METHOD OF CONTROLLING ROTOR REVOLUTION

PURPOSE: To compensate for a change which appears at the period of one rotation of a rotor by detecting the arrangement of marks to obtain a correction value before starting the operation of a motor. CONSTITUTION: Before starting the control of a motor 18, the motor 18 is rotated at a nominal speed. A time interval between pulses outputted from a sensor 17 is obtained together with the whole time of one rotation. The whole time is divided by the number of a pulse to obtain a time pattern which expresses the nominal distance of a pulse. Further, the correction value of of an interval between every pulses is computed and stored into a storage circuit 33 with a time interval between pulses and the time pattern measured by the above- mentioned measurement. At the time of controlling the motor 18, a multiplication circuit 34 multiplies a time interval between continuous pulses by a correction value to output a resultant to a PLL circuit 16.