Method of generating image scanning clock signals in optical scanning apparatus

A method of generating image scanning clock signals in an optical scanning apparatus in which a light beam is periodically deflected by a rotating light beam deflector to scan a surface area, and is detected by a light sensor disposed outside of the surface area being scanned for synchronizing main scanning cycles, said method comprising the steps of:

• selecting one of a plurality of pulse signal groups which are of the same frequency as that of image scanning clock signals and are shifted in phase from each other, as image scanning clock signals in response to an output signal from the light sensor;
• applying reference clock signals C.sub.0 of the same frequency as that of the image scanning clock signals to a shift register;
• applying corrective clock signals SCK of a higher frequency than that of the reference clock signals C.sub.0 as shift clock signals to the shift register;
• and
• delaying n output signals C.sub.1, C.sub.2, C.sub.3, . . . C.sub.n (n.gtoreq.2) from said shift register successively a phase .DELTA.t by delay circuits to produce the aforesaid plurality of pulse signal groups, said phase .DELTA.t meeting the relationship:
• ##EQU5## where C.sub.0 :
• f.sub.0 MHz, and SCK:
• n.multidot.f.sub.0 MHz