APPARATUS FOR SCAN LINE SKEW CORRECTION IN AN ELECTROSTATOGRAPHIC MACHINE
Original Publication Date: 1993-Oct-31
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
An optical element for the selective scan line skew correction in a raster output scanner (ROS) of an electrophotographic printer is disclosed. The optical element includes a chamber containing a nematic material having a variable index of refraction as a function of voltage applied thereacross. The chamber has a volume defined by surfaces having progressively decreasing areas in substantially perpendicular planes. The ROS includes a control and feedback system coupled to a variable voltage source for applying a biasing voltage across the optical element to control the variable index of refraction of the nematic material for selectively correcting scan line skew. FIG. 1 shows a general configuration of the optical system and the optical path of a ROS system used, for example, in an electrostatographic printing machine. Initially, input video data is transmitted to the laser source 12 which embodies a self-modulating light source for producing a modulated diverging beam of coherent light. The beam may be collimated by a spherical or an aspherical collimating lens 14 and then refocused by a cylinder lens 15 that is part of a wobble correction system. The beam is next incident upon a rotating polygon 16 having at least one mirrored facet 16a for reflecting the beam through a post scan optics system. Other suitable devices for scanning are known in the art, including rotating hologons, rotating diffraction gratings, etc. The post scan optics system reconfigures the beam reflected by facet 16a to a circular or elliptical cross-section, refocuses the beam to the proper point on the surface of photoreceptor/drum 2, and corrects for scan nonlinearity (f-theta correction) as well as wobble defects. A recollimating lens and a toroidal or cylindrical lens 18 can be disposed between the scanning device 16 and the photoreceptor 2 to correct for wobble (scanner motion or facet errors) and other defects where appropriate.