Distributed-mass micromachined gyroscopes operated with drive-mode bandwidth enhancement

• US 7,100,446 B1
• Filed: 07/20/2004
• Issued: 09/05/2006
• Est. Priority Date: 07/20/2004
• 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: Acar, Cenk, Shkel, Andrei M.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/895,508
• Time in Patent Office: 777 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.2, 735/041.3, 735/041.4, 735/041.5
• US Class Current: 73/504.13
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A micromachined z-axis rate gyroscope with multidirectional drive-mode has an increased drive-mode bandwidth for relaxing mode-matching requirement in which the drive and sense modes are completely decoupled. By utilizing multiple drive-mode oscillators with incrementally spaced resonance frequencies, wide-bandwidth response is achieved in the drive-mode, leading to reduced sensitivity to structural and thermal parameter fluctuations. Quadrature error and zero-rate-output are also minimized, due to the enhanced decoupling of multi-directional linear drive-mode and the torsional sense-mode. Bulk-micromachined prototypes have been fabricated in a one-mask SOI-based process, and is experimentally characterized.

Claims

1. A distributed-mass micromachined gyroscope comprising:

a supporting frame having a center of symmetry; and

multiple drive mode oscillators distributed symmetrically around the center of the supporting frame and coupled thereto, the multiple drive mode oscillators arranged and configured to have incrementally spaced drive mode resonance frequencies to allow all of the multiple drive mode oscillators to be excited together to jointly generate a resultant Coriolis torque, so that the Coriolis torque defines a wide-bandwidth drive mode.

2. The distributed-mass micromachined gyroscope of claim 1 where the multiple drive mode oscillators each include comb drive actuation.

3. The distributed-mass micromachined gyroscope of claim 1 where the multiple drive mode oscillators each include parallel plate actuation.

4. The distributed-mass micromachined gyroscope of claim 1 where the frame lies in a tangential plane, where the multiple drive mode oscillators each have a drive axis lying in the tangential plane and are driven in phase with each other.

5. The distributed-mass micromachined gyroscope of claim 4 where the frame has a multiplicity of tangent sides with a corresponding tangential direction, and where each of the multiple drive mode oscillators are driven in a direction normal to one of the multiplicity of tangent sides of the frame, and where each of the multiple drive mode oscillators are constrained in the tangential direction with respect to the frame.

6. The distributed-mass micromachined gyroscope of claim 1 where the frame has an anchored center and where multiple drive mode oscillators are distributed symmetrically around the anchored center of the frame.

7. The distributed-mass micromachined gyroscope of claim 5 where the frame has an anchored center and where multiple drive mode oscillators are distributed symmetrically around the anchored center of the frame.

8. The distributed-mass micromachined gyroscope of claim 7 where the drive axis of each of the multiple drive mode oscillators is radially directed with respect to the anchored center of the frame.

9. The distributed-mass micromachined gyroscope of claim 8 where each of the multiple drive mode oscillators includes a corresponding sensing capacitor and where in the presence of an angular rotation rate about a z axis, which is perpendicular to the frame, Coriolis forces are induced on each of the multiple drive mode oscillators orthogonal to each corresponding drive-mode oscillation direction so that each of the induced Coriolis forces lie in the tangential direction in the plane of the frame and combine to generate a resultant torque on the frame with a net Coriolis torque exciting the frame into torsional oscillations about the z-axis, which are detected by the sensing capacitors for angular rate measurement.

10. The distributed-mass micromachined gyroscope of claim 1 where each of the multiple drive mode oscillators include a drive actuation which applies a corresponding drive force to the drive mode oscillator and a sensing electrode attached to the frame to sense movement of the drive mode oscillator, and where the multiple drive mode oscillators have radial symmetry with respect to each other so that the drive forces applied to the drive-mode oscillators cancel out in all directions due to the radial symmetry and a net driving force on the gyroscope reduces to substantially zero, where the sensing electrodes do not deflect with respect to the frame due to drive-mode oscillations, so that instability and drift due to mechanical coupling between drive and sense modes is minimized, and complete decoupling of multi-directional linear drive-mode and a rotational sense-mode is achieved.

11. The distributed-mass micromachined gyroscope of claim 1 where the gyroscope is nominally operated in a flat region of a Coriolis torque frequency response by arrangement of the incremental spacing of drive mode resonance frequencies and where a sense-mode resonance frequency of the gyroscope is designed to be in the same frequency band so that the requirement on the degree of mode-matching is relaxed and robustness against structural and thermal parameter fluctuations is achieved.

12. The distributed-mass micromachined gyroscope of claim 11 where each of the multiple drive mode oscillators has a bandwidth and where the frequency separation of the incremental spacing of drive mode resonance frequencies between each of the multiple drive mode oscillators is less than the bandwidth of one oscillator.

13. The distributed-mass micromachined gyroscope of claim 12 where each of the multiple drive mode oscillators includes a parallel plate actuator and where each of the multiple drive mode oscillators were electrostatically tuned to achieve uniform and smaller separation of drive mode resonance frequencies.

14. The distributed-mass micromachined gyroscope of claim 1 where each of the multiple drive mode oscillators includes a sensing electrode with a corresponding sense-mode resonance frequency, the sense-mode resonance frequency being designed higher than the corresponding drive-mode frequency for tuning down to a center driving frequency.

15. A method of operating a micromachined gyroscope comprising:

driving multiple drive mode oscillators at incrementally spaced drive mode resonance frequencies, the multiple drive mode oscillators distributed symmetrically around a center of a supporting frame and coupled thereto, the supporting frame having a center of symmetry to allow all of the multiple drive mode oscillators to be excited together to jointly generate a resultant Coriolis torque, so that the Coriolis torque defines a wide-bandwidth drive mode; and

sensing the resultant Coriolis torque applied to the frame by the multiple drive mode oscillators, when the gyroscope is accelerated.

16. The method of claim 15 where driving the multiple drive mode oscillators comprises driving each of the multiple drive mode oscillators with a comb drive actuation.

17. The method of claim 15 where driving the multiple drive mode oscillators comprises driving each of the multiple drive mode oscillators with a parallel plate actuation.

18. The method of claim 15 where the frame lies in a tangential plane, and where driving the multiple drive mode oscillators comprises driving each of the multiple drive mode oscillators along a drive axis lying in the tangential plane and driving each of the multiple drive mode oscillators in phase with each other.

19. The method of claim 18 where the frame has a multiplicity of tangent sides with a corresponding tangential direction, and where driving the multiple drive mode oscillators comprises driving each of the multiple drive mode oscillators in a direction normal to one of the multiplicity of tangent sides of the frame, and constraining the motion of each of the multiple drive mode oscillators in the tangential direction with respect to the frame.

20. The method of claim 15 where the frame has an anchored center and where driving the multiple drive mode oscillators comprises driving the multiple drive mode oscillators in directions symmetrically distributed around the anchored center of the frame.

21. The method of claim 19 where the frame has an anchored center and where driving the multiple drive mode oscillators comprises driving the multiple drive mode oscillators in directions symmetrically distributed around the anchored center of the frame.

22. The method of claim 21 where driving the multiple drive mode oscillators in directions symmetrically distributed around the anchored center of the frame comprises driving each of the multiple drive mode oscillators in a radial direction with respect to the anchored center of the frame.

23. The method of claim 22 where each of the multiple drive mode oscillators includes a corresponding sensing capacitor and further comprising rotating the gyroscope about a z axis, which is perpendicular to the frame, inducing Coriolis forces in the tangential direction in the plane of the frame and orthogonal to each corresponding drive-mode oscillation direction in each of the multiple drive mode oscillators, generating a combined resultant torque on the frame with a net Coriolis torque, and exciting the frame into torsional oscillations about the z-axis, and where sensing the resultant Coriolis torque comprises detecting the torsional oscillations by the sensing capacitors for an angular rate measurement.

24. The method of claim 15 where driving the multiple drive mode oscillators comprises driving each of the multiple drive mode oscillators with a radial symmetry with respect to each other so that the drive forces applied to the drive-mode oscillators cancel out in all directions due to the radial symmetry and a net driving force on the gyroscope reduces to substantially zero, sensing motion of the frame derived from collective motion of the drive mode oscillators without deflection of sensing electrodes with respect to the frame due to drive-mode oscillations, minimizing that instability and drift due to mechanical coupling between drive and sense modes, and completely decoupling a multi-directional linear drive-mode and a rotational sense-mode.

25. The method of claim 15 further comprising operating the gyroscope in a flat region of a Coriolis torque frequency response by incrementally spacing the drive mode resonance frequencies, and detecting a sense-mode resonance frequency of the gyroscope in the same frequency band to relax the requirement on the degree of mode-matching and achieving robustness against structural and thermal parameter fluctuations.

26. The method of claim 25 where each of the multiple drive mode oscillators has a bandwidth and where incrementally spacing the drive mode resonance frequencies comprises separating the frequencies of the drive mode resonance frequencies between each of the multiple drive mode oscillators by less than the bandwidth of one oscillator.

27. The method of claim 26 where each of the multiple drive mode oscillators includes a parallel plate actuator and further comprising electrostatically tuning each of the multiple drive mode oscillators to achieve uniform and smaller separation of drive mode resonance frequencies.

28. The method of claim 15 where each of the multiple drive mode oscillators includes a sensing electrode with a corresponding sense-mode resonance frequency, where driving the multiple drive mode oscillators comprises tuning down to a center driving frequency by setting the sense-mode resonance frequency at a higher frequency than the corresponding drive-mode frequency.