CLOSED LOOP ANALOG GYRO RATE SENSOR

• US 20030200807A1
• Filed: 04/29/2002
• Published: 10/30/2003
• Est. Priority Date: 04/29/2002
• Status: Active Grant

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Hulsing, Rand H. II
• Granted Patent: US 6,701,786 B2
• Time in Patent Office: Days
• US Class Current: 73/514.01
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

The present invention provides an apparatus and method for measuring the angular rotation of a moving body. The apparatus comprises an upper sensor layer, a lower handle layer substantially parallel to the sensor layer, at least one dither frame formed of the upper sensor layer, the frame having a dither axis disposed substantially parallel to the upper sensor layer and the lower handle layer. The apparatus further comprises a first accelerometer formed of the upper sensor layer and having a first force sensing axis perpendicular to the dither axis for producing a first output signal indicative of the acceleration of the moving body along the first force sensing axis, the first accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis. The apparatus also comprises a second accelerometer formed of the upper sensor layer and having a second force sensing axis perpendicular to the dither axis for producing a second output signal indicative of the acceleration of the moving body along the second force sensing axis, the second accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis. The dither frame and proof masses have electrodes on an insulating layer for operating the first and second accelerometers and the upper sensor layer has a rate axis perpendicular to each of the first and second force sensing axes and the dither axis, whereby the first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about the rate axis.

Claims

1. An apparatus for measuring the angular rotation of a moving body, the apparatus comprising:

an upper sensor layer;

a lower handle layer substantially parallel to the sensor layer;

at least one dither frame formed of the upper sensor layer, the frame having a dither axis disposed substantially parallel to the upper sensor layer and the lower handle layer;

a first accelerometer formed of the upper sensor layer and having a first force sensing axis perpendicular to the dither axis for producing a first output signal indicative of the acceleration of the moving body along the first force sensing axis, the first accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis;

a second accelerometer formed of the upper sensor layer and having a second force sensing axis perpendicular to the dither axis for producing a second output signal indicative of the acceleration of the moving body along the second force sensing axis, the second accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis;

the dither frame and proof masses having electrodes on an insulating layer for operating the first and second accelerometers; and

the upper sensor layer having a rate axis perpendicular to each of the first and second force sensing axes and the dither axis, whereby the first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about the rate axis.

2. The apparatus of claim 1, wherein the lower handle layer is bonded to the sensor layer at the insulating layer.

3. The apparatus of claim 1, wherein the insulating layer is an oxide layer.

4. The apparatus of claim 1, wherein the insulating layer acts as an etch stop for an etching method.

5. The apparatus of claim 4, wherein the etching method is a potassium hydroxide or tetramethyl ammonium hydroxide method.

6. The apparatus of claim 1, wherein the proof masses of the first and second accelerometers are of H shape.

7. The apparatus of claim 1, wherein the first and second accelerometers are connected by a link.

8. The apparatus of claim 1, wherein the dither frame is driven magnetically, while the first and second accelerometers are driven capacitively.

9. The apparatus of claim 1, wherein the first and second accelerometers are translational masses.

10. The apparatus of claim 1, further comprising first and second capacitor plates positioned perpendicular to and spaced between the upper sensor layer and the lower handle layer.

11. The apparatus of claim 10, wherein each of the first and second capacitor plates comprise the electrodes.

12. The apparatus of claim 11, wherein the first and second accelerometers comprise capacitive force rebalance accelerometers.

13. The apparatus of claim 12, further comprising a force-rebalance circuit coupled to the first and second accelerometers for balancing applied acceleration forces to restore each of the proof masses to neutral position between the first and second capacitor plates.

14. The apparatus of claim 13, wherein the first and second force rebalancing accelerometers include an electronic bias voltage for cancellation of mechanical forces.

15. The apparatus of claim 1, wherein the apparatus is operated at one atmosphere pressure and a predetermined dither frequency is nominally 8 kHz.

16. The apparatus of claim 1, wherein the pair of flexures each comprise at least one dither leg.

17. The apparatus of claim 1, further comprising a magnetic circuit generating a magnetic flux that intersects the at least one dither frame.

18. The apparatus of claim 17, further comprising a conductive path deposited on at least one of the flexures.

19. The apparatus of claim 18, further comprising an electrical circuit coupled to the conductive path and generating a drive signal therein, the drive signal interacting with the magnetic flux to impart a dithering motion to each of the first and second accelerometer frames having a predetermined frequency along the dither axis to generate the first and second output signals.

20. The apparatus of claim 19, wherein the electrical circuit includes a signal processor for processing a pick-off signal and further comprising:

a second conductive path disposed on the upper sensor layer to traverse the first and second accelerometer frames, the second conductive path coupled to the electrical circuit and intersected by a magnetic flux which generates a pick-off signal in the second conductive path representative of the dithering of the first and second accelerometer frames along the dither axis.

21. The apparatus of claim 19, wherein the predetermined dither frequency and nominal accelerometer frequency are set equal.

22. A method of improving an accelerometer bias performance, the accelerometer having a force rebalance circuit coupled thereto for restoring a proof mass to its neutral position between capacitor plates, the method comprising the steps of:

adding a bias voltage across capacitor gaps by coupling a power supply to a sensor substrate; and

applying an electrical offset to the motor terminals, thereby resulting in an attractive force having a negative spring rate and effectively decreasing proof mass natural frequency.

23. A method of measuring the angular rotation of a moving body, the method comprising the steps of:

forming an upper sensor layer;

forming a lower handle layer substantially parallel to the sensor layer;

forming at least one dither frame of the upper sensor layer, the frame having a dither axis disposed substantially parallel to the upper sensor layer and the lower handle layer;

forming a first accelerometer of the upper sensor layer and having a first force sensing axis perpendicular to the dither axis for producing a first output signal indicative of the acceleration of the moving body along the first force sensing axis, the first accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis;

forming a second accelerometer of the upper sensor layer and having a second force sensing axis perpendicular to the dither axis for producing a second output signal indicative of the acceleration of the moving body along the second force sensing axis, the second accelerometer having a proof mass and at least one flexure connecting the proof mass to the dither frame such that the proof mass can be electrically rotated perpendicular to the dither axis;

the dither frame and proof masses having electrodes on an insulating layer for operating the first and second accelerometers; and

imparting a dithering motion to each of the first and second accelerometers of a predetermined frequency along the dither axis, whereby the first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about the rate axis.

24. The method of claim 23, further comprising the step of bonding the lower handle layer to the sensor layer at the insulating layer.

25. The method of claim 23, wherein the insulating layer is an oxide layer.

26. The method of claim 23, wherein the insulating layer acts as an etch stop for an etching method.

27. The method of claim 26, wherein the etching method is a potassium hydroxide or TMAH method.

28. The method of claim 23, wherein the proof masses of the first and second accelerometers are of H shape.

29. The method of claim 23, further comprising the step of forming a link connecting the first and second accelerometers to maintain same dither frequency between each of the first and second accelerometers.

30. The method of claim 23, further comprising the steps of driving the dither frame magnetically, and driving the first and second accelerometers capacitively.

31. The method of claim 23, wherein the first and second accelerometers are translational masses.

32. The method of claim 23, further comprising the step positioning the first and second capacitor plates perpendicular to and spaced between the upper sensor layer and the lower handle layer.

33. The method of claim 32, wherein each of the first and second capacitor plates comprise the electrodes.

34. The method of claim 33, wherein the first and second accelerometers comprise capacitive force rebalance accelerometers.

35. The method of claim 34, further comprising the step of coupling a force-rebalance circuit to the first and second accelerometers for balancing applied acceleration forces to restore each of the proof masses to neutral position between the first and second capacitor plates.

36. The method of claim 35, wherein the first and second force rebalancing accelerometers include an electronic bias voltage for cancellation of mechanical forces.

37. The method of claim 23, further comprising the step of operating the apparatus at one atmosphere pressure and dithering the first and second accelerometers at a predetermined dither frequency of nominally 8 kHz.

38. The method of claim 23, wherein the pair of flexures each comprise at least one dither leg.

39. The method of claim 23, further comprising the step of generating a magnetic flux with a magnetic circuit, the magnetic circuit disposed such that the magnetic flux intersects the at least one dither frame.

40. The method of claim 23, further comprising the step of depositing a conductive path on at least one of each of the flexures.

41. The method of claim 40, further comprising the step of coupling an electrical circuit to the conductive path and generating a drive signal therein, the drive signal interacting with the magnetic flux to impart a dithering motion to each of the first and second accelerometer frames having a predetermined frequency along the dither axis, whereby the first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about the dither axis.

42. The method of claim 41, wherein the electrical circuit includes a signal processor for processing a pick-off signal and further comprising the step of:

disposing a second conductive path on the upper sensor layer to traverse the first and second accelerometer frames, the second conductive path coupled to the electrical circuit and intersected by a magnetic flux, whereby the magnetic flux generates a pick-off signal in the second conductive path representative of the dithering of the first and second accelerometer frames along the dither axis.

43. The method of claim 41, wherein the predetermined dither frequency and nominal accelerometer frequency are set equal.