Patent ID: 7471308

Claim:
A frequency modulation apparatus used in an image forming apparatus having an image bearing body to be scanned by a laser beam, comprising: a segment dividing portion for dividing a main scan line scanned by said laser beam on the image bearing body into a plurality of segments each constituted by a plurality of pixels; an auxiliary clock calculating portion for calculating an auxiliary clock period based on a reference clock period and a modulation coefficient; an image clock generating portion for generating image clocks respectively corresponding to the plurality of segments based on an initial period value provided in advance and said auxiliary clock period; and a frequency variation device for generating fluctuation of a predetermined frequency of said reference clock, wherein said frequency variation device generates said reference clock having the fluctuation of the predetermined frequency by adding a constant clock to the fluctuation of the predetermined frequency by carrying a certain predetermined period for a constant clock which becomes the reference; wherein said reference clock is a clock having the predetermined frequency fluctuation, said auxiliary clock calculating portion calculates the auxiliary clock by setting the modulation coefficient corresponding to said respective segment, so as to reduce a fluctuation of said reference clock, and said image clock generating portion generates an image clock so as to reduce the fluctuation of the frequency of said reference clock based on said auxiliary clock.