Accelerometer systems and methods

Patent metadata

Field	Value
Publication number	US-9229026-B2
Application number	US-201113085900-A
Country	US
Kind code	B2
Filing date	Apr 13, 2011
Priority date	Apr 13, 2011
Publication date	Jan 5, 2016
Grant date	Jan 5, 2016

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.

First claim

What is claimed is:

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 towar

Assignees

• Stewart Robert E
• Sakaida Daryl
• Bulatowicz Michael D
• Li Ming
• Douglass John Thomson
• Northrop Grumman Guaidance And Electronics Company Inc

Inventors

• Stewart Robert E
• Sakaida Daryl
• Bulatowicz Michael D
• Li Ming
• Douglass John Thomson

Classifications

• G01C19/5705

  using masses driven in reciprocating rotary motion about an axis · CPC title

• G01P15/131 Primary

  with electrostatic counterbalancing means · CPC title

• G01P15/125

  by capacitive pick-up · CPC title

• G01P2015/0834

  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 · CPC title