Silicon bulk micromachined, symmetric, degenerate vibratorygyroscope, accelerometer and sensor and method for using the same

• US 5,894,090 A
• Filed: 05/31/1996
• Issued: 04/13/1999
• Est. Priority Date: 05/31/1996
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Bartman, Randall K., Kaiser, William J., Calvet, Robert J., Gutierrez, Roman C., Tang, Tony K., Wilcox, Jaroslava Z.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US08/657,685
• Time in Patent Office: 1,047 Days
• Field of Search: 73/504.12, 73/504.04, 73/514.15, 73/514.29, 73/662, 73/514.35, 73/502.02, 73/514.16, 73/514.32, 324/76.49, 331/158, 437/921
• US Class Current: 73/504.02
• 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
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape

Abstract

When embodied in a microgyroscope, the invention is comprised of a silicon, four-leaf clover structure with a post attached to the center. The whole structure is suspended by four silicon cantilevers or springs. The device is electrostatically actuated and capacitively detects Coriolis induced motions of the leaves of the leaf clover structure. In the case where the post is not symmetric with the plane of the clover leaves, the device can is usable as an accelerometer. If the post is provided in the shape of a dumb bell or an asymmetric post, the center of gravity is moved out of the plane of clover leaf structure and a hybrid device is provided. When the clover leaf structure is used without a center mass, it performs as a high Q resonator usable as a sensor of any physical phenomena which can be coupled to the resonant performance.

Claims

1. A micromachined resonator comprising:

a micromachined symmetric leaf structure having a plurality of symmetrically disposed leaves about a defined center;

at least one micromachined spring symmetrically disposed with respect to said symmetric leaf structure and supporting said symmetrical leaf structure;

a rim/base structure to which said spring is coupled, said rim/base structure including a plurality of sensing and drive electrodes; and

a circuit electrically coupled to said electrodes included within said rim/base structure, said circuit for providing drive signals to said drive electrodes to oscillate said symmetric leaf structure and to receive a sensing signal from said sensing electrodes to detect response of said oscillating symmetric leaf structure to physical phenomena exterior to said micromachined resonator,

whereby a rugged, small, low cost, high performance vibratory sensor is provided.

2. The resonator of claim 1 wherein a plurality of said springs are provided for coupling and supporting said symmetric leaf structure to said rim/base structure.

3. The resonator of claim 2 wherein said plurality of springs are symmetrically disposed with respect to said symmetric leaf structure.

4. The resonator of claim 3 wherein said symmetric leaf structure and plurality of springs are symmetric about at least two separate axes.

5. The resonator of claim 4 wherein one of said two separate axes of symmetry of said symmetric leaf structure and a plane in which said plurality of springs lie are orthogonal to each other.

6. The resonator of claim 5 further comprising a mass element coupled to said symmetric leaf structure.

7. The resonator of claim 6 wherein said mass element is symmetrically disposed to said symmetric leaf structure.

8. The resonator of claim 7 wherein said symmetric leaf structure is substantially defined in a plane and said mass element extends in a direction substantially perpendicular to said plane of said symmetric leaf structure.

9. The resonator of claim 8 wherein said mass element is a cylinder disposed through a center of mass of said symmetric leaf structure.

10. The resonator of claim 6 wherein said circuit drives said drive electrodes and senses said sensing electrodes to operate said resonator as a microgyroscope.

11. The resonator of claim 1 wherein said symmetric leaf structure is a clover leaf pattern comprised of four leaves symmetrically disposed about said center and wherein said clover leaf pattern is disposed within a plane.

12. The resonator of claim 11 further comprising four springs connected to said clover leaf pattern and symmetrically disposed between each of said four clover leaves to connect said center with said rim/base and to support said clover leaf pattern relative to said rim/base structure.

13. The resonator of claim 12 wherein said rim/base structure comprises a rim disposed in said plane of said clover leaf pattern and a base disposed beneath said rim and coupled to said rim.

14. The resonator of claim 13 wherein said electrodes provided within said rim/base structure are provided on said base, two electrodes being provided as said drive electrodes and two electrodes being provided as said sensing electrodes, said driving and sensing electrodes positioned on said base opposite corresponding ones of said leaves in said clover leaf pattern, each of said driving and sensing electrodes being positioned opposite a different one of said leaves.

15. The resonator of claim 13 wherein said rim is symmetric with said clover leaf pattern and said springs.

16. The resonator of claim 1 wherein said circuit differentially senses said sensing signal from said sensing electrodes to reject common mode signals from said sensing electrodes.

17. The resonator of claim 1 wherein said symmetric leaf structure has at least two resonant modes and wherein symmetry of said symmetric leaf structure causes two resonant modes to be degenerate.

18. The resonator of claim 1 wherein said leaves of said symmetric leaf structure and said sensing and drive electrodes of said rim/base structure define large coplanar opposing surfaces from each other for increased drive and sensing.

19. A method of operating a vibratory micromachined resonator comprising the steps of:

oscillating a micromachined symmetric leaf structure having a plurality of symmetrically disposed leaves about a defined center, said symmetric leaf structure including at least one micromachined spring symmetrically disposed with respect to said symmetric leaf structure and supporting said symmetrical leaf structure for providing a restoring force to said symmetric leaf structure; and

sensing Coriolis perturbations caused in said oscillating symmetric leaf structure;

whereby motion is detected in a rugged, small, low cost, high performance vibratory sensor.

20. The method of claim 19 where said step of sensing Coriolis perturbations is capacitively performed between said symmetric leaf structure and a plurality of sensing and drive electrodes disposed in a rim/base structure to which said spring is coupled.

21. The method of claim 20 where said step of sensing is performed by a circuit electrically coupled to said electrodes included within said rim/base structure, said circuit providing drive signals to said drive electrodes to oscillate said symmetric leaf structure and to receive a sensing signal from said sensing electrodes to detect response of said oscillating symmetric leaf structure to physical phenomena exterior to said micromachined resonator.

22. The method of claim 19 where said step of oscillating said symmetric leaf structure oscillates said symmetric leaf structure in one or more plurality of modes about a plurality of said springs supporting said symmetric leaf structure with respect to said rim/base structure.

23. The method of claim 22 where said step of oscillating said symmetric leaf structure oscillates said symmetric leaf structure about said plurality of springs, which are symmetrically disposed with respect to said symmetric leaf structure.

24. The method of claim 23 where said step of oscillating said symmetric leaf structure about said plurality of symmetric springs oscillates said symmetric leaf structure in at least two separate modes.

25. The method of claim 24 where said step of oscillating said symmetric leaf structure about said plurality of symmetric springs oscillates said symmetric leaf structure about at least two separate axes.

26. The method of claim 19 further comprising the step of oscillating a mass element rigidly connected to said symmetric leaf structure.

27. The method of claim 26 where said step of oscillating a mass element comprises the step of oscillating a mass element symmetrically disposed with respect to said symmetric leaf structure.

28. The method of claim 27 where said step of oscillating a mass element comprises the step of oscillating a cylinder disposed through a center of mass of said symmetric leaf structure and extending at least in part perpendicular to said symmetric leaf structure.

29. A sensor comprising:

a symmetric leaf structure having a plurality of symmetrically disposed leaves about a defined center;

at least one spring symmetrically disposed with respect to said symmetric leaf structure and supporting said symmetrical leaf structure;

a rim/base structure to which said spring is coupled, said rim/base structure including a plurality of sensing electrodes; and

a circuit electrically coupled to said electrodes included within said rim/base structure, said circuit for receiving a sensing signal from said sensing electrodes to detect response of said symmetric leaf structure to physical phenomena exterior to said sensor,

whereby a rugged, small, low cost, high performance sensor is provided.

30. The sensor of claim 29 wherein said symmetric leaf structure is a clover leaf pattern comprised of four leaves symmetrically disposed about said center and wherein said clover leaf pattern is disposed within a plane.

31. The resonator of claim 30 further comprising four springs connected to said clover leaf pattern and symmetrically disposed between each of said four clover leaves to connect said center with said rim/base and to support said clover leaf pattern relative to said rim/base structure.

32. The resonator of claim 31 wherein said rim/base structure comprises a rim disposed in said plane of said clover leaf pattern and a base disposed beneath said rim and coupled to said rim.

33. The resonator of claim 32 wherein said electrodes provided within said rim/base structure are provided on said base, said electrodes being provided as said sensing electrodes, said sensing electrodes positioned on said base opposite corresponding ones of said leaves in said clover leaf pattern, each of said sensing electrodes being positioned opposite a different one of said leaves.

34. The resonator of claim 32 wherein said rim is symmetric with said clover leaf pattern and said springs.