ANCHOR-TILT CANCELLING ACCELEROMETER

• US 20140360268A1
• Filed: 08/21/2014
• Published: 12/11/2014
• Est. Priority Date: 11/24/2010
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Qiu, Jin, Seeger, Joe, Castro, Alexander, Tchertkov, Igor, Li, Richard
• Granted Patent: US 9,766,264 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/02 by making use of inertia forces using solid seismic massesG01P15/14 takes precedence
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

Described herein is an accelerometer that can be sensitive to acceleration, but not anchor motion due to sources other than acceleration. The accelerometer can employ a set of electrodes and/or transducers that can register motion of the proof mass and support structure and employ and output-cancelling mechanism so that the accelerometer can distinguish between acceleration and anchor motion due to sources other than acceleration. For example, the effects of anchor motion can be cancelled from an output signal of the accelerometer so that the accelerometer exhibits sensitivity to only acceleration.

Claims

1. An accelerometer, comprising:

a mechanical structure, comprising;

a substrate;

an anchor coupled to the substrate;

a first proof mass coupled to the anchor by a first flexible member, the first proof mass moves in response to acceleration of the accelerometer; and

a second proof mass coupled to the anchor by a second flexible mass the second proof mass moves in response to the acceleration, wherein the first and second proof masses rotate about a first axis;

a first transducer configured to measure a first distance between a first reference area and a first portion of the first proof mass;

a second transducer configured to measure a second distance between a second reference area and a second portion of the first proof mass;

a third transducer configured to measure a third distance between a third reference area and a first portion of the second proof mass;

a fourth transducer configured to measure a fourth distance between a fourth reference area and a second portion of the second proof mass; and

a signal processing circuit coupled to the first transducer, the second transducer the third transducer, and the fourth transducer, the signal processing circuit configured to provide an output related to the acceleration,

2. The accelerometer of claim 1, wherein the signal processing circuit is operable to produce a first signal proportional to the difference of an output of the first and second transducers and a second signal proportional to the difference of an output of the third and fourth transducers.

3. The accelerometer of claim 1, further wherein the signal processing circuit is operable to determine a difference between the first signal and the second signal proportional to the motion of the first and second proof masses.

4. The accelerometer of claim 1, further comprising a support arm positioned between the anchor and the first and second flexible members.

5. The accelerometer of claim 1, wherein the first and second flexible members provide torsional compliance about the first axis.

6. The accelerometer of claim 1, wherein the first proof mass has a positive rotation about the first axis in response to acceleration and the second proof mass has a negative rotation about the first axis in response to acceleration.

7. The accelerometer of claim 1, wherein the first and second transducers are located on opposite sides of the first axis and the third and fourth transducers are located in opposite sides of the first axis.

8. The accelerometer of claim 1, wherein the first, second, third, and fourth transducers are positioned between the proof mass and the substrate.

9. The accelerometer of claim 1, wherein the first axis is the x-axis.

10. The accelerometer of claim 1, wherein the first, second, third, and fourth transducers are variable capacitors.

11. The accelerometer of claim 1, wherein the first, second, third and fourth transducers are electrodes or optical electrodes.

12. The accelerometer of claim 1, wherein the mechanical structure is disposed in a plane;

the first proof mass is configured to rotate out of the plane in response to acceleration normal to the plane;

the second proof mass is configured to rotate out of plane in response to acceleration normal to the plane;

the first transducer is configured to measure the first distance normal to the plane;

the second transducer is configured to measure the second distance normal to the plane;

the third transducer is configured to measure the third distance normal to the plane; and

the fourth transducer is configured to measure the fourth distance normal to the plane.

13. The accelerometer of claim 1, wherein the first and second proof masses move in opposing directions, further wherein the signal processing circuit measures differential motion of the proof masses and rejects common motion of the proof masses.

14. An accelerometer, comprising:

a mechanical structure, comprising;

a substrate;

an anchor coupled to the substrate;

a first proof mass coupled to the anchor by a first flexible member that moves in response to anchor motion relative to the substrate;

a second proof mass coupled to the anchor by a second flexible member that moves in response to the anchor motion relative to the substrate, wherein the first and second proof masses are aligned about a first axis;

a first transducer configured to measure a first distance between a first reference area and a first portion of the first proof mass;

a second transducer configured to measure a second distance between a second reference area and a second portion of the first proof mass;

a third transducer configured to measure a third distance between a third reference area and a first portion of the second proof mass;

a fourth transducer configured to measure a fourth distance between a fourth reference area and a second portion of the second proof mass; and

a signal processing circuit coupled to the first transducer, the second transducer the third transducer, and the fourth transducer, the signal processing circuit configured to measure the anchor motion,

wherein the signal processing circuit produces a first signal proportional to the difference of an output of the first and second transducers and a second signal proportional to the difference of the third and fourth transducers,

further wherein the signal processing circuit determines a difference between the first signal and the second signal proportional to the motion of the first and second proof masses.

15. The accelerometer of claim 14, wherein the first proof mass has a positive rotation about the first axis in response to anchor motion and the second proof mass has a negative rotation about the first axis in response to anchor motion.

16. The accelerometer of claim 14, wherein the first and second transducers are located on opposite sides of the first axis and the third and fourth transducers are located in opposite sides of the first axis.

17. The accelerometer of claim 14, wherein the first, second, third, and fourth transducers are positioned on top of the substrate.

18. The accelerometer of claim 14, wherein the first and second proof masses move in the same direction, further wherein the signal processing circuit is configured to measure acceleration and reject anchor motion.

19. The accelerometer of claim 14, wherein the first axis is the x-axis.

20. The accelerometer of claim 14, further including a support arm rigidly coupled to the anchor, the first proof mass is coupled to the support arm by the first flexible member, and the second proof mass is coupled to the support arm.