Vibratory angular rate sensor system

Abstract

A vibratory angular rate sensor system preferably consists of a Z-cut quartz plate forming a mounting frame with a rectangular opening. Within the opening are mounted two pairs of tines. Each pair of tines is parallel to each other, one pair forming the drive tines and the other pair the output tines. Each corresponding set of two tines is disposed along the same axis having a common stem or base. The tines are secured by four bridges integral with the frame and connected to the stem. The arrangement is such that the pair of input tines vibrates in opposition to each other, while the pair of output tines vibrates with one tine going up while the other moves downwardly. As a result, the angular rate sensors drive frequency and the structural torque frequency are unequal. Therefore large displacements of the stem are unnecessary. An angular rate sensor having a support structure and first and second forks each lying in a plane each having an axis of symmetry with each fork having first and second spaced apart tines. The first and second forks are mechanically coupled to each other to provide a dual fork structure. A mount is provided for mounting the dual fork structure on the support structure. Energy is coupled into the first fork of the dual fork structure to cause vibratory motion of the tines of that fork in the plane of the fork. vibratory motion of the tines of the other fork in a direction normal to the plane of the other fork is sensed to provide a angular rate about the measure axis of symmetry of the first fork. The mounting serves to isolate the dual fork structure from the support structure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

36 in FIG. 1. The rotation in the X-Y plane may be caused by the angular motion of the vehicle carrying the system. As a result, the stem 16 is twisted due to the Coriolis force which acts normal to the plane of vibration of tines 12 and 13. This, in turn, causes an up-and-down motion of the output thines 14, 15 in opposition directions.

It should be noted that the Y-Z flexural frequency is higher than the X-Y flexural frequency. Stated another way, a torque is felt by the stem 16. This, in turn, initiates or drives an Y-Z flexure in output tines 14, 15. This is so because the frequency is substantially similar to that of the tuning fork consisting of tines 12, 13. The X-Y flexure in tines 12 and 13 is piezoelectrically driven by the input electrodes 20 to 23 of FIG. 3. On the other hand, the Y-Z flexure caused by a rotation about the axis Y in tines 14, 15 is picked up piezoelectrically by the output electrodes 26 to 30 of FIG. 5.

The bridges 17, 18 have an X-Z flexural frequency which is substantially that of the flexural frequency of the tines 12, 13.

The electrodes and shielding connections for the input and output circuits are preferably made from the bridges 17, 18. It should be noted that the frequency and balance of the two pairs of tines 12, 13 and 14, 15 are adjusted by adding or removing material, such as a gold film, at the free ends of the tines on the appropriate sides. This may be effected by chemical etching or by a laser beam.

The rate sensors of the prior art depend on the flexural frequency of the drive tines being substantially the same as the torsional frequency of the entire system. According to the present invention, the drive frequency of the angular rate sensor and the structural torisonal frequency are not the same. Therefore, large displacements of the stem 16 are not necessary. The displacement of the stem 16 is extremely small relative to that of the pickup or output tines 14, 15. This is due to the Q multiplication of the displacement of the tines with respect to the entire structure. It will now be understood that the vibration of the angular rate sensor is easily isolated from the mounting frame 10 and hence from the environment.

Claims

1. A vibratory angular rate sensor system comprising:

(a) a mounting, frame of substantially rectangular configuration having a substantially rectangular opening said frame mounting consisting of a piezoelectric material of Z-cut crystalline quartz;

(b) a first pair and a second pair of tines forming a tine structure, disposed in said opening said first pair forming vibrating drive tines, vibrating toward and away from each other in a plane of motion and said second pair of tines forming vibrating output tines, vibrating in directions perpendicular to said plane of motion opposite directions up and down;

(c) a stem interconnecting means interconnecting said first and second pair pairs of tines to effect an interdependency between the first and second pairs of tines whereby motion in one pair of tines is transferred to the other pair of tines, the tines of each pair being disposed parallel to each other and corresponding tines of both pairs each pair being disposed along a common axis;

(d) means including two pairs of input electrodes in contact with the first pair of tines for exciting said tines substantially at the resonant frequency thereof, said input electrodes being in the X-Y and Y-Z planes of said wafer;

(e) means including two pairs of output electrodes disposed in contact with the second pair of tines in the Y-Z plane for deriving an output signal representative of the angular rate experienced by said system, the flexural resonant frequency of said first pair of tines being lower than different from that of said second pair of tines and

(f) a plurality of bridges, bridge means integral with said frame mounting and connected to said stem means interconnecting said first and second pairs of tines for supporting said first and second pairs of tines on said mounting.

2. A system as defined in claim 1 wherein the flexural frequency stiffness of said bridges is substantially equal to the flexual frequency of said tines bridge means isolates vibration of the tine structure from the mounting.

3. A system as defined in claim 2 wherein the bridge means in combination with the tine structure has a resonant frequency which is substantially equal to the resonant frequency of the first pair of tines. 4. A system as defined in claim 1 wherein the interconnecting means is positioned relative to the first and second pairs of tines so that the interconnecting means has an extremely small displacement relative to the

first and second tines. 5. A system as defined in claim 4 wherein said bridge means is disposed intermediate the first and second pairs of tines. 6. A system as defined in claim 1 wherein the resonant frequency of said first pair of tines is lower than that of

the second pair of tines. 7. An angular rate sensor comprising a support structure, first and second forks each lying in a plane and each having an axis of symmetry, each fork having first and second spaced apart tines, means mechanically coupling the first and second forks to each other to provide a dual fork structure to effect an interdependency between the first and second forks whereby motion in one fork is transferred to the other fork, mounting means including isolation means for mounting the dual fork structure on the support structure, means for coupling energy into said first fork of the dual fork structure to cause vibratory motion of the tines of said first fork in the plane of said first fork to provide a drive fork, said isolation means serving to isolate said vibratory motion of the dual fork structure from vibratory motion of the support structure, and means for sensing vibratory motion of the tines of said second fork independent of relative motion between the support structure and the dual fork structure in a direction normal to the plane of said second fork to provide a sense fork separate from the drive fork to give a measure of the input angular rate applied to the dual fork structure about the major axis of symmetry of said first fork. 8. A rate sensor as in claim 7 wherein the resonant frequency of said vibratory motion of the tines of said drive fork is different from the resonant frequency of said vibratory motion of the tines of said sense

fork. 9. A rate sensor as in claim 7 wherein said dual

fork structure is formed of a piezoelectric material. 10. A rate sensor as in claim 9 wherein said mounting means is formed of a piezoelectric material. 11. A rate sensor as in claim 7 wherein said dual fork structure and said mounting means are formed of a single sheet of single crystal piezoelectric material. 12. A rate sensor as in claim 7 wherein said mounting means supports the dual fork structure in a region intermediate the first and second forks. 13. A rate sensor as in claim 12 wherein said mounting means in combination with the dual fork structure has a resonant frequency which is substantially the same frequency as said vibratory motion of the

tines of the first fork. 14. A rate sensor as in claim 7 wherein the first and second forks have a common axis of symmetry. 15. A rate sensor as in claim 14 wherein the first and second forks lie in a common plane. 16. A rate sensor as in claim 7 wherein at least a portion of the mounting means is constructed so that it has an extremely small displacement relative to the displacement of the first and second forks.