Accelerometers

Patent metadata

Field	Value
Publication number	US-10775404-B2
Application number	US-201515321838-A
Country	US
Kind code	B2
Filing date	Jun 26, 2015
Priority date	Jun 27, 2014
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

A method for closed loop operation of a capacitive accelerometer uses a single current source ( 62 ) and a single current sink ( 64 ) to apply an in-phase drive signal V 1 ′ to a first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal V 2 ′ to a second set of fixed capacitive electrode fingers. This provides a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintains the proof mass at a null position.

First claim

The invention claimed is:

1. A method for closed loop operation of a capacitive accelerometer, the capacitive accelerometer comprising:
a substantially planar proof mass mounted to a fixed substrate by flexible support legs so as to be linearly moveable in an in-plane sensing direction in response to an applied acceleration;
first and second sets of moveable capacitive electrode fingers extending from the proof mass, substantially perpendicular to the sensing direction and spaced apart in the sensing direction; and
first and second sets of fixed capacitive electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction;
wherein the first set of fixed capacitive electrode fingers is arranged to interdigitate with the first set of moveable capacitive electrode fingers and the second set of fixed capacitive electrode fingers is arranged to interdigitate with the second set of moveable capacitive electrode fingers;
the method comprising:
using a single current source and a single current sink to apply an in-phase drive signal to the first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal to the second set of fixed capacitive electrode fingers so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position;
using a control signal to adjust at least one of the in-phase drive signal applied to the first set of fixed capacitive fingers and the anti-phase drive signal applied to the second set of fixed capacitive fingers by the single current source and the single current sink, such that a first slew rate of the drive signal applied to the first set of capacitive fingers is substantially equal to a second slew rate of the drive signal applied to the second set of capacitive fingers; and
determining an average amplitude of the in-phase and the anti-phase drive signals and comparing the average amplitude to a reference value to generate said control signal.

2. The method of claim 1 , further comprising:
applying said control signal to a variable current source and sink connected in parallel with the single current source and the single current sink so as to adjust the drive signal applied to at least one of the first and second sets of fixed capacitive fingers, wherein the single current source and the single current sink are fixed.

3. The method of claim 2 , wherein the variable current source and the single current sink provide a smaller current than the single fixed current source and sink.

4. The method of claim 1 , further comprising: measuring a pickoff signal from the proof mass and comparing the amplitude of the pickoff signal to a reference value that is substantially zero.

5. The method of claim 1 , comprising:
applying the in-phase and anti-phase drive signals as pulse width modulation (PWM) voltage waveforms.

6. A method for closed loop operation of a capacitive accelerometer, the capacitive accelerometer comprising:
a substantially planar proof mass mounted to a fixed substrate by flexible support legs so as to be linearly moveable in an in-plane sensing direction in response to an applied acceleration;
first and second sets of moveable capacitive electrode fingers extending from the proof mass, substantially perpendicular to the sensing direction and spaced apart in the sensing direction; and
first and second sets of fixed capacitive electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction;
wherein the first set of fixed capacitive electrode fingers is arranged to interdigitate with the first set of moveable capacitive electrode fingers and the second set of fixed capacitive electrode fingers is arranged to interdigitate with the second set of moveable capacitive electrode fingers;
the method comprising:
using a single current source and a single current sink to apply an in-phase drive signal to the first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal to the second set of fixed capacitive electrode fingers so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position;
using a control signal to adjust the in-phase drive signal and the anti-phase drive signal applied to the first and second sets of fixed capacitive fingers respectively by the single current source and the single current sink, such that a first slew rate of the drive signal applied to the first set of capacitive fingers is substantially equal to a second slew rate of the drive signal applied to the second set of capacitive fingers; and
determining an average amplitude of the in-phase and the anti-phase drive signals and comparing the average amplitude to a reference value to generate said control signal.

7. The method of claim 6 , further comprising:
applying said control signal to a variable current source and sink connected in parallel with the single current source and the single current sink so as to adjust the drive signal applied to at least one of the first and second sets of fixed capacitive fingers, wherein the single current source and the single current sink are fixed.

8. The method of claim 7 , wherein the variable current source and the single current sink provide a smaller current than the single fixed current source and sink.

9. The method of claim 6 , further comprising: measuring a pickoff signal from the proof mass and comparing the amplitude of the pickoff signal to a reference value that is substantially zero.

10. The method of claim 6 , comprising:
applying the in-phase and anti-phase drive signals as pulse width modulation (PWM) voltage waveforms.

11. A method for closed loop operation of a capacitive accelerometer, the capacitive accelerometer comprising:
a substantially planar proof mass mounted to a fixed substrate by flexible support legs so as to be linearly moveable in an in-plane sensing direction in response to an applied acceleration;
first and second sets of moveable capacitive electrode fingers extending from the proof mass, substantially perpendicular to the sensing direction and spaced apart in the sensing direction; and
first and second sets of fixed capacitive electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction;
wherein the first set of fixed capacitive electrode fingers is arranged to interdigitate with the first set of moveable capacitive electrode fingers and the second set of fixed capacitive electrode fingers is arranged to interdigitate with the second set of moveable capacitive electrode fingers;
the method comprising:
using a single current source and a single current sink to apply an in-phase drive signal to the first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal to the second set of fixed capacitive electrode fingers so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position;
using a control signal to adjust at least one of the in-phase drive signal applied to the first set of fixed capacitive fingers and the anti-phase drive signal applied to the second set of fixed capacitive fingers by the single current source and the single current sink, such that a first slew rate of the drive signal applied to the first set of capacitive fingers is substantially equal to a second slew rate of the drive signal ap

Assignees

• Atlantic Inertial Systems Ltd

Inventors

• Townsend Kevin
• Durston Michael
• Sitch Douglas

Classifications

• G01P15/131 Primary

  with electrostatic counterbalancing means · CPC title

• G01P2015/0814

  for translational movement of the mass, e.g. shuttle type · CPC title

• G01P15/125 Primary

  by capacitive pick-up · CPC title

• G01P15/13

  by measuring the force required to restore a proofmass subjected to inertial forces to a null position · CPC title