Dual-mass vibratory rate gyroscope with suppressed translational acceleration response and quadrature-error correction capability

• US 6,230,563 B1
• Filed: 05/28/1999
• Issued: 05/15/2001
• Est. Priority Date: 06/09/1998
• Status: Expired due to Term

• Current Assignee: Analog Devices IMI, Inc. (Analog Devices, Inc.)
• Original Assignee: Integrated Micro Instruments, Inc. (Analog Devices, Inc.)
• Inventors: Roessig, Allen W., Clark, William A., Lemkin, Mark A., Juneau, Thor N.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/321,972
• Time in Patent Office: 718 Days
• Field of Search: 735/040.4, 735/040.2, 735/040.3, 735/142.9, 735/143.7, 735/143.8, 735/143.2, 738/625.9, 735/041.2, 735/041.4, 735/041.5
• US Class Current: 73/504.04
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A microfabricated vibratory rate gyroscope to measure rotation includes two proof-masses mounted in a suspension system anchored to a substrate. The suspension has two principal modes of compliance, one of which is driven into oscillation. The driven oscillation combined with rotation of the substrate about an axis perpendicular to the substrate results in Coriolis acceleration along the other mode of compliance, the sense-mode. The sense-mode is designed to respond to Coriolis accelerationwhile suppressing the response to translational acceleration. This is accomplished using one or more rigid levers connecting the two proof-masses. The lever allows the proof-masses to move in opposite directions in response to Coriolis acceleration. The invention includes a means for canceling errors, termed quadrature error, due to imperfections in implementation of the sensor. Quadrature-error cancellation utilizes electrostatic forces to cancel out undesired sense-axis motion in phase with drive-mode position.

Claims

1. A microsensor for measuring angular motion comprising:

a substrate having a first surface;

a first movable mass connected to said substrate;

a second movable mass connected to said substrate;

an input axis normal to said first surface of said substrate; and

a suspension comprising a coupling extending from said first movable mass to said second movable mass, said suspension allowing anti-phase movement by said first and second movable masses along a first axis parallel to said first surface of said substrate while allowing anti-phase movement and resisting in-phase movement by said movable masses along a second axis parallel to said first surface of said substrate, said second axis being substantially orthogonal to said first axis.

2. The microsensor of claim 1 wherein said coupling includes at least one lever, said lever allowing anti-phase movement and resisting in-phase movement of said first and second masses along said second axis.

3. The microsensor of claim 2 wherein said coupling further includes two or more flexures allowing anti-phase movement along said first axis.

4. The microsensor of claim 1 wherein said suspension includes two or more flexures allowing anti-phase movement along said second axis, while providing a restoring force that generally tends to restore said first and second masses to a nominal position in the absence of external forces.

5. The microsensor of claim 1 further including a force transducer for exciting anti-phase motion of the first and second masses along said first axis.

6. The microsensor of claim 5 further including a detection device for detecting anti-phase motion of the first and second masses along said first axis.

7. The microsensor of claim 5 wherein the force transducer includes:

a first substantially stationary conductive comb anchored to said substrate having a first plurality of fingers extending towards the first mass;

a second conductive comb connected to the first mass having a second plurality of fingers that interdigitate with the first plurality of fingers, the first and second combs forming electrodes of a first capacitor;

a third substantially stationary conductive comb anchored to said substrate having a third plurality of fingers extending towards the second mass;

a fourth conductive comb connected to the second mass having a fourth plurality of fingers that interdigitate with the third plurality of fingers, the third and fourth combs forming electrodes of a second capacitor; and

an electrical connection between the first through fourth combs such that a voltage applied to said electrical connection provides anti-phase forces to the first and second masses along said first axis.

8. The microsensor of claim 6 wherein the detection device includes

a first substantially stationary conductive comb anchored to said substrate having a first plurality of fingers extending towards the first mass;

a second conductive comb connected to the first mass having a second plurality of fingers that interdigitate with the first plurality of fingers, the first and second combs forming electrodes of a first capacitor;

a third substantially stationary conductive comb anchored to said substrate having a third plurality of fingers extending towards the second mass;

a fourth conductive comb connected to the second mass having a fourth plurality of fingers that interdigitate with the third plurality of fingers, the third and fourth combs forming electrodes of a second capacitor; and

an electrical connection between the first through fourth combs, said electrical connection having an output, said output providing a differential capacitance representative of anti-phase motion of the first and second masses along said first axis.

9. The microsensor of claim 7 further including a detection device for detecting anti-phase motion of the first and second masses along said first axis.

10. The microsensor of claim 9 wherein the detection device comprises:

said first capacitor;

said second capacitor;

said electrical connection; and

further includes circuitry for frequency-multiplexing voltages applied to said connection for force transducing and motion detection.

11. The microsensor of claim 9 wherein the detection device comprises:

said first capacitor;

said second capacitor;

said electrical connection; and

further includes circuitry for time-multiplexing voltages applied to said connection for force transducing and motion detection.

12. The microsensor of claim 1 further including a detection device for detecting anti-phase motion of the first and second masses along said second axis.

13. The microsensor of claim 12 wherein said detection device includes:

a first set of one or more generally parallel substantially stationary first finger pairs anchored to said substrate extending towards the first mass, the first mass having at least two fingers interdigitated by a first anchored finger pair forming a first capacitor half-bridge;

a second set of one or more generally parallel substantially stationary second finger pairs anchored to said substrate extending towards the second mass, the second mass having at least two fingers interdigitated by a second anchored finger pair forming a second capacitor half-bridge; and

an electrical connection between the first and second capacitor half-bridges, said electrical connection having an output, said output providing a differential capacitance representative of anti-phase motion of the first and second masses along said second axis.

14. The microsensor of claim 1 further including:

a) a quadrature-cancellation structure comprising;

a1) a first set of one or more generally parallel substantially stationary first finger pairs anchored to said substrate extending towards the first mass, the first mass having at least two fingers interdigitated by a first anchored finger pair, the end of each first anchored finger pair terminating between fingers attached to the first mass, forming a first capacitor half-bridge;

a2) a second set of one or more generally parallel substantially stationary second finger pairs anchored to said substrate extending towards the second mass, the second mass having at least two fingers interdigitated by a second anchored finger pair, the end of each second anchored finger pair terminating between fingers attached to the second mass, forming a second capacitor half-bridge; and

b) an electrical circuit providing a first differential voltage with a common-mode component across the first half bridge, and a second differential voltage with a second common-mode component across the second half bridge thereby providing a position-dependent force to cause the first and second masses to vibrate absent a Coriolis force, more precisely along the direction of extension of said first axis.

15. The microsensor of claim 1 further including:

a) a quadrature-cancellation structure comprising;

a1) a first set of one or more generally parallel substantially stationary first finger pairs anchored to said substrate extending towards the first mass, the first mass having at least one finger interdigitated between at least one first anchored finger pair, the end of each finger extending from the first mass terminating between a first anchored finger pair, forming a first capacitor half-bridge;

a2) a second set of one or more generally parallel substantially stationary second finger pairs anchored to said substrate extending towards the second mass, the second mass having at least one finger interdigitated between at least one second anchored finger pair, the end of each finger extending from the second mass terminating between a second anchored finger pair, forming a second capacitor half-bridge; and

b) an electrical circuit providing a first differential voltage with a common-mode component across the first half bridge, and a second differential voltage with a second common-mode component across the second half bridge thereby providing a position-dependent force to cause the first and second masses to vibrate absent a Coriolis force, more Precisely along the direction of extension of said first axis.

16. The microsensor of claim 1 wherein said microsensor is formed by etching directly into a silicon or bonded silicon wafer.

17. The microsensor of claim 16 wherein the coupling includes one or more flexures having:

a flexure thickness at least 5 times flexure width; and

a flexure length at least 10 times flexure width.

18. The microsensor of claim 1 wherein said microstructure is formed by deposition and subsequent etching of a conductive material onto a silicon wafer, portions of the silicon wafer being potentially covered by a dielectric layer.

19. The microsensor of claim 18 wherein the coupling includes one or more flexures having:

a flexure thickness at least 2 times flexure width; and

a flexure length at least 5 times flexure width.

20. The microsensor of claim 1 wherein the coupling includes one or more composite flexures formed of two or more substantially parallel flexures attached at two or more points.

21. A vibratory gyroscope comprising:

a) a substrate having a first surface;

b) a first movable mass connected to said substrate;

c) a second movable mass connected to said substrate;

d) a coupling extending from said first movable mass to said second movable mass, said coupling allowing anti-phase movement by said first movable mass and said second movable mass along a first axis while allowing anti-phase movement along a second axis substantially orthogonal to said first axis, said first and second axes being generally parallel to said first surface of the substrate;

e) a quadrature-cancellation structure including;

e1) a first set of one or more generally parallel substantially stationary first finger pairs anchored to said substrate extending towards said first movable mass, said first movable mass having at least two fingers interdigitated by a first anchored finger pair, the end of each first anchored finger pair terminating between fingers attached to said first movable mass, forming a first capacitor half-bridge;

e2) a second set of one or more generally parallel substantially stationary second finger pairs anchored to said substrate extending towards said second movable mass, said second movable mass having at least two fingers interdigitated by a second anchored finger pair, the end of each second anchored finger pair terminating between fingers attached to said second movable mass, forming a second capacitor half-bridge; and

f) electrical circuitry for generation and application of a differential voltage with a common-mode component across said first half bridge, and a potentially different differential voltage with potentially different common-mode component across said second half bridge resulting in a position-dependent force that may be used to cancel quadrature-error.

22. A vibratory gyroscope comprising:

a) a substrate having a first surface;

b) a first movable mass connected to said substrate;

c) a second movable mass connected to said substrate;

d) a coupling extending from said first movable mass to said second movable mass, said coupling allowing anti-phase movement by said first movable mass and said second movable mass along a first axis while allowing anti-phase movement along a second axis substantially orthogonal to said first axis, said first and second axes being generally parallel to said first surface of the substrate;

e) a quadrature-cancellation structure including;

e1) a first set of one or more generally parallel substantially stationary first finger pairs anchored to said substrate extending towards said first movable mass, said first movable mass having at least one finger interdigitated between at least one first anchored finger pair, the end of each finger extending from said first movable mass terminating between a first anchored finger pair, forming a first capacitor half-bridge;

e2) a second set of one or more generally parallel substantially stationary second finger pairs anchored to said substrate extending towards said second movable mass, said second movable mass having at least one finger interdigitated between at least one second anchored finger pair, the end of each finger extending from said second movable mass terminating between a second anchored finger pair, forming a second capacitor half-bridge; and

f) electrical circuitry for generation and application of a differential voltage with a common-mode component across the first half bridge, and a potentially different differential voltage with potentially different common-mode component across the second half bridge resulting in a position-dependent force that may be used to cancel quadrature-error.