Abstract: An optical rotation detecting apparatus for a bushless dc motor detects rotation information of the shaft by the slits arranged at equal pitches along the circumference of a rotary disk and a photoelectric conversion element arranged circumferentially at a pitch which is an integral multiple of the slit pitch and including a first set of photoelectric conversion element pieces arranged alternately with the former thereby generating a first rotation information signal having a frequency proportional to the rotational speed of the shaft and a second rotation information signal having a 90-degree phase difference with the first rotation information signal. The phases of the first and second rotation information signals are compared to detect the direction of rotation of the shaft. The accuracy of rotation information can be further improved by increasing the number of photoelectric conversion element pieces per slit pitch.

Abstract: In an electronic commutated motor, ripple of driving torque is perfectly compensated into uniform torque by controlling stator current; therein mechanical 360.degree. angle of rotation of the rotor magnet is divided into e.g. 12 partitioned ranges (of 30.degree.), said compensation being made by repeatedly reading out the same compensation data for the 30.degree. range by utilizing an address counter which is reset at each beginning of said partitioned ranges.