Gyroscope that Compensates for Fluctuations in Sensitivity

• US 20170023364A1
• Filed: 03/20/2015
• Published: 01/26/2017
• Est. Priority Date: 03/20/2015
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Gregory, Jeffrey A.
• Granted Patent: US 9,869,552 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719
• CPC Class Codes: G01C 19/5642 using vibrating bars or beams
• CPC Class Codes: G01C 19/5649 Signal processing
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/13 by measuring the force required to restore a proofmass subjected to inertial forces to a null position
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A method compensates for a sensitivity of an inertial sensor having a resonator and an accelerometer. The method includes adding a test signal to a quadrature tuning voltage applied to the resonator of the inertial sensor. The method also includes receiving a quadrature error signal from the accelerometer of the inertial sensor. The method also includes detecting a phase difference between the quadrature error signal and the test signal. The method also includes determining a bandwidth of the accelerometer based on the detected phase difference, the bandwidth indicating the sensitivity of the accelerometer.

Claims

1. In an inertial sensor having a resonator and an accelerometer, a method of measuring sensitivity of the accelerometer, the method comprising:

adding a test signal to a quadrature tuning voltage applied to the resonator of the inertial sensor;

receiving a quadrature error signal from the accelerometer of the inertial sensor;

detecting a phase difference between the quadrature error signal and the test signal; and

determining a bandwidth of the accelerometer based on the detected phase difference, the bandwidth indicating the sensitivity of the accelerometer.

2. The method of claim 1, further comprising:

removing errors, caused by fluctuations in sensitivity of the accelerator, from an output rate signal of the accelerometer according to the determined bandwidth of the accelerometer.

3. The method of claim 1, wherein determining the bandwidth of the accelerometer comprises:

determining a time constant τ

of the accelerometer based on the detected phase difference.

4. The method of claim 3,

wherein the output rate signal is represented by xAgτ

Ω

, and

wherein the method further comprises removing errors, caused by fluctuations in sensitivity of the accelerator, from an output rate signal of the accelerometer according to the determined bandwidth of the accelerometer, by multiplying the output rate signal by the inverse of the determined time constant.

5. The method of claim 1, further comprising:

adjusting a frequency of the test signal until the phase difference is about equal to a predetermined value.

6. The method of claim 5, wherein adjusting the frequency of the test signal comprises:

adjusting the frequency of the test signal until the phase difference is about equal to 45 degrees.

7. The method of claim 5, wherein detecting the phase difference between the quadrature error signal and the test signal comprises:

demodulating the quadrature error signal with the test signal; and

determining a direct current (DC) component of the demodulated quadrature error signal.

8. The method of claim 7, wherein adjusting the frequency of the test signal until the phase difference is about equal to a predetermined value comprises:

adjusting the frequency of the test signal until the direct current (DC) component of the demodulated quadrature error signal is about zero (0).

9. The method of claim 1, wherein detecting the phase difference between the quadrature error signal and the test signal comprises:

demodulating the quadrature error signal with the test signal.

10. The method of claim 9, wherein determining the bandwidth of the accelerometer comprises:

determining an alternative current (AC) component of the demodulated quadrature error signal.

11. An inertial sensor that compensates for its own sensitivity, comprising:

a resonator;

an accelerometer;

a sensitivity circuit including

a phase difference detector that detects a phase difference between a quadrature error signal from the accelerometer and a test signal,

a test signal generator that (1) generates the test signal, (2) receives the phase difference from the phase difference detector, and (3) adjusts a frequency of the test signal based on the phase difference; and

a sensitivity gauge that generates a sensitivity signal, indicative of the bandwidth of the accelerometer, based on the phase difference;

a compensating circuit that adjusts an output rate signal from the accelerometer based on the sensitivity signal from the sensitivity gauge.

12. The inertial sensor of claim 11, wherein the phase difference detector demodulates the quadrature error signal with the test signal.

13. The inertial sensor of claim 11, wherein the test signal generator adjusts the frequency of the test signal until the quadrature error signal and the test signal are about 45 degrees out of phase.

14. The inertial sensor of claim 11, wherein the test signal generator adjusts the frequency of the test signal until the direct current (DC) component of the phase difference is about zero (0).

15. The inertial sensor of claim 11, wherein the sensitivity gauge generates the sensitivity signal based on the alternating current (AC) component of the phase difference.

16. The inertial sensor of claim 11, wherein the compensating circuit multiples the output rate signal by the sensitivity signal.