Microfabricated tuning fork gyroscope and associated three-axis inertial measurement system to sense out-of-plane rotation

• US 6,257,059 B1
• Filed: 09/24/1999
• Issued: 07/10/2001
• Est. Priority Date: 09/24/1999
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Lee, Tommy W., Bernstein, Jonathan J., Weinberg, Marc S., Kirkos, Gregory A., Petrovich, Anthony
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/405,721
• Time in Patent Office: 655 Days
• Field of Search: 73/504.02, 73/504.12, 73/504.15, 73/504.16, 73/510, 310/370
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A micromechanical tuning fork gyroscope has an input axis out of the plane of the structure. In one embodiment, capacitor plates are provided in parallel strips beneath two apertured, planar proof masses suspended from a substrate by a support structure. The proof masses are paired and set in opposed vibrational motion by an electrostatic comb drive. In response to an input angular rate about the out-of-plane input axis, the proof masses translate with respect to the striped capacitors, thereby varying the capacitance between the capacitor strips and the proof masses as a function of the input rate. In another embodiment, proof mass combs of a comb drive are meshed between fixed drive combs which are electrically excited in pairs 180° out of phase. As the proof masses translate in response to an angular input, the distance between the proof mass combs and the fixed combs varies, thereby varying the capacitance between the combs resulting in an unbalanced voltage on the proof masses that is detected as an indication of input rate. The out-of-plane tuning fork gyroscope can be combined with two in-plane tuning fork gyroscopes to provide a complete three-axis inertial measurement unit from a single wafer or on a single chip.

Claims

1. A microfabricated tuning fork structure comprising:

a substrate defining a major plane;

first and second proof masses supported by the substrate, the proof masses being supported in a manner allowing for driven vibration of the proof masses in opposite directions along a first axis parallel to the major plane and also allowing for translation of the proof masses along a second axis parallel to the major plane and oriented differently from the first axis, the translation occurring in response to an angular input with respect to an axis out of the major plane when the proof masses are being vibratingly driven along the first axis;

a drive structure in electrical communication with the proof masses to cause the proof masses to vibrate along the first axis while allowing for motion along the second axis; and

sense electrodes supported by the substrate, the sense electrodes being in spaced relation to and cooperatively configured with the proof masses to establish respective capacitances therewith that vary with axial motion of the proof masses along the second axis, the sense electrodes and the proof masses being further configured to enable the detection of differential variation of the capacitances in response to differential axial motion of the proof masses along the second axis.

2. The microfabricated tuning fork structure of claim 1, wherein each proof mass includes electrodes extending therefrom, and wherein the sense electrodes are supported by the substrate to mesh with the extending electrodes.

3. The microfabricated tuning fork structure of claim 2, wherein the sense electrodes comprise pairs of electrodes, the electrodes of each of the pair being electrically driven 180°

out of phase with each other.

4. The microfabricated tuning fork structure of claim 2, wherein the extending electrodes extend between the electrodes of each of the pairs of sense electrodes.

5. The microfabricated tuning fork structure of claim 2, wherein the proof masses each include an opening therein, the extending electrodes extending into the openings, the sense electrodes supported by the substrate within the openings.

6. The microfabricated tuning fork structure of claim 2, wherein the sense electrodes are in electrical communication with a drive system which provides a voltage on the sense electrodes at a drive resonance of the proof masses.

7. The microfabricated tuning fork structure of claim 2, wherein the sense electrodes are in electrical communication with a drive system which provides a voltage on the sense electrodes to provide a frequency different from a drive resonance of the proof masses.

8. The microfabricated tuning fork structure of claim 2, wherein the sense electrodes and the electrodes extending from the proof masses mesh such that unequal air gaps exist between each sense electrode and two adjacent electrodes extending from the corresponding proof mass with which the sense electrode meshes.

9. The microfabricated tuning fork structure of claim 8, wherein the electrodes extending from the proof masses and the sense electrodes form corresponding combs.

10. The microfabricated tuning fork structure of claim 8, wherein the sense electrodes are arranged as parallel elongated strips, and further comprising a conductive lead electrically interconnecting the strips.

11. The microfabricated tuning fork structure of claim 1, wherein the sense electrodes comprise parallel strips supported by the substrate in opposition to the proof masses, the strips extending parallel to the first axis.

12. The microfabricated tuning fork structure of claim 11, wherein each of the proof masses have a plurality of apertures disposed therethrough, and wherein the strips are arranged in pairs, one of the strips of each pair being electrically excitable 180°

out of phase with respect to another of the strips of each pair.

13. The microfabricated tuning fork structure of claim 12, wherein the pairs of strips have a first pitch and the apertures have a second pitch substantially equal to the first pitch.

14. The microfabricated tuning fork structure of claim 12, wherein edges of the apertures lie over the strips of each pair of strips.

15. The microfabricated tuning fork structure of claim 1, wherein each proof mass has regions of conductivity bordering regions of substantially no conductivity, the no-conductivity regions being disposed in opposition to the plurality of sense electrodes in a linear formation of a first selected pitch, and wherein the sense electrodes being disposed in a linear formation having a second selected pitch substantially the same as the first selected pitch.

16. The microfabricated tuning fork structure of claim 15, wherein the regions of substantially no conductivity comprise apertures through the proof masses.

17. The microfabricated tuning fork structure of claim 1, wherein the drive structure includes a comb drive comprising first driven electrodes extending from the proof masses and second drive electrodes extending from the substrate and meshing with the first driven electrodes.

18. The microfabricated tuning fork structure of claim 17, the drive structure further including first and second pluralities of drive sense electrodes extending from the substrate at a region between the proof masses and meshing with further driven electrodes extending from the proof masses.

19. The microfabricated tuning fork structure of claim 18, wherein the first and second pluralities of drive sense electrodes extend from the substrate at first and second separated anchor regions.

20. The microfabricated tuning fork structure of claim 1, wherein the proof masses are supported on the substrate by a suspension comprising:

two beams, the beams being disposed on opposite sides of the proof masses;

first flexural members connecting the beams to anchors on the substrate; and

second flexural members connecting the proof masses to the beams.

21. The microfabricated tuning fork structure of claim 1, wherein the proof masses are supported on the substrate by a suspension comprising:

two beams, the beams being anchored to the substrate on opposite sides of the proof masses; and

flexural members connecting the proof masses to the beams.

22. The microfabricated tuning fork structure of claim 1, wherein the proof masses are supported on the substrate by a suspension comprising flexural members disposed within corresponding cutouts in the proof masses, each flexural member being attached to the corresponding proof mass at an innermost region of the cutout within which the flexural member is disposed.

23. The microfabricated tuning fork structure of claim 1, wherein the proof masses are arranged side by side, and wherein the proof masses are supported on the substrate by a suspension comprising substantially identical flexural members attached to each proof mass, the flexural members being arranged at the tops and bottoms of the proof masses and being attached to corresponding anchors on the substrate at the tops and bottoms of the proof masses.

24. The microfabricated tuning fork structure of claim 1, wherein the second axis is orthogonal to the first axis.

25. The microfabricated tuning fork structure of claim 1, wherein the out of plane axis is orthogonal to the major plane.

26. An inertial measurement system comprising:

a substrate defining a major plane;

a first in-plane tuning fork gyroscope supported by the substrate comprising;

first and second proof masses suspended for vibratory motion along a first axis parallel to the major plane and rotation about a second axis orthogonal to the first axis,

a first drive structure in electrical communication with the first and second proof masses to cause vibration thereof along the first axis, and

a first sensor structure disposed to sense rotation of the first and second proof masses about the second axis;

a second in-plane tuning fork gyroscope supported by the substrate and oriented angularly with respect to the first in-plane tuning fork gyroscope, comprising;

third and fourth proof masses suspended for vibratory motion along a third axis parallel to the major plane and orthogonal to the first axis and for rotation about a fourth axis orthogonal to the third axis,

a second drive structure in electrical communication with the third and fourth proof masses to cause vibration along the third axis, and

a second sensor structure disposed to sense rotation of the third and fourth proof masses about the fourth axis; and

an out-of-plane tuning fork gyroscope supported by the substrate comprising;

fifth and sixth proof masses suspended for vibratory motion along a fifth axis parallel to the major plane and translation along a sixth axis parallel to the major plane and angled with respect to the fifth axis,

a third drive structure in electrical communication with the fifth and sixth proof masses to cause vibration along the fifth axis,

a third sensor structure disposed to sense translation of the fifth and sixth proof masses along the sixth axis.

27. The inertial measurement system of claim 26, wherein the third sensor structure of the out-of-plane tuning fork gyroscope includes:

sense electrodes supported by the substrate, the sense electrodes provided in pairs, the electrodes of each pair being electrically driven 180°

out of phase with respect to each other; and

electrodes extending from the fifth and sixth proof masses, each ex tending electrode disposed to mesh between the electrodes of an associated one of the pairs of sense electrodes.

28. The inertial measurement system of claim 26, wherein the third sensor structure of the out-of-plane tuning fork gyroscope includes:

sense electrodes comprising parallel strips supported by the substrate in opposition to the first and second proof masses and arranged in pairs extending parallel to the fifth axis, one strip of each pair being electrically excitable 180°

out of phase with respect to another of the strips of each pair; and

apertures disposed through the fifth and sixth proof masses, edges of the apertures disposed to lie over the strips of each pair.

29. The inertial measurement system of claim 26, wherein the first, second, and third drive structures each include a comb drive comprising first driven electrodes extending from an associated one of the first, second, third, fourth, fifth, and sixth proof masses, and second drive electrodes extending from the substrate and meshing with the first driven electrodes.

30. The inertial measurement system of claim 26, wherein the first in-plane tuning fork gyroscope, the second in-plane tuning fork gyroscope, and the out-of-plane tuning fork gyroscope are provided on a single wafer.

31. The inertial measurement system of claim 26, wherein the first in-plane tuning fork gyroscope, the second in-plane tuning fork gyroscope, and the out-of-plane tuning fork gyroscope are provided on a single chip.

32. The inertial measurement system of claim 26, wherein the frequency of vibration of the first and second proof masses along the first axis is sufficiently different from the frequency of vibration of the third and fourth proof masses along the third axis and both of these vibration frequencies are sufficiently different from the frequency of vibration of the fifth and sixth proof masses along the sixth axis so that cross talk between the three gyroscopes is substantially avoided.

33. The inertial measurement system of claim 32, wherein the difference in the respective frequencies of vibration is due to a difference between the mass of the first and second proof masses and the mass of the fifth and sixth proof masses.

34. The inertial measurement system of claim 32, wherein the difference in the respective frequencies of vibration is due to a difference between the spring constant of the suspension for the first and second proof masses and the spring constant for the suspension of the third and fourth proof masses and the spring constant for the suspension of the fifth and sixth proof masses.