Torsional nonresonant z-axis micromachined gyroscope with non-resonant actuation to measure the angular rotation of an object

• US 7,421,898 B2
• Filed: 08/12/2005
• Issued: 09/09/2008
• Est. Priority Date: 08/16/2004
• Status: Expired due to Fees

• 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:
  US11/203,254
• Publication Number:
  US 20060032308A1
• Time in Patent Office: 1,124 Days
• Field of Search: 735/041.2, 735/041.4
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A gimbal-type torsional z-axis micromachined gyroscope with a non-resonant actuation scheme measures angular rate of an object with respect to the axis normal to the substrate plane (the z-axis). A 2 degrees-of-freedom (2-DOF) drive-mode oscillator is comprised of a sensing plate suspended inside two gimbals. By utilizing dynamic amplification of torsional oscillations in the drive-mode instead of resonance, large oscillation amplitudes of the sensing element is achieved with small actuation amplitudes, providing improved linearity and stability despite parallel-plate actuation. The device operates at resonance in the sense direction for improved sensitivity, while the drive direction amplitude is inherently constant within the same frequency band.

Claims

1. A MEMS-based inertial torsional z-axis surface-micromachined gyroscope with only 3-DOF and with non-resonant actuation to measure the angular rotation of an object comprising:

a substrate;

a torsional 2-DOF drive-mode oscillator coupled to the substrate and comprised of one driven active gimbal and one passive gimbal to achieve large oscillation amplitudes by amplifying the small oscillation amplitude of the driven active gimbal, so that minimization of the nonlinear force profile and minimization of instability due to actuation of the driven active gimbal are achieved, while substantially eliminating any mode-matching requirement by obtaining a flat operational frequency band in the drive-mode, the 2-DOF drive-mode oscillator having at least two resonant drive peaks with a flattened frequency response therebetween; and

a sensing plate coupled to the torsional 2-DOF drive-mode oscillator which sensing plate oscillates with a third DOF with a sense resonance at a frequency in the flattened frequency between the two resonant peaks of the 2-DOF drive oscillator.

2. The gyroscope of claim 1 further comprising actuation and sensing electrodes and

where the active gimbal, passive gimbal and sensing plate lie in a common plane when at rest

where the actuation and sensing electrodes comprise out-of-plane actuation electrodes and out-of-plane sensing electrodes.

3. A MEMS gyroscope comprising:

a substrate;

a pair of anchors lying along a drive axis, spaced from each other and connected to the substrate;

a pair of first torsional beams lying along the drive axis, each first torsional beam coupled to one of the anchors;

an active gimbal coupled to the pair of first torsional beams and suspended above the substrate by the anchors and the first torsional beams;

a drive electrode disposed on the substrate proximate to the active gimbal to selectively drive the active gimbal into torsional oscillation;

a pair of second torsional beams lying along the drive axis, each second torsional beam coupled to the active gimbal;

a passive gimbal coupled to the pair of second torsional beams and suspended above the substrate by the second torsional beams;

a pair of third torsional beams lying along a sense axis, each third torsional beam coupled to the passive gimbal;

a sensing plate coupled to the pair of third torsional beams and suspended above the substrate by the third torsional beams; and

a sensing electrode disposed on the substrate proximate to the sensing plate to sense torsional oscillation of the sensing plate;

where the active and passive gimbals, and the first and second pair of torsional beams are arranged and configured to comprise a 2-DOF drive oscillator having at least two resonant drive peaks with a flattened frequency response therebetween and where the sensing plate and third pair of torsional beams are arranged and configured to comprise a 1-DOF sensor with a sense resonance at a frequency in the flattened frequency between the two resonant peaks of the 2-DOF drive oscillator to provide a MEMS gyroscope which has only 3-DOF.

4. A method of operating a 3-DOF MEMS-based inertial torsional z-axis surface-micromachined gyroscope with non-resonant actuation to measure the angular rotation of an object comprising:

driving a torsional 2-DOF drive-mode oscillator at nonresonance comprised of an active gimbal and passive gimbal in a flat operational frequency band to amplify small oscillation amplitudes of a driven active gimbal, to minimize the nonlinear force profile and minimize instability due to actuation of the active gimbal, while substantially eliminating any mode-matching requirement; and

sensing torsional oscillation in a third DOF at a resonance of a sensing plate coupled to the torsional 2-DOF drive-mode oscillator, where the resonance is within the flat operational frequency band of the 2-DOF drive oscillator.

5. The method of claim 4 where driving the torsional 2-DOF drive-mode oscillator at nonresonance comprises driving the torsional 2-DOF drive-mode oscillator with out-of-plane actuation electrodes and where sensing torsional oscillation at resonance comprises sensing with out-of-plane sensing.

6. The method of claim 4 where driving the torsional 2-DOF drive-mode oscillator at nonresonance comprises driving the 2 DOF drive-mode oscillator by parallel-plate actuation and dynamically amplifying torsional oscillations in the drive-mode instead of using matched resonance to achieve large drive-mode oscillation amplitudes of the sensing electrodes with small actuation amplitudes of the drive electrodes thereby providing linearity and stability despite parallel-plate actuation of the 2 DOF drive-direction oscillator.