Self-calibrating accelerometer

• US 20080236242A1
• Filed: 03/28/2007
• Published: 10/02/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Northrop Grumman Guidance & Electronics Co., Inc. (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Stewart, Robert E.
• Granted Patent: US 7,640,786 B2
• Time in Patent Office: Days
• US Class Current: 73/1.38
• CPC Class Codes: G01P 15/08 with conversion into electric or magnetic values
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

The method and apparatus in one embodiment may have: a sensing element for an accelerometer having a bias, the sensing element having a rectangular plate supported by flexures which allow rotation about a transverse center line thereof; a center of mass (CG) of the sensing element having two stable positions, one on each side of an axis of rotation defined by a centerline of suspension; a secondary mass within a proofmass translates in-plane to move the center of mass to thereby effect a self-calibration mechanization that continuously measures and nulls the accelerometer'"'"'s bias under dynamic operating conditions.

Claims

1. An apparatus, comprising:

a sensing element for an accelerometer having a bias, the sensing element having a plate supported by flexures which allow rotation about a transverse center line thereof;

a center of mass (CG) of the sensing element having two stable positions, one on each side of an axis of rotation defined by a centerline of suspension;

a secondary mass within a proofmass translates in-plane to move the center of mass to thereby effect a self-calibration mechanization that continuously measures and nulls the accelerometer'"'"'s bias under dynamic operating conditions.

2. The apparatus according to claim 1, wherein the secondary mass within the proofmass translates in-plane to move the center of mass right and left.

3. The apparatus according to claim 1, wherein the center of mass is relocated from one side of the centerline of suspension to the other side to thereby reverse a polarity of an input axis to enable self-calibration of accelerometer bias.

4. The apparatus according to claim 1, wherein under acceleration the sensing element is rotatable clockwise about a centerline of support (CS) with the center of mass in a first center of mass (CG1) position and counter clockwise with the center of mass in a second center of mass (CG2) position.

5. The apparatus according to claim 4, wherein to change polarity of the accelerometer, the centers of mass (CG1 and CG2) are vertically moveable between two bistable positions above and below a centerline of suspension (CS) of the sensing element.

6. The apparatus according to claim 5, wherein the secondary mass is translated up and down out-of-plane.

7. A method, comprising:

continuously self-calibrating accelerometer bias under both static and dynamic conditions to thereby remove accelerometer bias as an error source;

successively and simultaneously measuring acceleration by two accelerometers with sequentially alternating polarities; and

processing the measured acceleration from the outputs of the accelerometers in a digital signal processor using a real time bias estimator algorithm to thereby effect the bias self-calibration.

8. The method according to claim 7, wherein the alternating polarity reversal is accomplished by alternating a location of a center of mass of a sensing element to opposite sides of a centerline of support of the sensing element.

9. The method according to claim 7, wherein the method further comprises translating a secondary mass within a proofmass in-plane to move a center of mass right and left.

10. The method according to claim 9, wherein the method further comprises relocating the center of mass from one side of the centerline of suspension to the other side to thereby reverse a polarity of an input axis to enable self-calibration of accelerometer bias.

11. The method according to claim 9, wherein the method further comprises, under acceleration, rotating the sensing element clockwise about a centerline of support (CS) with the center of mass in a first center of mass (CG1) position and counter clockwise with the center of mass in a second center of mass (CG2) position.

12. The method according to claim 11, wherein to change polarity of the accelerometer, the centers of mass (CG1 and CG2) are vertically moveable between two bistable positions above and below a centerline of suspension (CS) of the sensing element.

13. The method according to claim 12, wherein the secondary mass is translated up and down out-of-plane.

14. An apparatus, comprising:

a sensing element in which a secondary mass is suspended within a proofmass of the sensing element for an accelerometer; and

a pair of buckled beam flexures that suspend the secondary mass within the proofmass, the suspension allowing the secondary mass to be in one of two bi-stable positions;

thereby effecting a self-calibration mechanization that continuously measures and nulls the accelerometer'"'"'s bias under dynamic operating conditions.

15. The apparatus according to claim 14, wherein the apparatus further comprises thermal actuators that reduce compressive force in the buckled beams allowing the secondary mass to move from one position of the two bi-stable positions to the other position of the bi-stable positions.

16. The apparatus according to claim 14, wherein a secondary mass is translatable within the proofmass in-plane to move a center of mass right and left.

17. The apparatus according to claim 14, wherein the apparatus further comprises relocating a center of mass from one side of the centerline of suspension of the secondary mass to the other side to thereby reverse a polarity of an input axis to enable self-calibration of accelerometer bias.

18. The apparatus according to claim 14, wherein the apparatus further comprises, under acceleration, rotating the sensing element clockwise about a centerline of support (CS) with the center of mass in a first center of mass (CG1) position and counter clockwise with the center of mass in a second center of mass (CG2) position.

19. The apparatus according to claim 18, wherein to change polarity of the accelerometer, the centers of mass (CG1 and CG2) are vertically moveable between two bistable positions above and below a centerline of suspension (CS) of the sensing element.

20. The apparatus according to claim 19, wherein the secondary mass is translated up and down out-of-plane.