D'arsonval movement mems accelerometer

• US 8,122,767 B2
• Filed: 10/08/2008
• Issued: 02/28/2012
• Est. Priority Date: 10/08/2008
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Dwyer, Paul W., Becka, Steve, Reddy, Matt
• Primary Examiner(s): Kwok, Helen C.
• Application Number:
  US12/247,937
• Publication Number:
  US 20100083761A1
• Time in Patent Office: 1,238 Days
• Field of Search: 735/143.1, 735/141.7, 735/141.8, 735/142.1, 735/142.2, 735/142.3, 735/143.2, 735/143.6, 735/143.7
• US Class Current: 73/514.31
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/132 with electromagnetic counterbalancing means
• 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

Abstract

Microelectromechanical (MEMS) accelerometer and acceleration sensing methods. A MEMS accelerometer includes a housing, a proof mass suspended within the housing by at least one torsional flexure, and a torsional magnetic rebalancing component. In an example embodiment, the torsional magnetic rebalancing component includes at least one planar coil on the proof mass that extends on both sides of an axis of rotation of the proof mass about the at least one torsional flexure and at least one magnet oriented such that a north-south axis of the at least one magnet is oriented approximately orthogonal to the rotational axis of the proof mass. A method includes sensing a change in capacitance of a pickoff in the MEMS accelerometer and rebalancing the MEMS accelerometer by sending a current through the planar coil.

Claims

1. A microelectromechanical (MEMS) accelerometer comprising:

a housing;

a proof mass suspended within the housing by at least one torsional flexure; and

a torsional magnetic rebalancing component, the torsional magnetic rebalancing component comprises;

at least one coil on the proof mass; and

at least one magnet,

wherein the at least one coil is a planar coil,

wherein the proof mass is configured to rotate about the at least one torsional flexure.

2. The MEMS accelerometer of claim 1, wherein the at least one coil comprises:

a first coil on a first surface of the proof mass; and

a second coil on a second surface of the proof mass,

wherein the first and second surfaces are not the same.

3. The MEMS accelerometer of claim 2, wherein the first coil is planar and the second coil is planar.

4. The MEMS accelerometer of claim 2, wherein the at least one magnet comprises:

a first magnet positioned near the first surface of the proof mass; and

a second magnet positioned near the second surface of the proof mass.

5. The MEMS accelerometer of claim 4, wherein the first and second magnets are located outside the housing.

6. The MEMS accelerometer of claim 5, wherein a north-south axis of the first magnet and a north-south axis of the second magnet are oriented approximately orthogonal to a rotational axis of the proof mass about the at least one torsional flexure.

7. The MEMS accelerometer of claim 1, further comprising:

a first capacitive pickoff located at a first end of the proof mass on a first side of the proof mass; and

a second capacitive pickoff located at a second end of the proof mass on a second side of the proof mass,

wherein the at least one torsional flexure is between the first capacitive pickoff and the second capacitive pickoff.

8. The MEMS accelerometer of claim 7, wherein the first pickoff and the second pickoff are electrically connected.

9. The MEMS accelerometer of claim 7, further comprising:

a third capacitive pickoff located on the first side of the proof mass on the same side of the at least one torsional flexure as the first pickoff; and

a fourth capacitive pickoff located on the second side of the proof mass on the same side of the at least one torsional flexure as the second pickoff.

10. The MEMS accelerometer of claim 9, wherein the first pickoff and the second pickoff are electrically connected, and wherein the third pickoff and the fourth pickoff are electrically connected.

11. The MEMS accelerometer of claim 1, wherein the at least one magnet is a Samarium Cobalt (SmCo) magnet.

12. The MEMS accelerometer of claim 1, further comprising:

at least one pickoff having a first side located on the proof mass and a second side located on an interior portion of the housing;

a sense electronics component in signal communication with the at least one pickoff, the sense electronics component configured to generate at least one sense signal based on at least one capacitance value of the at least one pickoff;

a drive electronics component in signal communication with the at least one coil; and

a controller in signal communication with the sense electronics component and the drive electronics component,

wherein the controller is configured to direct the drive electronics component to send a current through the at least one coil based on the at least one sense signal and wherein the controller is further configured to provide an output signal indicative of an acceleration experienced by the accelerometer, the output based on at least one of the current and the at least one sense signal.

13. A method of sensing acceleration with a MEMS accelerometer that includes a proof mass having an axis of rotation about at least one flexure and at least one magnet positioned such that a magnetic flux field flows approximately orthogonally to the axis of rotation, the method comprising:

sensing a change in capacitance of a pickoff in the MEMS accelerometer; and

rebalancing the MEMS accelerometer by sending a current through a planar coil positioned on the proof mass such that the coil extends on both sides of the axis of rotation of the proof mass through the magnetic flux field.

14. The method of claim 13, wherein rebalancing includes sending a current through a first planar coil on a first side of the proof mass and through a second planar coil on a second side of the proof mass.

15. The method of claim 13, wherein sensing a change in capacitance of a pickoff in the MEMS accelerometer includes sensing a change in capacitance of a first pickoff.

16. A microelectromechanical (MEMS) accelerometer comprising:

a housing;

a proof mass suspended within the housing by at least one torsional flexure; and

a torsional magnetic rebalancing component comprising;

a first planar coil on a first side of the proof mass;

a second planar coil on a second side of the proof mass;

a first magnet disposed near a first side of the proof mass; and

a second magnet disposed near a second side of the proof mass,

wherein a north-south axis of the first magnet and a north-south axis of the second magnet are oriented approximately orthogonal to a rotational axis of the proof mass about the at least one torsional flexure.