Position detection apparatus using magnetoresistive effect element
A circular surface of a magnet is magnetized to an N-pole, and a back surface is magnetized to an S-pole. A detection unit moves in an X-Y plane at a position apart from the surface of the magnet. An X-direction detection element and a Y-direction detection element are installed in the detection unit. Both the X-direction detection element and the Y-direction detection element are magnetoresistive effect elements each having the bias magnetic field in a B-direction applied to a free magnetic layer directed perpendicular to the surface of the magnet. Each bias magnetic field is stabilized both in the X-direction detection element and the Y-direction detection element such that the detection unit accurately provides position detection output values in the X- and Y-directions.
1. A position detection apparatus which includes a fixed portion and a movable portion which moves along a plane opposite the fixed portion, a magnet is provided for one of the fixed portion and the movable portion, and a detection unit for detecting a magnetic field generated from the magnet is provided for the other of the fixed portion and the movable portion, wherein:
the magnet has a surface to which the detection unit is oppositely disposed, and the surface and a back side portion are magnetized to opposite magnetic poles;
the detection unit includes a magnetoresistive effect element which is provided with a fixed magnetic layer having a magnetizing direction fixed, and a free magnetic layer magnetized by the magnetic field applied from the magnet, and has an electric resistance value changed in accordance with a relative angle defined by a fixing magnetizing direction of the fixed magnetic layer and a magnetizing direction of the free magnetic layer so that the fixing magnetizing direction of the fixed magnetic layer is directed along the plane, and a bias magnetic field orthogonal to the plane is applied to the free magnetic layer; and
a change in a resistance of the magnetoresistive effect element allows detection of a position of the movable portion in the plane.
2. The position detection apparatus according to claim 1 , wherein each displacement of the detection unit toward one side and the other side with respect to a center of the magnet at which a magnetic field component in a direction of the plane becomes theoretically zero is allowed to be detected.
3. The position detection apparatus according to claim 1 , wherein the detection unit includes two units of the magnetoresistive effect elements, which have fixing magnetizing directions of the fixed magnetic layers orthogonal with each other, and directions of the bias magnetic fields perpendicular to the plane.
4. The position detection apparatus according to claim 1 , wherein the surface of the magnet has a circular shape.