Magnetic detection apparatus
In a magnetic detection apparatus that prevents the output waveform from deviating regardless of whether two magneto-resistance elements are displaced relative to a magnet or accurately disposed relative to the magnet, the above two magneto-resistance elements are angled in consideration of a change in the direction of application of the magnetic field during displacement of the positional relationship and the anisotropy of the magneto-resistance elements so that the magneto-resistance elements are oriented in a direction in which the deviation of the output waveform caused by a change in the magnitude of application of the magnetic field during displacement of the positional relationship is cancelled, thereby preventing the detection accuracy of a magnetic moving body (detection target) being affected even if the magneto-resistance elements are displaced relative to the magnet due to manufacturing variations.
1. A magnetic detection apparatus comprising:
a magnetic moving body having a shape changing a magnetic field, the magnetic moving body rotating in sync with a rotary shaft;
magneto-resistance elements detecting a change in the magnetic field by the magnetic moving body, the magneto-resistance elements being anisotropic;
a magnet applying the magnetic field to the magneto-resistance elements; and
a processing circuit unit having a bridge circuit including the magneto-resistance elements, the processing circuit unit detecting the change in the magnetic field acting on the magneto-resistance elements by converting a change in resistance values of the magneto-resistance elements to a change in voltages,
wherein the magneto-resistance elements are separately disposed in a rotational direction of the magnetic moving body, and
a pattern shape of each of the magneto-resistance elements is a zigzag shape having a plurality of turn-back portions oriented at an angle α relative to a direction orthogonal to a direction of the magnetic field applied to cancel a change of the direction and a magnitude of the magnetic field depending on a displacement in the rotational direction of the magneto-resistance elements relative to the magnet.
2. The magnetic detection apparatus according to claim 1 , wherein the angle α is optimized by measurement in consideration of an amount of the displacement of the magneto-resistance elements in the rotational direction relative to the magnet.
3. The magnetic detection apparatus according to claim 1 , wherein each of the magneto-resistance elements includes a giant magneto-resistance element (GMR element).
4. The magnetic detection apparatus according to claim 1 , wherein the magnetic moving body is a gear-shaped magnetic moving body rotating in sync with the rotary shaft.
5. The magnetic detection apparatus according to claim 1 , wherein the bridge circuit comprises the magneto-resistance elements and resistors.
6. The magnetic detection apparatus according to claim 1 , wherein the magneto-resistance elements are disposed so as to be separated in the rotation direction of the magnetic moving body on the processing circuit unit.
7. The magnetic detection apparatus according to claim 1 , wherein the pattern shape of each of the magneto-resistance elements is oriented at the angle α relative to the direction orthogonal to the direction of the magnetic field so as to cancel an amount of a change in a resistance value of a respective one of the magneto-resistance elements caused by the change in the magnitude of the magnetic field caused by changing the direction of the magnetic field applied.