Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-10-05
2001-04-10
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207220, C324S207240, C335S302000
Reexamination Certificate
active
06215299
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a sensor system for measuring linear displacement of a first member relative to a second member, comprising an analogue Hall Effect sensor secured to the first member in an orientation to sense magnetic flux in a sensing direction perpendicular to said direction of a relative movement, and a permanent magnet secured to the second member and having a front surface facing the Hall Effect sensor and extending along the direction of relative movement between the first and second members.
An analogue Hall Effect sensor produces an output voltage related to the component of the flux density of a magnetic field in which it is located which is perpendicular to its sensing surface. The sensor produces zero output voltage when subject to a magnetic field of sufficient strength in one direction and its maximum output voltage when subject to a magnetic field of the same magnitude in the opposite direction. In the absence of a magnetic field, the sensor produces an output voltage of half its maximum voltage.
GB-A-1109220 disclosed a sensor system of this type in which the front surface is concave in the direction of relative movement so that the magnetic flux at the Hall Effect sensor has a minimum value when the latter is positioned opposite a central location at which the concavity of the surface has maximum depth. A second Hall Effect sensor is mounted adjacent to the first sensor for simultaneous movement therewith. The outputs of the two sensors are combined electronically in order to determine the side of the central location on which the sensors are located.
SUMMARY OF THE INVENTION
According to the invention, in a sensor system of the type described above, the permanent magnet is magnetized so that the front surface has a first magnetic pole of a first magnetic polarity at a first end and a second magnetic pole of a second magnetic polarity at a second end spaced from the first end in the direction of travel.
With this arrangement, the Hall Effect sensor is exposed to a magnetic field which changes polarity as the first and second members pass through a relative position in the center of their range. Consequently, the sensor can be arranged to produce its full range of output voltages, thus maximizing the resolution obtained.
Preferably, the front surface is concave extending along the direction of relative movement between the first and second members and is shaped to cause the magnetic field to vary. The Hall Effect sensor is responsive to the component or normalized vector of the magnetic flux produced by the magnetic field that extends perpendicular to the direction of relative movement between the magnet and sensor. The concave front surface is shaped such that the density of the normalized vector of flux that passes through the Hall Effect sensor varies in a substantially linear manner along the path of the Hall Effect sensor. Consequently, the output voltage of the Hall Effect sensor bears a substantially linear relation to position and the output voltage varies substantially linearly between the extremes of relative movement between the sensor and the magnet.
It is a principal object of the invention to provide a position sensing arrangement in which the output of a sensor varies substantially linearly between the extreme end points of relative movement between the sensor and a permanent magnet.
It is another object of the invention to provide a position sensing arrangement in which a permanent magnet is magnetized to produce a flux field having a sensor responsive component or vector whose density or strength varies substantially linearly along the entire length of the magnet.
It is a further object of the invention to provide an improved position sensing arrangement having a permanent magnet that is magnetized and shaped to produce a plurality of different flux fields along the path of relative movement between a sensor and the permanent magnet.
It is also an object of the invention to provide an improved permanent magnet for use in a position sensing device.
REFERENCES:
patent: 4107604 (1978-08-01), Bernier
patent: 4268814 (1981-05-01), Henrion et al.
patent: 5159268 (1992-10-01), Wu
patent: 5493216 (1996-02-01), Asa
patent: 5955881 (1999-09-01), White et al.
patent: 1339956 (1964-01-01), None
patent: 1109220 (1968-04-01), None
European Search Report of European Patent Application No. EP 98 30 7998.
Konson Dmitri
Reynolds David William
Swindon David Mark
Britax Rainsfords Pty. Limited
Jones Day Reavis & Pogue
Snow Walter E.
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