Optical scanning apparatus and color image forming apparatus using the same

An optical scanning apparatus, comprising:

• a plurality of light source unit, each of which includes four or more light emitting portions for radiating light beams which are optically modulated based on image data;
• a deflecting unit for deflecting the plurality of light beams emitted from each of the plurality of light source unit for scanning;
• and
• an imaging optical system for imaging the plurality of light beams which are deflected for scanning by a deflecting surface of the deflecting unit onto a plurality of surfaces to be scanned which are provided for the respective light source unit, in which each of the plurality of surfaces to be scanned is simultaneously scanned with the plurality of light beams emitted from corresponding one of the light source unit and a plurality of scanning lines are simultaneously drawn on each of the plurality of surfaces to be scanned,
• wherein the plurality of light beams emitted from the four or more light emitting portions of the corresponding one of the light source unit are simultaneously deflected for scanning by the deflecting surface of the deflecting unit, and
• wherein, when a first scanning line on the surfaces to be scanned is defined as a scanning line located on an uppermost stream side in a direction in which corresponding one of the surfaces to be scanned is moved, of a plurality of scanning lines formed by the plurality of light beams emitted from the four or more light emitting portions of the corresponding one of the light source unit, image data corresponding to a first scanning line on at least one of the plurality of surfaces to be scanned in a k-th scanning operation of the deflecting unit is displaced by at least one line space from image data corresponding to a first scanning line on another one of the plurality of surfaces to be scanned in the k-th scanning operation of the deflecting unit,
• wherein in the k-th scanning operation of the deflecting unit, pieces of image data corresponding to first scanning lines on the surfaces to be scanned are displaced by at least one line space from one another,
• wherein a number of light emitting portions “n1” of a light source unit which is provided corresponding to at least one of the plurality of surfaces to be scanned is different from the minimum number of light emitting portions “n2” of at least another one of the light source units which is provided corresponding to another one of the plurality of surfaces to be scanned, and
• wherein n1=n2×a and “a” is a positive integer.