Xerox Corporation

George A Charnitski

Stephen C Corona

Thomas J Hammond

James D Rees

James J Appel

Steven C Hart

Aron Nacman

Richard F Lehman

Charles J Urso, Iii

Jacob N Kluger

Robert H Melino

Donald E Wiedrich

A printbar assembly comprised of an array of light emitters, and array of gradient index lenses, and a light control film. The light control film, which is comprised of a plurality of microlouvers, is disposed such that it limits the angle at which light from the light emitters can enter the gradient index lenses. The light control film increases the depth of focus of the gradient index lens array without significantly reducing the effective radiometric efficiency.

LED printbars with depth of focus enhancement

An image bar printing system, which, in a preferred embodiment, utilizes a plurality of LED arrays to provide a plurality of color images. The print bars are used in conjunction with a plurality of gradient index lens arrays which optically couple and focus the LED outputs onto a photosensitive surface. In order to maintain image-to-image registration, out of spec deviations in active write length of the image bar and scan line bow are identified and compensated for by selective deformation of one or more lens arrays in a specified manner. The lens deformation serves to reorient the position of certain of the lens elements, redirecting the transmitted LED outputs so as to shorten or lengthen the active write length, or to eliminate bow in the scan line.

Method and apparatus to correct for active write length and bow changes

Uniformity light output of an LED printbar is achieved by a technique which senses the operational on time of each LED. When the on time difference between the LED with the longest on time and the LED with the shortest on time exceeds a predetermined value, the outputs of at least some LEDs comprising the printbar are compensated for to normalize their light output. This normalization is achieved via a drive circuit which drives each LED based upon correction data, and by determining an update of the correction data based upon the difference between the on time of individual LEDs. The correction data is determined when the difference between the on time of the LED with the longest on time and the on time of the LED with the shortest on time exceeds a predetermined maximum difference.

Automatic LED printbar uniformity and adjustment

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.

Lower resolution led bars used for 600 SPI printing

An image bar recording system, which, in a preferred embodiment, utilizes a plurality of LED image bars to provide a plurality of latent images which may subsequently be developed in different colors. The print bars are initially aligned so that each color image is precisely registered at the same relative position along the exposed area of a photoreceptor belt. The alignment is accomplished by adding non-image fiduciary pixels to the ends of each print bar and by forming a pair of opposed alignment apertures in the surface of the belt. Y-axis alignment of the print bars is accomplished by detecting edge locations of a first pixel and using this location to select a centrally located fiduciary pixel. The X-axis alignment is then obtained by rotating the print bar to bring a second selected image pixel into alignment as sensed through a second aperture. Once the initial X and Y-axis alignments are complete, subsequent alignment is maintained through subsequent passes by checking the positions of the previously identified pixels as they advance past additional lead edge apertures formed in the process direction along the belt surface.

Method and apparatus for aligning multiple print bars in a single pass

An apparatus and method for detecting the seam in a photoreceptor belt is provided. A sensor is positioned on one side of the belt in opposed relationship to a light source which can be a lamp dedicated solely to that purpose or light from an imager such as an LED array or a Raster Output Scanner. Illumination from the light source of the end of the array is detected by a sensor when the seam passes therebetween creating a characteristic output signal which is recognized by system software and used to control imager operation to ensure that latent images are not formed across the seam.

Photoreceptor belt seam detection and process control

An image bar recording system, which, in a preferred embodiment, utilizes a plurality of LED image bars, forms a plurality of latent images, which may subsequently be developed in different colors. The print bars are initially aligned so that each color image is in precise lateral registration on the surface of a photoreceptor belt. The registration is accomplished by first forming a Z-shaped pattern along the non-image edge of a photoreceptor belt, the pattern extending in the direction of the belt motion (process direction). Each print bar is positioned adjacent the belt surface and the pixels of the LED array are selectively energized to form the desired image. An array of non-imaging pixels is contiguous to the image-forming pixels and positioned along the belt so as to be periodically visible through the Z-shaped pattern by photosensors positioned beneath each of the print bars. By an iterative energization process, one of the end pixels of each array is identified as a fiduciary pixel lying at the center trace line of the Z-shaped pattern. Upon recognition of the fiduciary pixel, the system controller establishes a #1 write pixel at the other end of the array. Each bar is initially laterally aligned by enabling fiduciary and #1 pixels in the same manner. A predetermined tolerance is stored in system memory and in circuitry associated with detecting the position of the fiduciary pixel. During operation, if the tolerance is found to be exceeded (the fiduciary pixel is detected as no longer along the center trace line of the Z-shaped pattern), correction signals are generated which select a new fiduciary pixel which is within the tolerance range, the new fiduciary pixel also establishing a new #1 write pixel. The detection circuitry is designed to discriminate between the exceeding of tolerance conditions caused by lateral motion of a print bar or by lateral motion of the photoreceptor belt, and to generate the appropriate correction signals.

Method and apparatus for lateral registration of sequential images in a

Overall length of LED print bars arranged in a single pass printing system is controlled by controlling the operating temperature of the LED arrays forming the light emitting portion of the print bar. Rather than trying to maintain the arrays at some predetermined temperature, the array temperatures are allowed to vary over a predetermined range but within this range, the arrays are all at the same temperature. This is accomplished by mounting the arrays on a common subframe which is adapted to circulate a cooling medium through each of the arrays in parallel rather than in series. Thus, each array is cooled at the same rate and will attain the same equilibrium temperature, thus ensuring that registration will be accomplished within each single pass operation.

Method and apparatus to control overall write length in LED print bars

A test procedure is provided for obtaining optimum illumination exposure in a document scanning an exposure system. A document illumination lamp is energized and reflection images from a document platen is transmitted through an optical system onto a linear photosensor array which is positioned in the normal exposure (image) plane. The array outputs, corresponding to individual photodiodes outputs, are amplified and processed under the control of a computer controlled software program to provide a real time display of the illumination characteristics on a display screen. The screen, in one embodiment, displays a colored bar graph which is superimposed against the horizontal line representing an in specification illumination level. The lamp and, or, illuminator, is repositioned while observing the bar graph until an optimum bar graph value is measured below the specification line. Other displays are provided to monitor and adjust performance of an infrared densitometer and to adjust the gain of the individual photodiodes which form the photosensitive array.

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Fairport, NY, United States of America

George A Charnitski