Speed detecting device

摘要

A speed detecting device for an electric motor in which the angular stopping position of a rotary shaft is controlled with a high precision. A magnet is mounted on a rotary shaft of the motor, and a position detector detects the position of the magnet as rotated by the motor, thereby producing an output signal having a linear region. A speed calculator samples this signal in the liner region at predetermined time intervals and performs a division operation whereby a difference between a present sampled value and a preceding sampled value of the output signal is divided by the time interval, thereby to produce a speed signal which is applied to the motor as a control signal.