FORCE REBALANCING FOR MEMS INERTIAL SENSORS USING TIME-VARYING VOLTAGES

• US 20080000296A1
• Filed: 06/29/2006
• Published: 01/03/2008
• Est. Priority Date: 06/29/2006
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Johnson, Burgess R.
• Granted Patent: US 7,444,868 B2
• Time in Patent Office: Days
• US Class Current: 73/514.18
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

MEMS devices and methods employing one or more electrodes coupled to a time-varying rebalancing voltage are disclosed. A MEMS inertial sensor in accordance with an illustrative embodiment can include one or more proof masses, at least one sense electrode positioned adjacent to each proof mass, and one or more torquer electrodes. Rebalancing voltages can be applied to the torquer electrodes to electrostatically null quadrature and/or Coriolis-related proof mass motion along a sense axis of the device. The rebalancing voltages applied to each of the torquer electrodes can be adjusted using feedback from one or more force rebalancing control loops.

Claims

1. A MEMS inertial sensor, comprising:

one or more proof masses adapted to oscillate at a motor drive frequency;

at least one sense electrode positioned adjacent to each of the one or more proof masses, the sense electrode adapted to sense proof mass motion along a sense axis perpendicular to a drive axis of the one or more proof masses; and

one or more time-varying rebalancing voltages adapted to maintain a fixed capacitance between each sense electrode and corresponding proof mass.

2. The MEMS inertial sensor of claim 1, wherein the time-varying rebalancing voltages includes an AC rebalancing voltage.

3. The MEMS inertial sensor of claim 2, wherein the AC rebalancing voltage includes a rebalancing voltage signal component and a carrier voltage signal component.

4. The MEMS inertial sensor of claim 3, wherein the frequency of the rebalancing voltage signal component is approximately half the motor drive frequency.

5. The MEMS inertial sensor of claim 3, wherein the rebalancing voltage signal component is 90°

out-of-phase with the carrier voltage signal component.

6. The MEMS inertial sensor of claim 2, wherein the AC rebalancing voltage is a sinusoidal rebalancing voltage.

7. The MEMS inertial sensor of claim 1, wherein the one or more time-varying rebalancing voltages are outputs from at least one force rebalancing control loop.

8. The MEMS inertial sensor of claim 7, wherein said at least one force rebalancing control loop comprises a single force rebalancing control loop.

9. The MEMS inertial sensor of claim 7, wherein said at least one force rebalancing control loop comprises multiple force rebalancing control loops.

10. The MEMS inertial sensor of claim 1, further comprising one or more torquer electrodes positioned adjacent to each of the one or more proof masses.

11. The MEMS inertial sensor of claim 10, wherein said one or more rebalancing voltages comprises:

an AC rebalancing voltage coupled to the one or more torquer electrodes and adapted to control Coriolis-related motion of the one or more proof masses; and

a DC rebalancing voltage coupled to the one or more torquer electrodes and adapted to control quadrature-related motion of the one or more proof masses.

12. The MEMS inertial sensor of claim 10, wherein said one or more torquer electrodes comprises:

a first number of torquer electrodes adapted to selectively control Coriolis-related motion of the one or more proof masses along the sense axis, and

a second number of torquer electrodes adapted to selectively control quadrature-related motion of the one or more proof masses along the sense axis.

13. The MEMS inertial sensor of claim 12, wherein said first number of torquer electrodes are coupled to a first rebalancing voltage signal outputted from a first force rebalance controller, and wherein said second number of torquer electrodes are coupled to a second rebalancing voltage signal outputted from a second force rebalance controller.

14. The MEMS inertial sensor of claim 13, wherein the first rebalancing voltage signal is 90°

out-of-phase with the second rebalancing voltage signal.

15. The MEMS inertial sensor of claim 13, wherein the first and second force rebalance controllers are separate controllers.

16. The MEMS inertial sensor of claim 13, wherein the first and second force rebalance controllers comprise a single controller.

17. The MEMS inertial sensor of claim 16, wherein said single controller is a multiple-input multiple-output controller.

18. The MEMS inertial sensor of claim 1, wherein said MEMS inertial sensor is a MEMS gyroscope.

19. The MEMS inertial sensor of claim 18, wherein said MEMS gyroscope is an in-plane MEMS gyroscope.

20. The MEMS inertial sensor of claim 18, wherein said MEMS gyroscope is an out-of-plane MEMS gyroscope.

21. The MEMS inertial sensor of claim 1, wherein said MEMS inertial sensor is an accelerometer.

22. A MEMS inertial sensor, comprising:

one or more proof masses adapted to oscillate at a motor drive frequency;

at least one sense electrode positioned adjacent to each of the one or more proof masses, the sense electrode adapted to capacitively sense proof mass motion along a sense axis perpendicular to a drive axis of the one or more proof masses; and

at least one additional electrode positioned adjacent to each of the one or more proof masses, each additional electrode coupled to one or more time-varying rebalancing voltages adapted to electrostatically null Coriolis and/or quadrature related proof mass motion along the sense axis;

wherein the rebalancing voltages applied to each of the one or more additional electrodes is adapted to maintain a fixed capacitance between each sense electrode and corresponding proof mass based on feedback from one or more force rebalancing control loops.

23. A method of force rebalancing a MEMS inertial sensor, the MEMS inertial sensor including one or more proof masses adapted to oscillate at a motor drive frequency, and at least one sense electrode positioned adjacent to each of the one or more proof masses, each sense electrode coupled to a sense bias voltage source for sensing displacement of the one or more proof masses along a sense axis perpendicular to a drive axis of the one or more proof masses, the method comprising the steps of:

applying one or more time-varying rebalancing voltages to at least one electrode adjacent to each proof mass;

sensing any displacement of the one or more proof masses along the sense axis and outputting a sense voltage having an amplitude in proportion to the proof mass displacement; and

electrostatically nulling any proof mass motion along the sense axis based on the outputted sense voltage.

24. The method of claim 23, wherein the rebalancing voltages applied to each of the electrodes are adapted to maintain a fixed capacitance between each sense electrode and corresponding proof mass.

25. The method of claim 23, wherein said step of electrostatically nulling proof mass motion along the sense axis is accomplished by adjusting the rebalancing voltages using at least one force rebalancing control loop.

26. The method of claim 25, wherein said at least one force rebalancing control loop comprises a single force rebalancing control loop.

27. The method of claim 25, wherein said at least one force rebalancing control loop comprises multiple force rebalancing control loops.

28. The method of claim 23, wherein said step of applying rebalancing voltages to the at least one electrode includes the steps of:

providing a first rebalancing voltage to a first number of torquer electrodes adapted to selectively control Coriolis-related motion of the one or more proof masses along the sense axis; and

providing a second rebalancing voltage to a second number of torquer electrodes adapted to selectively control quadrature-related motion of the one or more proof masses along the sense axis.

29. The method of claim 23, wherein the time-varying rebalancing voltage includes an AC rebalancing voltage.

30. The method of claim 29, wherein the AC rebalancing voltage includes a rebalancing voltage signal component and a carrier voltage signal component.

31. The method of claim 30, wherein the frequency of the rebalancing voltage signal component is approximately half of the motor drive frequency.

32. The method of claim 30, wherein the rebalancing voltage signal component is 90°

out-of-phase with the carrier voltage signal component.