Vibratory angular rate sensing system

• US 4,538,461 A
• Filed: 01/23/1984
• Issued: 09/03/1985
• Est. Priority Date: 01/23/1984
• Status: Expired due to Term

• Current Assignee: Piezoelectric Technology Investors
• Original Assignee: Piezoelectric Technology Investors
• Inventors: Macy, David F., Staudte, Juergen H., Juptner, William F.
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): Chapman, Jr., John E.
• Application Number:
  US06/572,782
• Time in Patent Office: 589 Days
• Field of Search: 73/505, 310/329, 310/333, 310/370
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719

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 symmetry 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.

Claims

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 pair of tines extending at a predetermined acute angle within said opening;

(c) a base interconnecting said tines near their origin;

(d) a first and a second suspension bridge, each being secured at its ends to said mounting frame;

(e) a pivot extending between the axis of symmetry of said tines and through said base, said pivot being secured near both ends by said suspension bridges;

(f) a reaction mass secured to said pivot at its end extending beyond the wide opening of said tines;

(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 tines substantially at their resonant frequency determined by said pair of masses, said tines and said base; and

(i) a second pair of electrodes secured to said pivot for picking up an output signal representative of torsion which produces a shear strain resulting in an amplitude variation of the 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 wafer 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 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 a flexural and torsional stiffness which is small compared to that of said tines and of said pivot.

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.