Epitaxial coriolis rate sensor

• US 6,257,057 B1
• Filed: 06/02/1999
• Issued: 07/10/2001
• Est. Priority Date: 12/16/1998
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Hulsing, Rand H. II
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US09/324,522
• Time in Patent Office: 769 Days
• Field of Search: 735/040.4, 735/041.2, 735/041.4, 735/041.6, 735/10
• US Class Current: 73/504.04
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01G 19/035 using electrical weight-sensitive devices

Abstract

An apparatus for measuring the specific force and angular rotation rate of a moving body having multiple micromachined force-rebalance accelerometers formed in a layer of epitaxial material. The apparatus further includes a frame formed of the epitaxial material; two accelerometers, flexibly connected to the frame, which are also formed of the epitaxial material and each having a force sensing axis perpendicular to the vibration axis for producing an output signal indicative of the acceleration of the moving body along the force sensing axis; an electrical circuit imparting a dithering motion to the two accelerometers along the vibration axis; and a rate axis perpendicular to the force sensing axes and the vibration axis, whereby the 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 specific force and angular rotation rate of a moving body, the apparatus comprising:

a) a layer of epitaxial material having first and second substantially planar surfaces disposed substantially parallel to each other;

b) a frame formed of said layer of epitaxial material, said frame having a vibration axis disposed substantially parallel to said first and second surfaces;

c) a first accelerometer formed of said layer of epitaxial material and having a first force sensing axis perpendicular to said vibration axis for producing a first output signal indicative of the acceleration of the moving body along said first force sensing axis, said first accelerometer having a proof mass and at least one flexure connecting said proof mass to said frame such that said proof mass can be moved along each of said first force sensing axis and said vibration axis;

d) a second accelerometer formed of said layer of epitaxial material and having a second force sensing axis perpendicular to said vibration axis for producing a second output signal indicative of the acceleration of the moving body along said second force sensing axis, said second accelerometer having a proof mass and at least one flexure connecting said proof mass to said frame such that said proof mass can be moved along each of said second force sensing axis and said vibration axis;

e) an electrical circuit coupled to each of said first and second accelerometers for imparting a dithering motion thereto of a predetermined frequency along said vibration axis; and

f) said layer of epitaxial material having a rate axis perpendicular to each of said first and second force sensing axes and said vibration axis, whereby said first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about said rate axis.

2. The measuring apparatus of claim 1, wherein said first and second force sensing axes are both oriented at the same angle with respect to said first and second surfaces.

3. The measuring apparatus of claim 1, wherein said first and second force sensing axes are both oriented essentially perpendicular to said first and second surfaces.

4. The measuring apparatus of claim 3, wherein said first force sensing axis extends in a direction opposite to that of said second force sensing axis.

5. The measuring apparatus of claim 1, wherein said flexure of said first accelerometer connecting said proof mass to said frame comprises a first pair of flexures;

and said flexure of said second accelerometer connecting said proof mass to said frame comprises a second pair of flexures.

6. The measuring apparatus of claim 5, wherein each of said first and second pairs of flexures is primarily an S-bend flexure.

7. The measuring apparatus of claim 6, wherein each of said first and second pairs of flexures is formed of said layer of epitaxial material.

8. The measuring apparatus of claim 7, further comprising a link having first and second points connected respectively to said first and second accelerometers, a pivot point disposed between said first and second connected points, and one or more supports affixedly disposing said pivot point with respect to said frame to permit said link to pivot thereabout and, when one of said first and second accelerometers is moved, to impart a substantially equal and opposite motion to said other of said first and second accelerometers.

9. The measuring apparatus of claim 8, wherein each of said supports comprises a pivot flexure.

10. The measuring apparatus of claim 9, wherein each of said pivot flexures has a length and cross-sectional dimensions such that said pivot flexures flex with a combination of simple bending and S-bend motion.

11. The measuring apparatus of claim 8, wherein each of said accelerometer vibrates at its natural frequency and link has a natural frequency essentially matched to said natural frequency of said accelerometers.

12. The measuring apparatus of claim 8, wherein said pivot point is disposed intermediate between said first and second connected points.

13. The measuring apparatus of claim 12, wherein said frame further comprises one or more surfaces restricting the motion of said link.

14. The measuring apparatus of claim 12, wherein said frame further comprises one or more surfaces restricting the motion of each said proof mass.

15. The measuring apparatus of claim 12, wherein said link is formed having a shape essentially symmetrical about said pivot point.

16. The measuring apparatus of claim 12, wherein said link is formed having an essentially rectangular shape symmetrical about said pivot point.

17. The measuring apparatus of claim 12, wherein each said proof mass is flexibly connected to said frame for motion along a respective one of said force sensing axes and each said proof mass includes a free end, said free end of a first of said proof masses connected to said link on one side of said pivot point and said free end of a second of said proof masses connected to another side of said link opposite said pivot point.

18. The measuring apparatus of claim 17, wherein each said proof mass is connected to said link by flexures.

19. The measuring apparatus of claim 18, wherein said free ends of said first and second proof masses are connected to said frame.

20. The measuring apparatus of claim 18, wherein said free ends of said first and second proof masses are connected to said frame by flexures.

21. The measuring apparatus of claim 5, further comprising a conductive path coupled to said electrical circuit, said conductive path disposed on at least one of said first and s econd surfaces of said layer of epitaxial material to traverse said first and second accelerometers.

22. The measuring apparatus of claim 21, further comprising a magnetic flux generator producing magnetic flux intersecting said conductive path and wherein said electrical circuit comprises a signal generator for producing a periodic drive signal having a predetermined frequency to said conductive path, whereby said drive signal interacting with said magnetic flux causes said first and second accelerometers to vibrate along said vibration axis.

23. The measuring apparatus of claim 21, wherein said conductive path forms a first conductive path and said electrical circuit includes a signal processor for processing a pick-off signal;

and

further comprising a second conductive path disposed on at least one of said first and second surfaces of said layer of epitaxial material to traverse said first and second accelerometers, said second conductive path coupled to said electrical circuit and intersected by said magnetic flux, whereby said magnetic flux generates a pick-off signal in said second conductive path representative of the vibration of said first and second accelerometers along said vibration axis.

24. The measuring apparatus of claim 23, wherein one of said first and second conductive path is disposed across one of said first pair of flexures connecting said proof mass of said first accelerometer to said frame, across said link, and across one of said second pair of flexures connecting said proof mass of said second accelerometer to said frame.

25. The measuring apparatus of claim 23, wherein one of said first and second conductive path is disposed across that flexure of said first and second pairs of flexures disposed closest to said link.

26. The measuring apparatus of claim 25, wherein the other one of said first and second conductive path is disposed across that flexure of said first and second pairs of flexures disposed farthest from said link.

27. The measuring apparatus of claim 23, wherein each of said first and second conductive paths is disposed on the same one of said first and second surfaces of said layer of epitaxial material.

28. The measuring apparatus of claim 27, wherein said first conductive path is disposed across that flexure of said first and second pairs of flexures disposed closest to said link and said second conductive path is disposed across that flexure of said first and second pairs of flexures disposed farthest from said link.

29. The measuring apparatus of claim 28, wherein said first conductive path is additionally disposed across said link.

30. The measuring apparatus of claim 7, further comprising a link having first and second points connected respectively to said first and second accelerometers and a pivot point disposed a radial length from each of said first and second connected points, one or more flexures mounting said link to said frame to permit said link to pivot about said pivot point and, when one of said first and second accelerometers is moved, to impart an equal and opposite motion to the other one of said first and second accelerometers, each of said first and second pairs of flexures providing an effective radius of a length essentially equal to that of said radial length of said link.

31. The measuring apparatus of claim 30, wherein said frame includes first and third inner peripheral edges disposed substantially parallel to said vibration axis and wherein said first pair of flexures connect a first peripheral edge of said proof mass of said first accelerometer to said first innerperipheral edge and said second pair of flexures connect a first peripheral edge of said proof mass of said second accelerometer to said third innerperipheral edge such that each said first peripheral edge of each said proof mass moves substantially parallel with respect to said first and third innerperipheral edges of said frame.

32. The measuring apparatus of claim 31, wherein said first and third inner peripheral edges form two sides of an essentially rectangular configuration.

33. The measuring apparatus of claim 1, further comprising first and second capacitor plates positioned parallel to and spaced away from said first and second surfaces of said layer of epitaxial material.

34. The measuring apparatus of claim 33, wherein each of said first an d second capacitor plates comprise electrodes disposed on insulating surfaces.

35. The measuring apparatus of claim 34, wherein each of said first and second capacitor plates further comprise edge portions extending toward and contacting respective ones of said first and second surfaces of said layer of epitaxial material, whereby said electrodes are positioned parallel to and spaced away from respective ones of said first and second surfaces of said layer of epitaxial material.

36. The measuring apparatus of claim 35, wherein each of said first and second accelerometers comprise capacitive force rebalance accelerometers.

37. The measuring apparatus of claim 36, further comprising a force-rebalance circuit coupled to said first and second accelerometers for balancing applied acceleration forces to restore each of said proof masses to neutral position between said first and second capacitor plates.

38. The measuring apparatus of claim 37, wherein said force-rebalance circuit further comprises an alignment signal summed into a feed-back signal to each said first and second accelerometer.

39. The measuring apparatus of claim 38, wherein said alignment signal is subtracted from said output signals.

40. The measuring apparatus of claim 8, wherein each said proof mass is formed with a plurality of air passages.

41. The measuring apparatus of claim 8, wherein said link is formed with a plurality of air passages.

42. The measuring apparatus of claim 8, wherein each of said supports comprises a pivot flexure mounted to a support member formed in said frame, said support members formed with a plurality of air passages.

43. Apparatus for measuring the specific force and angular rotation rate of a moving body, the apparatus comprising:

a) a layer of epitaxial material having first and second opposing substantially planar surfaces disposed substantially parallel to each other;

b) a frame formed of said layer of epitaxial material, said frame having first and third opposing inner peripheral edges disposed substantially parallel to one another, a vibration axis disposed substantially parallel to said first and third opposing inner peripheral edges, and a rate axis disposed substantially parallel to said first and second opposing planar surfaces and substantially perpendicular to said vibration axis;

c) first and second substantially planar electrodes, one of said electrodes disposed substantially parallel to and spaced a predetermined distance away from each of said first and second planar surfaces of said layer of epitaxial material;

d) a first accelerometer formed of said first and second electrodes and a first proof mass formed of said layer of epitaxial material and pivotally suspended from said first innerperipheral edge of said frame by a first pair of flexures for motion along each of said vibration axis and a first force sensing axis, said first force sensing axis perpendicular to said first and second surfaces and said vibration axis for producing a first output signal indicative of the acceleration of the moving body along said first force sensing axis;

e) a second accelerometer formed of said first and second electrodes and a second proof mass formed of said layer of epitaxial material and pivotally suspended from said third innerperipheral edge of said frame by a second pair of flexures for motion along each of said vibration axis and a second force sensing axis, said second force sensing axis perpendicular to said first and second surfaces and said vibration axis for producing a second output signal indicative of the acceleration of the moving body along said second force sensing axis;

f) a magnetic circuit generating a magnetic flux, said magnetic circuit disposed such that said magnetic flux intersects said first and second accelerometers;

f) a conductive path deposited on at least one of each of said first and second pairs of flexures; and

g) an electrical circuit coupled to said conductive path and generating a drive signal therein, said drive signal interacting with said magnetic flux to impart a dithering motion to each of said first and second accelerometers having a predetermined frequency along said vibration axis, whereby said first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about said rate axis.

44. The measuring apparatus of claim 43, wherein said first force sensing axis extends in a direction opposite to that of said second force sensing axis.

45. The measuring apparatus of claim 44, wherein said first and second pairs of flexures each comprise two or more legs.

46. The measuring apparatus of claim 44, further comprising a link having first and second points connected respectively to said first and second accelerometers, said first and second connected points disposed on respectively on a portion of said first and second proof masses opposite said flexures, a pivot point disposed between said first and second connected points, and one or more supports affixedly disposing said pivot point with respect to said frame to permit said link means to pivot thereabout and, when one of said first and second accelerometers is moved, to impart a substantially equal and opposite motion to said other of said first and second accelerometers.

47. The measuring apparatus of claim 46, wherein each of said first and second pairs of flexures exhibits an S-bend motion, whereby each said proof mass moves substantially parallel with respect to said first and third inner peripheral edges of said frame.

48. The measuring apparatus of claim 47, wherein said conductive path forms a first conductive path and said electrical circuit includes a signal processor for processing a pick-off signal;

and further comprising;

a second conductive path disposed on at least one of said first and second surfaces of said layer of epitaxial material to traverse said first and second accelerometers, said second conductive path coupled to said electrical circuit and intersected by said magnetic flux, whereby said magnetic flux generates a pick-off signal in said second conductive path representative of the vibration of said first and second accelerometers along said vibration axis.

49. A method for measuring the specific force and angular rotation rate of a moving body, the method comprising:

forming a frame of a layer of epitaxial material having first and second substantially planar surfaces disposed substantially parallel to each other, said frame formed with a vibration axis disposed substantially parallel to said first and second surfaces and a rate axis perpendicular to said vibration axis;

forming a first accelerometer of said layer of epitaxial material, said first accelerometer formed with a first force sensing axis perpendicular to each of said vibration axis and said rate axis for producing a first output signal indicative of the acceleration of the moving body along said first force sensing axis, said first accelerometer formed with a proof mass and at least one flexure connecting said proof mass to said frame such that said proof mass can be moved along each of said first force sensing axis and said vibration axis;

forming a second accelerometer of said layer of epitaxial material, said second accelerometer formed with a second force sensing axis perpendicular to each of said vibration axis and said rate axis for producing a second output signal indicative of the acceleration of the moving body along said second force sensing axis, said second accelerometer formed with a proof mass and at least one flexure connecting said proof mass to said frame such that said proof mass can be moved along each of said second force sensing axis and said vibration axis; and

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

50. The method of claim 49, wherein each of said first and second accelerometers is coupled to an electrical circuit for imparting said dithering motion.

51. The method of claim 50, further comprising forming a link of said layer of epitaxial material, said link formed with first and second points connected respectively to said first and second accelerometers, disposing a pivot point between said first and second connected points, and supporting said pivot point with respect to said frame, whereby said link may pivot thereabout said pivot point and, when one of said first and second accelerometers is moved, impart a substantially equal and opposite motion to the other of said first and second accelerometers.

52. The measuring apparatus of claim 51, wherein said pivot point is disposed intermediate between said first and second connected points.

53. A method for measuring the specific force and angular rotation rate of a moving body, the method comprising:

forming a frame of a layer of epitaxial material having first and second opposing substantially planar surfaces disposed substantially parallel to each other, said frame having first and third opposing inner peripheral edges disposed substantially parallel to one another, a vibration axis disposed substantially parallel to said first and third opposing inner peripheral edges, and a rate axis disposed substantially parallel to said first and second planar surfaces and substantially perpendicular to said vibration axis;

forming a first proof mass of said layer of epitaxial material and pivotally suspending said first proof mass from said first inner peripheral edge of said frame by a first pair of flexures for motion along each of said vibration axis and a first force sensing axis perpendicular to said first and second surfaces and said vibration axis;

forming a second proof mass of said layer of epitaxial material and pivotally suspended from said third inner peripheral edge of said frame by a second pair of flexures for motion along each of said vibration axis and a second force sensing axis perpendicular to said first and second surfaces and said vibration axis;

forming a link of said layer of epitaxial material, said link formed with first and second points connected respectively to said first and second proof mass, a pivot point disposed intermediate between said first and second connected points, and one or more supports affixedly disposing said pivot point with respect to said frame to permit said link to pivot thereabout and, when one of said first and second accelerometers is moved, to impart a substantially equal and opposite motion to said other of said first and second accelerometers;

forming first and second substantially planar electrodes, each of said electrodes disposed substantially parallel to and spaced a predetermined distance away from a respective one of said first and second planar surfaces of said layer of epitaxial material;

producing a first output signal indicative of the acceleration of the moving body along said first force sensing axis and a second output signal indicative of the acceleration of the moving body along said second force sensing axis;

generating a magnetic flux intersecting said first and second accelerometers; and

depositing a conductive path on at least one of each of said first and second pairs of flexures and generating a drive signal therein interacting with said magnetic flux to impart a dithering motion to each of said first and second proof mass having a predetermined frequency along said vibration axis, whereby said first and second output signals have a Coriolis component indicative of the angular rotation of the moving body about said rate axis.

54. The method of claim 53, wherein said first and second output signals indicative of the acceleration of the moving body along said first and second force sensing axes are produced by detecting differential electrostatic forces between each said first and second proof mass and each said first and second electrodes.