Patent ID: 8605130

Claim:
An image forming apparatus comprising: a plurality of optical systems, each optical system provided for an associated one of a plurality of colors printable by the image forming apparatus, each of the optical systems including, a light-beam generating unit that generates a light beam of the associated color, a rotary polygon mirror that deflects the light beam of the associated color generated by the light-beam generating unit so as to scan an image carrier with the light beam, and a light-beam detecting unit that generates a light-beam detecting signal, if the light-beam detecting unit detects the light beam of the associated color that is deflected for scanning at a predetermined position on a scanning path by rotationally driving the rotary polygon mirror; and a control unit configured to control operation of all of the plurality of optical systems, the control unit including, a time-difference measuring unit that measures a relative time difference between one of the light-beam detecting signals detected by a respective light-beam detecting units and a rest of the light-beam detecting signals detected by associated light-beam detecting units, a generation-timing determining unit that determines a generation-timing for generating a start signal that designates a start of an image writing operation so that the generation timing does not overlap another timing when each of the light-beam detecting signals is output from the corresponding time-difference measuring unit based on a measurement result of the time-difference measuring unit, and a start-signal generating unit that generates the start signal based on the time for the generation timing that is determined by the generation-timing determining unit.