Electricity: measuring and testing – Magnetic – Displacement
Patent
1994-05-05
1997-06-10
O'Shea, Sandra L.
Electricity: measuring and testing
Magnetic
Displacement
32420725, 336 79, G01B 714, G01B 730
Patent
active
056379978
DESCRIPTION:
BRIEF SUMMARY
This application is a continuation of International application Ser. No. PCT/BG92/02034, filed on Nov. 4, 1992.
TECHNICAL FIELD
This invention relates to devices comprising angular displacement sensors.
BACKGROUND ART
Inductive brushless angle sensing principles are described in our patent specifications WO88/06716 and WO90/04152. The present invention concerns their adaptation to provide angle sensing means suitable for use within a device such as a torque motor or vehicle throttle actuator, preferably requiring little or no extension to the housings of such mechanisms.
There are many applications in motion control systems in which shaft angle must be accurately measured and electrically transmitted. Embodiments of the invention may enable one to achieve this with utmost economy in manufacturing cost and space envelope.
DISCLOSURE OF THE INVENTION
The invention provides an angular displacement sensor, particularly for a restricted angular range (which generally means substantially less than 360.degree., and usually 180.degree. or less, particularly 120.degree. or less. The sensor comprises first and second relatively rotatable components. (These will generally be a rotor for coupling to a rotatable element of a device such as a shaft, and a stator for coupling to a housing of the device). These components confront one another axially. One provides a plurality of axially extending poles arranged around at least part of a circle, suitably provided by an annular projection having gaps dividing it into discrete poles. Some (only) of the poles bear winding coils. Preferably a ferromagnetic element is axially adjacent the poles. In one type of embodiment it is shaped to overly only some of the poles and is provided by the second relatively rotatable component. In a second type of embodiment the ferromagnetic element (if present) may be fixed relative to the first component but, interposed between the element and the first component there is a screening element of non-magnetic conducting material which is rotatable relative to the first component and is shaped to overlie only some of the poles. In a further embodiment, the rotatable element may comprise a combination of ferromagnetic coupling and non-magnetic screening materials. In all cases, relative rotation leads to variation in inductance of the individual poles. By applying alternating voltages across them and detecting voltage drops, one can derive electrical output data related to angular displacement. The data can be processed and the results displayed in ways that will be apparent to the skilled reader.
The axial construction enables simple, compact sensors to be produced, highly suitable for incorporation in rotary devices such as automotive throttle position sensors and torque motors. In another aspect the invention provides a rotary device having a housing, a rotatable shaft extending within the housing, and an angular displacement sensor of the above type mounted at least partly within the housing, with one of said relatively rotatable components rotationally coupled to the shaft.
The poles may be connected as a homopolar or heteropolar array.
Some embodiments of the invention will now be described with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-D shows a first embodiment mounted to a rotary device such as an actuator: FIG. 1A is an axial section; FIG. 1B is a view of the stator of the sensor showing the poles and their windings; FIG. 1C is a section on X--X in FIG. 1A; and FIG. 1D is a schematic representation of the sensor;
FIG. 2 is a graph showing the relationship between the angular position of a rotor of a sensor and an output voltage for an embodiment such as that of FIG. 1;
FIGS. 3A to 3G illustrate a second embodiment of sensor, FIGS. 3A and 3B being views equivalent to FIGS. 1B and 1C respectively, while FIGS. 3C, 3D and 3E correspond to FIG. 1D and show alternative modes of connection;
FIG. 3F shows a graph analogous to that of FIG. 2 for the alternative connections of FIGS. 3C and 3D;
REFERENCES:
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patent: 4507638 (1985-03-01), Brosh
patent: 5025213 (1991-06-01), Dobler et al.
patent: 5109193 (1992-04-01), Pike
patent: 5126665 (1992-06-01), Hachtel et al.
patent: 5175497 (1992-12-01), Dobler et al.
patent: 5214378 (1993-05-01), Hore
Hore Donald L.
Slade Robert A.
O'Shea Sandra L.
Patidar Jay M.
Radiodetection Limited
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