Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-03-08
2001-11-27
Snow, Walter (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207220
Reexamination Certificate
active
06323643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to position transducers, and more particularly to non-contact position transducers with Hall-effect position sensing.
2. Description of the Related Art
Prior art position transducers include a shaft that pivots or rotates with respect to a stationary housing. The shaft is typically connected to a wiper mechanism that brushes against a resistor strip when the shaft is rotated. The wiper mechanism, when rotated, causes a change in electrical resistance to thereby indicate the relative rotational position of the shaft with respect to the housing. Although relatively inexpensive in construction, position transducers of this type are subject to wear due to the sliding effect of the wiper against the resistor strip. Worn parts may result in mechanical breakdown of the transducer or, at the very least, inaccurate position sensing.
In an attempt of overcome such problems, contactless position sensors have been developed. Such position sensors include inductively coupled ratio detectors, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, radio wave directional comparators, and electrostatic ratio detectors, among others. These position sensors tend to offer much value for one or more applications, but none meet all application requirements for all position sensing applications. The limitations may be due to high cost, sensitivity to particular energies or fields, instability, resistance to contamination and environment, ruggedness, linearity, precision, and so on.
SUMMARY OF THE INVENTION
According to the invention, a position transducer comprises a stationary member, a movable member spaced from the stationary member and being displaceable with respect to the stationary member, a magnetic sensor fixedly connected to the stationary member, and a magnet connected to the movable member for movement therewith. The magnet has a polarized surface (positive or negative) that faces the magnetic sensor to thereby generate a magnetic field coincident with the magnetic sensor. The polarized surface is shaped to form a gap between the magnetic sensor and the polarized surface that varies as the movable member is displaced with respect to the stationary member to thereby vary the strength of the magnetic field at the magnetic sensor. With this arrangement, the strength of the magnetic field sensed by the magnetic sensor is indicative of the amount of relative movement between the stationary member and the movable member.
Further according to the invention, an angular position sensor comprises a housing, a rotor connected to the housing for rotation about a rotational axis, a sensor base fixedly connected to the housing and spaced from the rotor, a magnetic sensor fixedly connected to the sensor base, and a magnet connected to the rotor for movement therewith. The magnet has a polarized surface that faces the magnetic sensor to thereby generate a magnetic field coincident with the magnetic sensor. The polarized surface is shaped to form a gap between the magnetic sensor and the polarized surface that varies as the rotor is rotated with respect to the stationary member to thereby vary the strength of the magnetic field at the magnetic sensor. With this arrangement, the strength of the magnetic field sensed by the magnetic sensor is indicative of the amount of relative movement between the rotor and the housing.
Other objects, advantages and features of the invention will become apparent upon reading the following detailed description and appended claims, with reference to the accompanying drawings.
REFERENCES:
patent: 3112464 (1963-11-01), Ratajski
patent: 4570118 (1986-02-01), Tomczak
patent: 4726338 (1988-02-01), Decker
patent: 4744343 (1988-05-01), Bisenius
patent: 5757179 (1998-05-01), McCurley
Borgman Mark W.
Bourgeois Mark P.
CTS Corporation
Snow Walter
Wirthlin Alvin
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