Speed control circuit for an optical scanning system driving motor for

Abstract

A speed controlling circuit for controlling an optical scanning system driving motor in use with an image forming apparatus such as a copier and a printer. The speed controlling circuit includes; an encoder for generating pulse signals according to a rotation of the optical scanning system driving motor; a generating circuit for generating reference clock signals; a first memory for storing a first set of numbers for dividing a frequency of the pulse signals; a second memory for storing a second set of numbers corresponding to a target rotation speed of the optical scanning system driving motor; a first setting circuit and a second setting circuit for respectively reading one of the first set of numbers from the first memory and one of the second set of numbers from the second memory, and for setting those numbers at every predetermined interval time while the optical scanning system driving motor is accelerating or decelerating; a frequency-dividing circuit for dividing the frequency of the pulse signals according to the set number of the first set of numbers; a detecting circuit for detecting a rotating speed of the optical scanning system driving motor according to the reference signals and pulse signals at every frequency period which is divided by the frequency-dividing circuit; a comparator circuit for comparing the rotating speed, detected by the detecting circuit, with the set number of the second set of numbers at every frequency period which is divided by the frequency-dividing circuit; and a control circuit for controlling the rotating speed of the optical scanning system driving motor according to a result of the comparing of the comparator circuit.