Electricity: measuring and testing – Magnetic – Displacement
Patent
1993-06-23
1995-09-12
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Displacement
32420724, 32420725, G01B 730, G01B 714, G01R 3306
Patent
active
054500095
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a magnetic sensor and mounting structure therefor, which uses a magnetism-to-electricity converting element, such as a magneto-resistive element made of a thin ferromagnetic film material or a semiconductor crystalline element.
BACKGROUND ART
Conventionally, a linear position sensor or a rotary encoder employs a magnetic sensor with a thin ferromagnetic film magneto-resistive element made of, for example, an Fe-Ni alloy or a Co-Ni alloy. The thin ferromagnetic film magneto-resistive element (hereinafter referred to as an MR element) is generally magneto-anisotropic with respect to a particular direction beneath the film surface. It has high sensitivity to the magnetic field parallel to the film surface while having low sensitivity to the magnetic field generated along the thickness of the film surface.
With respect to this, in a magnetic sensor having an MR element, a magnet is used to generate the magnetic field in the direction of the film thickness of the MR element. Movement of the magnetic sensor along a magnetic scale, or a detected member, causes change in the magnetic flux of the component parallel to the film surface, with the amount of the change being considerable, thereby improving the detection sensitivity of the magnetic sensor. (See, Japanese Published Examined Patent Application (B2) No. 1-41226.) More particularly, as shown in FIG. 8(A), an MR element 12, affected by the bias magnetic field generated by a magnet 10 positioned at right angles to the film surface, moves along an arrow A, relative to a scale 14 having its magnetic characteristics varied by, for example, profile changes, to either the position illustrated in FIG. 8(B) or the position illustrated in FIG. 8(C), which results in the magnetic flux .phi. with gradient. Consequently, the magnetic field component parallel to the element surface acts upon the MR element, varying its electrical resistance to produce a detection signal.
However, the electrical resistance of the MR element 12 varies, as shown in FIG. 9, symmetrically with the direction of the magnetic field. Thus, as described above, the application of the bias magnetic field at right angles to the film surface of the MR element 12 causes the direction of the magnetic flux .phi. to be bent to the right in FIG. 8(B) and to the left in FIG. 8(C). No linearity can be obtained at a position along the film surface where the component of magnetic field intensity is approximately equal to zero. This results in a distortion of the output signal. With respect to this, it has been proposed to arrange the MR element in an inclined manner relative to the scale 14, and to apply a bias magnetic field (so-called transverse bias magnetic field) having a component parallel to the film surface in the MR element 12, in order to use it in linear regions a and b in FIG. 9. (See, Japanese Published Unexamined Patent Application (A) No. 60-155917.)
However, the magnetic sensor of the type described requires the arrangement of the MR element 12 in an inclined manner to the scale 14. This means that the MR element 12 is difficult to assemble, and besides, only a complicated structure can hold an inclined MR element 12. In addition, it has another disadvantage of impossibility of axial-symmetrical application of the transverse magnetic field to the sensor surface.
Additionally, a conventional magnetic sensor protects the MR element 12 by containing the MR element 12 in a sensor housing. Such conventional housing is made of a non-magnetic material to prevent, to the extent possible, the MR element 12 from being affected magnetically. It is designed to position the magnet 10 in an ideal space. Further, it has a structure such that a magnetic shield is sufficiently away from the magnet 10 for the bias magnetic field, even when the magnetic shield of the magnetic sensor is required, to avoid in every way any effect on the magnetic field generated by the magnet 10.
However, a magnetic sensor 11 used under highly loaded hostile environment in constru
REFERENCES:
patent: 3928802 (1975-12-01), Reinecke
patent: 4745363 (1988-05-01), Carr et al.
patent: 4992733 (1991-02-01), Griebeler
Kabushiki Kaisha Komatsu Seisakusho
Snow Walter E.
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