Accelerometer systems and methods

• US 9,229,026 B2
• Filed: 04/13/2011
• Issued: 01/05/2016
• Est. Priority Date: 04/13/2011
• Status: Active Grant

• Current Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Original Assignee: Northrop Grumman Guidance And Electronics Company, Inc.
• Inventors: Stewart, Robert E., Sakaida, Daryl, Bulatowicz, Michael D., Li, Ming, Douglass, John Thomson
• Primary Examiner(s): SCHECHTER, ANDREW M
• Assistant Examiner(s): Kuan, John
• Application Number:
  US13/085,900
• Publication Number:
  US 20120265481A1
• Time in Patent Office: 1,728 Days
• Field of Search: 702/141, 702/33, 702/47, 702/52, 702/53, 702/54, 702/91, 702/93, 702/104
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5705 using masses driven in reciprocating rotary motion about an axis
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0834 the mass constituting a pendulum having the pivot axis disposed symmetrically between the longitudinal ends, the center of mass being shifted away from the plane of the pendulum which includes the pivot axis

Abstract

An accelerometer system can include a sensor element comprising first and second proofmasses, the first proofmass accelerating in a first direction and the second proofmass accelerating in a second direction opposite the first direction in response to an external acceleration. A force rebalance controller applies control signals to at least one control element to provide a first force to accelerate the first proofmass toward a first null position and to at least one control element to provide a second force to accelerate the second proofmass toward a second null position. The force rebalance controller can also generate opposite polarity first and second output signals associated with respective displacements of the first and second proofmasses relative to the respective first and second null positions. An acceleration component calculates the external acceleration based on the first and second output signals.

Claims

1. An accelerometer system comprising:

a sensor element comprising a first proofmass and a second proofmass, the first proofmass being configured to rotate in a first direction and the second proofmass being configured to rotate in a second direction opposite the first direction about a common axis in response to an external acceleration;

a force rebalance controller configured to apply control signals to at least one control element associated with the first proofmass to provide a first force to accelerate the first proofmass toward a first null position associated with the first proofmass and to apply control signals to at least one control element associated with the second proofmass to provide a second force to accelerate the second proofmass toward a second null position associated with the second proofmass, the force rebalance controller being further configured to generate a first output signal associated with a displacement of the first proofmass relative to the first null position and a second output signal associated with a displacement of the second proofmass relative to the second null position based on applying the control signals to the at least one control element associated with the first and second proofmasses, the second output signal having a polarity opposite the first output signal; and

an acceleration component configured to calculate the external acceleration based on both the first and second output signals.

2. The system of claim 1, wherein the acceleration component is configured to subtract the first output signal from the second output signal to substantially cancel bias error in the calculated external acceleration.

3. The system of claim 2, wherein the acceleration component is configured to scale a difference between the first output signal and the second output signal to calculate the external acceleration having an uncorrelated noise that is reduced by approximately the square root of two.

4. The system of claim 1, wherein the first proofmass and the second proofmass are fabricated as substantially matched components, such that the first and second proofmasses are substantially identical with respect to temperature and process variation.

5. The system of claim 1, wherein the first proofmass is configured to rotate about a first fulcrum in the first and second directions and the second proofmass is configured to rotate about a second fulcrum in the first and second directions.

6. The system of claim 5, wherein the first proofmass comprises a center of mass that is offset from a centroid location of the first proofmass by a distance that is approximately equal and opposite an offset of a center of mass associated with the second proofmass relative a centroid location of the second proofmass.

7. The system of claim 6, wherein a portion of each of the first and second proofmasses is etched away during fabrication to shift the center of mass associated with each of the first and second proofmasses to equal and opposite distances offset from the common axis.

8. The system of claim 1, wherein the at least one control element associated with each of the respective first and second proofmasses comprises at least one electrode associated with each of the respective first and second proofmasses, and wherein the force rebalance controller comprises:

a pulse generator configured to generate the control signals as charge pulses;

a multiplexer configured to alternate application of the charge pulses between the at least one electrode associated with the first proofmass and the at least one electrode associated with the second proofmass in a predetermined sequence to generate the respective first and second forces as respective first and second electrostatic forces; and

a processor configured to generate the first output signal in response to a first measured voltage associated with the at least one electrode associated with the first proofmass and to generate the second output signal in response to a second measured voltage associated with the at least one electrode associated with the second proofmass, the first and second measured voltages resulting from the alternate application of the charge pulses to the at least one electrode associated with the respective first and second proofmasses.

9. The system of claim 8, wherein the pulse generator is configured to generate the charge pulses at a first duty-cycle with respect to the at least one electrode associated with the first proofmass based on the first output signal and at a second duty-cycle with respect to the at least one electrode associated with the second proofmass based on the second output signal.

10. The system of claim 8, wherein each of the at least one electrode associated with the first and second proofmasses comprises a first pair of electrodes that are electrically-coupled with respect to each other and a second pair of electrodes that are electrically-coupled with respect to each other, the multiplexer being configured to apply the charge pulses to the first pair of electrodes to accelerate the respective first and second proofmasses in a first direction and to apply the charge pulses to the second pair of electrodes to accelerate the respective first and second proofmasses in a second direction opposite the first direction.

11. A method for measuring an external acceleration in an accelerometer system, the method comprising:

applying control signals to at least one control element associated with a first proofmass to provide a first force to accelerate the first proofmass toward a first null position associated with the first proofmass, the first proofmass being configured to accelerate in a first direction in response to the external acceleration;

generating a first output signal of a first polarity associated with a displacement of the first proofmass relative to the first null position;

applying the control signals to at least one control element associated with a second proofmass to provide a second force to accelerate the second proofmass toward a second null position associated with the second proofmass, the second proofmass being configured to accelerate in a second direction opposite the first direction in response to the external acceleration, the first proofmass comprising a center of mass that is offset from a centroid location of the first proofmass by a distance that is approximately equal and opposite an offset of a center of mass associated with the second proofmass relative a centroid location of the second proofmass;

generating a second output signal of a second polarity associated with a displacement of the second proofmass relative to the second null position; and

generating a difference between the first output signal and the second output signal to calculate the external acceleration that is substantially free from bias error.

12. The method of claim 11, further comprising scaling the difference between the first output signal and the second output signal to calculate the external acceleration having an uncorrelated noise that is reduced by approximately the square root of two.

13. The method of claim 11, wherein the first proofmass and the second proofmass are fabricated as substantially matched components, such that the first and second proofmasses are substantially identical with respect to temperature and process variation.

14. The method of claim 11, wherein applying the control signals comprises:

applying charge pulses to at least one electrode associated with the first proofmass to provide a first electrostatic force to rotate the first proofmass about a first fulcrum in the first direction toward the first null position; and

applying the charge pulses to at least one electrode associated with the second proofmass to provide a second electrostatic force of the second polarity to rotate the second proofmass about a second fulcrum in the second direction toward the second null position, and wherein the first proofmass comprises a center of mass that is offset from a centroid location of the first proofmass by a distance that is approximately equal and opposite an offset of a center of mass associated with the second proofmass relative a centroid location of the second proofmass.

15. The method of claim 14, wherein applying the charge pulses comprises alternately applying the charge pulses to the at least one electrode associated with the first proofmass and to the at least one electrode associated with the second proofmass in a predetermined sequence.

16. The method of claim 15, wherein applying the charge pulses to the at least one electrode associated with the first proofmass comprises alternately applying the charge pulses to a first pair of electrically-coupled electrodes and to a second pair of electrically-coupled electrodes at a first duty-cycle that is based on the first output signal to accelerate the first proofmass toward the first null position, the first and second pairs of electrically-coupled electrodes generating opposite electrostatic forces, and wherein applying the charge pulses to the at least one electrode associated with the second proofmass comprises alternately applying the charge pulses to a third pair of electrically-coupled electrodes and to a fourth pair of electrically-coupled electrodes at a second duty-cycle that is based on the second output signal to accelerate the second proofmass toward the second null position, the third and fourth pairs of electrically-coupled electrodes generating opposite electrostatic forces.

17. An accelerometer system comprising:

a sensor element comprising a first proofmass and a second proofmass, the first proofmass being configured to accelerate in a first direction and the second proofmass being configured to accelerate in a second direction opposite the first direction in response to an external acceleration, the first proofmass and the second proofmass being fabricated as substantially matched components, such that the first and second proofmasses are substantially identical with respect to temperature and process variation;

a force rebalance controller configured to alternately apply charge pulses to at least one electrode associated with the first proofmass and at least one electrode associated with the second proofmass in a predetermined sequence, the charge pulses being applied to the at least one electrode associated with the first proofmass to provide a first electrostatic force to accelerate the first proofmass toward a first null position associated with the first proofmass and to apply the charge pulses to the at least one electrode associated with the second proofmass to provide a second electrostatic force to accelerate the second proofmass toward a second null position associated with the second proofmass, the force rebalance controller being further configured to generate a first output signal associated with a displacement of the first proofmass relative to the first null position and a second output signal associated with a displacement of the second proofmass relative to the second null position based on applying the charge pulses to the at least one electrode associated with the respective first and second proofmasses, the second output signal having a polarity opposite the first output signal; and

an acceleration component configured to subtract the first output signal from the second output signal to calculate the external acceleration that is substantially free from bias error.

18. The system of claim 17, wherein the first proofmass is configured to rotate about a first fulcrum in the first and second directions and the second proofmass is configured to rotate about a second fulcrum in the first and second directions, wherein the first proofmass comprises a center of mass that is offset from a centroid location of the first proofmass by a distance that is approximately equal and opposite an offset of a center of mass associated with the second proofmass relative a centroid location of the second proofmass.

19. The system of claim 17, wherein the force rebalance controller comprises:

a pulse generator configured to generate the charge pulses; and

a processor configured to generate the first output signal in response to a first measured voltage associated with the at least one electrode associated with the first proofmass and to generate the second output signal in response to a second measured voltage associated with the at least one electrode associated with the second proofmass, the first and second measured voltages resulting from the alternate application of the charge pulses to the at least one electrode associated with the respective first and second proofmasses.

20. The system of claim 19, wherein each of the at least one electrode associated with the first and second proofmasses comprise a first pair of electrodes that are electrically-coupled with respect to each other and a second pair of electrodes that are electrically-coupled with respect to each other, wherein the force rebalance controller further comprises a multiplexer being configured to apply the charge pulses to the first pair of electrodes to accelerate the respective first and second proofmasses in the first direction and to apply the charge pulses to the second pair of electrodes to accelerate the respective first and second proofmasses in the second direction.