Single pass color printer having improved process and slow registration

An imaging system for forming image exposure frames on a photoreceptor belt moving in a process direction during a single pass including:

• a plurality of Raster Output Scanners (ROS) units, each ROS unit generating image-modulated scan lines which are transmitted along an optical path to form said image exposure frames, said ROS units located in a common housing and positioned symmetrically on opposite sides of two polygon scanners mounted vertically on a common rotating shaft, said ROS units each comprising:
• a diode laser for generating a beam output,
• means for modulating the beam output of said laser with input video data,
• optical means for collimating and expanding the modulated laser beam output and directing the collimated and expanded output against an associated polygon scanner,
• post polygon lens group for correcting f.theta. and distortion in the reflected beam thereby producing a corrected scanning beam,
• a 90.degree. roof mirror assembly mounted on a movable mirror carriage which folds the corrected scanning beam from the post polygon lens group in a 180.degree. path reversal and
• a folding mirror for directing the corrected scanning beam out of the common housing and onto the photoreceptor belt, each scanning beam being parallel to each other,
• the improvement wherein said roof mirror carriage is integrally mounted to a focus carriage and secured to the common housing at a position providing an optically focused scan line at the photoreceptor belt surface, means for incrementally moving, said roof mirror carriage to provide a skew registration correction to the scan line at the photoreceptor belt surface, and to provide a process registration direction correction to the scan line at the photoreceptor surface;