Abstract: Pre-polygon optics are provided which consist of a compact design such that the number of pre-polygon elements in the pre-polygon optics is reduced while achieving desired light beam characteristic. The pre-polygon optics may consist of a hybrid toroidal diffractive optical element, refractive cross-cylindrical optical elements, refractive spherical and cylindrical optical elements, a refractive sagittal cylindrical optical element or a refractive tangential cylindrical optical element. Accordingly, advantages such as lower cost and ease of alignment are achieved.

Abstract: Scan line bow correction for raster output scanners, and systems that use raster output scanners. Scan line bow correction is performed in raster output scanners having a post-polygon optical system that includes an f-&thgr; lens system that has at least two multiple scan lenses by controllably tilting a second scan lens along the fast-scan axis. Beneficially, the tiltable scan lens is mounted on a mounting pad that includes a threaded hole. A threaded set screw screws into the threaded hole to provide an adjustable support. In practice the threaded hole-set screw should have a high number of threads per millimeter to provide fine bow correction adjustment.

Abstract: Raster output scanners having piezoelectric-activated lens movers comprised of a mounting base, an electrically operated piezoelectric element connected to the mounting base, a flexible linkage having a lens mount, and a lens attached to the lens mount. The flexible linkage includes flexible arms that can flex in the predominate direction of motion of the piezoelectric element, but that are substantially rigid in another direction. The flexible linkage is mounted such that the flexible arms bias the lens toward the piezoelectric element. Expansion and contraction of the piezoelectric element, combined with the bias of the flexible arms cause the lens mount and its attached lens to follow the expansion and contraction of the piezoelectric element. The rigidity of the flexible arms hold the lens in the proper focal plane. Beneficially, the piezoelectric element is driven so as to compensate for scan line position errors.

Abstract: Electrophotographic printers having raster output scanners that correct for polygon facet phasing errors and photoreceptor position errors by aerial scan line adjustments. A photoreceptor position sensor senses the position of the photoreceptor and a facet position sensor senses the position of the polygon facets. A scan line position controller produces a position signal that depends upon the photoreceptor position sensor and the facet position sensor. A piezoelectric-actuated lens mover assembly receives the position signal and moves a pre-polygon lens to adjust the scan line plane to correct for any misregistration. The piezoelectric-actuated lens mover assembly includes a large displacement piezoelectric element and a flexible arm assembly that holds the pre-polygon lens.

Abstract: Correcting color banding problems resulting from facet-to-facet jitter in a color imaging device having a multifaceted polygon are corrected by starting each color separation using the same facet. This facet synchronization has been shown to reduce the objectionable color banding. Imaging offsets that result from either advancing or retarding the exposure of a latent image such that the latent image begins with the same facet as other latent images are compensated for using a rotating cylinder mirror whose rotation is controlled by a piezoelectric element.

Abstract: Correcting motion quality induced color banding problems resulting from photoreceptor motion defects in a color imaging device having a laser based multifaceted polygon and a rotating cylindrical mirror whose rotation is set by a controlled rotation inducing element. A motion sensor senses the motion of the photoreceptor. Based upon motion errors a controller either advances or delays the production of a latent image. The controller further controls the rotation inducing element, beneficially a piezoelectric element, such that a latent image is produced in a predetermined location. When multiple latent images are produced, the controller beneficially causes the latent images to be properly registered.

Abstract: A system controls the laser-induced discharging of pixel-sized image areas on a photoreceptor in a multi-color xerographic printer where multiple layers of toner are placed on the photoreceptor surface. A light collector, disposed to collect light either reflected from or passing through the photoreceptor, detects conditions in which the laser must pass through one or more layers of previously-placed toner to discharge the photoreceptor. When such a condition is detected, the system increases either the intensity or exposure duration of the laser.

Abstract: Raster scanner assemblies, and machines which use such raster scanner assemblies, which produce spots having a variable spot dimension. Raster scanner assemblies according to the present invention include an electronic subsystem which produces both image data and a spot size control signal, a laser assembly which produces a polarized laser beam having a beam with a first dimension and which is modulated in accord with the image data, a variable aperture assembly which changes the first dimension of the laser beam, a rotating polygon having a plurality of facets sweeping the laser beam in a sweep plane, and a scan lens for focusing the laser beam onto an image plane. The variable aperture assembly beneficially includes both a liquid crystal cell, which receives the laser beam and the spot size control signal, and a polarizing filter.

Abstract: Color banding resulting from facet-to-facet jitter in a color imaging device having a plurality of multifaceted polygons is reduced by matching the facets of the various polygons such that the composite image produced by the matched facets result in minimal color banding. The latent images are registered by starting each latent image with a selected "starting" facet such that the matched facets trace corresponding scan lines. Imaging offsets that would result from either advancing or retarding the exposure of a latent image such that the latent images begin with the correct facet are compensated for by moving a rotating cylinder mirror in each polygon such that the latent images are registered. Moving of the cylinder mirror is beneficially achieved using a controlled piezoelectric element.

Abstract: Compact raster scanner assemblies, and systems which use such assemblies, having a laser source generating laser light; a photoreceptor moving in a process direction; and a raster scanner raster sweeping the photoreceptor. The raster scanner includes a rotating polygon, an F-.theta. scan lens in the sweep plane, and a first folding mirror positioned along a first axis for reflecting laser light passing through the F-.theta. scan lens toward the photoreceptor. The first folding mirror being aligned along an axis which is at an angle with both the process direction and the resulting fast scan direction. The raster scanner assembly further including a second folding mirror for receiving laser light reflected by the first folding mirror and for directing that laser light toward the photoreceptor such that the laser light sweeps across the photoreceptor in a direction perpendicular to the process direction.

Abstract: A semi-automatic exit window cleaner which includes a wiper for contacting an exit window. The wiper attaches to a wiper operation mechanism which swipes the wiper across the exit window when an operator accessed compartment or drawer is moved. Beneficially, the wiper mechanism is comprised of a cable which is spaced between two pulleys, one of which also connects to a gear or other rotation train.

Abstract: The present invention provides a means and method for efficiently and automatically monitoring and adjusting the power output of either a single or a dual beam laser diode array used to provide the scanning beams in a ROS system. Collimated light outputs from a collimator lens assembly following either a single or dual beam laser are reflected along an optical path to impinge on one or two photodiodes positioned so as to intercept the reflected light. The photodiode output is proportional to the power output of the laser diode associated with the photodiode. In one multi-beam embodiment, polarization of the laser diode output is controlled so as to ensure that only outputs from an associated laser diode is sensed by an associated photodiode. In another embodiment, a half wave plate is used to rotate the polarization of one of the laser diodes.

Abstract: A method for achieving high resolution printing using low resolution LED bars is performed by arranging the bars at particular angles to the photoreceptor and timing the activation of the pixels within the LED bars according to the movement of the photoreceptor. In addition, the LED bars may be segmented and arranged so that the segments abut one another at different locations. Each of the abutting segments is disposed at a particular angle to the photoreceptor in the process direction. A lens arrangement is used to image the LED bars.

Abstract: The present invention presents an apparatus and method for efficiently and automatically monitoring and adjusting the power output of laser diodes used to provide the scanning beams in a ROS system. Light radiated from the back facet of the laser diode is directed onto at least a pair of back facet photodiodes. The photodiode outputs are proportional to the power output of the laser diode associated with the photodiode. The polarization of the laser diode back facet output is controlled so as to ensure that the only outputs from an associated laser diode is sensed by an associated photodiode. In one embodiment, a half wave plate is used to rotate the polarization of one of the laser diodes and in another embodiment optical fibers efficiently transmit light emitted from the back facets to the photodiode.

Abstract: The present invention is a method and apparatus for improving the depth of focus in a raster output scanner (ROS), and more particularly to a system for maximizing the line separation depth of focus of a multispot ROS while maintaining the system common depth of focus. In a preferred design for a ROS-based system, the system common depth of focus (system common DOF) is maximized, where the system common DOF is characterized as the depth-of-focus over which all performance parameters are met. More specifically, the performance parameters are intended to include the following five factors: (1) scan and cross-scan spot size; (2) wobble; (3) differential bow; (4) line separation; and (5) scan linearity. Maximizing the system common DOF means to maximize the depth-of-focus while at all times meeting or exceeding the performance requirements for the five listed parameters. The optical system design achieves a desirable system common DOF while maintaining a line separation of 127 .mu.m (1/200 inch).

Abstract: In order to correct for keystoning distortion when projecting a transparency onto a projection screen, computer software is used to deliberately distort an electronic image. A transparency, which can be a slide or a projection panel display such as an LCD panel, is then produced with the intentionally distorted image. The oblique angle between the horizontal plane through the projector and the viewing screen is compensated for by an inverse tapered compression of the electronic image. In one embodiment, a test slide is generated with a plurality of non parallel line pairs, each line pair representing a different distortion correction to an image. The test slide is projected to the screen to be used. A pair of line pairs most parallel to each other is identified. The line pair identification is used to activate the portion of software which generates that particular image distortion.

Abstract: In an overfilled polygon ROS architecture, fast scan jitter is reduced by uniformly illuminating the overfilled facets. In one embodiment, the collimator lens is designed with a long focal length to transmit only the more uniform central portion of the Gaussian shaped intensity profile output of a laser diode. In another embodiment, the light level at the polygon facet is made uniform by introducing a variable transmission filter along the optical path.

Abstract: A raster output scanner is capable of creating images at a wide range of selectable resolutions. A laser source for creating an image is modulated at a pixel clock rate. A clock command value is determined as a function of a value related to the pixel clock rate and a value related to a desired resolution in the fast-scan direction and a desired resolution in the slow-scan direction of an image to be created on the photosensitive surface. The pixel clock rate is controlled in response to the clock command value. A polygon command value is determined as a function of the value related to the pixel clock rate, a value related to a desired resolution in the fast-scan direction of an image to be created on the photosensitive surface, and a value related to a rotational velocity of the polygon mirror. The rotational velocity of the polygon mirror is controlled in response to the polygon command value.

Abstract: Facet-to-facet pyramidal wobble is corrected without resorting to cylindrical optics by adapting agile beam concepts to provide real-time control of the light beam position on the photoreceptor. The agile beam is provided by either or both of a variable wavelength light source or a variable index of refraction prism. The position of the light beam is determined by either or both of a super linear position detector directly detecting the position of the light beam, or a facet detector and a look-up table for indirectly estimating the position of the light beam. By actively compensating for pyramidal wobble, the passive but expensive and difficult-to-position cylindrical optics can be replaced with cheap and easy-to-position spherical optics.

Abstract: The raster scanning system of the present invention includes a beam generator which generates a beam of radiant energy in response to a drive signal. The drive signal comprising a series of pulses. The raster scanning system further includes a polygon having an overfilled facet design in which a plurality of facets are at least partially positioned in the optical path of the beam of radiant energy regardless of the rotational position of the polygon. The polygon being adapted to scan a spot across a beam receiving surface. Additionally the raster scanning system includes spot size correcting means for maintaining a constant spot size of the scanned spot by modulating the pulse width of the drive signal provided to the beam generator.