Non-resonant four degrees-of-freedom micromachined gyroscope

• US 20040149035A1
• Filed: 03/26/2004
• Published: 08/05/2004
• Est. Priority Date: 05/02/2001
• 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: Shkel, Andrei M, Acar, Cenk
• Granted Patent: US 6,845,669 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• CPC Class Codes: B81B 3/0062 Devices moving in two or more dimensions, i.e. having special features which allow movement in more than one dimension
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: Y10T 74/1275 Electrical

Abstract

A micromachined design and method with inherent disturbance-rejection capabilities is based on increasing the degrees-of-freedom (DOF) of the oscillatory system by the use of two independently oscillating proof masses. Utilizing dynamical amplification in the 4-degrees-of-freedom system, inherent disturbance rejection is achieved, providing reduced sensitivity to structural and thermal parameter fluctuations and damping changes over the operating time of the device. In the proposed system, the first mass is forced to oscillate in the drive direction, and the response of the second mass in the orthogonal direction is sensed. The response has two resonant peaks and a flat region between peaks. Operation is in the flat region, where the gain is insensitive to frequency fluctuations. An over 15 times increase in the bandwidth of the system is achieved due to the use of the proposed architecture. In addition, the gain in the operation region has low sensitivity to damping changes. Consequently, by utilizing the disturbance-rejection capability of the dynamical system, improved robustness is achieved, which can relax tight fabrication tolerances and packaging requirements and thus result in reducing production cost of micromachined methods.

Claims

1. A micromachined gyroscope comprising:

a substrate;

two independently oscillating interconnected proof masses, one of the two proof masses being defined as an active proof mass and the other one of the two proof masses being defined as a passive proof mass;

a plurality of flexures coupling the substrate to the active proof mass, and allowing the active proof mass to move in both a drive and a sense direction;

a plurality of flexures coupling the passive proof mass to the active proof mass, and allowing the passive proof mass to move in both the drive and sense direction;

an oscillator to drive the active proof mass in the drive direction; and

a sensor to detect the response of the passive proof mass in the sense direction orthogonal to the drive direction,

whereby two resonant peaks for the sense Coriolis force are generated with a flat region therebetween and whereby the gyroscope is operated in the flat regions so that it is insensitive to parameter fluctuations.

2. The gyroscope of claim 1 where the oscillator is an electrostatic comb-dive, electrostatic parallel plate actuator, magnetic drive or alternative actuator.

3. The gyroscope of claim 1 where the sensor is at least one capacitor with movable plates, or an alternative position sensing means.

4. The gyroscope of claim 1 where the at least one capacitor is an air gap capacitor.

5. The gyroscope of claim 1 where the active and passive proof masses are shaped and are coupled through the plurality of flexures to comprise a linear gyroscope.

6. The gyroscope of claim 1 where the active and passive proof masses are shaped and are coupled through the plurality of flexures to comprise a torsional gyroscope.

7. The gyroscope of claim 1 where the oscillator drives the active proof mass as a system with two degrees of freedom.

8. The gyroscope of claim 1 where the passive proof mass has a mass magnitude m₂ which is optimized for maximal oscillations of the passive proof mass in the sense direction.

9. The gyroscope of claim 1 where an optimal ratio μ

=m₂/m₁ for the masses of the active proof mass and passive proof mass is selected to achieve insensitivity in damping, a wide bandwidth, and maintenance of gain.

10. The gyroscope of claim 1 where the active proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₁₁ dependent on drive spring constant κ

_1x and mass m₁ of the active proof mass, where the passive proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₂₂ dependent on drive spring constant k₂x and mass m₂ of the passive proof mass, and where the ratio Y=ω

₁₁/ω

₂₂ is optimized for both high mechanical amplification and high oscillation amplitudes of the active mass.

11. The gyroscope of claim 9 where the active proof mass has in its corresponding isolated mass-spring system a resonant frequency wri dependent on drive spring constant k_1x and mass m₁ of the active proof mass, where the passive proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₂₂ dependent on drive spring constant k_2x and mass m₂ of the passive proof mass, and where the ratio Y=ω

₁₁/ω

₂₂ is optimized for both high mechanical amplification and high oscillation amplitudes of the active mass.

12. The gyroscope of claim 11 where the drive direction spring constant k_1x of the plurality of flexures for the active mass are determined according to the optimal resonant frequency ω

₁₁ and optimal mass ratio μ

.

13. The gyroscope of claim 1 further comprising a feedback sensor for sensing motion of the passive proof mass, a circuit coupled to the feedback sensor to generate an error signal relative to a reference signal, and a controller to control the oscillator to drive the active proof mass toward a zero error signal for closed loop control.

14. A method of operating a micromachined gyroscope comprised of the steps of:

providing two interconnected proof masses, one of the two proof masses being defined as an active proof mass and the other one of the two proof masses being defined as a passive proof mass, a plurality of flexures coupling a substrate to the active proof mass, and allowing the active proof mass to move in both a drive and a sense direction, a plurality of flexures coupling the passive proof mass to the active proof mass, and allowing the passive proof mass to move in both the drive and sense direction;

oscillating the active proof mass in the drive direction; and

independently oscillating the passive proof mass by means of its interconnection with the active proof mass; and

sensing the response of the passive proof mass in the sense direction orthogonal to the drive direction,

whereby two resonant peaks for the sense Coriolis force are generated with a flat region therebetween and whereby the gyroscope is operated in the flat regions so that it is insensitive to parameter fluctuations.

15. The method of claim 14 where oscillating the active proof mass in the drive direction comprises driving the active proof mass with an electrostatic comb or magnetic drive.

16. The method of claim 14 where sensing the response of the passive proof mass in the sense direction orthogonal to the drive direction comprises sensing the change in capacitance of at least one capacitor with movable plates.

17. The method of claim 16 where sensing the change in capacitance of at least one capacitor senses the change of capacitance in an air gap capacitor.

18. The method of claim 14 where providing the active and passive proof masses comprises shaping the active and passive proof masses and coupling them through their respective flexures to comprise a linear gyroscope.

19. The method of claim 14 where providing the active and passive proof masses comprises shaping the active and passive proof masses and coupling them through their respective flexures to comprise a torsional gyroscope.

20. The method of claim 14 where oscillating the active proof mass in the drive direction drives the active proof mass as a system with two degrees of freedom.

21. The method of claim 14 where the passive proof mass has a mass magnitude m₂ and further comprises optimizing the passive proof mass has a mass magnitude m₂ for maximal oscillations of the passive proof mass in the sense direction.

22. The method of claim 14 further comprising optimizing a ratio μ

=m₂/m₁ for the masses of the active proof mass and passive proof mass to achieve insensitivity in damping, a wide bandwidth, and maintenance of gain.

23. The method of claim 14 where the active proof mass has in its corresponding isolated mass-spring system a resonant frequency wi, dependent on drive spring constant k_1x and mass m₁ of the active proof mass, where the passive proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₂₂ dependent on drive spring constant k₂x and mass m₂ of the passive proof mass, and further comprising optimizing the ratio Y=ω

₁/ω

₂₂ for both high mechanical amplification and high oscillation amplitudes of the active mass.

24. The method of claim 22 where the active proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₁₁ dependent on drive spring constant k_1x and mass ml of the active proof mass, where the passive proof mass has in its corresponding isolated mass-spring system a resonant frequency ω

₂₂ dependent on drive spring constant k_2x and mass m₂ of the passive proof mass, and further comprising optimizing the ratio Y=ω

₁₁/ω

₂₂ for both high mechanical amplification and high oscillation amplitudes of the active mass.

25. The method of claim 24 further comprising determining the drive direction spring constant k_1x of the plurality of flexures for the active mass according to the optimal resonant frequency ω

₁₁ and optimal mass ratio μ

.

26. The method of claim 14 further comprising sensing motion of the passive proof mass, generating an error signal relative to a reference signal, and controlling the drive of the active proof mass toward a zero error signal for closed loop control.