Apparatus and Method for Providing an In-Plane Inertial Device with Integrated Clock

• US 20130247669A1
• Filed: 03/21/2012
• Published: 09/26/2013
• Est. Priority Date: 03/21/2012
• 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 the navy
• Inventors: Swanson, Paul D., Waters, Richard L.
• Granted Patent: US 8,875,576 B2
• Time in Patent Office: Days
• US Class Current: 73/514.38
• CPC Class Codes: G01C 19/5747 each sensing mass being connected to a driving mass, e.g. driving frames
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

An in-plane, monolithically-integrated, inertial device comprising: a support structure and first and second spring mass systems springedly coupled to the support structure. The first spring mass system comprises first and second time domain digital triggers configured to measure rotation and displacement respectively of the support structure about a first axis and along an orthogonal second axis respectively. The second spring mass system comprises third and fourth time domain digital triggers configured to measure acceleration and displacement respectively of the support structure about the second axis and along the first axis respectively.

Claims

1. An in-plane, monolithically-integrated, inertial device comprising:

a support structure;

a first spring mass system springedly coupled to the support structure, wherein the first spring mass system is configured to use a first time domain digital trigger operatively coupled between a first drive mass and a first sense mass to measure rotation of the support structure about a first axis, and wherein the first spring mass system is further configured to use a second time domain digital trigger operatively coupled between the support structure and the first drive mass to measure acceleration of the support structure in a second direction that corresponds to direction along a second axis, which is orthogonal to the first axis; and

a second spring mass system springedly coupled to the support structure, wherein the second spring mass system is configured to use a third time domain digital trigger operatively coupled between a second drive mass and a second sense mass to measure rotation of the support structure about the second axis, and wherein the second spring mass system is further configured to use a fourth time domain digital trigger operatively coupled between the support structure and the second drive mass to measure acceleration of the support structure in a first direction that corresponds to direction along the first axis.

2. The device of claim 1, wherein:

the first drive mass is springedly coupled to the support structure such that movement of the first drive mass with respect to the support structure is substantially restricted to movement in the second direction, and wherein the first drive mass is driven to oscillate with respect to the support structure in the second direction; and

the first sense mass is springedly coupled to the first drive mass such that movement of the first sense mass with respect to the first drive mass is substantially restricted to movement in a third direction corresponding to direction along a third axis that is orthogonal to the first and second axes.

3. The device of claim 2, wherein:

the second drive mass is springedly coupled to the support structure such that movement of the second drive mass with respect to the support structure is substantially restricted to movement in the first direction, and wherein the second drive mass is driven to oscillate with respect to the support structure in the first direction; and

the second sense mass is springedly coupled to the second drive mass such that movement of the second sense mass with respect to the second drive mass is substantially restricted to movement in the third direction.

4. The device of claim 3, wherein:

the first digital trigger is configured to switch from an open state to a closed state each time the first sense mass is in a reference position with respect to the first drive mass;

the second digital trigger is configured to switch from an open state to a closed state each time the first drive mass is in a reference position with respect to the support structure;

the third digital trigger is configured to switch from an open state to a closed state each time the second sense mass is in a reference position with respect to the second drive mass; and

the fourth digital trigger is configured to switch from an open state to a closed state each time the second drive mass is in a reference position with respect to the support structure.

5. The device of claim 4, wherein the second spring mass system is further configured to use a fifth time domain digital trigger operatively coupled between the second drive mass and a third sense mass to measure rotation of the support structure about the third axis.

6. The device of claim 5, wherein:

the third sense mass is springedly coupled to the second drive mass such that movement of the third sense mass with respect to the second drive mass is substantially restricted to movement in the second direction; and

the fifth digital trigger is configured to switch from an open state to a closed state each time the third sense mass is in a reference position with respect to the second drive mass.

7. The device of claim 6, further comprising an accelerometer configured to measure acceleration of the support structure in the third direction, wherein the accelerometer comprises a fourth sense mass and a sixth time domain digital trigger, wherein the fourth sense mass is springedly coupled to the support structure such that movement of the fourth sense mass with respect to the support structure is substantially restricted to movement in the third direction, and wherein the sixth time domain digital trigger is configured to switch from an open state to a closed state each time the fourth sense mass is in a reference position with respect to the support structure.

8. The device of claim 7, wherein all of the digital triggers are multiple-reference-position electron-tunneling-tip proximity switches, wherein each switch experiences at least two closed states with each relative oscillation between the respective elements to which each proximity switch is coupled.

9. The device of claim 8, further comprising a dual-mass resonator that is springedly coupled to the support structure, wherein the dual-mass resonator is configured to use a seventh time domain digital trigger to provide a clock signal, and wherein the dual-mass resonator comprises:

a first oscillator mass configured to oscillate with respect to the support structure;

a first oscillator driver configured to drive the first oscillator mass to oscillate with respect to the support structure at the first oscillator mass'"'"' resonant frequency;

a second oscillator mass having substantially the same resonant frequency as the first oscillator mass, wherein the first and second oscillator masses are designed to respond in substantially the same manner to external perturbations to the support structure;

wherein the seventh digital trigger comprises a seventh electron-tunneling-tip switch coupled between the first oscillator mass and the second oscillator mass; and

wherein as the first oscillator mass oscillates there is relative motion between the first and second oscillator masses such that the seventh switch passes through a closed state in each oscillation when the first and second oscillator masses pass by each other.

10. The device of claim 9, wherein the support structure, the dual sense mass gyroscope, the single sense mass gyroscope, the accelerometer, and the dual mass resonator are sealed in a vacuum between two capping wafers.

11. A method for providing a single monolithic device to measure the rotation of a support structure about first, second, and third axes of a three-axis orthogonal coordinate system as well as the acceleration of the support structure in first, second, and third directions corresponding to directions along the first, second, and third axes respectively, the method comprising the following steps:

driving a first drive mass to oscillate with respect to the support structure in the second direction;

measuring rotation of the support structure about the first axis by monitoring a time interval between successive trigger events from a first pair of third-direction-stacked proximity switches coupled between the first drive mass and a first sense mass which is springedly coupled to the first drive mass such that movement of the first sense mass with respect to the first drive mass is substantially restricted to movement in the third direction;

measuring acceleration of the support structure in the second direction by monitoring a time interval between successive trigger events from a second pair of second-direction-stacked proximity switches coupled between the first drive mass and the support structure;

driving a second drive mass to oscillate with respect to the support structure in the first direction;

measuring rotation of the support structure about the second axis by monitoring a time interval between successive trigger events from a third pair of third-direction-stacked proximity switches coupled between the second drive mass and a second sense mass which is springedly coupled to the second drive mass such that movement of the second sense mass with respect to the second drive mass is substantially restricted to movement in the third direction;

measuring acceleration of the support structure in the first direction by monitoring a time interval between successive trigger events from a fourth pair of first-direction-stacked proximity switches coupled between the second drive mass and the support structure;

measuring rotation of the support structure about the third axis by monitoring a time interval between successive trigger events from a fifth pair of second-direction-stacked proximity switches coupled between the second drive mass and a third sense mass which is springedly coupled to the second drive mass such that movement of the third sense mass with respect to the second drive mass is substantially restricted to movement in the second direction;

driving a fourth sense mass to oscillate with respect to the support structure in the third direction at the fourth sense mass'"'"' resonant frequency; and

measuring acceleration of the support structure in the third direction by monitoring a time interval between successive trigger events from a sixth pair of third-direction-stacked proximity switches coupled between the fourth sense mass and the support structure.

12. The method of claim 11, further comprising the steps of:

driving a first oscillator mass to oscillate with respect to the support structure at the first oscillator mass'"'"' resonant frequency;

generating a clock signal by monitoring each closed state of a resonator proximity switch that is coupled between the first oscillator mass and a second oscillator mass, wherein the second oscillator mass has substantially the same resonant frequency as the first oscillator mass and the second oscillator mass oscillates out of phase with the first oscillator mass, and wherein the first and second oscillator masses are designed to respond in substantially the same manner to external perturbations to the support structure, and wherein the resonator proximity switch switches from an open state to a closed state each time the first and second oscillator masses are in a reference position with respect to each other.

13. The method of claim 12, wherein the time intervals are measured based on the clock signal.

14. The method of claim 13, further comprising the step of calculating the amplitude of a given rotation of the support structure based on the corresponding time interval between successive trigger events.

15. The method of claim 14, further comprising the step of calculating the amplitude of an acceleration of the support structure in a given direction based on the corresponding time interval between successive trigger events.

16. A method for providing a monolithic device to measure the rotation of the device about x, y, and z mutually orthogonal axes as well as the acceleration of the support structure in x, y, and z directions corresponding to directions along the x, y, and z axes respectively, the method comprising the following steps:

forming a support structure in the xy plane of a substrate;

forming in the xy plane of the substrate a single-sense-mass gyroscope that is springedly coupled to the support structure, wherein the single-sense-mass gyroscope is configured to use a first time domain digital trigger to measure rotations of the support structure about the x-axis, and wherein the single-sense-mass gyroscope is further configured to use a second time domain digital trigger to measure acceleration of the support structure in the y-direction;

forming in the xy plane of the substrate a dual-sense-mass gyroscope that is springedly coupled to the support structure, wherein the dual-sense-mass gyroscope is configured to use a third and fifth time domain digital triggers to measure rotations of the support structure about the y- and z- axes respectively, and wherein the dual-sense-mass gyroscope is further configured to use a fourth time domain digital trigger to measure acceleration of the support structure in the x-direction;

forming in the xy plane of the substrate an accelerometer that is springedly coupled to the support structure, wherein the accelerometer is configured to use a sixth time domain digital trigger to measure acceleration of the support structure in the z-direction; and

forming in the xy plane of the substrate a dual-mass resonator that is springedly coupled to the support structure, wherein the dual-mass resonator is configured to use a seventh time domain digital trigger to generate a clock signal.

17. The method of claim 16, wherein the single-mass gyroscope comprises:

a first drive mass springedly coupled to the support structure;

a first drive mass driver configured to drive the first drive mass to oscillate with respect to the support structure in approximately only the y-direction;

a first sense mass springedly coupled to the first drive mass, wherein the first sense mass is configured to move with respect to the first drive mass in approximately only the z-direction in response to Coriolis forces from rotation of the support structure about the x-axis;

wherein the first digital trigger comprises a first pair of z-direction-stacked proximity switches coupled between the first drive mass and the first sense mass, wherein the first digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the first sense mass with respect to the first drive mass such that rotation and rotation rate of the support structure about the x-axis may be determined by measuring the time interval between closed states of the first pair of proximity switches; and

wherein the second digital trigger comprises a second pair of y-direction-stacked proximity switches coupled between the first drive mass and the support structure, wherein the second digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the first drive mass with respect to the support structure such that acceleration and displacement amplitude of the support structure in the y-direction may be determined by measuring the time interval between closed states of the second pair of proximity switches.

18. The method of claim 17, wherein the dual-mass gyroscope comprises:

a second drive mass springedly coupled to the support structure;

a second drive mass driver configured to drive the second drive mass to oscillate with respect to the support structure in approximately only the x-direction;

a second sense mass springedly coupled to the second drive mass, wherein the second sense mass is configured to move with respect to the second drive mass in approximately only the z-direction in response to Coriolis forces from rotation of the support structure about the y-axis;

a third sense mass springedly coupled to the second drive mass, wherein the third sense mass is configured to move with respect to the second drive mass in approximately only the y-direction in response to Coriolis forces from rotation of the support structure about the z-axis;

wherein the third digital trigger comprises a third pair of z-direction-stacked proximity switches coupled between the second drive mass and the second sense mass, wherein the third digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the second sense mass with respect to the second drive mass such that rotation and rotation rate of the support structure about the y-axis may be determined by measuring the time interval between closed states of the third pair of proximity switches;

wherein the fourth digital trigger comprises a fourth pair of x-direction-stacked proximity switches coupled between the second drive mass and the support structure, wherein the fourth digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the second drive mass with respect to the support structure such that acceleration and displacement amplitude of the support structure in the x-direction may be determined by measuring the time interval between closed states of the fourth pair of proximity switches; and

wherein the fifth digital trigger comprises a fifth pair of y-direction-stacked proximity switches coupled between the second drive mass and the third sense mass, wherein the fifth digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the third sense mass with respect to the second drive mass such that rotation and rotation rate of the support structure about the z-axis may be determined by measuring the time interval between closed states of the fifth pair of proximity switches.

19. The method of claim 18, wherein the accelerometer comprises:

a fourth sense mass springedly coupled to the support structure, wherein the fourth sense mass is configured to move with respect to the support structure in approximately only the z-direction in response to accelerations of the support structure in the z-direction;

an accelerometer driver configured to drive the fourth sense mass to oscillate with respect to the support structure at the fourth sense mass'"'"' resonant frequency in approximately only the z-direction; and

wherein the sixth digital trigger comprises a sixth pair of z-direction-stacked proximity switches coupled between the fourth sense mass and the support structure, wherein the sixth digital trigger is configured to pass from an open state to closed state at least twice during each oscillation of the fourth sense mass with respect to the support structure such that acceleration and displacement amplitude of the support structure in the z-direction may be determined by measuring the time interval between closed states of the sixth pair of proximity switches.

20. The method of claim 19, wherein the dual-mass resonator comprises:

a first oscillator mass configured to oscillate with respect to the support structure;

a first oscillator driver configured to drive the first oscillator mass to oscillate with respect to the support structure at the first oscillator mass'"'"' resonant frequency;

a second oscillator mass having substantially the same resonant frequency as the first oscillator mass, wherein the first and second oscillator masses are designed to respond in substantially the same manner to external perturbations to the support structure;

wherein the seventh digital trigger comprises a seventh proximity switch coupled between the first oscillator mass and the second oscillator mass; and

wherein as the first oscillator mass oscillates there is relative motion between the first and second oscillator masses such that the seventh switch is configured to pass from an open state to closed state during each oscillation of the first oscillator mass with respect to the second oscillator mass.