Micromachined device utilizing electrostatic comb drives to filter mechanical vibrations

• US 7,355,318 B2
• Filed: 06/10/2005
• Issued: 04/08/2008
• Est. Priority Date: 06/12/2004
• Status: Expired due to Fees

• Current Assignee: Auburn University
• Original Assignee: Auburn University
• Inventors: Dean, Robert Neal Jr., Flowers, George Timothy
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US11/149,922
• Publication Number:
  US 20050274186A1
• Time in Patent Office: 1,033 Days
• Field of Search: 735/141.8, 735/143.2, 310/309
• US Class Current: 310/309
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A micromachined device for filtering mechanical vibrations caused by an external disturbance is disclosed. The device can include a first electrostatic vertical comb drive assembly having a first array of stationary elements and a second array of movable elements correspondingly interspersed with the first array. The device can also include a plurality of springs, each springs coupled between a support frame and a proof mass. The first drive assembly can be configured for motion in the z-direction. The device can include a sensor for sensing a position of the proof mass relative to the support frame by measuring displacement between each of the stationary and movable elements. The device can further include a second electrostatic vertical comb drive assembly. The device can have multiple electrostatic comb drive assemblies. An optional feedback network signal processes a displacement measurement to control one of the drive assemblies.

Claims

1. A micromachined device for filtering vibrations caused by an external disturbance, the device comprising:

(a) a support frame;

(b) a proof mass;

(c) a first electrostatic comb drive assembly for filtering the vibrations caused by external disturbance including;

(i) a first array of stationary elements coupled to the support frame, wherein each of the first array of stationary elements is electrically insulated from the others; and

(ii) a second array of movable elements interspersed with the first array and coupled to the proof mass;

(d) a position sensor coupled to the device for sensing displacement of the proof mass relative to the support frame; and

(e) a control system for applying an external voltage across the first array and second array to change a frequency response of the device, wherein a drive voltage is independently set by the external voltage and one of the second array of movable elements is pulled electrostatically closer to one of the first array of stationary elements.

2. The device of claim 1 further including a plurality of springs, each spring coupled between a support frame and a proof mass.

3. The device of claim 2 wherein the proof mass, the support frame and the springs are made of a same material.

4. The device of claim 2 wherein the proof mass, the support frame and the springs are made of a different material.

5. The device of claim 1 wherein the first drive assembly is configured for filtering vibrations in the z-direction, wherein the support frame and the proof mass lie in a plane defined by an x and y-axis, and the z-direction is perpendicular to the x-y plane.

6. The device of claim 1 wherein the position sensor comprises one of:

a capacitance sensor, a piezoresistive sensor, a magnetic sensor and an interferometer.

7. The device of claim 1 further including a second electrostatic vertical comb drive assembly.

8. The device of claim 7 wherein at least one of the first drive assembly and the second drive assembly are made of the same material.

9. The device of claim 7 wherein the second drive assembly includes a third array of stationary elements and a fourth array of movable elements correspondingly interspersed with the third array.

10. The device of claim 9 further including a plurality of springs, each spring coupled between a support frame and a proof mass.

11. The device of claim 10 wherein the first array of stationary elements and the third array of stationary elements are coupled to the support frame and wherein the second array of movable elements and the fourth array of movable elements are coupled to the proof mass.

12. The device of claim 10 wherein at least one of the first drive assembly and the second drive assembly is configured for motion filtering vibrations in the z-direction, wherein the support frame and the proof mass lie in a plane defined by an x and y-axis, and the z-direction is perpendicular to the x-y plane.

13. The device of claim 9 wherein an external voltage is applied across at least one of the first array and the second array and the third array and the fourth array.

14. The device of claim 9 wherein the first drive assembly generates a restoring force on the proof mass and the second drive assembly measures displacement of the proof mass with respect to the frame.

15. The device of claim 14 further including a feedback network to signal process the displacement measurement to control at least one of the first drive assembly and the second drive assembly.

16. The device of claim 9 wherein the second drive assembly is positioned orthogonally about the z-axis from the first drive assembly, wherein the support frame and the proof mass lie in a plane defined by an x and y-axis, and the z-axis is perpendicular to the x-y plane.

17. The device of claim 9 wherein the second drive assembly is positioned in line with the first drive assembly.

18. A micromachined device for filtering mechanical vibrations caused by an external disturbance, the device including a plurality of springs, each spring coupled between a support frame and a proof mass, the device comprising:

(a) a first electrostatic comb drive assembly for generating a restoring force on the proof mass wherein the first electrostatic comb drive assembly includes a set of fixed comb drive structure electrodes, each of which are electrically insulated from one another; and

(b) a second electrostatic comb drive assembly for measuring displacement of the proof mass with respect to the frame, wherein the second electrostatic comb drive assembly includes a set of movable comb drive structure electrodes, wherein a drive voltage of each electrode is independenly set by an external voltage and one of the movable electrodes is pulled electrostatically closer to one of the fixed electrodes by a potential difference established through the independently set drive voltage of the movable electrode and the fixed electrode.

19. The device of claim 18 further including a feedback network to signal process the displacement measurement to control at least one of the first drive assembly and the second drive assembly.

20. The device of claim 18 wherein the first drive assembly includes a first array of stationary elements and a second array of movable elements correspondingly interspersed with the first array and the second drive assembly includes a third array of stationary elements and a fourth array of movable elements correspondingly interspersed with the third array.

21. The device of claim 20 wherein the first array of stationary elements and the third array of stationary elements are coupled to the support frame and wherein the second array of movable elements and the fourth array of movable elements are coupled to the proof mass.

22. The device of claim 20 wherein an external voltage is applied across at least one of the first array and the second array and the third array and the fourth array to change a frequency response of the device.

23. The device of claim 18 wherein at least one of the first drive assembly and the second drive assembly is configured for filtering vibrations in the z-direction, wherein the support frame and the proof mass lie in a plane defined by an x and y-axis, and the z-direction is perpendicular to the x-y plane.

24. The device of claim 18 wherein the second drive assembly is positioned orthogonally about the z-axis from the first drive assembly, wherein the support frame and the proof mass lie in a plane defined by an x and y-axis, and the z-axis is perpendicular to the x-y plane.

25. The device of claim 18 wherein the second drive assembly is positioned in line with the first drive assembly.

26. The device of claim 18 further comprising a signal processing means wherein at least one of a momentary velocity and acceleration of the proof mass is estimated by signal processing the displacement measurements with the signal processing means.

27. The device of claim 26 wherein the signal processed displacement measurements are used to calculate a driving voltage for the first drive assembly.

28. A micromachined device for filtering mechanical vibrations caused by an external disturbance, the device comprising:

(a) a first set of fixed individual comb drive structure elements having outer fixed electrodes and inner fixed electrodes wherein each fixed electrode is electrically insulated from one another; and

(b) further including a first set of movable individual comb drive electrodes, wherein a drive voltage of each electrode is independently set by an external voltage and the movable electrode is pulled electostatically closer to one of the fixed electrodes by a potential difference established through the independently set drive voltages of the movable electrode and the fixed electrode.

29. The device of claim 28 further including a proof mass, a support frame and at least one spring, the first set of fixed elements coupled to the support frame, the second set of movable electrodes coupled to and protruding from the proof mass, the at least one spring coupled between the proof mass and the support frame.

30. The device of claim 29 wherein the outer fixed electrodes determine a relative position of the proof mass with respect to the fixed electrodes by measuring capacitance between each fixed electrode and one of the movable electrodes closest to the fixed electrode.

31. The device of claim 30 further including a feedback network for processing displacement measurements and generating control voltages for the inner fixed electrodes.

32. The device of claim 29 wherein the inner fixed electrodes move the proof mass by electrostatic actuation in at least one of:

one-dimensional motion, two-dimensional motion, and three-dimensional motion.