Vibratory linear acceleration and angular rate sensing system

• US 4,930,351 A
• Filed: 03/24/1988
• Issued: 06/05/1990
• Est. Priority Date: 03/24/1988
• Status: Expired due to Term

• Current Assignee: David F. Macy, Dennis O. Freund, Evert C. Alsenz, Paul W. Becker, William F. Juptner
• Original Assignee: WJM Corporation
• Inventors: Alsenz, Evert C., Macy, David F.
• Primary Examiner(s): Chapman, John
• Application Number:
  US07/172,380
• Time in Patent Office: 803 Days
• Field of Search: 73/505, 73/510, 73/517 R, 73/517 AV
• US Class Current: 73/504.04
• 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

An inertial sensing system includes a geometric structure having several independent mechanically resonant modes of vibration such that when the structure is subjected to outside inertial motions that are to be sensed, a driven mode of vibration will couple energy in a specific manner into a pickup mode. The driven mode serves as a reference motion. The system measures angular rotation rate by sensing the vibrations in the pickup mode caused by the action of the Coriolis effect on the balanced driven mode which couples energy into the pickup mode. The system includes a portion of the geometric structure that is subject to strain caused by linear acceleration in one direction. The strain introduces an imbalance in the driven mode which causes energy to be coupled to the pickup mode of vibration in a nominally linear manner. A sensing circuit is provided to sense the amount of energy coupled into the pickup system as a measure of applied angular rotation and applied acceleration. The coupling of energy into the pickup caused by linear acceleration is orthogonal to the coupling of energy caused by angular rotation rate, and the effects of the two sources of coupled energy can be separated by the system circuitry such that independent determination of the two types of input motion is realized. The sensing system is preferably made of a material such as crystalline quartz that is mechanically stable and is also piezoelectric so that the driving and sensing can be accomplished by piezoelectric techniques.

Claims

1. An apparatus for sensing acceleration, comprising:

a tuning fork formed from a single crystal of piezoelectric material, said tuning fork comprising;

first and second drive tines disposed in a common plane, said first and second drive tines having free first ends and commonly mounted second ends, said tuning fork including drive electrodes disposed on surfaces of said first and second drive tines, said first and second drive tine responsive to a periodic voltage applied to said drive electrodes to cause said free first ends of said first and second drive tines to vibrate in said common plane, said first tine including an intermediate portion proximate to said free first end of said first tine, said intermediate portion having increased flexibility in first and second directions perpendicular to said common plane, said increased flexibility causing said free second end of said first tine to deflect in said first direction when said tuning fork is subjected to acceleration in said second direction thereby causing said free second end of said first tine to vibrate in a plane parallel to said common plane and causing a torsional effect on said second ends of said first and second tines, said torsional effect synchronized with said vibrations of said first and second tines;

first and second sensing tines, commonly mounted with said first and second drive tines, said first and second sensing tines having sensing electrodes disposed on surfaces thereof, said first and second sensing tines responsive to said torsional effect to vibrate in said first and second directions, the vibration of said first and second sensing tines generating voltage gradients within said first and second sensing tines detectable by said sensing electrodes, said voltage gradients varying in time and having phases and magnitudes responsive to the magnitude and direction of said acceleration.

2. The apparatus for sensing acceleration as defined in claim 1, wherein said tuning fork has a resonant frequency, said apparatus further including means for generating said periodic voltage at said resonant frequency.

3. The apparatus for sensing acceleration as defined in claim 1, further including a sensing circuit electrically connected to said sensing electrodes, said sensing circuit responsive to said voltage gradients within said first and second sensing tines to generate a sensing circuit output signal having a magnitude proportional to the acceleration of said tuning fork in said second direction.

4. The apparatus for sensing acceleration as defined in claim 1, wherein said first and second drive tines are symmetrically disposed about an axis in said common plane, and wherein said first and second drive tines are responsive to a component of angular rotation about said axis to cause an additional torsional effect on said second ends of said first and second tines, said additional torsional effect also synchronized with said vibrations of said first and second tines, said additional torsional effect being out of phase with said torsional effect caused by said acceleration and distinguishable therefrom, said additional torsional effect also causing vibration in said first and second tines.

5. The apparatus for sensing acceleration as defined in claim 4, further including a sensing circuit electrically connected to said sensing electrodes, said sensing circuit responsive to said voltage gradients within said first and second sensing tines to generate a first sensing circuit output signal having a magnitude representing the acceleration of said tuning fork in said second direction and to generate a second sensing circuit output signal having a magnitude representing the component of angular rotation about said axis.

6. The apparatus for sensing acceleration as defined in claim 5, wherein said voltage gradients within said first and second sensing tines include first components responsive to said torsional effect caused by said acceleration and second components caused by said additional torsional effect caused by said component of angular rotation.

7. The apparatus for sensing acceleration as defined in claim 6, wherein said sensing circuit includes first and second synchronous demodulators, said first and second synchronous demodulators electrically connected to receive an input signal responsive to said voltage gradients in said first and second sensing tines, said first synchronous demodulator driven by a reference signal having a first phase relationship to the vibration of said first and second drive tines, said second synchronous demodulator having a second phase relationship to the vibration of said first and second tines, said first and second phase relationships being 90 degrees out of phase with each other, said first synchronous demodulator providing a first demodulator output signal responsive to said acceleration, said second synchronous demodulator providing a second demodulator output signal responsive to said component of angular rotation.

8. An apparatus for sensing acceleration, comprising:

a common base;

a first vibrating element connected to said common base that vibrates in a first plane;

a second vibrating element that vibrates in said first plane, said second vibrating element having an end portion supported by an intermediate portion, said intermediate portion having enhanced flexibility in directions perpendicular to said first plane, and said end portion responsive to a component of acceleration in one of said perpendicular directions to cause said end portion to vibrate in a second plan parallel to said first vibration plane thereby causing a torsional effect at said common base;

a first sensing element connected to said common base, said first sensing element vibrating in a third plane, perpendicular to said first plane in response to said torsional effect at said base, said first sensing element including sensing electrodes for sensing an electrical effect induced in said first sensing element when said first sensing element is vibrating in said third plane; and

a sensing circuit connected to said sensing electrodes that receives said sensed electrical effect and that generates an output signal having a magnitude representing said component of acceleration.

9. A system for measuring acceleration, comprising:

first vibrating means having plural elements;

means for driving said first vibrating means so that said elements of said first vibrating means vibrate in a balanced vibration mode in the absence of acceleration;

means responsive to acceleration for causing said elements of said first vibrating means to vibrate in an unbalanced vibration mode in the presence of acceleration;

second vibrating means coupled to receive energy from said first vibrating means for vibrating in a sensing vibration mode when said first vibrating means vibrates in said unbalanced vibration mode, said sensing vibration mode having an amplitude and a phase responsive to said unbalanced vibration mode of said first vibrating means caused by acceleration; and

means coupled to said second vibrating means for sensing vibration in said sensing vibration mode and for providing an output signal responsive to said vibration in said sensing vibration mode, said output signal having an amplitude and a phase responsive to said amplitude and said phase of said sensing vibration mode.

10. A system for sensing acceleration, comprising:

first and second vibrating elements that vibrate in a balanced mode in a common plane in the absence of acceleration;

means for causing said first vibrating element to vibrate in a plane different from said second vibrating element in the presence of acceleration to cause said first and second vibrating elements to vibrate in an unbalanced mode;

sensing means;

means for coupling energy from said first and second vibrating elements to said sensing means when said first and second vibrating elements vibrate in said unbalanced mode; and

means for detecting said energy coupled to said sensing means and for providing an output signal responsive to said input acceleration.