Tuning fork gyroscope

• US 7,617,728 B2
• Filed: 05/17/2006
• Issued: 11/17/2009
• Est. Priority Date: 05/17/2006
• Status: Expired due to Fees

• Current Assignee: Milli Sensor Systems & Actuators, Inc.
• Original Assignee: Milli Sensor Systems & Actuators, Inc.
• Inventors: Cardarelli, Donato
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US11/383,814
• Publication Number:
  US 20070266785A1
• Time in Patent Office: 1,280 Days
• Field of Search: 733/18, 735/040.3, 735/040.4, 735/141.6, 735/143.5, 736/52, 735/041.2, 735/041.6
• 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 gyroscope for detecting rotation about a gyro input axis, having a support structure, at least one mass flexibly coupled to the support structure such that it is capable of motion in two directions along a drive axis, the mass offset from the gyro output axis, one or more drives for oscillating the flexibly-coupled masses along the drive axis, one or more mass motion sensors that sense motion of the flexibly-coupled masses along their drive axes, and one or more gyro output sensors that detect rotation of the support structure about the output axis.

Claims

1. A monolithic, generally planar gyroscope for detecting rotation about a gyro input axis that is coincident with the gyro output axis, comprising:

a substrate defining a non-conductive surface;

a post coupled to the substrate and projecting from the surface of the substrate, the post defining a center;

a generally planar rigid frame spaced above the surface of the substrate and comprising a pair of spaced parallel rails that define an interior region between them;

a plurality of radial flexures that couple the frame to the post so as to allow rotation of the frame relative to the substrate about an output axis that is orthogonal to the substrate surface, the flexures lying along radii from the center of the post;

first and second masses lying in the plane of the frame and flexibly coupled to the frame such that each mass is capable of motion in two directions along a common drive axis that is parallel to the substrate surface and orthogonal to the gyro input and output axes;

four bending flexures that couple each mass to the frame, two spaced flexures coupling each mass to one rail and two spaced flexures coupling each mass to the other rail;

two capacitive comb actuators for oscillating the first mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb actuators for oscillating the second mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the first mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the second mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that provide a sinusoidal drive voltage to the comb actuators, the drive voltage applied to the comb actuator for a first mass at a first phase and the drive voltage applied to the comb actuator for a second mass at the opposite phase, to drive the masses in opposition along the drive axis;

phase-lock loop electronics, responsive to the mass motion sensors, for controlling the actuators such that the masses oscillate in opposition, at the same frequency and at resonance;

amplitude control loop electronics, responsive to the mass motion sensors, for controlling the actuators to maintain the oscillation amplitude of the masses constant;

one or two pairs of capacitive comb gyro output sensors radially arranged about the output axis, the output sensors detecting rotation of the frame relative to the substrate about the gyro output axis, each output sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and lying along radii from the center of the post and a rotor made from a plurality of spaced fingers coupled to the frame and lying along different radii from the center of the post, the fingers of the rotor interdigitated among the fingers of the stator, wherein the stator and rotor fingers of one the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move closer to the stator fingers, and wherein the stator and rotor fingers of the other of the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move farther away from the stator fingers, and wherein the stator and rotor fingers of each of the output sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that subtract the output of one output sensor from the output of the other output sensor of a pair of sensors, to obtain a differential signal indicative of rotation of the frame about the output axis;

wherein the frame, the masses, the flexures and the combs are all fabricated from a monolithic layer of material, wherein the stators are electrically isolated from one another by the non-conductive surface of the substrate, and wherein the gyroscope is designed to separate in frequency the two modes of oscillation of the two masses along the drive axis;

one mode in which the masses oscillate together in the same direction and one mode in which the masses oscillate in opposition, the frequency separation sufficiently large such that the drive voltage excites only the oscillation in opposition, and wherein the two masses couple when driven so that they oscillate at the same frequency.

2. The gyroscope of claim 1 in which there are at least two pairs of flexibly-coupled masses, the masses of each such pair moving in opposition along a common drive axis, in which the drive axes are radial about a center of rotation.

3. The gyroscope of claim 1 further comprising a regular tetrahedron base member defining at least three faces, wherein the substrate is coupled to a face of the base member.

4. The gyroscope of claim 1 in which the frame further comprises a ring spaced from and surrounding the post, wherein the flexures couple the ring to the post.

5. The gyroscope of claim 4 in which the ring is rigidly coupled to the beams.

6. A monolithic, generally planar gyroscope for detecting rotation about a gyro input axis that is coincident with the gyro output axis, comprising:

a substrate defining a non-conductive surface;

a generally planar rigid frame spaced above the surface of the substrate and comprising a pair of spaced parallel rails that define an interior region between them;

a plurality of posts coupled to the substrate and projecting from the surface of the substrate, wherein the posts are located outside of the rails;

a plurality of radial flexures that couple the frame to the posts so as to allow rotation of the frame relative to the substrate about an output axis that is orthogonal to the substrate surface, the flexures lying along radii from the center of the gyroscope;

first and second masses lying in the plane of the frame and flexibly coupled to the frame such that each mass is capable of motion in two directions along a common drive axis that is parallel to the substrate surface and orthogonal to the gyro input and output axes;

four bending flexures that couple each mass to the frame, two spaced flexures coupling each mass to one rail and two spaced flexures coupling each mass to the other rail;

two capacitive comb actuators for oscillating the first mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb actuators for oscillating the second mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the first mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the second mass along the drive axis, one comb motion sensor on one side of the drive axis and theother comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that provide a sinusoidal drive voltage to the comb actuators, the drive voltage applied to the comb actuator for a first mass at a first phase and the drive voltage applied to the comb actuator for a second mass at the opposite phase, to drive the masses in opposition along the drive axis;

phase-lock loop electronics, responsive to the mass motion sensors, for controlling the actuators such that the masses oscillate in opposition, at the same frequency and at resonance;

amplitude control loop electronics, responsive to the mass motion sensors, for controlling the actuators to maintain the oscillation amplitude of the masses constant;

one or two pairs of capacitive comb gyro output sensors radially arranged about the output axis, the output sensors detecting rotation of the frame relative to the substrate about the gyro output axis, each output sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and lying along radii from the center of the post and a rotor made from a plurality of spaced fingers coupled to the frame and lying along different radii from the center of the post, the fingers of the rotor interdigitated among the fingers of the stator, wherein the stator and rotor fingers of one the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move closer to the stator fingers, and wherein the stator and rotor fingers of the other of the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move farther away from the stator fingers, and wherein the stator and rotor fingers of each of the output sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that subtract the output of one output sensor from the output of the other output sensor of a pair of sensors, to obtain a differential signal indicative of rotation of the frame about the output axis;

wherein the frame, the masses, the flexures and the combs are all fabricated from a monolithic layer of material, wherein the stators are electrically isolated from one another by the non-conductive surface of the substrate, and wherein the gyroscope is designed to separate in frequency the two modes of oscillation of the two masses along the drive axis;

one mode in which the masses oscillate together in the same direction and one mode in which the masses oscillate in opposition, the frequency separation sufficiently large such that the drive voltage excites only the oscillation in opposition, and wherein the two masses couple when driven so that they oscillate at the same frequency.

7. A monolithic, generally planar gyroscope for detecting rotation about a gyro input axis that is coincident with the gyro output axis, comprising:

a substrate defining a non-conductive surface;

a post coupled to the substrate and projecting from the surface of the substrate, the post defining a center;

a generally planar rigid frame spaced above the surface of the substrate and comprising a pair of spaced parallel rails that define an interior region between them;

a plurality of colinear torsional flexures that couple the frame to the post so as to allow rotation of the frame relative to the substrate about an output axis that is parallel to the substrate surface, the flexures lying along radii from the center of the post;

first and second masses lying in the plane of the frame and flexibly coupled to the frame such that each mass is capable of motion in two directions along a common drive axis that is parallel to the substrate surface and orthogonal to the gyro input and output axes;

four bending flexures that couple each mass to the frame, two spaced flexures coupling each mass to one rail and two spaced flexures coupling each mass to the other rail;

two capacitive comb actuators for oscillating the first mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb actuators for oscillating the second mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the first mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the second mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that provide a sinusoidal drive voltage to the comb actuators, the drive voltage applied to the comb actuator for a first mass at a first phase and the drive voltage applied to the comb actuator for a second mass at the opposite phase, to drive the masses in opposition along the drive axis;

phase-lock loop electronics, responsive to the mass motion sensors, for controlling the actuators such that the masses oscillate in opposition, at the same frequency and at resonance;

amplitude control loop electronics, responsive to the mass motion sensors, for controlling the actuators to maintain the oscillation amplitude of the masses constant;

one or two pairs of capacitive plate gyro output sensors, one plate of each pair located on the surface of the substrate underneath a mass, the output sensors detecting rotation of the masses relative to the substrate about the gyro output axis;

electronics that subtract the output of one output sensor from the output of the other output sensor of a pair of sensors, to obtain a differential signal indicative of rotation of the frame about the output axis;

wherein the frame, the masses, the flexures and the combs are all fabricated from a monolithic layer of material, wherein the stators are electrically isolated from one another by the non-conductive surface of the substrate, and wherein the gyroscope is designed to separate in frequency the two modes of oscillation of the two masses along the drive axis;

one mode in which the masses oscillate together in the same direction and one mode in which the masses oscillate in opposition, the frequency separation sufficiently large such that the drive voltage excites only the oscillation in opposition, and wherein the two masses couple when driven so that they oscillate at the same frequency.

8. A monolithic, generally planar gyroscope for detecting rotation about a gyro input axis that is coincident with the gyro output axis, comprising:

a substrate defining a non-conductive surface;

a post coupled to the substrate and projecting from the surface of the substrate, the post defining a center;

a generally planar rigid frame spaced above the surface of the substrate and comprising a pair of spaced parallel rails that define an interior region between them;

a plurality of radial flexures that couple the frame to the post so as to allow rotation of the frame relative to the substrate about an output axis that is orthogonal to the substrate surface, the flexures lying along radii from the center of the post;

first and second masses lying in the plane of the frame, one movable mass flexibly coupled to the frame such that it is capable of motion in two directions along a common drive axis that is parallel to the substrate surface and orthogonal to the gyro input and output axes, and the other mass fixed relative to the frame;

four bending flexures that couple the movable mass to the frame, two spaced flexures coupling the movable mass to one rail and two spaced flexures coupling the movable mass to the other rail;

two capacitive comb actuators for oscillating the movable mass along the drive axis, one comb actuator on one side of the drive axis and the other comb actuator on the other side of the drive axis, each comb actuator comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the comb actuators are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

two capacitive comb motion sensors for sensing motion of the movable mass along the drive axis, one comb motion sensor on one side of the drive axis and the other comb motion sensor on the other side of the drive axis, each comb motion sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and a rotor comprising a plurality of spaced fingers coupled to the mass, the fingers of the rotor interdigitated among the fingers of the stator, and wherein the stator and rotor fingers of each of the motion sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that provide a sinusoidal drive voltage to the comb actuators, to drive the movable mass along the drive axis;

phase-lock loop electronics, responsive to the mass motion sensors, for controlling the actuators such that the movable mass oscillates at resonance;

amplitude control loop electronics, responsive to the mass motion sensors, for controlling the actuators to maintain the oscillation amplitude of the movable mass constant;

one or two pairs of capacitive comb gyro output sensors radially arranged about the output axis, the output sensors detecting rotation of the frame relative to the substrate about the gyro output axis, each output sensor comprising a stator made of a plurality of spaced fingers on the surface of the substrate and lying along radii from the center of the post and a rotor made from a plurality of spaced fingers coupled to the frame and lying along different radii from the center of the post, the fingers of the rotor interdigitated among the fingers of the stator, wherein the stator and rotor fingers of one the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move closer to the stator fingers, and wherein the stator and rotor fingers of the other of the pair of output sensors are arranged such that as the frame rotates clockwise about the output axis the rotor fingers move farther away from the stator fingers, and wherein the stator and rotor fingers of each of the output sensors are further arranged in pairs, one stator finger and one rotor finger making up each pair, the fingers of each pair separated by a small gap, and adjacent pairs separated from one another by a larger gap;

electronics that subtract the output of one output sensor from the output of the other output sensor of a pair of sensors, to obtain a differential signal indicative of rotation of the frame about the output axis;

wherein the frame, the masses, the flexures and the combs are all fabricated from a monolithic layer of material, and wherein the stators are electrically isolated from one another by the non-conductive surface of the substrate.