Vibratory angular rate sensing system

Abstract

.[.A vibratory angular rate sensing system may have one pair of tines forming an angle of about 60 degrees, resulting from the crystalline orientation of the Z-cut quartz wafer of the system. In one configuration each of the tines is provided with a mass offset from the axis of the associated tine, a pivot extends through the plane of symmery of the tines and may be connected to a dummy reaction mass. The resonant system is suspended from a mounting frame by a pair of suspension bridges. A second embodiment of the invention features two groups of tines, each group including two pairs of tines arranged in the form of a cross. Again, an offset mass is associated with the free end of each tine and each group of tines is secured to its frame by a suspension bridge..]..Iadd.Vibratory angular rate sensing system having a support structure and a driven fork lying in a plane and having an axis of symmetry. The fork has first and second spaced apart tines. A mouting is provided for mounting said fork on said support structure. Energy is coupled into the driven fork to cause vibratory motion of the tines of the driven fork in the plane of the driven fork. A torsionally resonant member is coupled to the fork. A pickoff is provided which is isolated from the support structure for sensing motion of the torsionally resonant member to provide a measure of the input angular rate about the axis of symmetry of the driven fork. .Iaddend.

What is claimed is: 
     
       1. A vibratory angular rate sensing system comprising: (a) a wafer of crystalline quartz having piezoelectric properties and forming a .[.substantially rectangular.]. mounting .[.frame and having a substantially rectangular central opening.].;   (b) a .Iadd.fork having a .Iaddend.pair of tines extending at a predetermined acute angle .[.within said opening.]. .Iadd.from an origin and having an axis of symmetry.Iaddend.;   (c) .Iadd.and .Iaddend.a base interconnecting said tines near their origin;   (d) .[.a first and a second suspension bridge, each being secured at its ends to.]. .Iadd.bridge means supporting said fork on .Iaddend.said mounting .[.frame.].;   (e) a .[.pivot.]. .Iadd.torsion member .Iaddend.extending .[.between.]. .Iadd.along .Iaddend.the axis of symmetry of said .[.tines.]. .Iadd.fork .Iaddend.and through said base.[., said pivot.]. .Iadd.and .Iaddend.being secured .[.near both ends by said suspension bridges.]. .Iadd.to said bridge means for forming bridges.Iaddend.;   (f) a reaction mass secured to said .[.pivot at its end extending beyond the wide opening of said tines.]. .Iadd.torsion member.Iaddend.;   (g) a pair of masses, each being secured to the free end of one of said tines, said tines having large fundamental and small harmonic thrust components, .[.and.]. said pair of masses being each disposed with the center of mass offset from the axis of the associated tine.[.,.]. whereby the centers of each mass move in arcs having substantially no thrust component;   (h) means .[.including a first pair of electrodes secured to said tines.]. for driving said .Iadd.fork to cause said .Iaddend.tines .Iadd.to vibrate .Iaddend.substantially at their resonant frequency .[.determined by said pair of masses, said tines and said base.].; and   (i) .[.a second pair of electrodes secured.]. .Iadd.means coupled .Iaddend.to said .[.pivot.]. .Iadd.torsion member .Iaddend.for picking up an output signal representative of torsion which produces a shear strain resulting in an amplitude variation of .[.the.]. .Iadd.an .Iaddend.electric field.   
     
     
       2. A system as defined in claim 1 wherein said reaction mass has substantially the same moment of inertia as do said masses, said base and said tines, combined. 
     
     
       3. A system as defined in claim 1 wherein said water is of a Z-cut quartz plate and the angle between said tines is substantially 60 degrees. 
     
     
       4. A system as defined in claim 3 wherein said .[.second pair of electrodes.]. .Iadd.means coupled to said torsion member .Iaddend.picks up a reciprocating change of amplitude proportional to the torsional strain and hence to the Coriolis torque acting on said system. 
     
     
       5. A system as defined in claim 1 wherein said .[.bridges have.]. .Iadd.bridge means has .Iaddend.a flexural and torsional stiffness which is small compared to that of said tines and of said .[.pivot.]. .Iadd.torsion member.Iaddend.. 
     
     
       6. A vibratory angular rate sensing system comprising: (a) a wafer of crystalline quartz having piezoelectric properties and forming a substantially rectangular mounting frame having a substantially rectangular central opening;   (b) a first group of two pairs of tines, each pair of tines forming the same predetermined angle between each other as does the other pair, to provide substantially a configuration of a first cross;   (c) a second group of two pairs of tines arranged in the form of a cross and substantially like said first group and with substantially the same angles between each pair of tines of said second group, said two groups being disposed within said opening of said frame and along the long sides of said mounting frame;   (d) a first two pairs of masses, each being secured to the free ends of said tines of said first group and a second two pairs of masses, each being secured to the free ends of said tines of said second group, said masses being each disposed with the center of mass offset from the axis of the associated tine;   (e) a pivot passing through the axis of symmetry of said tines and passing through the centers of said groups;   (f) a pair of suspension bridges, each extending between said frame and supporting one group of tines at the center thereof and passing through an associated one of said group of tines;   (g) means including two pairs of electrodes secured to said groups of tines for driving each pair of tines of a group out of phase with respect to each other; and   (h) means including a further pair of electrodes for picking up an output signal from said pivot.   
     
     
       7. A system as defined in claim 6 wherein said wafer is of a Z-cut quartz plate and the angle between said pairs of tines is substantially 60 degrees. 
     
     
       8. A system as defined in claim 6 wherein said means for driving generates a wave at a frequency substantially equal to the resonant frequency determined by said masses and said tines, the wave applied to said first group of tines being out of phase with respect to that applied to said second group of tines, whereby the thrust component on said two pairs of tines of each group are equal and opposite, thereby substantially cancelling any force which might otherwise react on said frame. 
     
     
       9. A system as defined in claim 6 wherein said bridges have a flexural and torsional stiffness which is small compared to that of said tines and of said pivot. .Iadd. 
     
     
       10.  In a vibratory angular rate sensing system, a wafer of crystalline quartz having piezoelectric properties and providing a mounting, a fork having a pair of tines extending at a predetermined acute angle from an origin about an axis of symmetry and having a base interconnecting the pair of tines near their origin, means for forming a bridge supporting and isolating said fork on said mounting, a torsion member extending along the axis of symmetry of said fork and being secured to the bridge means, a reaction mass secured to said torsion member, means for driving said fork to cause said tines to vibrate substantially at their resonant frequency and sensing means isolated from the mounting for sensing the vibratory motion of the reaction mass to provide a measure of the input rate about the axis of symmetry of said fork. .Iaddend..Iadd. 
     
     
       11.  A system as in claim 10 wherein said sensing means is isolated from the mounting by the bridge means. .Iaddend..Iadd.12. In a vibratory angular rate sensing system, a support structure, a driven fork lying in a plane and having an axis of symmetry, said driven fork having first and second tines having at least their outer extremities spaced apart, a torsion member having first and second ends with the first end being secured to the fork and with the torsion member extending between the first and second tines, a mass secured to the second end of torsion member, said driven fork, said torsion member and said mass forming a single unitary rotatable structure to effect an interdependency between the driven fork, the torsion member and the mass, connecting means connecting said rotatable structure to said support structure, means coupling energy into said driven fork to cause vibratory motion of the tines of the said driven fork in the plane of said driven fork, said connecting means including means for isolating said rotatable structure from said support structure so that minimal disturbance is transferred from the support structure to said rotatable structure, and pickoff means mounted on the torsion member and being substantially independent of vibratory motion of the support structure for sensing torsional oscillatory motion with respect to the driven fork to provide a measure of the input angular rate to the support structure about said axis of symmetry of said driven fork so that vibratory motion of the support structure is of minimal significance in the measurement of the input 
     
     
        angular rate. .Iaddend..Iadd.13.  A system as in claim 12 wherein said 
     
     
        connecting means is in the form of bridges. .Iaddend..Iadd.14.  A system as in claim 12 wherein said torsion member extends along the axis of 
     
     
        symmetry. .Iaddend..Iadd.15.  A system as in claim 12 together with an additional mass carried by the free end of each of the tines of the driven 
     
     
        fork. .Iaddend..Iadd.16.  A system as in claim 12 wherein said tines of said driven fork extend at an acute angle with respect to each other. .Iaddend..Iadd.17. A system as in claim 14 wherein said connecting means is secured to said rotational structure at two spaced apart points. .Iaddend..Iadd.18. A system as in claim 17 wherein said connecting means is in the form of first and second bridge members. .Iaddend..Iadd.19. A system as in claim 18 wherein the mass secured to the torsion member is beyond the outer extremities of the tines of the driven fork. .Iaddend..Iadd.20. A system as in claim 12 wherein said support structure, said connecting means and said rotatable structure are formed of a piezoelectric material. .Iaddend..Iadd.21. In a method for sensing angular rate by the use of a support structure and a single unitary rotatable structure connected to the support structure with the rotatable structure comprising a driven fork having a major axis of symmetry, a torsion member, the steps of substantially isolating the rotatable structure from the support structure so that minimal disturbance is transferred from the support structure to the rotatable structure with respect to relative motion between the support structure and the rotatable structure, supplying energy to the driven fork to cause vibratory motion of the driven fork in a plane of the driven fork and sensing on the torsion member the torsional oscillatory motion of the torsion member with respect to the driven fork with minimal input from the vibratory motion of the support structure to provide a measure of the input angular rate about the major axis of symmetry of the driven fork. .Iaddend.