Navigation grade micromachined rotation sensor system

• US 5,987,986 A
• Filed: 07/30/1997
• Issued: 11/23/1999
• Est. Priority Date: 07/29/1994
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Fersht, Samuel H., Stewart, Robert E., Wyse, Stanley F.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/903,499
• Time in Patent Office: 846 Days
• Field of Search: 73/504.12, 73/504.14, 73/510
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape

Abstract

An angular rate sensor provides a digital delta theta output signal. A drive member is formed of a single, silicon wafer having a pair of oppositely-facing planar surfaces. The drive member includes a frame and a drive member central portion connected to the frame and arranged to have rotational compliance between the frame and the central portion about an axis perpendicular to the planar surfaces of the silicon wafer. Drive signals are applied to a plurality of electrodes on the central portion to cause rotational oscillation of the drive member central portion about a drive axis perpendicular to the planar surfaces of the silicon wafer. A silicon sensing member is connected to the drive member. The sensing member has a central support member connected to the drive member central portion such that rotational oscillations of the drive member central portion are transmitted to the sensing member central portion. A sensing portion is connected to the sensing member central support member to allow the sensing portion to oscillate about the drive axis and to allow an input rotation rate about an axis perpendicular to the drive axis to produce out-of-plane oscillations of the sensing portions. Signal processing apparatus is connected to the sensing portion for producing a signal indicative of the input rotational rate as a function of the amplitude of the out-of-plane oscillations of the sensing portion.

Claims

1. A rotation sensor, comprising:

a frame;

a drive member connected to the frame through a rotationally compliant mounting device;

a driving mechanism connected to the drive member to produce rotational oscillations of the drive member about a drive axis; and

a sensing apparatus having a support element connected to the drive member such that rotational oscillations of the drive member about the drive axis are transmitted to the support element, the sensing apparatus further including;

a sensing element connected to the support element and arranged to oscillate with the support element about the drive axis, the sensing element being arranged to oscillate rotationally relative to the support element about a sensing axis perpendicular to the drive axis for input rotation rates of the frame about an input axis which is perpendicular to both the sensing axis and the drive axis, the sensing element being formed such that its moment of inertia about the drive axis is substantially equal to the sum of the moments of inertia about its two principal axes perpendicular to the drive axis; and

apparatus for generating a signal indicative of the input rotation rate as a function of the amplitude of the oscillations of the sensing element.

2. The rotation sensor of claim 1 wherein the sensing element is arranged to oscillate rotationally relative to the support element about a pair of sensing axes that are mutually perpendicular and perpendicular to the drive axis.

3. The rotation sensor of claim 1 wherein the driving mechanism comprises:

a driving element that includes;

a substrate;

a first set of drive electrodes formed on a surface of the substrate; and

a driven element that includes;

a wafer; and

a second set of drive electrodes formed on a surface of the wafer corresponding to the first set of drive electrodes, the wafer and substrate being arranged in facing relationship such that corresponding members of the first and second sets of electrodes are angularly displaced from one another so that application of an electrical signal to the first and second sets of electrodes produces a torque on the driven element.

4. The rotation sensor of claim 1 wherein a pair of torsion bars extend between the support element and the sensing element in alignment with the sensing axis.

5. The rotation sensor of claim 1 wherein the sensing element is arranged to oscillate rotationally relative to the support element about a pair of sensing axes that are mutually perpendicular and perpendicular to the drive axis, the sensing apparatus further including a first pair of leaf springs extending between the support element and the sensing element in alignment with a first one of the sensing axes and a second pair of leaf springs extending between the support element and the sensing element in alignment with the other sensing axis.

6. The rotation sensor of claim 3 wherein the driving mechanism includes a plurality of flexure beams extending from a central portion of the driven element perpendicular to the drive axis and formed to allow the driven element to oscillate angularly about the drive axis.

7. A rotation sensor, comprising:

a housing;

a mounting plate placed in the housing with a plurality of compliant, damped pads arranged between the housing and the mounting plate;

a hub extending from the mounting plate;

a first drive member connected to the hub, the first drive member being arranged to produce rotational oscillations about a drive axis;

a first sensing apparatus having a support element connected to the drive member such that rotational oscillations of the drive member about the drive axis are transmitted to the support element, the first sensing apparatus further including;

a sensing element connected to the support element and arranged to oscillate with the support element about the drive axis, the sensing element being arranged to oscillate rotationally relative to the support element about a sensing axis perpendicular to the drive axis for input rotation rates of the frame about an input axis which is perpendicular to both the sensing axis and the drive axis, the sensing element being formed such that its moment of inertia about the drive axis is substantially equal to the sum of the moments of inertia about its two principal axes perpendicular to the drive axis; and

apparatus for generating a signal indicative of the input rotation rate as a function of the amplitude of the oscillations of the sensing element about the first sensing axis;

a second drive member connected to the first drive member, the second drive member being arranged to produce rotational oscillations about the drive axis that are opposite in direction to the rotational oscillations produced by the first drive member;

a second sensing apparatus connected to the drive member, the second sensing apparatus being substantially identical to the first sensing apparatus and having a second sensing element arranged to oscillate rotationally relative to the support element about second sensing axis that is parallel to the first sensing axis and including apparatus for generating a signal indicative of the input rotation rate as a function of the amplitude of the oscillations of the second sensing element about the second sensing axis.

8. The rotation sensor of claim 7 wherein the second sensing axis is perpendicular to the first sensing axis.

9. A rotation sensor, comprising:

a base;

a hub extending from the base;

a first set of drive electrodes formed on the base;

a drive element mounted to the hub and including a second set of drive electrodes formed thereon corresponding to the first set of drive electrodes, the base and drive element being arranged in facing relationship such that corresponding members of the first and second sets of electrodes are angularly displaced from one another so that application of an electrical signal to the first and second sets of electrodes produces a torque on the drive element that produces rotational oscillations of the drive element in a plane about a drive axis;

a sensor member that includes;

an outer support ring mounted to the drive element so that rotational oscillations of the drive element are transmitted to the sensor member, the sensor member further including a sensing element inside the support ring and a pair of torsion bars connected between the outer support ring and the sensing element, the pair of torsion bars being aligned to define an output sensing axis; and

apparatus for generating a signal indicative of an input rotation rate about an axis perpendicular to the drive axis and the sensing axis as a function of the amplitude of the oscillations of the sensing element about the output sensing axis.

10. The rotation sensor of claim 9, further comprising:

a first metallized section formed on the drive element; and

a second metallized section formed on the sensing element, the first and second metallized sections forming a capacitor having a capacitance that depends upon the rotation rate of the sensing element about an axis perpendicular to the drive axis and the sensing axis.

11. The rotation sensor of claim 10, further including apparatus connected to the first and second metallized sections for applying feedback torque to the sensing element to null the output angular oscillations and maintain the sensing element in a null position.

12. The rotation sensor of claim 10, further comprising:

apparatus for applying an oscillatory electrical signal having a frequency ω

_D /2 to the first and second sets of drive electrodes such that the drive element mechanically oscillates at the drive frequency ω

_D, wherein the sensing element is formed to have a natural frequency of oscillation about the torsion bars that differs from drive frequency ω

_D so that the sensor operates open loop; and

apparatus for demodulating signals at the drive frequency ω

_D indicative of the capacitance between the metallized sections.

13. A rotation sensor, comprising:

a base;

drive apparatus comprising;

a first drive member having a first frame mounted to the base, the first drive member being formed of a silicon wafer having a first pair of oppositely-facing planar surfaces, the first drive member further including a first drive member central portion connected to the frame such that there is rotational compliance between the frame and the central portion about an axis perpendicular to the planar surfaces of the silicon wafer, and a first plurality of drive electrodes formed on the first drive member central portion;

a second drive member having a second frame mounted to the first frame, the second drive member being formed of a silicon wafer having a second pair of oppositely-facing planar surfaces, the second drive member further including a second drive member central portion connected to the second frame such that there is rotational compliance between the second frame and its central portion about an axis perpendicular to the planar surfaces of the silicon wafer, and a second plurality of drive electrodes formed on the second drive member central portion;

drive signal apparatus for applying a drive signal having a drive signal frequency ω

_D to the plurality of drive electrodes, the plurality of drive electrodes being arranged such that the drive signal causes counter rotational oscillations of the two drive member central portions at the frequency ω

_D about a drive axis perpendicular to the planar surfaces of the wafer;

first and second sensing members mounted to the first and second drive members, respectively, each of the first and second sensing members including;

a sensing member central support member connected to the corresponding drive member central portion such that rotational oscillations of the drive member central portion are transmitted to the sensing member central portion; and

a sensing element connected to the sensing member central support member to allow the sensing element to oscillate about the drive axis and to allow an input rotation rate about an input axis perpendicular to the drive axis to produce out-of-plane oscillations of the sensing element about a sensing axis perpendicular to the input axis and the drive axis at an oscillation amplitude that is a function of the input rotation rate; and

signal processing apparatus connected to the sensing elements for producing a sensor output signal indicative of the input rotational rates as a function of the amplitude of the out-of-plane oscillations of the sensing element.

14. The rotation sensor of claim 13 wherein each of the first and second drive members includes a plurality of flexure beams extending between its frame and the corresponding drive member central portion to provide the rotational compliance.

15. The rotation sensor of claim 13, wherein each of the sensing members comprises a plurality of generally planar leaf spring members connected between the sensing member central support member and the sensing element such that the out-of-plane oscillations in the sensing element are perpendicular to the planes of the leaf spring members.

16. The rotation sensor of claim 15, further comprising a capacitive pickoff formed between one of the sensing elements and the drive apparatus to provide the sensor output signal.

17. The rotation sensor of claim 13, further comprising a plurality of base mounts connected between the base and the drive member, each base mount being formed to comprise a damped compliant element for providing a single mechanical resonant frequency in the rotation sensor and for attenuating external vibration inputs.

18. The rotation sensor of claim 13 wherein the first and second sensing members include first and second elements, respectively, which are arranged to oscillate in opposite directions in response to an input rotation rate.

19. The rotation sensor of claim 13, further comprising:

a first capacitive pickoff arranged to provide a first electrical pickoff signal indicative of the amplitude of out-of-plane oscillations of the first sensing element; and

a second capacitive pickoff arranged to provide a second electrical pickoff signal indicative of the amplitude of out-of-plane oscillations of the second sensing element.