Phase insensitive quadrature nulling method and apparatus for coriolis angular rate sensors

• US 6,619,121 B1
• Filed: 07/25/2001
• Issued: 09/16/2003
• Est. Priority Date: 07/25/2001
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Stewart, Robert E., Wyse, Stanley F.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/915,026
• Publication Number:
  US 20030159510A1
• Time in Patent Office: 783 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.2, 735/041.4, 735/143.2, 735/142.9, 735/141.6, 735/141.7, 735/141.8, 735/142.4, 73/13.7, 73/13.8, 73/13.9, 73/17.5, 73/17.7
• US Class Current: 73/504.02
• CPC Class Codes: G01C 19/5705 using masses driven in reciprocating rotary motion about an axis
• CPC Class Codes: G01C 19/5755 the devices having a single sensing mass
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00

Abstract

Quadrature error occurs in Corolis based vibrating rate sensors because of manufacturing flaws that permit the sensing element to oscillate either linearly along or angularly about an axis that is not orthogonal to the output axis. This creates an oscillation along or about the output axis that is a component of the sensing element'"'"'s vibration acceleration. This output axis oscillation is in phase with the driven acceleration of the sensing element and is called quadrature error since it is ninety degrees out of phase with the angular rate induced Coriolis acceleration. Rather than applying forces that reorient the axis of the driven vibration to be orthogonal to the output axis to eliminate the output axis oscillation, the present invention applies sinusoidal forces to the sensing element by means of a quadrature servo to cancel the output oscillation. In order to avoid the phase uncertainty associated with electronic modulation, the quadrature servo feeds back a DC signal that is modulated mechanically by means of an interdigitated variable area electrostatic forcer.

Claims

1. A method for nulling quadrature in an angular rate sensor, having a proof mass connected by a flexure to a dither mass, the dither mass mounted for vibration along a drive axis, the steps of the method comprising:

applying driving forces to the dither mass causing vibration of the dither mass along the drive axis and vibration of the proof mass along a dithered axis; and

applying a restoring force to the proof mass in phase with the displacement along the dithered axis, the restoring force nulling the quadrature by aligning the proof mass dithered axis without changing the path of vibration of the dither mass along the drive axis.

2. The method of claim 1 wherein the restoring force is generated by applying appropriate level d.c. signals to electrodes adjacent to the proof mass.

3. The method of claim 1 wherein the applying a restoring force step comprises:

applying a bias voltage to the proof mass;

applying a plus or minus d.c. control voltage to spaced electrodes adjacent to the proof mass; and

adjusting the d.c. control voltages on the spaced electrodes to null the quadrature.

4. The method of claim 3 wherein the plus or minus d.c. control voltages are applied to spaced electrodes located at the top side and bottom side of the proof mass at fixed locations.

5. The method of claim 1 wherein said proof mass has a scalloped edge opposite to the flexure connection to the drive mass.

6. The method of claim 5 wherein the restoring force is generated by applying appropriate level d.c. signals to electrodes adjacent the scalloped edge of the proof mass.

7. The method of claim 5 wherein the applying a restoring force step comprises:

applying a bias voltage to the proof mass;

applying a plus or minus d.c. control voltage to spaced electrodes adjacent to the scalloped edge of the proof mass; and

adjusting the d.c. control voltages on the spaced electrodes to null the quadrature.

8. The method of claim 7 wherein the plus or minus d.c. control voltages are applied to electrodes which are spaced to overlap one half of a scallop on the scalloped edge of the proof mass when the proof mass is at rest.

9. The method of claim 7 wherein the plus or minus d.c. control voltages are applied to electrodes which are spaced to be adjacent to each scallop on the proof mass.

10. The method of claim 9 wherein the plus or minus d.c. control voltages are applied to spaced electrodes located at the top and bottom sides of the proof mass adjacent to each scallop on the proof mass.

11. An apparatus for nulling the quadrature in an angular rate sensor, the apparatus comprising:

a dither mass suspended for vibration along a drive axis;

a proof mass having a first and second end, the first end being connected to the dither mass by a flexure, the second end having a scalloped edge;

a source of driving forces to cause vibration of the dither mass along the drive axis;

a source of bias voltage applied to the proof mass;

electrodes located adjacent to the scalloped edge of the proof mass; and

a source of d.c. control voltages applied to the electrode, to null the quadrature.

12. The apparatus of claim 11 wherein the d.c. control voltage source comprises plus and minus d.c. voltages.

13. The apparatus of claim 11 wherein the d.c. control voltages are applied to electrodes which overlap one half of a scallop on the scalloped edge of the proof mass when the proof mass is at rest.

14. The apparatus of claim 12 wherein the plus and minus d.c. voltages are applied to electrodes spaced to be adjacent to a scallop on the proof mass.

15. The apparatus of claim 13 wherein the d.c. control voltages are applied to electrodes at the top and bottom sides of the proof mass adjacent to each scallop of the proof mass.

16. An apparatus for nulling the quadrature in a coriolis angular rate sensor, comprising:

a dither mass mounted within a frame for vibration along a drive axis;

a proof mass connected to said dither mass by a flexure for oscillating at a predetermined frequency along a dithered axis;

a source of driving forces applied to the dither mass;

a source of bias voltage applied to the proof mass; and

a source of d.c. control voltages applied to electrodes adjacent to the proof mass for providing a restoring force to the oscillating proof mass which is in phase with its displacement to align the proof mass dithered axis without changing the path of vibration of the dither mass along the drive axis.

17. The apparatus of claim 16 wherein the source of d.c. control voltages comprise plus and minus d.c. voltages.

18. The apparatus of claim 16 wherein the proof mass has a scalloped edge at an end opposite to the flexure connection to the dither base.

19. The apparatus of claim 18 wherein the plus and minus d.c. voltages are applied to electrodes which overlap one half of a scallop on the scalloped edge of the proof mass.

20. The apparatus of claim 18 wherein the plus and minus d.c. voltages are applied to electrodes adjacent to each scallop on the proof mass.

21. A method for nulling quadrature in an angular rate sensor having a dither mass mounted for movement about a Z axis within an X-Y plane and a proof mass mounted within the dither mass by a flexure for movement with respect to the dither mass, the steps of the method comprising:

applying driving signals to the dither mass to vibrate the dither mass and the proof mass at a combined resonant frequency about the Z axis; and

applying a restoring force to the proof mass which is in phase with the dithered displacement of the proof mass for nulling the quadrature without affecting the dither mass.

22. The method of claim 21 wherein the applying a restoring force step comprises:

applying a bias voltage to the proof mass;

applying plus and minus control voltages to electrodes adjacent to the proof mass; and

adjusting the control voltages to null the quadrature.

23. The method of claim 22 wherein the plus and minus d.c. control voltages are applied to top and bottom electrodes adjacent to the proof mass at fixed locations.

24. The method of claim 22 wherein said proof mass has a scalloped edge along a portion of the perimeter of the proof mass.

25. The method of claim 24 wherein the plus and minus control voltages are d.c. signals.

26. The method of claim 24 wherein the applying a restoring force step comprises:

applying a bias voltage to the proof mass;

applying plus and minus d.c. control voltages to electrodes adjacent to the scalloped edge of the proof mass; and

adjusting the d.c. voltages to null the quadrature.

27. The method of claim 26 wherein the d.c. control voltages are applied to electrodes which overlap one half of a scallop on the scalloped edge of the proof mass.

28. The method of claim 25 wherein the d.c. signals are applied to electrodes adjacent to each scallop on the proof mass.

29. The method of claim 26 wherein the plus and minus d.c. control voltages are applied to electrodes at both top and bottom sides of the proof mass adjacent to each scallop of the proof mass.

30. An apparatus for nulling the quadrature in an angular rate sensor, the apparatus comprising:

a dither mass mounted for motion about a Z axis in an X-Y plane;

a proof mass mounted within the dither mass by a flexure for movement with respect to the dither mass;

a source of bias voltage applied to the proof mass; and

a source of d.c. control voltages applied to electrodes adjacent to an edge of the proof mass for providing a restoring force to the proof mass which is in phase with the dither displacement of the proof mass.

31. The apparatus of claim 30 wherein the source of d.c. control voltage comprises plus and minus d.c. voltages.

32. The apparatus of claim 31 wherein the proof mass has a scalloped edge at a portion of the perimeter of the proof mass.

33. The apparatus of claim 32 wherein the plus and minus d.c. control voltages are applied to electrodes adjacent to each scallop on the scalloped edge of the proof mass.

34. The apparatus of claim 33 wherein the plus and minus d.c. control voltages are applied to electrodes which overlap one half of a scallop on the scalloped edge of the proof mass when the proof mass is at rest.

35. An apparatus for nulling the quadrature in a coriolis angular rate sensor, comprising:

a dither mass flexurally mounted within a frame for vibrating about a Z axis in an X-Y plane;

a proof mass mounted within said dither mass by a flexure for movement with respect to the dither mass;

a source of bias voltage applied to the proof mass; and

a source of d.c. control voltages applied to electrodes adjacent to the proof mass for providing a restoring force to the oscillating proof mass which is in phase with the displacement of the proof mass.

36. The apparatus of claim 35 wherein the source of d.c. control voltages comprise plus and minus d.c. voltages.

37. The apparatus of claim 36 wherein the proof mass has a scalloped edge around a portion of the perimeter of the proof mass.

38. The apparatus of claim 37 wherein the plus and minus d.c. voltages are applied to electrodes which overlap one half of a scallop on the scalloped edge of the proof mass.

39. The apparatus of claim 37 wherein the plus and minus d.c. control voltages are applied to electrodes adjacent to each scallop on the proof mass.