Multi-color image forming apparatus and method of controlling the same

A method of controlling a multi-color image forming apparatus including a plurality of laser scanning units and a plurality of development units in order to print a multi-color image, the plurality of development units including focusing members to focus laser beams corresponding to horizontal synchronization signals outputted from the laser scanning units and optical sensors to output the horizontal synchronization signals, the pulse widths of which are changed according to the lengths of traces of the laser beams passing through the focusing members, the method comprising:

• detecting the lengths of the traces of the horizontal synchronization signals sent from the plurality of laser scanning units to the optical sensors through the focusing members;
• determining whether the pulse widths of the horizontal synchronization signals are changed based on the detected lengths of the traces of the horizontal synchronization signals;
• correcting timings of vertical offsets so as to correct alignment errors of the plurality of laser scanning units and the plurality of development units in a vertical direction based on the change in the pulse widths of the horizontal synchronization signals if the pulse widths of the horizontal synchronization signals are changed;
• and
• outputting video data to scan the multi-color image based on the corrected timings of the vertical offsets.

A computer-readable recording medium having embodied thereon a computer program to execute a method of controlling a multi-color image forming apparatus including a plurality of laser scanning units and a plurality of development units in order to print a multi-color image, the plurality of development units including focusing members to focus laser beams corresponding to horizontal synchronization signals, the pulse widths of which are changed according to the lengths of traces of the laser beams passing through the focusing members, wherein the method comprises:

• detecting the lengths of the traces of the horizontal synchronization signals sent from the plurality of laser scanning units to the optical sensors through the focusing members;
• determining whether the pulse widths of the horizontal synchronization signals are changed based on the detected lengths of the traces of the horizontal synchronization signals;
• correcting timings of vertical offsets so as to correct alignment errors of the plurality of laser scanning units and the plurality of development units in a vertical direction based on the change in the pulse widths of the horizontal synchronization signals if the pulse widths of the horizontal synchronization signals are changed;
• and
• outputting video data to scan the multi-color image based on the corrected vertical offsets.