Magnetic detection apparatus for detecting movement of an object having a nonuniform system of teeth

摘要

A magnetic detection apparatus detects movement of an object having a nonuniform system of teeth by means of magneto-electric conversion devices, wherein technical problems such as too large an amplified output signal, a nonuniform pulse period and a complicated circuit configuration can be solved. A plurality of uniform triangular teeth are formed on the circumference of a gear at equal angular intervals, and in a predetermined region a trapezoidal tooth is formed, where the height of the trapezoidal tooth is smaller than the height of the uniform teeth but greater than half their height. The magnetized surface of a bias magnet facing the gear generates a bias magnetic field directed toward the gear. Magneto-resistive devices are provided in the bias magnetic field. Variations in state of the bias magnetic field generated by the bias magnetic magnet when the gear is rotated are converted into an output electrical signal by the magneto-resistive devices. A binary conversion circuit converts the electrical signal output into a binary signal. Receiving the binary signal, a processing circuit detects a reference position and the rotational direction of the object.