Patent ID: 7129967

Claim:
A frequency modulation apparatus comprising: a segmentalizing device for dividing, into a plurality of segments in units of pixel, a main scan line on an image bearing member scanned by a laser beam; an auxiliary clock calculation device for employing a reference clock period, and variable-magnification coefficients corresponding to the respective segments, to calculate auxiliary clock periods for the respective segments; an image clock generating device for generating image clocks for the respective segments based on an initial predesignated period value and the auxiliary clock periods for the respective segments; a reference value storing device for storing a reference value; a detecting device for detecting a difference between the reference value and an actual laser irradiation location; and a correcting device for correcting a shift in the laser irradiation location in accordance with the detection results obtained by the detecting device, wherein the detecting device separates the segments into blocks of continuous segments, and detects a shift between a laser irradiation position based on a value predesignated for each of the blocks and an actual laser irradiation position; and wherein, in accordance with the detection results obtained by the detecting device, the correcting device controls a pixel period of the segment, and corrects the shift of the laser irradiation position.