VARIABLE REGISTRATION SENSING
Original Publication Date: 1988-Feb-29
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
Figure 1 shows a document imaging system wherein a document 10, placed on a platen 12, is illuminated by light produced within the illumination cavity 14. Lamp 16 is caused to flash and light is reflected by the walls of the cavity to produce a uniform illumination at the platen surface. Lens 18, mounted on a carriage (not shown) is adapted to move laterally across aperture 20 by lens servo drive motor 22. When photoreceptor belt 24 reaches a predetermined position, lamp 16 is energized. Lens 22 moves in the same direction (scans) as a belt at a predetermined velocity to project a light image of the document onto the surface of the belt. The system has a magnification capability enabled by moving the lens towards and away from the image plane (belt 24). In order to maintain image registration, an illuminator 30 (fig. 2) mounted along the trail path of the lens carriage, which can be a lamp or LED array, directs a beam of light to an illumination detector 32 set at a distance of 4 - 5 inches. System control generates appropriate signals to move the lens along the a generally vertical path to a start of scan position appropriate for that magnification. A mechanical flag 36, which may be mounted on the lens carriage, interrupts the light beam from illuminator 30 causing an output signal from detector 32 to be sent to a servo control motor. During the lens exposure cycle, the lens is driven at a speed and along a path adapted to maintain registration at the image plane consistent with the magnification selected. The scan length covered will vary throughout the magnification range.