Electricity: measuring and testing – Magnetic – Displacement
Patent
1994-06-20
1997-11-25
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Displacement
3242072, 338 32H, G01B 714, G01B 730, G01R 3312, G01D 520
Patent
active
056916370
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a magnetic flux transducer for indicating position in space with reference to a three dimensional coordinate system, and in particular to a transducer which electronically measures and compares magnetic flux from a movable element through a plurality of geometrically congruent areas arranged around an axis of symmetry in a sensing plane to determine both the relative position of the movable element in a plane perpendicular to the axis of symmetry and the distance of that plane from the sensing plane.
DESCRIPTION OF THE PRIOR ART
Electronic measurement of magnetic flux emanating from a permanently magnetized element with Hall effect and magneto-resistive sensors for the purpose of position indication along a single axis is well known.
For example, U.S. Pat. No. 4,107,604, Bernier (1978) describes a position transducer with a stationary Hall effect sensor located proximate the side of a sliding longitudinal permanent magnet. The reference teaches that the Hall effect sensor will generate a zero or null signal when the sensor is located centrally between the respective pole faces of the magnet, and will generate a signal upon axial translation of the magnet, either positive or a negative depending on direction. The magnitude of the positive or negative signal is related to the magnitude of the translation of the magnet from the central or null position.
U.S. Pat. No. 4,359,677, Dennon (1982), describes a linear indexer controlling a proportional valve to a hydraulic cylinder for positioning a "setworks" system in a lumber mill in which a Hall effect sensor generates a null signal as the sensor translates past a "position indicating" thin magnet having a magnetic axis aligned parallel to the direction of sensor translation. Dennon specifically points out that the Hall effect sensor produces a electrical voltage signal proportional to the incident magnetic flux and that the polarity of the voltage signal reverses when the magnetic field direction reverses.
U.S. Pat. No. 4,691,185, Loubier et al, (1987) describes a "change of state" magnetic switch in which a stationary Hall effect sensor generates an voltage signal which reverses polarity responsive a reverse in polarity of a magnetic field along the central axis of a permanent annular magnet translating along its axis toward and away from the Hall sensor. Loubier et al specifically teaches that an annular geometry of the permanent magnet provides high gradient field reversals at specific distances from the annular pole face of the magnet. The graph presented in FIG. 4 of Loubier et al illustrates an almost linear region of high gradient or rate of change of field strength along the central axis of a annular magnet within a certain range from the annular face of the magnet and a field reversal at a particular distance from the face.
U.S. Pat. No. 3,419,798, Walton, (1968) describes a displacement transducer in which outputs from a pair Hall effect sensors sensing magnetic flux from a curved permanent magnetic strip are algebraically summed to produce an output signal related to the relative positions of the sensors and the strip along a given axis.
U.S. Pat. No. 3195,043, Burig (1965) describes a proximity transducer in which a tapered pole piece composed of a magnetically susceptible material mounted on one end of a permanent magnet concentrates magnetic flux through a Hall effect device mounted on the small end pole piece when a magnetically susceptible material is moved into proximity of the pole piece.
U.S. Pat. No. 4,908,527, Van Antwerp (1990) describes a Hall effect integrated circuit transducer chip which changes switching states responsive to the changes in magnetic field intensity prompted by relative movement a permanent magnet between two different positions. Van Antwerp discuses the necessity to provide such a system with temperature compensating features to off set effects of temperature on magnetic field intensity emanating from a permanent magnetized element of the system.
However, neither Hal
REFERENCES:
patent: 3331971 (1967-07-01), Moller
patent: 4639667 (1987-01-01), Andresen
patent: 4661773 (1987-04-01), Kawakita et al.
patent: 5504502 (1996-04-01), Arita et al.
Oswald Richard K.
Smith Ronald A.
Newhouse, Esq. David E.
Snow Walter E.
True Position Magnetics, Inc.
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