Image Number 6 for United States Patent #4070089.
An intensity modulated laser beam is directed to a rotating scanner having a plurality of facets which scans the beam across the surface of a movable mirror in a first scan direction. The mirror is movable in a manner whereby the beam is deflected in a second scan direction. The light reflected from the movable mirror is directed through a focusing lens onto a movable cylinder lens located adjacent the platen which is movable in a direction corresponding to the second scan direction, thereby providing two-dimensional scanning of a document. In one embodiment, the movable mirror and the movable cylinder lens are driven by a single motor and are coupled together in the manner whereby the movement thereof is mechanically interlocked thereby providing perfect tracking of the scanned laser beam within the clear aperture of the cylinder lens. In a second embodiment, the movable mirror and the movable cylinder lens may be independently driven and interlocked electronically. By proper focusing of the laser beam such that the sagittal focal plane is located between the movable mirror and the rotating scanner, a compromise of sagittal motion compensation due to pyramidal errors of the scanner facets and sagittal angular variations of the movable mirror is achieved. The rotating scanner may also be tilted in a predetermined manner whereby unsymmetrical scan linearity in the first scan direction upon each side of the scan line center is minimized.