Torque measuring apparatus and method employing a crystal oscillator
First Claim
1. An apparatus for measuring torque in a torsion member, that apparatus comprising:
- a transducer adapted to be attached to the torsion member and having a first resonant frequency which changes with variation of strain in the torsion member;
a transducer oscillator connected to the transducer and producing a first signal having a first frequency that is a function of the first resonant frequency;
a reference element having a second resonant frequency that is unaffected by variation of strain in the torsion member;
a reference oscillator connected to the reference element and producing a second signal having a second frequency that is a function of the second resonant frequency; and
a mixer connected to the transducer oscillator and to the reference oscillator to heterodyne the first signal and second signal thereby producing a resultant signal having a frequency which corresponds to torque applied to in the torsion member.
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Accused Products
Abstract
Torque in a torsion member, such as a rotating shaft, is sensed by a piezoelectric element that is attached to the torsion member. The piezoelectric element has a resonant frequency that varies with changes in the torque and is part of a transducer oscillator that produces a first signal. A reference oscillator has a similar piezoelectric element and produces a second signal having a frequency that varies in response to environmental parameters. The first and second signals are heterodyned, thereby cancelling the effects due to environmental parameters acting on both piezoelectric elements and producing a resultant signal that has a frequency which corresponds to the torque applied to the torsion member.
11 Citations
19 Claims
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1. An apparatus for measuring torque in a torsion member, that apparatus comprising:
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a transducer adapted to be attached to the torsion member and having a first resonant frequency which changes with variation of strain in the torsion member;
a transducer oscillator connected to the transducer and producing a first signal having a first frequency that is a function of the first resonant frequency;
a reference element having a second resonant frequency that is unaffected by variation of strain in the torsion member;
a reference oscillator connected to the reference element and producing a second signal having a second frequency that is a function of the second resonant frequency; and
a mixer connected to the transducer oscillator and to the reference oscillator to heterodyne the first signal and second signal thereby producing a resultant signal having a frequency which corresponds to torque applied to in the torsion member. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
a plurality of disks attached to the torsion member in a spaced apart manner, each disk having a first major surface with a first electrically conductive region and a second major surface with a second electrically conductive region major surface connected to the first electrically conductive region; and
a plurality of stationary plates interleaved with the plurality of disks, and each stationary plate having two major surfaces and an electrical conductor on each major surface.
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13. The apparatus as recited in claim 12 wherein the first and second electrically conductive regions on each of the plurality of disks and the electrical conductor on the major surfaces of each plurality of stationary plates being covered by a coating of electrically insulating material.
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14. The apparatus as recited in claim 1 further comprising:
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a triaxial cable having a center conductor coupling the transducer to the transducer oscillator, an inner shield around the center conductor, and an outer shield around the inner shield and coupling the transducer to the transducer oscillator; and
an amplifier having an input coupled to the center conductor and having an output connected to the inner shield.
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15. A method for measuring torque in a torsion member, that method comprising:
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attaching a transducer to the torsion member wherein the transducer has a first resonant frequency which varies with variation of strain in the torsion member;
exciting the transducer as part of a transducer oscillator to produce a first signal having a first frequency that is a function of the first resonant frequency;
driving a reference oscillator to produce a second signal having a second frequency that is unaffected by variation of strain in the torsion member; and
a heterodyning the first signal and second signal thereby producing a resultant signal having a frequency that indicates the torque in the torsion member. - View Dependent Claims (16, 17, 18, 19)
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Specification