 45 degrees to sides of the beam;

driving, during a first period, the beam along a drive axis of the beam in a direction normal to one pair of faces of the beam while Coriolis coupled vibration is sensed along a sense axis of the beam normal to an orthogonal pair of faces of the beam;

reversing, during a second period, drive and sense axes driving the beam;

reducing a bias of the beam to zero; and

reducing a quadrature of the beam to zero.

20. The method according to claim 19, wherein the method further comprises reducing, by increasing a drive signal on one face of the beam and decreasing a signal of the orthogonal face of the beam, an angle, between a drive axis of the beam and a principal damping axis of the beam, to zero while maintaining a constant drive amplitude.

21. The method according to claim 20, wherein a servo is operatively coupled to the beam, and wherein the method further comprises controlling proportioning of a drive signal to two orthogonal faces of the beam by the servo that nulls a bias that is being estimated.

22. The method according to claim 21, wherein the beam is driven by drive and sense electrodes that are operatively coupled to the beam, and

wherein in the step of reducing a quadrature of the beam to zero, the method further comprises:

applying DC voltages to the drive and sense electrodes;

proportioning, via the DC voltages, between orthogonal faces of the beam, to thereby introduce a negative electrostatic spring which alters orientation of the principal elastic axes of the beam.

23. The method according to claim 19, wherein a rate servo is operatively coupled to the oscillator, and wherein magnitude and ratio of the DC voltages are servoed to align the principal elastic axes to a drive axis and reduce a quadrature portion of the rate servo to zero.

24. The method according to claim 23, wherein the drive components comprise at least one of electrostatic drive components, magnetic drive and piezoelectric drive components.

25. The method according to claim 19, wherein the sensor components comprise at least one of capacitive pickoff sensors, magnetic pickoff sensors, piezoresistive sensors, and piezoelectric pickoff sensors.

26. The method according to claim 19, wherein a resulting 45°

drive orientation substantially matches an orientation of the principal elastic axis of the beam when small dimensional tolerances cause resonant frequencies along the principal elastic axes to be different.