LIGHTING CONTROL METHOD FOR LIGHT SOURCE, AND IMAGE FORMING DEVICE

摘要

PROBLEM TO BE SOLVED: To make stably performable an image forming operation and to keep the effective scanning rate high n the case where the rotation control of a polygon motor is switched between an internal control based on an encoder in the motor and an external control based on a horizontal synchronizing signal on the outside of the motor. SOLUTION: The detection period of main scanning start timing (hereinafter referred to as the SOS period) at the time when a driving motor is rotated with a prescribed rotational frequency is denoted as T (referred to (A)), and the SOS period is shortened by T2 by accordance with switching from internal control to external control (refer to (B)). In the transition period form internal control to external control, a light source is so lit that the period T1 (SOS pre-lighting period) after the start of lighting for main scanning timing detection till SOS signal detection may be longer than the period T2 (refer to (C)). Thus, SOS pre-lighting is started before SOS signal detection timing (refer to (B)) at the time of switching from internal control to external control without fail.