HIGH RANGE DIGITAL ANGULAR RATE SENSOR BASED ON FREQUENCY MODULATION

• US 20130098153A1
• Filed: 10/21/2011
• Published: 04/25/2013
• Est. Priority Date: 10/21/2011
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Trusov, Alexander, Shkel, Andrei, Zotov, Sergei
• Granted Patent: US 8,991,247 B2
• Time in Patent Office: Days
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A digital angular rate sensor system based on frequency modulation (FM) of the rotation rate. The new approach relies on tracking of the resonant frequencies of two high-Q mechanical modes of vibration in a MEMS vibratory gyroscope to produce an inherently digital measurement of the input angular rate. The disclosed system is enabled by a combination of a MEMS vibratory high-Q gyroscope and a new signal processing scheme which takes advantage of a previously ignored gyroscope dynamics effect. The FM nature of the system eliminates noise versus bandwidth and resolution versus dynamic range tradeoffs of conventional vibratory rate gyroscopes. The FM approach allows achieving superior signal-to-noise-ratio through the use of ultra-high Q (1 million) mechanical structure without limiting the measurement bandwidth. Stability of 1e-9 can be achieved in the FM system, providing a 1000 times improvement over the state-of-the-art conventional AM gyroscopes with capacitive pick-off.

Claims

1. A micromachined angular rate sensor system based on frequency modulation (FM) comprising:

a vibratory gyroscope with at least two mechanical modes of vibration;

a control subsystem coupled to the gyroscope; and

a signal processing subsystem coupled to the gyroscope capable of tracking the resonant frequencies of the at least two mechanical modes of vibration,

wherein the gyroscope has an inherently digital output.

2. The system of claim 1 where the control subsystem comprises means for periodic excitation of at least one of the mechanical modes of vibration.

3. The system of claim 1 where the control subsystem comprises means for continuous excitation of at least one of the mechanical modes of vibration.

4. The system of claim 1 where the signal processing subsystem comprises means for monitoring at least one of the resonant frequencies of the at least two mechanical modes of vibration.

5. The system of claim 1 where the signal processing subsystem comprises means for monitoring the difference between the resonant frequencies of the at least two mechanical modes of vibration.

6. The system of claim 1 where the vibratory gyroscope comprises:

a lumped quadruple mass structure; and

a dual mass tuning fork.

7. The system of claim 1 where the control subsystem comprises:

a positive feedback self-resonant system; and

at least one phase locked loop.

8. A method for operating a micromachined angular rate sensor system based on frequency modulation (FM) comprising:

exciting at least two mechanical modes of vibration of a vibratory gyroscope;

monitoring at least two resonant frequencies of the at least two mechanical modes of vibration; and

producing a measurement of the inertial rotation of the gyroscope with an inherent FM output proportional to the input angular velocity.

9. The method of claim 8 further comprising monitoring the difference between the at least two resonant frequencies of the at least two mechanical modes of vibration of the vibratory gyroscope.

10. The method of claim 8 where monitoring at least two resonant frequencies of the at least two mechanical modes of vibration comprises monitoring each of the resonant frequencies with a corresponding frequency counting phase locked loop.

11. The method of claim 8 where monitoring at least two resonant frequencies of the at least two mechanical modes of vibration comprises sequentially mixing the at least two resonant frequencies and then frequency counting the mixed signal with a phase locked loop.

12. The method of claim 8 where exciting at least two mechanical modes of vibration of a vibratory gyroscope comprises continually exciting the at least two mechanical modes of vibration.

13. The method of claim 8 where exciting at least two mechanical modes of vibration of a vibratory gyroscope comprises periodically exciting the at least two mechanical modes of vibration.

14. The method of claim 8 further comprising providing insensitivity to variations in operational temperature, pressure, device Q, and frequency.

15. The method of claim 8 further comprising automatically self-sensing and self-calibrating the vibratory gyroscope against fluctuations in temperature, drift, aging in Q, or natural frequency.

16. The method of claim 8 where exciting at least two mechanical modes of vibration of a vibratory gyroscope comprises exciting the at least two mechanical modes of vibration with piezoelectric, piezoresistive, or electromagnetic means.

17. The method claim 8 where monitoring at least two resonant frequencies of the at least two mechanical modes of vibration comprises operating each of the mechanical modes of vibration in a closed loop and monitoring each of the resonant frequencies with a corresponding frequency counter.

18. A micromachined vibratory gyroscope used within an angular rate sensor system based on frequency modulation (FM) comprising:

a dynamically balanced lumped quadruple mass;

a dual mass tuning fork; and

at least two mechanical modes of vibration coupled by the Coriolis effect.

19. The gyroscope of claim 18 where the at least two mechanical modes of vibration comprise mode-matched natural frequencies.

20. The gyroscope of claim 18 where the at least two mechanical modes of vibration comprise an initial mismatch between the natural frequencies of each of the mechanical modes of vibration.