Nonresonant micromachined gyroscopes with structural mode-decoupling

• US 7,377,167 B2
• Filed: 02/27/2004
• Issued: 05/27/2008
• Est. Priority Date: 02/27/2004
• 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: Acar, Cenk, Shkel, Andrei M.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US10/789,037
• Publication Number:
  US 20050199061A1
• Time in Patent Office: 1,551 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.2, 735/041.4, 735/041.6
• US Class Current: 73/504.14
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A four-degrees-of-freedom (DOF) nonresonant micromachined gyroscope utilizes a dynamical amplification both in the drive-direction oscillator and the sense-direction oscillator, which are structurally decoupled, to achieve large oscillation amplitudes without resonance. The overall dynamical system is comprised of three proof masses. The second and third masses form the sense-direction oscillator. The first mass and the combination of the second and third masses form the drive-direction oscillator. The frequency responses of the drive and sense-mode oscillators have two resonant peaks and a flat region between the peaks. The device is nominally operated in the flat regions of the response curves belonging to the drive and sense-mode oscillators, where the gain is less sensitive to frequency fluctuations. This is achieved by designing the drive and sense anti-resonance frequencies to match.

Claims

1. A micromachined gyroscope adapted to operate in a nonresonant mode, comprising:

a drive-mode oscillator; and

a sense-mode oscillator,

wherein the drive-mode oscillator comprises three interconnected oscillating masses capable of moving in a drive direction, and the sense-mode oscillator comprises two masses out of the three interconnected oscillating masses capable of moving in an orthogonal sense direction, and

where the oscillation in the drive direction of one of the masses of the drive-mode oscillator is mechanically constrained to the drive direction and where the relative oscillation of the masses of the sense-mode oscillator is mechanically constrained to the sense direction, so that the one mass of the drive-mode oscillator is dynamically decoupled from one mass of the sense-mode oscillator.

2. The micromachined gyroscope of claim 1, wherein the drive-mode oscillator and sense-mode oscillator are each characterized by a frequency response curve having a flat nonresonant region, where the drive mode oscillator is capable of being operated within the flat nonresonant region of the drive frequency response curve, and where the sense mode oscillator is capable of being operated within the flat nonresonant region of the sense frequency response curve with a maximized operational oscillation amplitudes at the frequency of operation.

3. The micromachined gyroscope of claim 1,

wherein at least one of the three masses is included in an intermediate mass and another one of the three masses is a sensing element, wherein the intermediate mass is larger than the sensing element, and

wherein flexures in the drive-mode oscillator and sense-mode oscillator are physically configured so that only Coriolis excitations without additional drive excitations are capable of being coupled into the sense-mode oscillator, so that a Coriolis force generated by means of the larger intermediate mass results in a corresponding larger Coriolis force being transferred to the sensing element for increased sensitivity.

4. The micromachined gyroscope of claim 1,

wherein the drive-mode oscillator and sense-mode oscillator include a drive means for driving a mass in a drive direction and a sense means for sensing motion of a mass in a sense direction, and

wherein the three interconnected masses comprise a first mass, a second mass and a third mass, the first mass being the only mass directly excited by the drive means, the first mass oscillating in the drive direction and the first mass being constrained from movement in the sense direction, the second and third masses being constrained from movement with respect to each other in the drive direction and oscillating together in the drive direction but oscillating independently from each other in the sense direction, the third mass being fixed with respect to the second mass in the drive direction, but free to oscillate in the sense direction with respect to the second mass, the drive-mode oscillator comprising the three interconnected masses, the second and third masses comprising the sense-mode oscillator.

5. The micromachined gyroscope of claim 4,

wherein the second mass oscillates in the drive and sense directions to generate a rotation-induced force that excites the sense-mode oscillator, and

wherein a sense direction response of the third mass, which acts as a vibration absorber of the sense-mode oscillator, is detected for measuring an input angular rate.

6. The micromachined gyroscope of claim 1, further comprising a substrate on which the drive-mode oscillator and sense-mode oscillator are disposed,

wherein the three interconnected masses comprise a first mass, a second mass and a third mass, wherein the first mass is anchored to the substrate by a first flexure that allows movement substantially only in the drive direction, wherein the second mass is coupled to the first mass by a second flexure that allows movement in the drive and the sense directions, and wherein the third mass is coupled to the second mass by a third flexure that allows movement relative to the second mass substantially only in the sense direction, and

wherein the drive-mode oscillator and the sense-mode oscillator comprise a drive means for driving the first mass, the second mass and the third mass in a drive direction, a sense means for sensing motion of the third mass in a sense direction.

7. The micromachined gyroscope of claim 6, wherein the first and third flexures are folded micromachined springs having a resiliency substantially in only a first direction and wherein the second flexure is comprised of two coupled folded micromachined springs, one of the two coupled folded micromachined springs having a resiliency substantially in only one of the first and a second direction orthogonal to the first direction and the other one of the two coupled folded micromachined springs having a resiliency substantially in only the other one of the first and second directions.

8. The micromachined gyroscope of claim 1, wherein the drive-mode oscillator and the sense-mode oscillator are structurally arranged and configured such that the drive-mode oscillator and sense-mode oscillator together collectively comprise a gyroscope each having a frequency response curve with two resonant peaks and a flat region between the two peaks, the flat regions of the drive-mode and sense-mode oscillator overlapping each other, the gyroscope capable of being operated at a frequency in the overlapping flat regions of the frequency response curves.

9. The micromachined gyroscope of claim 8,

wherein the drive-mode oscillator has a drive direction anti-resonance frequency, wherein the sense-mode oscillator has a sense direction anti-resonance frequency, and

wherein the drive-mode oscillator and the sense mode oscillator are arranged and configured to have matching anti-resonance frequencies.

10. The micromachined gyroscope of claim 1,

wherein the three interconnected masses comprise a first mass, a second mass, a third mass, and coupled flexures,

wherein the first mass oscillates, the second and the third masses combining to comprise a vibration absorber of the drive-mode oscillator, which vibration absorber mechanically absorbs the oscillations of the first mass to result in larger oscillations of the second and third masses than the first mass, and

wherein the drive-mode oscillator and the sense-mode oscillator further comprise a drive means for driving the first mass, the second mass and the third mass in a drive direction, and a sense means for sensing motion of the third mass in a sense direction.

11. The micromachined gyroscope of claim 10, wherein the first mass is driven at a driving frequency, ω

_drive, by means of an input force F_d, which driving frequency, ω

_drive, is matched with a resonant frequency of an isolated mass-spring system comprised of the second and third masses and coupled flexures, which mass-spring system is in resonance with the first mass, so that maximum dynamic motion of at least one of the three interconnected masses is achieved.

12. The micromachined gyroscope of claim 1,

wherein the third mass absorbs vibrations such that the sense-mode oscillator achieves increased sense direction oscillation amplitudes, and

wherein the drive-mode oscillator and the sense-mode oscillator further comprise a drive means for driving the first mass, the second mass and the third mass in a drive direction, and a sense means for sensing motion of the third mass in a sense direction;

and

wherein the third mass absorbs sense direction oscillations and is capable of achieving greater sense direction oscillation amplitudes due to application of a larger Coriolis force coupled to the third mass from the second mass than would have been applied to the third mass without coupling to the second mass in the sense direction.

13. The micromachined gyroscope of claim 12,

wherein the third mass comprises an isolated mass-spring system, and wherein a Coriolis force is induced on the second mass, and

wherein the frequency of the Coriolis force is matched with a resonant frequency of the isolated mass-spring system of the third mass and its coupled flexures, so that the third mass achieves maximum motion.

14. The micromachined gyroscope of claim 1:

wherein the drive-mode oscillator comprises a drive means for driving the three interconnected masses in a drive direction, and the sense-mode oscillator comprises a sense means for sensing motion of one of the three interconnected masses in a sense direction,

wherein the three interconnected masses comprise a first mass, a second mass, a third mass, and flexures coupled to each of the first, second and third masses, wherein the drive-mode oscillator and the sense-mode oscillator each have a frequency response defined by a response curve,

wherein each of the frequency responses of both the drive-mode oscillator and sense-mode oscillator has two resonant peaks and a flat region of the response curve between the peaks,

wherein both of the drive-mode oscillator and the sense-mode oscillator are operated in the flat region of their respective response curves between the peaks of the respective response curve,

wherein the second mass has a drive anti-resonance frequency, ω

_2x, and the third mass has a sense anti-resonance frequency, ω

_3y, and

wherein ω

_2x, and ω

_3y are matched, namely where ω

_3y=ω

_2x, or equivalently (k_3y/m₃)^1/2=(k_2x/(m₂+m₃))^1/2 determines maximized operational system parameters, together with the maximized operational ratios μ

_x=(m₂+m₃)/m₁, y_x=ω

_2x/ω

_1x, μ

_y=m₃/m₂, and Y_y=ω

_3y/ω

_2y, where k_3y is a spring constant of the flexures coupled to the third mass, where m₃ is a magnitude of the third mass, k_2x is a spring constant of the flexures coupled to the second mass, m₂ is a magnitude of the second mass, ω

_1x is the drive anti-resonance frequency of the first mass, and ω

_2y is the sense anti-resonance frequency of the second mass.

15. A method of nonresonantly operating a micromachined gyroscope formed in a substrate comprising:

oscillating in a drive direction a drive-mode oscillator with an applied force;

oscillating in a sense direction a sense-mode oscillator with a Coriolis force derived from the drive-mode oscillator; and

wherein oscillating the drive-mode oscillator comprises oscillating relative to the substrate three interconnected masses in the drive direction, and

wherein oscillating the sense-mode oscillator comprises oscillating relative to the substrate two masses out of the three interconnected masses in the sense direction as sense masses,

where oscillating the three interconnected masses of the drive-mode oscillator further comprises mechanically constraining oscillation relative to the substrate of one of the three interconnected masses to the drive direction and

where oscillating the two masses out of the three interconnected masses comprises mechanically constraining relative motion of the two masses with respect to each other to the sense direction, so that oscillation in the drive direction with respect to the substrate of the one constrained mass of the drive-mode oscillator is dynamically decoupled from relative oscillation in the sense direction of the two masses.

16. The method of claim 15, wherein driving the drive-mode oscillator and driving the sense-mode oscillator are capable of dynamically increasing a motion of at least one of the three interconnected masses to achieve increased oscillation amplitudes without resonance to result in an increased operational frequency range and reduced sensitivity to structural and thermal parameter fluctuations and damping changes.

17. The method of claim 15 wherein oscillating in a sense direction a sense-mode oscillator with a Coriolis force derived from the drive-mode oscillator comprises

exciting a sense mass in the sense-mode oscillator by a force arising from one of the three interconnected masses employed in both the drive-mode and sense mode oscillators,

wherein the mass employed in both the drive-mode and sense-mode oscillators is a substantially larger mass than the other of the two interconnected masses used as a sense mass, resulting in increased sensitivity of the gyroscope.

18. The method of claim 15, wherein driving the drive-mode oscillator comprises driving a first, second and third masses in a drive direction with a drive means, and driving the sense-mode oscillator comprises driving second and third a mass in a sense direction by exciting the first mass only by the drive means, by causing the first mass to oscillate in the drive direction with a driving force and by constraining movement of the first mass from the sense direction, by constraining movement of the second and third masses with respect to each other from the drive direction, causing the second and third masses to oscillate together in the drive direction but causing the second and third masses to oscillate independently from each other in the sense direction, by fixing the third mass with respect to the second mass in the drive direction, and by causing the third mass to oscillate in the sense direction by means of a Coriolis force only.

19. The method of claim 18, wherein causing the second mass to oscillate in the drive and sense directions excites the sense-mode oscillator through the Coriolis force, and further comprising detecting a sense direction response of the third mass, which acts as a vibration absorber of the sense-mode oscillator for measuring an input angular rate.

20. The method of claim 15, wherein the three interconnected masses comprise a first mass, a second mass and a third mass, and wherein the drive-mode oscillator comprises a drive means for driving a mass in a drive direction and the sense-mode oscillator comprises a sense means for sensing motion of the third mass in a sense direction, and a substrate on which the drive-mode oscillator and the sense-mode oscillator are disposed, the method further comprising anchoring the first mass to the substrate by a first flexure and moving the first mass substantially only in the drive direction, moving the second mass coupled to the first mass by means of transferring force through a second flexure in the drive and the sense directions, and moving the third mass coupled to the second mass by means of transferring force through a third flexure substantially only in the sense direction.

21. The method of claim 20,

wherein coupling the first mass to the substrate by the first flexure comprises coupling the first mass using a folded micromachined spring having a resiliency substantially in only the drive direction, and

wherein moving the third mass by means of the third flexure uses two coupled folded micromachined springs, one of the two coupled folded micromachined springs having a resiliency substantially in only the drive direction, and the other one of the two coupled folded micromachined springs having a resiliency substantially in only the sense direction.

22. The method of claim 15, wherein the drive-mode oscillator and sense-mode oscillator are structurally arranged and configured to have the flat regions of their respective frequency response curves at least partially overlapping to define a common flat region, the gyroscope of operating in the common flat regions of response curves of the drive-mode and sense-mode oscillators between two resonant peaks in the response curves.

23. The method of claim 22, further comprising matching an anti-resonance drive frequency of the drive-mode oscillator with an anti-resonance sense frequency of the sense-mode oscillator.

24. The method of claim 15, wherein the three interconnected masses comprise a first mass, a second mass, a third mass, and coupled flexures, the second and the third masses combining to comprise a vibration absorber of the drive-mode oscillator, the method further comprising

mechanically absorbing the oscillations of the first mass by means of the vibration absorber and

generating oscillations of at least a portion of the vibration absorber at a greater oscillation amplitude,

wherein the drive-mode oscillator and the sense-mode oscillator comprise a drive means for driving the first mass, the second mass, and the third mass in a drive direction, and a sense means for sensing a motion of the third mass in a sense direction.

25. The method of claim 24, further comprising driving the first mass at a driving frequency, ω

_drive, by means of an input force F_d, matching the driving frequency, ω

_drive, with a resonant frequency of an isolated mass-spring system comprised of the second and third masses and coupled flexures, and moving the isolated mass-spring system in resonance with the first mass, so that a maximized dynamic response of the second motion to the first motion is achieved.

26. The method of claim 15,

wherein driving the drive-mode oscillator comprises driving three interconnected masses in a drive direction and driving the sense-mode oscillator comprises driving motion of one of the three interconnected masses in a sense direction, and

wherein driving the drive-mode oscillator comprises driving three interconnected masses in a drive direction and driving the sense-mode oscillator comprises mechanically increasing sense direction oscillation amplitudes in a vibration absorber in the sense-mode oscillator.

27. The method of claim 26, wherein the three interconnected masses comprise a first mass, a second mass, and a third mass, the method further comprising:

applying a Coriolis force to the second mass, and

matching the frequency of the Coriolis force with a resonant frequency of an isolated mass-spring system comprised of the third mass and its coupled flexures, so that the third mass achieves a maximized dynamic increase in its oscillation amplitudes.

28. The method of claim 15,

wherein driving the drive-mode oscillator comprises driving a first, second and third mass in a drive direction, and driving the sense-mode oscillator comprises driving the second mass in a sense direction, and sensing motion of the third mass in the sense direction,

wherein the drive-mode oscillator and sense-mode oscillator each have a frequency response defined by a response curve,

wherein the frequency response of both the drive-mode oscillator and sense-mode oscillator have two resonant peaks and a flat region of the response curve between the peaks, operating both the drive-mode oscillator and sense-mode oscillator in the flat region of their response curves,

wherein the second mass has a drive anti-resonance frequency, ω

_2x, and the third mass has a sense anti-resonance frequency, ω

_3y, and

matching ω

_2x and ω

_3y, namely setting ω

_3y=ω

_2x, or equivalently (k_3y/m₃)^1/2=(k_2x/(m₂+m₃))^1/2 and

determining therefrom maximized system parameters, together with the optimized ratios μ

_x=(m₂+m₃)/m₁, y_x=ω

_2x/ω

_1x, μ

_y=m₃/m₂, and y_y=ω

_3y/ω

_2y, wherein k_3y is a spring constant of the flexures coupled to the third mass, m₃ is a magnitude of the third mass, k_2x is a spring constant of the flexures coupled to the second mass, m₂ is a magnitude of the second mass, ω

_1x is a drive anti-resonance frequency of the first mass, and ω

_2y is a sense anti-resonance frequency of the second mass.