Torsional nonresonant z-axis micromachined gyroscope with non-resonant actuation to measure the angular rotation of an object

• US 20060032308A1
• Filed: 08/12/2005
• Published: 02/16/2006
• Est. Priority Date: 08/16/2004
• 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.
• Granted Patent: US 7,421,898 B2
• Time in Patent Office: Days
• US Class Current: 73/504.120
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A gimbal-type torsional z-axis micromachined gyroscope with a non-resonant actuation scheme measures angular rate of an object with respect to the axis normal to the substrate plane (the z-axis). A 2 degrees-of-freedom (2-DOF) drive-mode oscillator is comprised of a sensing plate suspended inside two gimbals. By utilizing dynamic amplification of torsional oscillations in the drive-mode instead of resonance, large oscillation amplitudes of the sensing element is achieved with small actuation amplitudes, providing improved linearity and stability despite parallel-plate actuation. The device operates at resonance in the sense direction for improved sensitivity, while the drive direction amplitude is inherently constant within the same frequency band.

Claims

1. A MEMS-based inertial torsional z-axis surface-micromachined gyroscope with non-resonant actuation to measure the angular rotation of an object comprising:

a substrate;

a torsional 2-DOF drive-mode oscillator coupled to the substrate and comprised of one active gimbal and one passive gimbal to achieve large oscillation amplitudes by amplifying the small oscillation amplitude of the driven active gimbal, so that minimization of the nonlinear force profile and minimization of instability due to actuation of the active gimbal are achieved, while substantially eliminating any mode-matching requirement by obtaining a flat operational frequency band in the drive-mode; and

a sensing plate coupled to the torsional 2-DOF drive-mode oscillator.

2. The gyroscope of claim 1 where the torsional 2-DOF drive-mode oscillator includes drive electrodes and where the sensing plate includes sensing electrodes.

3. The gyroscope of claim 2 where the drive electrodes comprise a plurality of electrostatic electrodes and where the sensing plate includes a plurality of parallel plate sensing electrodes.

4. The gyroscope of claim 1 where the active gimbal, passive gimbal and sensing plate lie in a common plane when at rest and are arranged and configured with respect to each other to allow out-of-plane actuation electrodes and out-of-plane sensing electrodes with large actuation electrode areas and large detection electrode areas.

5. The gyroscope of claim 1 where the 2 DOF drive-mode oscillator is driven by parallel-plate actuation and where the 2 DOF drive-mode oscillator dynamically amplifies torsional oscillations in the drive-mode instead of using matched resonance to achieve large drive-mode oscillation amplitudes of the sensing plate with small actuation amplitudes of the drive electrodes to provide linearity and stability despite parallel-plate actuation of the 2 DOF drive-direction oscillator.

6. The gyroscope of claim 1 where the 2 DOF drive-mode oscillator is arranged and configured to have a wide bandwidth in the drive mode;

so that the mode-matching requirement between the 2 DOF drive-mode oscillator and the sensing plate is relaxed to reduce sensitivity to structural and thermal parameter fluctuations and damping changes introduced in the MEMs fabrication of the gyroscope.

7. The gyroscope of claim 1 where the 2 DOF drive-mode oscillator is arranged and configured to have a generally flat operation region between two resonance peaks in the frequency response curves of the 2-DOF drive-mode oscillator to ensure that the drive-mode oscillation amplitude is insensitive to parameter fluctuations in the operation frequency band resulting in robustness to fluctuations in residual stresses, variations in elastic modulus from run to run in MEMs fabrication, and also insensitivity to thermal fluctuations throughout operation time.

8. The gyroscope of claim 1 where the sensing plate is arranged and configured to operate at resonance in a frequency band in a sense direction for optimal sensitivity, while the 2 DOF drive-mode oscillator is arranged and configured to have a drive direction amplitude which is inherently constant within the same frequency band.

9. A MEMS gyroscope comprising:

a three-mass structure comprised of two gimbals and a sensing plate, a first one of the two gimbals comprising a passive gimbal which contains the sensing plate, the passive gimbal executing large oscillation amplitudes by amplifying small amplitude oscillations of a second one of the two gimbals comprising a driven active gimbal; and

parallel-plate actuators dynamically coupled to the active gimbal, the actuation range of the parallel-plate actuators being narrow to minimize nonlinear force profile applied to the two gimbals and to minimize instability of the gyroscope.

10. The gyroscope of claim 9 further comprising sensing electrodes capacitively coupled to the sensing plate, the sensing electrodes having a large detection capacitance to improve performance and low actuation voltages, to reduce drive-signal interference and lower noise, and to improve robustness against parameter fluctuations.

11. The gyroscope of claim 9 where the two gimbals combine to operate as a 2 DOF oscillator with a wide, flat bandwidth to eliminate any mode-matching requirement with the sensing plate by utilizing dynamic amplification of rotational oscillations of the active gimbal by the passive gimbal instead by resonance matching in the drive direction between the two gimbals and the sensing plate so that small actuation and sensing capacitance limitation of surface-micromachined gyroscopes is overcome, while achieving excitation stability and robustness against fabrication imperfections and fluctuations in operating conditions.

12. A MEMS gyroscope comprising:

a substrate;

a pair of anchors lying along a drive axis, spaced from each other and connected to the substrate;

a pair of first torsional beams lying along the drive axis, each first torsional beam coupled to one of the anchors;

an active gimbal coupled to the pair of first torsional beams and suspended above the substrate by the anchors and the first torsional beams;

a drive electrode disposed on the substrate proximate to the active gimbal to selectively drive the active gimbal into torsional oscillation;

a pair of second torsional beams lying along the drive axis, each second torsional beam coupled to the active gimbal;

a passive gimbal coupled to the pair of second torsional beams and suspended above the substrate by the second torsional beams;

a pair of third torsional beams lying along a sense axis, each third torsional beam coupled to the passive gimbal;

a sensing plate coupled to the pair of third torsional beams and suspended above the substrate by the third torsional beams; and

a sensing electrode disposed on the substrate proximate to the sensing plate to sense torsional oscillation of the sensing plate.

13. The gyroscope of claim 12 where the active gimbal has an interior space and where the passive gimbal is disposed in the interior space of the active gimbal, where the passive gimbal has an interior space and where the sensing plate is disposed in the interior space of the passive gimbal, the active and passive gimbals arranged and configured to torsionally oscillate about the drive axis as a drive-mode oscillator so that the torsional oscillations of the active gimbal are dynamically amplified in the oscillation of the sensing plate.

14. The gyroscope of claim 12 where the substrate, the active gimbal, passive gimbal and sensing plate are each generally planar and each have bilateral symmetry, and where the drive electrode and sensing electrode each comprise at least two separate electrode elements which are generally planar and are symmetrically arranged and configured with respect to the active gimbal and sensing plate respectively.

15. The gyroscope of claim 13 where the active gimbal and passive gimbal are formed in the shape of a rectangular frame and where the sensing plate is a rectangular shaped plate.

16. A method of operating a MEMS-based inertial torsional z-axis surface-micromachined gyroscope with non-resonant actuation to measure the angular rotation of an object comprising:

driving a torsional 2-DOF drive-mode oscillator at nonresonance comprised of an active gimbal and passive gimbal in a flat operational frequency band to amplify small oscillation amplitudes of a driven active gimbal, to minimize the nonlinear force profile and minimize instability due to actuation of the active gimbal, while substantially eliminating any mode-matching requirement; and

sensing torsional oscillation at resonance of a sensing plate coupled to the torsional 2-DOF drive-mode oscillator.

17. The method of claim 16 where driving the torsional 2-DOF drive-mode oscillator at nonresonance comprises electrostatically driving the torsional 2-DOF drive-mode oscillator the torsional 2-DOF drive-mode oscillator and where sensing torsional oscillation at resonance comprises sensing by means of parallel plate capacitance.

18. The method of claim 16 where driving the torsional 2-DOF drive-mode oscillator at nonresonance comprises driving the torsional 2-DOF drive-mode oscillator with out-of-plane actuation electrodes with a large actuation electrode area and where sensing torsional oscillation at resonance comprises sensing with out-of-plane sensing electrodes with a large detection electrode area.

19. The method of claim 16 where driving the torsional 2-DOF drive-mode oscillator at nonresonance comprises driving the 2 DOF drive- mode oscillator by parallel-plate actuation and dynamically amplifying torsional oscillations in the drive-mode instead of using matched resonance to achieve large drive-mode oscillation amplitudes of the sensing electrodes with small actuation amplitudes of the drive electrodes to provide linearity and stability despite parallel-plate actuation of the 2 DOF drive-direction oscillator.

20. The method of claim 16 where driving the torsional 2-DOF drive-mode oscillator at nonresonance in a flat operational frequency band comprises providing the 2 DOF drive-mode oscillator with a wide bandwidth in the drive mode;

so that the mode-matching requirement between the 2 DOF drive-mode oscillator and the sensing plate is relaxed to reduce sensitivity to structural and thermal parameter fluctuations and damping changes introduced in the MEMs fabrication of the gyroscope.

21. The method of claim 16 where driving the torsional 2-DOF drive-mode oscillator at nonresonance in a flat operational frequency band comprises providing a generally flat operational region between two resonance peaks in the frequency response curves of the 2-DOF drive-mode oscillator to ensure that the drive-mode oscillation amplitude is insensitive to parameter fluctuations in the operation frequency band resulting in robustness to fluctuations in residual stresses, variations in elastic modulus from run to run in MEMs fabrication, and also insensitivity to thermal fluctuations throughout operation time.

22. The method of claim 16 where sensing torsional oscillation at resonance comprises operating the sensing plate at resonance in a frequency band in a sense direction for optimal sensitivity, while the 2 DOF drive-mode oscillator is driven with a drive direction amplitude which is inherently constant within the same frequency band.

23. An improvement in a method of operating a MEMS gyroscope comprising:

driving two gimbals of a three-mass structure comprised of two gimbals and a sensing plate with parallel-plate actuators dynamically coupled to the active gimbal, in which the actuation range of the parallel-plate actuators are narrow to minimize nonlinear force profile applied to the two gimbals and to minimize instability of the gyroscope; and

dynamically amplifying small amplitude oscillations of the driven active gimbal to generate large oscillation amplitudes of the passive gimbal.

24. The method of claim 23 where sensing torsional oscillation at resonance of a sensing plate comprises sensing torsional oscillation with sensing electrodes capacitively coupled to the sensing plate with a large detection capacitance to improve performance and low actuation voltages, to reduce drive-signal interference and lower noise, and to improve robustness against parameter fluctuations.

25. The method of claim 23 where driving two gimbals of a three-mass structure comprises combining the operation of the two gimbals to function as a 2 DOF oscillator with a wide, flat bandwidth to eliminate any mode-matching requirement with the sensing plate by utilizing dynamic amplification of rotational oscillations of the active gimbal by the passive gimbal instead by resonance matching in the drive direction between the two gimbals and the sensing plate so that small actuation and sensing capacitance limitation of surface-micromachined gyroscopes is overcome, while achieving excitation stability and robustness against fabrication imperfections and fluctuations in operating conditions.