Accelerometer strain isolator

• US 6,634,231 B2
• Filed: 04/05/2002
• Issued: 10/21/2003
• Est. Priority Date: 05/15/2001
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Malametz, David L.
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US10/117,299
• Publication Number:
  US 20020170355A1
• Time in Patent Office: 564 Days
• Field of Search: 735/140.1, 735/143.6, 735/143.7, 735/143.8, 735/142.9, 735/040.4, 738/621.95
• US Class Current: 73/514.01
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0181 See-saws
• CPC Class Codes: B81B 2203/058 Rotation out of a plane parallel to the substrate
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: B81C 2201/0133 Wet etching
• CPC Class Codes: G01P 1/006 used for thermal compensation
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

An apparatus and method for suspending and strain isolating a structure is provided, the apparatus having a first elongated flexure having first and second ends structured for connection to a support structure, and a second elongated flexure having first and second ends structured for connection to a structure to be isolated from the support structure. A portion of the second flexure intermediate the first and second ends thereof is interconnected to a portion of the first flexure intermediate the first and second ends thereof.

Claims

1. A suspension structure comprising:

a first elongated flexure having first and second ends structured for connection to a support structure; and

a second elongated flexure having first and second ends structured for connection to a structure to be isolated from the support structure, a portion of the second flexure intermediate the first and second ends thereof being interconnected to a portion of the first flexure intermediate the first and second ends thereof.

2. The structure of claim 1 wherein the first and second flexures are spaced apart and interconnected by an interconnecting structure connected between the intermediate portion of the first flexure and the intermediate portion of the second flexure.

3. The structure of claim 1 wherein each of the first and second flexures are formed in a substrate having substantially parallel opposing offset upper and lower surfaces, the first and second flexures being defined by a plurality of slots formed through the substrate between the upper and lower surfaces.

4. The structure of claim 1 wherein in an unconstrained condition each of the first and second flexures is substantially straight between its respective first and second ends.

5. The structure of claim 4 wherein in an unconstrained condition the first and second flexures are spaced apart and substantially mutually parallel and having an interconnecting structure connected therebetween.

6. The structure of claim 1 further comprising:

a structure to be suspended;

a support structure at least partially surrounding the structure to be suspended and spaced away therefrom; and

wherein;

the first and second ends of the first flexure are connected to the support structure, and

the first and second of the second flexure are connected to the structure to be suspended.

7. The structure of claim 6 wherein the structure to be suspended further comprises an accelerometer sensor mechanism.

8. An accelerometer suspension apparatus comprising:

a means for measuring acceleration applied along an input axis;

a means for supporting the acceleration measuring means;

a means interconnected between the supporting means and the acceleration measuring means for suspending the acceleration measuring means from the supporting means for limited motion in a plane substantially perpendicular to the input axis, the suspending means comprising;

a plurality of first flexure means each having spaced apart interconnecting means for interconnecting to the supporting means,

a plurality of second flexure means each having spaced apart interconnecting means for interconnecting to the acceleration measuring means, and

means for interconnecting each of the plurality of first flexure means with a respective one of the plurality of second flexure means at a position substantially intermediate between the respective spaced apart interconnecting means.

9. The apparatus of claim 8 wherein:

a first of the interconnecting means is positioned on a first side of acceleration measuring means; and

a second of the interconnecting means is positioned on a second side of the acceleration measuring means opposite from the first interconnecting means.

10. The apparatus of claim 8 wherein the acceleration measuring means, the supporting means, and each of the interconnecting means is formed in a substrate having a thickness extending between substantially parallel spaced apart surfaces.

11. The apparatus of claim 10 wherein the first and second flexure means of each of the plurality of interconnecting means extends through substantially the entire thickness between the spaced apart surfaces of the substrate.

12. The apparatus of claim 8 wherein the spaced apart interconnecting means of each of the plurality of second flexure means for interconnecting to the acceleration measuring means further comprises means for converting into a torque a strain transmitted by the respective second flexure means.

13. The apparatus of claim 12 wherein the strain-to-torque converting means at each of the spaced apart interconnecting means further comprises a means for converting the strain into equal and opposite torques.

14. A suspension structure comprising:

a substrate having substantially parallel and spaced apart top and bottom surfaces;

an inner frame member formed in the substrate;

an outer frame member formed in the substrate, the outer frame member spaced away from and substantially surrounding the inner frame member;

a separation slot formed between the inner and outer frame members, the separation slot being defined by an outer side wall of the inner frame member and an inner side wall of the outer frame member spaced away from the outer side wall of the inner frame member and being contiguous therewith;

a plurality of beams formed in the substrate within the separation slot at spaced positions around an outer periphery of the inner frame member, each of the beams being interconnected between the inner and outer frame members;

an inner slot formed in the outer periphery of the inner frame member and adjacent to but spaced away from the outer side wall thereof, the inner slot having first and second spaced apart ends positioned on opposite sides of a first beam substantially equidistantly therefrom; and

an outer slot formed in an inner periphery of the outer frame member and adjacent to but spaced away from the inner side wall, the outer slot having first and second spaced apart ends positioned on opposite sides of the first beam substantially equidistantly therefrom.

15. The suspension structure of claim 14 wherein the inner and outer slots are formed substantially contiguously.

16. The suspension structure of claim 14 wherein the inner slot is formed substantially parallel with the separation slot, and the first and second ends of the inner slot are spaced apart a predetermined elongated distance, such that an inner flexure is formed between the inner slot and the separation slot.

17. The suspension structure of claim 14 wherein the outer slot is formed substantially parallel with the separation slot, and the first and second ends of the outer slot are spaced apart a predetermined elongated distance, such that an outer flexure is formed between the outer slot and the separation slot.

18. The suspension structure of claim 14, further comprising:

a second inner slot formed in the outer periphery of the inner frame member and adjacent to but spaced away from the outer side wall thereof, the inner slot having first and second spaced apart ends positioned on opposite sides of a second one of the beams substantially equidistantly therefrom; and

a second outer slot formed in an inner periphery of the outer frame member and adjacent to but spaced away from the inner side wall, the outer slot having first and second spaced apart ends positioned on opposite sides of the second one of the beams substantially equidistantly therefrom.

19. The suspension structure of claim 18 wherein:

the first beam, the first inner slot and the first outer slot are formed at a first position on a first side of the inner frame member; and

the second beam, the second inner slot and the second outer slot are formed at a second position on a second side of the inner frame member opposite from the first beam, inner slot and outer slot.

20. The suspension structure of claim 19 wherein:

the first beam, the first inner slot and the first outer slot cooperate to form a first flexure that is operable along a line passing through the first beam;

the second beam, the second inner slot and the second outer slot cooperate to form a second flexure that is operable along a line passing through the second beam; and

the first and second flexures are oriented such that the are operable along respective substantially parallel first and second lines.

21. The suspension structure of claim 20, further comprising an acceleration sensing mechanism formed within the inner frame member.

22. The suspension structure of claim 21 wherein the acceleration sensing mechanism further comprises:

a proof mass formed in the substrate and suspended for relative rotation from the inner frame member, and

a plurality of force/displacement sensors coupled between the proof mass and the inner frame member; and

the first and second flexures are oriented such that the are operable along respective lines substantially passing through one of a center of percussion, a center of mass, and a center of gravity of the proof mass.

23. An apparatus comprising:

a silicon substrate formed with substantially planar and parallel opposing offset upper and lower surfaces;

an outer frame structure formed in the substrate;

an inner frame structure formed in the substrate, the inner frame structure being at least partially surrounded by the outer frame structure and separated therefrom by a space; and

a plurality of isolators formed in the substrate and extending between the upper and lower surfaces thereof, each of the isolators comprising a pair of inner flexures and a pair of outer flexures spaced away therefrom, proximal ends of each of the inner and outer flexures being interconnected, distal ends of the inner flexures being interconnected with the inner frame structure, and distal ends of the outer flexures being interconnected with the outer frame structure.

24. The apparatus of claim 23 wherein the pair of inner flexures are spaced away from the pair of outer flexures by the space separating the inner frame member from the outer frame member.

25. The apparatus of claim 23 wherein the inner and outer flexures are elongated between the respective proximal and distal ends thereof.

26. The apparatus of claim 23 wherein each of the plurality of isolators further comprises a beam formed in the substrate and extending between the upper and lower surfaces thereof, the beam being interconnected between the proximal ends of each of the inner and outer flexures.

27. The apparatus of claim 26 wherein the respective pairs of inner and outer flexures of each of the plurality of isolators are spaced apart by the beam interconnected therebetween.

28. The apparatus of claim 27 wherein the respective pairs of inner and outer flexures of each of the plurality of isolators are substantially parallel.

29. The apparatus of claim 23 wherein two of the plurality of isolators are positioned on opposite sides of the inner frame structure.

30. The apparatus of claim 23 wherein the outer frame structure further comprises the pair of outer flexures of each of the plurality of isolators.

31. The apparatus of claim 23 wherein the inner frame structure further comprises the pair of inner flexures of each of the plurality of isolators.

32. The apparatus of claim 23 wherein the inner frame structure further comprises:

a proof mass suspended by one or more flexures from the inner frame structure; and

a pair of force/displacement sensors coupled between the proof mass and the inner frame structure for measuring forces applied to the proof mass.

33. The apparatus of claim 32 wherein the force/displacement sensors further comprise mechanical resonators formed as double-ended tuning fork (DETF) force sensors.

34. An accelerometer comprising:

a silicon substrate having substantially parallel and spaced apart top and bottom surfaces;

an accelerometer sensor mechanism having a inner sensor frame and proof mass formed in the substrate, the proof mass suspended pendulum fashion within the inner sensor frame by one or more flexures, and two mechanical resonators interconnected in push-pull fashion between the proof mass and the inner sensor frame;

an outer frame formed in the substrate and substantially surrounding and spaced away from the accelerometer sensor mechanism; and

a plurality of strain-isolating suspension members positioned in the space between the accelerometer sensor mechanism and the outer frame and coupled between the accelerometer sensor mechanism and the outer frame, pairs of the strain-isolating suspension members positioned on opposite sides of the accelerometer sensor mechanism, each of the strain-isolating suspension members being formed in the substrate and comprising;

a first thin and elongated flexure having first and second ends coupled to an inner wall of the outer frame, and

a second thin and elongated flexure having first and second ends coupled to an inner wall of the outer frame opposite from the first flexure, a portion of the second flexure intermediate between the first and second ends being interconnected to the first flexure at a portion thereof intermediate between the first and second ends thereof.

35. The accelerometer of claim 34 wherein the first and second ends of the first flexure of each of the plurality of strain-isolating suspension members is coupled to the inner wall of the outer frame along a portion extending substantially the entire distance between the top and bottom surfaces of the substrate.

36. The accelerometer of claim 34 wherein the first and second ends of the second flexure of each of the plurality of strain-isolating suspension members is coupled to the outer wall of the inner frame along a portion extending substantially the entire distance between the top and bottom surfaces of the substrate.

37. The accelerometer of claim 34 wherein each of the plurality of strain-isolating suspension members further comprises a beam interconnecting the first and second flexures, the beam being coupled between the portion of the first flexure intermediate between the first and second ends thereof and the second flexure intermediate between the first and second ends thereof.

38. The accelerometer of claim 34 wherein the second flexures of each of the plurality of strain-isolating suspension members is spaced away from and aligned substantially parallel with the respective first flexures thereof.

39. The accelerometer of claim 34 wherein one of the pairs of the strain-isolating suspension members positioned on opposite sides of the accelerometer sensor mechanism is further aligned to act through a center of percussion of the proof mass.

40. The accelerometer of claim 34 wherein one of the pairs of the strain-isolating suspension members positioned on opposite sides of the accelerometer sensor mechanism is further aligned to act through a center of mass of the proof mass.

41. The accelerometer of claim 34 wherein one of the pairs of the strain-isolating suspension members positioned on opposite sides of the accelerometer sensor mechanism is further aligned to act through a center of gravity of the proof mass.

42. A method for suspending and isolating an apparatus comprising:

substantially surrounding an inner frame member with an outer frame member spaced apart therefrom by a slot formed between an inner peripheral edge of the outer frame member and an outer peripheral edge of the inner frame member;

interconnecting a plurality of first flexures spaced about the inner peripheral edge of the outer frame member;

interconnecting a plurality of second flexures spaced about the outer peripheral edge of the inner frame member at a position opposite from a corresponding one of the first flexures; and

interconnecting a center portion of each of the second flexures with a center portion of the corresponding first flexure.

43. The method of claim 42, further comprising:

positioning a first pair of the first and second interconnected flexures on a first side of the inner frame member; and

positioning a second pair of the first and second interconnected flexures on a second side of the inner frame member opposite from the first pair of the first and second interconnected flexures.

44. The method of claim 42, further comprising forming each of inner frame member, the outer frame member, and each of the first and second flexures in a substrate and extending between substantially parallel spaced apart surfaces of the substrate.

45. The method of claim 44, further comprising forming each of the first and second flexures to extend through substantially the entire thickness between the spaced apart surfaces of the substrate.

46. The method of claim 42, further comprising converting into a torque a strain transmitted by each of the first and second flexures.

47. The method of claim 46 wherein converting into a torque a strain transmitted by each of the first and second flexures further comprises converting the strain into equal and opposite torques at opposite ends of the second flexures.

48. The method of claim 42, further comprising providing as part of the inner frame member a means for measuring acceleration applied along an input axis.