Measuring and testing – Dynamometers – Responsive to torque
Patent
1995-06-05
1997-04-15
Williams, Hezron E.
Measuring and testing
Dynamometers
Responsive to torque
73862332, 32420716, 32420725, G01B 730
Patent
active
056211791
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a rotary transducer and is more particularly, but not exclusively, concerned with a rotary variable transducer, especially a rotary variable differential transducer.
It has been previously proposed to provide a rotary variable differential transducer having a body in which a primary and two secondary coils are wound on respective portions of a stator, such portions being equally-angularly spaced about the axis of rotation of a rotor mounted on a shaft in a plane perpendicular to the shaft. Each such stator portion extends over the same length of the rotor and carries an arcuate pole piece which is disposed close to the peripheral surface of the rotor. The rotor has an asymmetric pole piece which is arranged relative to the stator pole pieces associated with the primary coil and the secondary coils such that, upon angular movement of the shaft about its axis of rotation, the inductive coupling between the primary coil and one of the secondary coils increases whilst there is a corresponding decrease in the inductive coupling between the primary coil and the other of the secondary coils. The electrical output signals from the secondary coils can then be compared to give an indication of the angular position of the shaft relative to the body. Such a construction of transducer is relatively complicated to manufacture and can be difficult to assemble. Additionally, it does not have a particularly compact construction and the effective angular range is limited to .+-.60.degree. max approx. The linearity of signal output is dependent on the eddy current effects in the pole pieces. Use of solid magnetic pole pieces is desirable for constructional simplicity but eddy currents cannot be ignored in these. While eddy currents can be minimised by constructing the poles from thin laminations, their use makes assembly difficult and mechanical accuracy poor.
GB-A-2231161 discloses a rotary position transducer having a fixed primary coil which is substantially coaxial with a rotor shaft, and two fixed secondary coils symmetrically disposed on opposite sides of the primary coil axis with their common axis at right angles to that of the primary coil. The rotor shaft carries an asymmetrical rotor which provides inductive coupling between the primary coil and each of the secondary coils. The asymmetry causes the combined output of the secondary coils to vary, possibly linearly, with the angular position of the rotor. With such a construction it is also relatively difficult to achieve consistent results in manufacture and signal output is low due to poor magnetic coupling through the relatively large air gap between the rotor and the stator pole pieces. The linear range is also limited to about .+-.45.degree. to .+-.60.degree..
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved rotary transducer which can be capable of operating over a large angular range of up to .+-.90.degree. and which can be of compact construction, easy to manufacture and efficient in operation.
According to the present invention, there is provided a rotary transducer comprising a first electrical coil, an electrical output, and an inductive coupling which inductively couples said electrical output with the first electrical coil and which includes a rotor rotatable about an axis relative to said first electrical coil so that, in use, the electrical output varies in dependence upon the angular position of said rotor about said axis, wherein the first electrical coil comprises first and second coil regions which are mutually displaced axially of the rotor, and wherein the rotor has first and second formations thereon which are mutually axially displaced and which are respectively inductively associated with the first and second coil regions of the first electrical coil.
In the rotary transducer according to the present invention, the arrangement is such that, in use, as the rotor is rotated, the strengths of the magnetic fluxes in magnetic circuits associated with
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Moller Richard A.
Penny & Giles Blackwood Limited
Williams Hezron E.
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