Electrophotography – Diagnostics – By inspection of copied image
Reexamination Certificate
2001-02-12
2002-12-03
Pendegrass, Joan (Department: 2852)
Electrophotography
Diagnostics
By inspection of copied image
C399S395000, C399S401000
Reexamination Certificate
active
06490421
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to image forming devices capable of forming text, graphics and/or other symbols on both sides of a media sheet. Specifically, the present invention relates to a method for adjusting the rotational skewing of text, graphics and/or other symbols to be formed on opposing sides of a media sheet relative to one another, as well as relative to the edges of the media sheet.
BACKGROUND OF THE INVENTION
Image forming devices, such as laser printers, inkjet printers, copiers, facsimile devices, and the like, adapted for forming text, graphics and/or other symbols—which will be referred to herein collectively as simply “images”—on a media sheet are well known in the art. These image forming devices typically apply ink or toner to the media sheet—for example, a pre-cut paper sheet—in a specified pattern to form the images thereon. Such devices may also be adapted to form images on both of the opposing sides of a media sheet, the process of forming images on opposing sides of a media sheet commonly being referred to as duplex printing. The advantages of duplex printing include reducing the quantity of paper required for a print set as compared to one-sided (simplex) printing, and generating print sets with layouts resembling that of professionally printed books.
Conventional image forming devices adapted for duplex printing, such as duplex printers, typically include a source device, such as a paper tray, and a feed mechanism or pick roller to draw an individual media sheet from the source device and to feed the media sheet to a print engine. The print engine is configured to receive the media sheet and to form images on one side thereof To form images on the media sheet, the print engine includes a printing apparatus, wherein the printing apparatus may be of the ink jet type or the electrophotographic type (i.e., a laser printer), or any other suitable printing apparatus known in the art. Subsequently, the media sheet—having images formed on one side thereof—is transferred to a path selection gate. If simplex printing is desired, the path selection gate directs the media sheet to an output device, such as an output tray, where the media sheet is retained for pick-up by an operator. If duplex printing is desired, the path selection gate routes the media sheet to a duplexer. The duplexer is an apparatus configured to enable printing of a second, opposing side of the media sheet by the print engine.
In one type of duplexer known in the art, the path selection gate directs the media sheet to a secondary tray where the media sheet is temporarily held. Once all of the media sheets in a print set have received the appropriate images on a first side thereof, respectively, the media sheets are drawn out of the secondary tray and are fed back to the print engine for application of images to a second, opposing side thereof, respectively. In an alternative approach, the duplexer comprises a duplexing paper path configured to directly reverse and return a media sheet (having images applied to one side thereof) to the print engine for application of images to a second side thereof. Operation of the pick roller, print engine, path selection gate, and duplexer is typically controlled by a controller. The controller typically includes firmware, which stores data and routines that enable operation of the image forming device. Also, an image forming device usually includes a control panel for inputting data and/or commands into the controller.
As a media sheet travels through an image forming device, it may become misaligned relative to the print engine, resulting in application of images to the media sheet that are skewed relative to the media sheet, as well as resulting in images on one side of a media sheet that are skewed relative to images on a second, opposing side of the media sheet. Generally, there are two types of skewing, including translational skew and rotational skew. Translational skew occurs when images are offset horizontally and/or vertically from a desired location on a media sheet, and/or when images on one side of a media sheet are horizontally and/or vertically offset from images on a second, opposing side thereof. Rotational skew occurs when images are rotationally offset through an angle from a desired rotational orientation on a media sheet, and/or when images on one side of a media sheet are rotationally offset through an angle relative to the rotational orientation of images on a second, opposing side thereof.
Skew, whether translational or rotational, can result from any one of a number of circumstances, or a combination thereof For example, a media sheet may be misaligned in the source device and this misalignment may not be corrected as the media sheet is drawn out of the source device. Misalignment in the source device may result from wear and tear of the source device and/or from a source device or component thereof that fails to meet design tolerance specifications. Misalignment may also be imparted to a media sheet as it travels from the source tray to the print engine and/or as it travels through a duplexer and back to the print engine. Typically, an image forming device includes a plurality of rollers and guides, as well as one or more actuators, configured to move media sheets through the image forming device and between the pick roller, print engine, path selection gate, and duplexer. Due to extended use, these mechanical parts may become worn or damaged and fail to operate effectively. Also, a roller, guide, actuator, or other mechanical part, may not function properly due to manufacturing defects and/or a failure to meet design tolerance specifications.
The condition of a media sheet itself may affect the manner in which an image forming device is able to manipulate that media sheet. For example, variation in media sheet dimensions may result in skewing, especially in duplex printing wherein both opposing edges of a media sheet may be used for alignment or registration. Variation in media sheet dimensions may be the inherent result of manufacturing processes or such variation may be introduced by a printing process. For instance, electrophotographic printing generally involves passing a media sheet through a heated fuser in order to create a permanent image. Passing the media sheet through a heated fuser may reduce the moisture content of the media sheet and thereby alter one or more of the dimensions of the media sheet during printing. Moreover, the moisture content of a media sheet before printing may affect manipulation of the media sheet by an image forming device. For example, a very high moisture content (i.e., as may be found in a humid climate) or a very low moisture content (i.e., as may be found in a dry climate) of a media sheet may impact the ability of that media sheet to be manipulated by an image forming device, thereby resulting in skew.
It is known in the art to perform duplex registration to compensate for translational skew. Duplex registration generally comprises adjusting the horizontal and/or vertical positions of images on one or both sides of a media sheet to align these images relative to one another in the horizontal and vertical directions. One method for performing duplex registration of an image forming device—such as described in U.S. Pat. No. 6,118,950 to Wibbels et al.—includes printing a test page having, on one side, a first set of horizontal and vertical demarcation elements (i.e., a first portion of a vernier scale) and, on an opposing side, a second set of horizontal and vertical demarcation elements (i.e., a second portion of a vernier scale). The test page can be held up to a light, enabling an operator to compare the second set of demarcation elements against the first set of demarcation elements and, thus, providing the operator with a means for determining horizontal and vertical correction values for images on one or both sides of a media sheet. These horizontal and vertical correction values are then input via a control panel to the image forming device's c
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