Cloverleaf microgyroscope with electrostatic alignment and tuning

• US 7,159,441 B2
• Filed: 05/11/2004
• Issued: 01/09/2007
• Est. Priority Date: 08/09/2001
• Status: Expired due to Term

• Current Assignee: California Institute of Technology, The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Gutierrez, Roman C., Challoner, A. Dorian, Tang, Tony K.
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): FAYYAZ, NASHMIYA SAQIB
• Application Number:
  US10/843,139
• Publication Number:
  US 20040237626A1
• Time in Patent Office: 973 Days
• Field of Search: 73/13.7, 73/13.8, 735/141.5, 735/040.4, 735/142.9, 73/17.7, 735/040.2
• US Class Current: 73/1.77
• 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 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• 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
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape

Abstract

A micro-gyroscope (10) having closed loop output operation by a control voltage (V_ty), that is demodulated by a drive axis (x-axis) signal V_thx of the sense electrodes (S1, S2), providing Coriolis torque rebalance to prevent displacement of the micro-gyroscope (10) on the output axis (y-axis) V_thy˜0. Closed loop drive axis torque, V_tx maintains a constant drive axis amplitude signal, V_thx. The present invention provides independent alignment and tuning of the micro-gyroscope by using separate electrodes and electrostatic bias voltages to adjust alignment and tuning. A quadrature amplitude signal, or cross-axis transfer function peak amplitude is used to detect misalignment that is corrected to zero by an electrostatic bias voltage adjustment. The cross-axis transfer function is either V_thy/V_ty or V_tnx/V_tx. A quadrature signal noise level, or difference in natural frequencies estimated from measurements of the transfer functions is used to detect residual mistuning, that is corrected to zero by a second electrostatic bias voltage adjustment.

Claims

1. A method for aligning a cloverleaf micro-gyroscope having a resonator having an affixed central proof mass, the resonator being elastically suspended in an x-y plane defining a resonator having rocking inertia and rocking suspension, at least four electrodes in an electrode plane adjacent the x-y plane, the at least four electrodes for actuating and sensing a rocking motion of the resonator rocking suspension, and closed loop control of the resonator rocking motion about the x and y axes, said method comprising the steps of:

detecting mechanical misalignment in rocking vibration of the resonator in the x-y plane; and

nulling the mechanical misalignment of the resonator to zero by applying an electrostatic bias adjustment to an electrode of the at least four electrodes in the electrode plane to produce a cross-coupling spring stiffness, K^e_xy and resulting dynamic alignment torques to cancel dynamic mechanical misalignment torques caused by misalignment of the resonator rocking suspension and rocking inertia in the x-y plane.

2. The method as claimed in claim 1 wherein the step of detecting mechanical misalignment further comprises, detecting mechanical misalignment by sensing a quadrature signal amplitude obtained by demodulation of a signal of the y-axis using a signal in quadrature to an x-axis rate signal.

3. The method as claimed in claim 1 further comprising the step of nulling an in-phase bias.

4. The method as claimed in claim 3 wherein the step of nulling an in-phase bias further comprises electronically coupling a torque component of the x-axis with the y-axis.

5. A method for tuning a cloverleaf micro-gyroscope having a resonator having an affixed central proof mass, the resonator being elastically suspended in an x-y plane defining a resonator having rocking inertia, mechanical stiffness and rocking suspension about the x and y axes, at least four electrodes in an electrode plane adjacent the x-y plane, the at least four electrodes for actuating and sensing a rocking motion of the resonator in the x-y plane, and closed loop control of the rocking motion in the x-y plane, said method comprising the steps of:

detecting residual mistuning that is a result of mechanical asymmetry of the resonator rocking inertia or mechanical stiffness by detecting a predefined signal at an output of the micro-gyroscope; and

correcting the residual mistuning to zero by applying an electrostatic bias adjustment to an electrode of the at least four electrodes in the electrode plane to produce an electrostatic stiffness and dynamic torque asymmetry that counteracts a mismatch in dynamic torques due to the resonator rocking inertia or mechanical stiffness.

6. The method as claimed in claim 5 wherein the step of detecting a predefined signal further comprises detecting a quadrature signal noise level.

7. The method as claimed in claim 5 wherein the step of detecting a predefined signal further comprises calculating the difference in estimated resonance frequencies of two direct transfer functions.

8. A method for independently aligning and tuning a cloverleaf micro-gyroscope having a resonator having an affixed central proof mass, the resonator being elastically suspended in an x-y plane defining a resonator having rocking inertia and rocking suspension, at least four electrodes in an electrode plane adjacent the x-y plane, the electrodes for actuating and sensing a rocking motion of the resonator in the x-y plane, and closed loop control of the resonator rocking motion about the x and y axes, said method comprising the steps of:

detecting a mechanical misalignment in rocking vibration of the resonator in the x-y plane;

nulling the effect of the mechanical misalignment of the resonator rocking vibration in the x-y plane to zero by applying an electrostatic bias adjustment to an electrode of the at least four electrodes to produce a cross-coupling electrostatic spring stiffness K^e_xy and resulting dynamic alignment torques to cancel the mechanical misalignment arising from the misalignment of the resonator rocking inertia and rocking suspension in the x-y plane;

detecting a residual mistuning that is a result of mechanical asymmetry by detecting a predefined signal at an output of the micro-gyroscope; and

correcting the residual mistuning by applying an electrostatic bias adjustment to an electrode of the at least four electrodes to produce an electrostatic stiffness that counteracts a mismatch of dynamic torques due to mechanical asymmetry of the resonator rocking inertia or rocking suspension.

9. The method as claimed in claim 8 wherein the step of detecting a predefined signal further comprises detecting a quadrature signal noise level.

10. The method as claimed in claim 8 wherein the step of detecting a predefined signal further comprises measuring a transfer function.

11. The method as claimed in claim 8 further comprising the step of nulling in-phase bias.

12. The method as claimed in claim 8 wherein the step of correcting the residual mistuning to zero further comprises the step of adjusting a total stiffness of said micro-gyroscope.

13. The method as claimed in claim 8 wherein the micro-gyroscope closed loop control further comprises:

using electrodes in addition to the at least four electrodes as sensors and actuators for the step of nulling the effect of the mechanical misalignment of the resonator rocking vibration and for the step of correcting the residual mistuning.

14. The method as claimed in claim 8 further comprising the step of applying a bias voltage to an electrode of the at least four electrodes that is different from a bias voltage applied to another electrode of the at least four electrodes.

15. The method as claimed in claim 8 further comprising the step of introducing a relative gain mismatch, δ

_T≠

0, to each electrode of the at least four electrodes.

16. The method as claimed in claim 8 further comprising the step of maximizing a stiffness matrix K.