Coriolis gyro sensor

• US 6,009,751 A
• Filed: 10/27/1998
• Issued: 01/04/2000
• Est. Priority Date: 10/27/1998
• Status: Expired due to Fees

• Current Assignee: Bo Hans Gunnar Ljung
• Original Assignee: Bo Hans Gunnar Ljung
• Inventors: Ljung, Bo Hans Gunnar
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Kwok, Helen C.
• Application Number:
  US09/179,676
• Time in Patent Office: 434 Days
• Field of Search: 73/504.02, 73/504.03, 73/504.04, 73/504.08, 73/504.09, 73/504.12, 73/514.32, 74/5 R, 74/5.34, 74/5.37, 74/5.4, 74/5.47, 74/5 F
• US Class Current: 73/504.02
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A single or dual input-axis Coriolis gyro sensor is comprised of a single planar inertia-member (10) connected to a coplanar counter-inertia (13) by a first set of elastic beams (12). The counter-inertia is in turn supported by a second set of coplanar elastic beams (15). The counter-inertia counteracts the reaction forces from the vibrating inertia-member and isolates the inertia-member from external vibrations. The inertia-member is angularly dithered about its center of gravity along an axis perpendicular to the plane. An input rate about a first or second orthogonal axis, locate in the plane of the sensor results in Coriolis moments, causing angular oscillations of the inertia-member. The angular oscillations are restrained by squeeze film damping and voltages applied to electrostatic damping electrodes. The electrode voltages are representative of the angular input rates.

Claims

1. A Coriolis gyro sensor comprising:

(a) an inertia-member, and a counter-inertia;

(b) a first suspension means connecting said inertia-member to said counter-inertia; and

(c) a second suspension means connecting said counter-inertia to a fixed mounting frame;

wherein

(d) said first, and said second suspension means allow separate and limited angular motion of said inertia-member, and said counter-inertia;

further including

(e) a driving means to drive said inertia-member in an angular dither motion;

(f) a sensing means generating signals representative of angular oscillatory motions of said inertia-member relative said fixed mounting frame; and

(g) a restraining means generating damping forces acting on said inertia-member;

wherein

(h) said forces from said restraining means are representative of input rate rotation of said Coriolis gyro sensor to form a single or dual input-axis Coriolis gyro sensor; and

wherein

(i) said counter-inertia counteracts reaction forces from said inertia-member.

2. A Coriolis gyro sensor according to claim 1, wherein:

(a) said inertia-member, said first suspension means, said counter-inertia, said second suspension means, and said mounting frame extend substantially in a plane; and

(b) said inertia-member, and said counter-inertia are formed to locate the center of gravity of said inertia-member, and said counter-inertia substantially coincident.

3. A Coriolis gyro sensor according to claim 2, further including:

(a) a fixed support to which said mounting frame is rigidly attached;

(b) a first, second, and third reference axes located to form an orthogonal set intersecting said center of gravity of said inertia-member, and said counter-inertia;

wherein

(c) said first, and said second reference axes are located in said plane;

(d) said inertia-member is formed to align the principal axes of symmetry of said inertia-member along said first, second and third reference axes;

(e) said counter-inertia is formed to align the principal axes of symmetry of said counter-inertia along said first, second and third reference axes; and

(f) said angular dither motion of said inertia-member is directed about said third reference axis.

4. A Coriolis gyro sensor according to claim 3, wherein:

(a) said first suspension means is formed to impart said inertia-member with a first rotational resonant frequency about said third reference axis; and

(b) said second suspension means is formed to impart said counter-inertia with a second rotational resonant frequency about said third reference axis;

wherein

(c) the polar inertia of said counter-inertia about said third reference axis is substantially larger than the polar inertia of said inertia-member about said third reference axis.

5. A Coriolis gyro sensor according to claim 4, wherein:

said inertia-member, said counter-inertia, said first suspension means, said second suspension means, and said mounting frame are formed from a unitary material selected from a group of low loss materials that include single crystal silicon, single crystal quartz, and fused silica.

6. A Coriolis gyro sensor according to claim 5, wherein:

(a) said fixed support is shaped to form a substantially uniform gap between said inertia-member and said fixed support, and between said counter-inertia and said fixed support;

(b) said restraining means comprise electrostatic electrodes attached to said fixed support, proximate said inertia-member, and a gas of predetermined pressure and composition; and

wherein

(c) said pressure and said composition of said gas is selected to cause substantial damping forces of said inertia-member and said counter-inertia for motions perpendicular to said plane, and negligible damping forces for motions parallel to said plane.

7. A Coriolis gyro sensor according to claim 6, wherein:

(a) said sensing means comprise electrostatic electrodes attached to said fixed support, proximate said inertia-member; and

(b) said sensing means comprise a signal representative of said angular dither motion of said inertia-member about said third reference axis.

8. A Coriolis gyro sensor according to claim 7, wherein:

said driving means to drive said inertia-member in an angular dither motion about said third reference axis comprise electrostatic electrodes rigidly attached to said fixed support, proximate said inertia-member.

9. A Coriolis gyro sensor according to claim 3, wherein:

(a) said first suspension means comprise a first set of multiple elastic beams;

(b) said second suspension means comprise a second set of multiple elastic beams;

(c) said first set of multiple elastic beams are formed to locate the longitudinal axes of said first set of multiple elastic beams to intersect said center of gravity of said inertia-member; and

(d) said second set of multiple elastic beams are formed to locate the longitudinal axes of said second set of multiple elastic beams to intersect said center of gravity of said counter-inertia.

10. A Coriolis gyro sensor according to claim 9, wherein:

(a) said inertia-member is formed to have substantially equal moments of inertia about said first axis and about said second axis; and

(b) said first set of multiple elastic beams are formed to provide substantially equal rotational resonant frequencies of said inertia-member about said first, second and third axis;

wherein

(c) a dual input-axis Coriolis gyro sensor is formed.

11. A Coriolis gyro sensor according to claim 10, wherein:

(a) said first set of multiple elastic beams comprise four elastic beams arranged in a cruciform orientation; and

(b) said second set of multiple elastic beams comprise four elastic beams arranged in a cruciform orientation.

12. A Coriolis gyro sensor according to claim 9, wherein:

(a) said inertia-member and said first set of multiple elastic beams are formed to provide substantially equal rotational resonant frequencies about said first axis and about said third axis; and

(b) said inertia-member and said first set of multiple elastic beams are formed to provide a rotational resonant frequency about said second axis that is substantially different than the rotational resonant frequency of said inertia-member about said first axis;

wherein

(c) a single input-axis Coriolis gyro sensor is formed.

13. A Coriolis gyro sensor according to claim 12, wherein:

(a) said first set of multiple elastic beams comprise two collinear elastic beams; and

(b) said second set of multiple elastic beams comprise four elastic beams arranged in a cruciform orientation.

14. A Coriolis gyro sensor according to claim 9, wherein:

said second set of multiple elastic beams is formed to impart high stiffness for linear displacement of said counter-inertia along said third axis, and low stiffness for angular displacement of said counter-inertia about said third axis.

15. A single or dual input-axis Coriolis gyro sensor comprising:

(a) an inertia-member attached to a counter-inertia by a first flexible connecting means;

(b) a second flexible connecting means attaching said counter-inertia to a fixed frame;

(c) a driving means to impart a predetermined angular oscillation to said inertia-member;

where

(d) said predetermined angular oscillation of said inertia-member generates a polar angular oscillating torque;

(e) said first flexible connecting means transfer said polar angular oscillating torque to said counter-inertia; and

where

(f) said polar angular oscillating torque is balanced by said counter-inertia;

(g) a damping means generating restraining forces acting on said inertia-member;

wherein

(h) said forces from said damping means are representative of input rate rotation.