The present invention is directed to a precise method of registering a plurality of ROS imagers, so as to form sequential registered images on a photoreceptor belt in a single pass. Pairs of belt holes are formed in the photoreceptor belt, outside the image area and outside of the scan width of the ROS imagers. A pair of light sources are incorporated into the post polygon optics of each ROS imager so as to produce a light spot at the photoreceptor surface which will periodically illuminate the holes on the belt. As the leading edge of the belt holes advances into the beams, detectors placed beneath the belt and beneath the exposure station provide signals representing the exposure level of the light source output. The detectors produce a current output representative of the exposure level. The current output is converted into page sync signals which are reproducible through each of the imaging stations to produce registration of the first scan line of each image sequence. The current outputs are also converted into error signals which correct for lateral and skew registration errors.

A fiber optic system is used in a laser ROS scanning system to generate a start of scan signal. In one embodiment, a single optical fiber is positioned at the beginning of a scan line sweep. The fiber transmits a portion of a scan beam energy to a photodetector located on a main electronics system board. The photodiode generates an output signal which is sent as an input to a high speed comparator. A second input to the comparator is a second signal derived from said first signal but having a lower amplitude. The comparator compares two wave forms and generates a sharp electrical transition at the precise time the two wave forms cross which, in preferred embodiment, occurs when the first wave form amplitude level falls to about 1/2 of maximum. The comparator output is used to initiate the SOS signal of a laser diode ROS.

The present invention is an apparatus for eliminating differential scanline bow in a raster output scanner (ROS) printing system. The apparatus employs a field lens device at the output of a pre-scanning optical assembly in order to direct the laser beams toward the scanning surface, or facet, at a right angle to the scanning surface, thereby eliminating a source of scanline bow.

A procedure is provided for adjusting for image line skew caused by tolerance accumulation between a Raster Output Scanning (ROS) assembly and a photoreceptor which is being scanned. The ROS housing is adjustably mounted in relation to the photoreceptor, so that incremental adjustments can be made to cause the output scan lines emerging from the ROS housing to be moved in the process or reverse process direction vis-a-vis the photoreceptor. A test print is generated which provides measurable scan delineators to identify the amount of scan line skew created by a photoreceptor misalignment. The measured scan line skew alignment is correlated with adjustments made by a hex head screw to provide a very precise alignment. The effective adjustment range is .+-.4 mm in the process direction which corresponds to .+-.6.3 milliradians of scan line skew.

An optical scanner feedback system. The feedback system provides a feedback signal representative of a laser beam focused along an optical path onto a scanning surface. The feedback system includes a cylinder lens having a longitudinal axis and a transverse axis, located along the optical path having an optical surface for shaping and focusing the laser beam in a first direction. A photodetector is provided having an active region sensitive to light. The laser beam includes a scanning portion which passes through the lens and a reflected portion which reflects off the lens. The reflected portion is reflected such that it is incident on the photodetector active region for providing an output signal representative of the laser beam.