Tuning fork gyroscope time domain inertial sensor

• US 8,991,250 B2
• Filed: 09/11/2012
• Issued: 03/31/2015
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Waters, Richard L., Swanson, Paul David
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US13/610,618
• Publication Number:
  US 20140069188A1
• Time in Patent Office: 931 Days
• Field of Search: 735/041.6, 735/041.2, 735/040.4, 310/370
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719
• CPC Class Codes: G01C 19/5621 the devices involving a micromechanical structure

Abstract

A gyroscope comprising: a frame; a tuning fork comprising a base and first and second prongs, wherein the base has proximal and distal ends, and wherein the proximal end is coupled to the frame and the distal end is coupled to the first and second prongs; first and second drivers configured to drive the first and second prongs respectively to oscillate with respect to the frame in a first direction, such that the prongs oscillate at their respective resonant frequencies and 180° out of phase with each other; and at least two digital position triggers operatively coupled to the frame and to the tuning fork, wherein each position trigger is configured to experience at least two trigger events during each oscillation of the tuning fork in a second direction, wherein the second direction is orthogonal to the first direction.

Claims

1. A gyroscope comprising:

a frame;

a tuning fork comprising a base and first and second prongs, wherein the base has proximal and distal ends, and wherein the proximal end is coupled to the frame and the distal end is coupled to the first and second prongs;

first and second drivers configured to drive the first and second prongs respectively to oscillate with respect to the frame in a first direction, such that the prongs oscillate at respective resonant frequencies of the first and second prongs and 180°

out of phase with each other; and

at least two digital position triggers operatively coupled to the frame and to the tuning fork, wherein each position trigger is configured to experience at least two trigger events during each oscillation of the tuning fork in a second direction, wherein the second direction is orthogonal to the first direction, and wherein each position trigger comprises a pair of second-direction-stacked electron-tunneling-tip switches, wherein each pair of electron-tunneling-tip switches comprises;

at least two conductive, tuning-fork-mounted elements aligned with, and electrically insulated from, each other in the second direction; and

at least two conductive, frame-mounted elements aligned with, and electrically insulated from, each other in the second direction such that a triggering event occurs when at least one of the tuning-fork-mounted elements is substantially aligned with one of the frame-mounted elements creating a closed state wherein electrons tunnel from the at least one of the tuning-fork-mounted elements over a gap to the substantially-aligned, frame-mounted element.

2. The gyroscope of claim 1, further comprising a third driver configured to drive the tuning fork to oscillate with respect to the frame in the second direction.

3. The gyroscope of claim 1, wherein the position triggers are located on distal ends of the first and second prongs.

4. The gyroscope of claim 3, wherein when a given prong is in a zero force position with respect to the frame, at least two of the given prong'"'"'s electron-tunneling-tip switches are in closed states.

5. The gyroscope of claim 3, wherein the frame-mounted elements of the position triggers are conductive planes configured such that during a triggering event electrons tunnel from one of the tuning-fork-mounted elements to an edge of one of the conductive planes.

6. The gyroscope of claim 5, wherein the edges of the conductive planes are curved such that as the prongs oscillate in the first direction the size of the gap remains substantially the same.

7. The gyroscope of claim 1, wherein the position triggers are located on opposite sides of the distal end of the base.

8. The gyroscope of claim 7, wherein the tuning fork further comprises first and second arms having proximal and distal ends, wherein the proximal ends of the first and second arms are coupled to the distal end of the base, and wherein the position triggers are located on the distal ends of the first and second arms.

9. A method for inertial sensing using a time-domain, tuning-fork gyroscope comprising the following steps:

driving first and second prongs of a tuning fork of the tuning fork gyroscope to oscillate with respect to a frame of the tuning fork gyroscope in a first direction, such that the prongs oscillate at respective resonant frequencies of the first and second prongs and 180°

out of phase with each other;

monitoring closed and open states of two pairs of second-direction-stacked electron-tunneling-tip switches, wherein a second direction is orthogonal to the first direction, and wherein each pair of switches is operatively coupled to the frame and the tuning fork such that each pair of switches passes through at least two closed states during each oscillation of the tuning fork in the second direction;

measuring a time interval between closed states of each switch pair to characterize an offset of the tuning fork in the second direction; and

determining a Coriolis force acting on the tuning fork gyroscope by calculating the offset of the tuning fork in the second direction.

10. The method of claim 9, wherein the two pairs of second-direction-stacked electron-tunneling-tip switches are mounted to a section of the tuning fork where the prongs meet a base of the tuning fork.

11. The method of claim 9, wherein one of the two pairs of second-direction-stacked electron-tunneling-tip switches are mounted to distal ends of each of the prongs.

12. The method of claim 11, further comprising the step of calculating an oscillation amplitude of a given prong in the second direction based on the time interval between successive closed states of the prong'"'"'s switch pair.

13. The method of claim 12, further comprising the step of driving the prongs to oscillate with respect to the frame in the second direction.

14. The method of claim 12, wherein the Coriolis force is expressed as a change in amplitude of the second-direction oscillation of a given prong when both a second-direction resonant frequency and a first-direction resonant frequency of the given prong match.

15. The method of claim 14, wherein the Coriolis force is expressed as a second-direction offset of the resonant oscillation of the tuning fork in the second direction when the resonant frequency of the tuning fork in the second direction is much greater than that of the prong'"'"'s resonant frequency in the first direction.

16. A gyroscope comprising:

a frame;

a tuning fork comprising a base and first and second prongs, wherein a proximal end of the base is coupled to the frame and wherein proximal ends of the first and second prongs are coupled to a distal end of the base;

a first driver operatively coupled to the first prong such that the first driver is configured to drive the first prong to oscillate with respect to the frame in a first direction at a first prong'"'"'s resonant frequency;

a second driver operatively coupled to the second prong such that the second driver is configured to drive the second prong to oscillate with respect to the frame in the first direction at a second prong'"'"'s resonant frequency and 180°

out of phase with the first prong;

a first pair of electron-tunneling tip switches operatively coupled to the frame and a first location on the tuning fork such that the first pair of switches is configured to switch from an open state to a closed state at least twice during a complete oscillation of the tuning fork with respect to the frame in a second direction; and

a second pair of electron-tunneling tip switches operatively coupled to the frame and a second location on the tuning fork such that the second pair of switches is configured to switch from an open state to a closed state at least twice during a complete oscillation of the tuning fork with respect to the frame in the second direction.

17. The gyroscope of claim 16, wherein the first and second locations are on the distal end of the base near where the first and second prongs are respectively coupled to the base.

18. The gyroscope of claim 16, wherein the tuning fork further comprises first and second arms having proximal and distal ends, wherein the proximal ends of the first and second arms are coupled to the distal end of the base such that the first and second arms protrude from the base in the first direction, orthogonal to the first and second prongs, and wherein the first and second locations are on the distal ends of the first and second arms respectively.

19. The gyroscope of claim 16, wherein the first and second prongs each further comprises a distal end, which is separated from an edge of the frame by a gap, and wherein the edge of the frame is curved such that as the prongs oscillate in the first direction the size of the gap remains substantially the same, and wherein the first and second locations are on the distal ends of the first and second prongs respectively.