Patent Publication Number: US-2023138562-A1

Title: Electrophotographic printing system including lateral translations to reduce burn-in artifacts

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior U.S. patent application Ser. No. 17/518,664, filed Nov. 4, 2021, which is hereby incorporated herein by reference in its entirety. 
     Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 17/518,645, entitled: “Electrophotographic printing system with reduced burn-in artifacts”, by T. Schwartz et al.; to commonly assigned, co-pending U.S. patent application Ser. No. 17/516,800, entitled: “Printing system for media with non-uniform thickness”, by T. Schwartz et al.; to commonly assigned, co-pending U.S. patent application Ser. No. 17/516,820, entitled: “Printing system for media with asymmetric characteristics”, by C. H. Kuo et al.; to commonly assigned, co-pending U.S. patent application Ser. No. 17/516,827, entitled: “Printing system for printing on tabbed media”, by C. H. Kuo et al.; and to commonly assigned, co-pending U.S. Patent Application Ser. No. 63/166,266, entitled: “Electrophotographic printing system with reduced burn-in artifacts”, by T. Schwartz et al., each of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to the field of digital printing, and more particularly to printing on media having non-uniform thickness profile characteristics. 
     BACKGROUND OF THE INVENTION 
     Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium (e.g., glass, fabric, metal, or other objects) as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (i.e., a “latent image”). 
     After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a toner image. Note that the toner image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner). 
     After the latent image is developed into a toner image on the photoreceptor, a suitable receiver is brought into juxtaposition with the toner image. A suitable electric field is applied to transfer the toner particles of the toner image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors. 
     The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (i.e., “fuse”) the print image to the receiver. Plural print images (e.g., separation images of different colors) can be overlaid on the receiver before fusing to form a multicolor print image on the receiver. 
     One problem that can occur in electrophotographic printing systems is known as “image burn-in” which occurs when a sequence of the same or similar pages having similar image data or patterns are printed. In this case, the performance of various system components can change as a function of position due to the repeated printing of the similar image data or patterns. This can cause subsequently printed images to have characteristics that vary in accordance with the repeated image data or pattern, thereby having a negative impact on image quality. Such artifacts are commonly referred to as “image burn-in artifacts.” This can require that the affected system components be more frequently serviced or even replaced to eliminate the artifacts which can add significant cost and system down-time. 
     There remains a need for an improved method to reduce image burn-in artifacts in an electrophotographic printing system when printing an extended sequence of similar pages. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method for reducing image burn-in artifacts in an electrophotographic printing system, including: 
     receiving a print job including image data for a set of pages to be printed with the electrophotographic printing system; 
     determining that the image data for a sequence of pages in the print job are similar; and 
     using an electrophotographic print engine to print the similar pages using a pattern of lateral translations wherein the image data is laterally translated such that it is printed at a different lateral position on the printed page. 
     This invention has the advantage that image burn-in artifacts can be reduced. 
     It has the additional advantage that components of the printing system will need to be replaced or reconditioned less frequently, thereby reducing cost and system downtime. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an elevational cross-section of an electrophotographic printer suitable for use with various embodiments; 
         FIG.  2    is an elevational cross-section of one printing module of the electrophotographic printer of  FIG.  1   ; 
         FIG.  3 A  is an example of a page having image content that is susceptible to producing image burn-in artifacts; 
         FIG.  3 B  illustrates a fuser roller having a roughened surface in regions corresponding to the dark image content in the page of  FIG.  3 A ; 
         FIG.  3 C  illustrates image burn-in artifacts formed from the fuser roller of  FIG.  3 B ; 
         FIG.  4    is a flowchart of a method for printing similar pages using a pattern of page orientations in accordance with an exemplary embodiment; 
         FIG.  5    is a flowchart of a method for analyzing image data for a sequence of pages to identify similar pages in accordance with an exemplary embodiment; 
         FIG.  6    illustrates a cross-track image profile determined from the image data for the exemplary page of  FIG.  3 A ; 
         FIG.  7    illustrates an exemplary pattern of page orientations; 
         FIG.  8    illustrates a finishing system which offsets the lateral positions of the printed pages with different orientations; 
         FIG.  9    illustrates a finishing system which sends the printed pages with different orientations to different output trays; 
         FIG.  10    illustrates a finishing system which rotates the orientation of the pages printed with the second orientation; 
         FIG.  11    shows a flowchart of a method for printing similar pages using a pattern of page translations in accordance with an alternate embodiment; 
         FIG.  12    illustrates an exemplary pattern of page translations; 
         FIG.  13 A  illustrates an example of a printed similar page where the image content is printed in a nominal position; and 
         FIG.  13 B  illustrates an example of a printed similar page where the image content is printed in a translated position. 
     
    
    
     It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is inclusive of combinations of the embodiments described herein. References to “a particular embodiment” and the like refer to features that are present in at least one embodiment of the invention. Separate references to “an embodiment” or “particular embodiments” or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated, or as are readily apparent to one of skill in the art. The use of singular or plural in referring to the “method” or “methods” and the like is not limiting. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense. 
     As used herein, “toner particles” are particles of one or more material(s) that are transferred by an electrophotographic (EP) printer to a receiver to produce a desired effect or structure (e.g., a print image, texture, pattern, or coating) on the receiver. Toner particles can be ground from larger solids, or chemically prepared (e.g., precipitated from a solution of a pigment and a dispersant using an organic solvent), as is known in the art. Toner particles can have a range of diameters (e.g., less than 8 μm, on the order of 10-15 μm, up to approximately 30 μm, or larger), where “diameter” preferably refers to the volume-weighted median diameter, as determined by a device such as a Coulter Multisizer. When practicing this invention, it is preferable to use larger toner particles (i.e., those having diameters of at least 20 μm) in order to obtain the desirable toner stack heights that would enable macroscopic toner relief structures to be formed. 
     “Toner” refers to a material or mixture that contains toner particles, and that can be used to form an image, pattern, or coating when deposited on an imaging member including a photoreceptor, a photoconductor, or an electrostatically-charged or magnetic surface. Toner can be transferred from the imaging member to a receiver. Toner is also referred to in the art as marking particles, dry ink, or developer, but note that herein “developer” is used differently, as described below. Toner can be a dry mixture of particles or a suspension of particles in a liquid toner base. 
     As mentioned already, toner includes toner particles; it can also include other types of particles. The particles in toner can be of various types and have various properties. Such properties can include absorption of incident electromagnetic radiation (e.g., particles containing colorants such as dyes or pigments), absorption of moisture or gasses (e.g., desiccants or getters), suppression of bacterial growth (e.g., biocides, particularly useful in liquid-toner systems), adhesion to the receiver (e.g., binders), electrical conductivity or low magnetic reluctance (e.g., metal particles), electrical resistivity, texture, gloss, magnetic remanence, florescence, resistance to etchants, and other properties of additives known in the art. 
     In single-component or mono-component development systems, “developer” refers to toner alone. In these systems, none, some, or all of the particles in the toner can themselves be magnetic. However, developer in a mono-component system does not include magnetic carrier particles. In dual-component, two-component, or multi-component development systems, “developer” refers to a mixture including toner particles and magnetic carrier particles, which can be electrically-conductive or -non-conductive. Toner particles can be magnetic or non-magnetic. The carrier particles can be larger than the toner particles (e.g., 15-20 μm or 20-300 μm in diameter). A magnetic field is used to move the developer in these systems by exerting a force on the magnetic carrier particles. The developer is moved into proximity with an imaging member or transfer member by the magnetic field, and the toner or toner particles in the developer are transferred from the developer to the member by an electric field, as will be described further below. The magnetic carrier particles are not intentionally deposited on the member by action of the electric field; only the toner is intentionally deposited. However, magnetic carrier particles, and other particles in the toner or developer, can be unintentionally transferred to an imaging member. Developer can include other additives known in the art, such as those listed above for toner. Toner and carrier particles can be substantially spherical or non-spherical. 
     The electrophotographic process can be embodied in devices including printers, copiers, scanners, and facsimiles, and analog or digital devices, all of which are referred to herein as “printers.” Various embodiments described herein are useful with electrostatographic printers such as electrophotographic printers that employ toner developed on an electrophotographic receiver, and ionographic printers and copiers that do not rely upon an electrophotographic receiver. Electrophotography and ionography are types of electrostatography (printing using electrostatic fields), which is a subset of electrography (printing using electric fields). The present invention can be practiced using any type of electrographic printing system, including electrophotographic and ionographic printers. 
     A digital reproduction printing system (“printer”) typically includes a digital front-end processor (DFE), a print engine (also referred to in the art as a “printing module” or a “marking engine”) for applying toner to the receiver, and one or more post-printing finishing system(s) (e.g., a UV coating system, a glosser system, or a laminator system). A printer can reproduce pleasing black-and-white or color images onto a receiver. A printer can also produce selected patterns of toner on a receiver, which patterns (e.g., surface textures) do not correspond directly to a visible image. 
     The DFE receives input electronic files (such as Postscript command files) composed of images from other input devices (e.g., a scanner, a digital camera or a computer-generated image processor). Within the context of the present invention, images can include photographic renditions of scenes, as well as other types of visual content such as text or graphical elements. Images can also include invisible content such as specifications of texture, gloss or protective coating patterns. 
     The DFE can include various function processors, such as a raster image processor (RIP), image positioning processor, image manipulation processor, color processor, or image storage processor. The DFE rasterizes input electronic files into image bitmaps for the printing module to print. In some embodiments, the DFE permits a human operator to set up parameters such as layout, font, color, paper type, or post-finishing options. The printing module takes the rasterized image bitmap from the DFE and renders the bitmap into a form that can control the printing process from the exposure device to transferring the print image onto the receiver. The finishing system applies features such as protection, glossing, or binding to the prints. The finishing system can be implemented as an integral component of a printer, or as a separate machine through which prints are fed after they are printed. 
     The printer can also include a color management system that accounts for characteristics of the image printing process implemented in the printing module (e.g., the electrophotographic process) to provide known, consistent color reproduction characteristics. The color management system can also provide known color reproduction for different inputs (e.g., digital camera images or film images). Color management systems are well-known in the art, and any such system can be used to provide color corrections in accordance with the present invention. 
     In an embodiment of an electrophotographic modular printing machine useful with various embodiments (e.g., the NEXPRESS SX 3900 printer manufactured by Eastman Kodak Company of Rochester, N.Y.) color-toner print images are made in a plurality of color imaging modules arranged in tandem, and the print images are successively electrostatically transferred to a receiver adhered to a transport web moving through the modules. Colored toners include colorants, (e.g., dyes or pigments) which absorb specific wavelengths of visible light. Commercial machines of this type typically employ intermediate transfer members in the respective modules for transferring visible images from the photoreceptor and transferring print images to the receiver. In other electrophotographic printers, each visible image is directly transferred to a receiver to form the corresponding print image. 
     Electrophotographic printers having the capability to also deposit clear toner using an additional imaging module are also known. The provision of a clear-toner overcoat to a color print is desirable for providing features such as protecting the print from fingerprints, reducing certain visual artifacts or providing desired texture or surface finish characteristics. Clear toner uses particles that are similar to the toner particles of the color development stations but without colored material (e.g., dye or pigment) incorporated into the toner particles. However, a clear-toner overcoat can add cost and reduce color gamut of the print; thus, it is desirable to provide for operator/user selection to determine whether or not a clear-toner overcoat will be applied to the entire print. A uniform layer of clear toner can be provided. A layer that varies inversely according to heights of the toner stacks can also be used to establish level toner stack heights. The respective color toners are deposited one upon the other at respective locations on the receiver and the height of a respective color toner stack is the sum of the toner heights of each respective color. Uniform stack height provides the print with a more even or uniform gloss. 
       FIGS.  1 - 2    are elevational cross-sections showing portions of a typical electrophotographic printer  100  useful with various embodiments. Printer  100  is adapted to produce images, such as single-color images (i.e., monochrome images), or multicolor images such as CMYK, or pentachrome (five-color) images, on a receiver. Multicolor images are also known as “multi-component” images. One embodiment involves printing using an electrophotographic print engine having five sets of single-color image-producing or image-printing stations or modules arranged in tandem, but more or less than five colors can be combined on a single receiver. Other electrophotographic writers or printer apparatuses can also be included. Various components of printer  100  are shown as rollers; other configurations are also possible, including belts. 
     Referring to  FIG.  1   , printer  100  is an electrophotographic printing apparatus having a number of tandemly-arranged electrophotographic image-forming printing modules  31 ,  32 ,  33 ,  34 ,  35 , also known as electrophotographic imaging subsystems. Each printing module  31 ,  32 ,  33 ,  34 ,  35  produces a single-color toner image for transfer using a respective transfer subsystem  50  (for clarity, only one is labeled) to a receiver  42  successively moved through the modules. In some embodiments one or more of the printing module  31 ,  32 ,  33 ,  34 ,  35  can print a colorless toner image, which can be used to provide a protective overcoat or tactile image features. Receiver  42  is transported from supply unit  40 , which can include active feeding subsystems as known in the art, into printer  100  using a transport web  81 . In various embodiments, the visible image can be transferred directly from an imaging roller to a receiver, or from an imaging roller to one or more transfer roller(s) or belt(s) in sequence in transfer subsystem  50 , and then to receiver  42 . Receiver  42  is, for example, a selected section of a web or a cut sheet of a planar receiver media such as paper or transparency film. 
     In the illustrated embodiments, each receiver  42  can have up to five single-color toner images transferred in registration thereon during a single pass through the five printing modules  31 ,  32 ,  33 ,  34 ,  35  to form a pentachrome image. As used herein, the term “pentachrome” implies that in a print image, combinations of various of the five colors are combined to form other colors on the receiver at various locations on the receiver, and that all five colors participate to form process colors in at least some of the subsets. That is, each of the five colors of toner can be combined with toner of one or more of the other colors at a particular location on the receiver to form a color different than the colors of the toners combined at that location. In an exemplary embodiment, printing module  31  forms black (K) print images, printing module  32  forms yellow (Y) print images, printing module  33  forms magenta (M) print images, and printing module  34  forms cyan (C) print images. 
     Printing module  35  can form a red, blue, green, or other fifth print image, including an image formed from a clear toner (e.g., one lacking pigment). The four subtractive primary colors, cyan, magenta, yellow, and black, can be combined in various combinations of subsets thereof to form a representative spectrum of colors. The color gamut of a printer (i.e., the range of colors that can be produced by the printer) is dependent upon the materials used and the process used for forming the colors. The fifth color can therefore be added to improve the color gamut. In addition to adding to the color gamut, the fifth color can also be a specialty color toner or spot color, such as for making proprietary logos or colors that cannot be produced with only CMYK colors (e.g., metallic, fluorescent, or pearlescent colors), or a clear toner or tinted toner. Tinted toners absorb less light than they transmit, but do contain pigments or dyes that move the hue of light passing through them towards the hue of the tint. For example, a blue-tinted toner coated on white paper will cause the white paper to appear light blue when viewed under white light, and will cause yellows printed under the blue-tinted toner to appear slightly greenish under white light. 
     Receiver  42   a  is shown after passing through printing module  31 . Print image  38  on receiver  42   a  includes unfused toner particles. Subsequent to transfer of the respective print images, overlaid in registration, one from each of the respective printing modules  31 ,  32 ,  33 ,  34 ,  35 , receiver  42   a  is advanced to a fuser module  60  (i.e., a fusing or fixing assembly) to fuse the print image  38  to the receiver  42   a . Transport web  81  transports the print-image-carrying receivers to the fuser module  60 , which fixes the toner particles to the respective receivers, generally by the application of heat and pressure. The receivers are serially de-tacked from the transport web  81  to permit them to feed cleanly into the fuser module  60 . The transport web  81  is then reconditioned for reuse at cleaning station  86  by cleaning and neutralizing the charges on the opposed surfaces of the transport web  81 . A mechanical cleaning station (not shown) for scraping or vacuuming toner off transport web  81  can also be used independently or with cleaning station  86 . The mechanical cleaning station can be disposed along the transport web  81  before or after cleaning station  86  in the direction of rotation of transport web  81 . 
     In the illustrated embodiment, the fuser module  60  includes a heated fusing roller  62  and an opposing pressure roller  64  that form a fusing nip  66  therebetween. In an embodiment, fuser module  60  also includes a release fluid application substation  68  that applies release fluid, e.g., silicone oil, to fusing roller  62 . Alternatively, wax-containing toner can be used without applying release fluid to the fusing roller  62 . Other embodiments of fusers, both contact and non-contact, can be employed. For example, solvent fixing uses solvents to soften the toner particles so they bond with the receiver. Photoflash fusing uses short bursts of high-frequency electromagnetic radiation (e.g., ultraviolet light) to melt the toner. Radiant fixing uses lower-frequency electromagnetic radiation (e.g., infrared light) to more slowly melt the toner. Microwave fixing uses electromagnetic radiation in the microwave range to heat the receivers (primarily), thereby causing the toner particles to melt by heat conduction, so that the toner is fixed to the receiver. 
     The fused receivers (e.g., receiver  42   b  carrying fused image  39 ) are transported in series from the fuser module  60  along a path either to an output tray  69 , or back to printing modules  31 ,  32 ,  33 ,  34 ,  35  to form an image on the backside of the receiver (i.e., to form a duplex print). Receivers  42   b  can also be transported to any suitable output accessory. For example, an auxiliary fuser or glossing assembly can provide a clear-toner overcoat. Printer  100  can also include multiple fuser modules  60  to support applications such as overprinting, as known in the art. 
     In various embodiments, between the fuser module  60  and the output tray  69 , receiver  42   b  passes through a finishing system  70 . Finishing system  70  performs various paper-handling operations, such as folding, stapling, saddle-stitching, collating, and binding. 
     Printer  100  includes main printer apparatus logic and control unit (LCU)  99 , which receives input signals from various sensors associated with printer  100  and sends control signals to various components of printer  100 . LCU  99  can include a microprocessor incorporating suitable look-up tables and control software executable by the LCU  99 . It can also include a field-programmable gate array (FPGA), programmable logic device (PLD), programmable logic controller (PLC) (with a program in, e.g., ladder logic), microcontroller, or other digital control system. LCU  99  can include memory for storing control software and data. In some embodiments, sensors associated with the fuser module  60  provide appropriate signals to the LCU  99 . In response to the sensor signals, the LCU  99  issues command and control signals that adjust the heat or pressure within fusing nip  66  and other operating parameters of fuser module  60 . This permits printer  100  to print on receivers of various thicknesses and surface finishes, such as glossy or matte. 
     Image data for printing by printer  100  can be processed by a raster image processor (RIP; not shown), which can include a color separation screen generator or generators. The output of the RIP can be stored in frame or line buffers for transmission of the color separation print data to each of a set of respective LED writers associated with the printing modules  31 ,  32 ,  33 ,  34 ,  35  (e.g., for black (K), yellow (Y), magenta (M), cyan (C), and red (R) color channels, respectively). The RIP or color separation screen generator can be a part of printer  100  or remote therefrom. Image data processed by the RIP can be obtained from a color document scanner or a digital camera or produced by a computer or from a memory or network which typically includes image data representing a continuous image that needs to be reprocessed into halftone image data in order to be adequately represented by the printer. The RIP can perform image processing processes (e.g., color correction) in order to obtain the desired color print. Color image data is separated into the respective colors and converted by the RIP to halftone dot image data in the respective color (for example, using halftone matrices, which provide desired screen angles and screen rulings). The RIP can be a suitably-programmed computer or logic device and is adapted to employ stored or computed halftone matrices and templates for processing separated color image data into rendered image data in the form of halftone information suitable for printing. These halftone matrices can be stored in a screen pattern memory. 
       FIG.  2    shows additional details of printing module  31 , which is representative of printing modules  32 ,  33 ,  34 , and  35  ( FIG.  1   ). Photoreceptor  206  of imaging member  111  includes a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated. In various embodiments, photoreceptor  206  is part of, or disposed over, the surface of imaging member  111 , which can be a plate, drum, or belt. Photoreceptors can include a homogeneous layer of a single material such as vitreous selenium or a composite layer containing a photoconductor and another material. Photoreceptors  206  can also contain multiple layers. 
     Charging subsystem  210  applies a uniform electrostatic charge to photoreceptor  206  of imaging member  111 . In an exemplary embodiment, charging subsystem  210  includes a wire grid  213  having a selected voltage. Additional necessary components provided for control can be assembled about the various process elements of the respective printing modules. Meter  211  measures the uniform electrostatic charge provided by charging subsystem  210 . 
     An exposure subsystem  220  is provided for selectively modulating the uniform electrostatic charge on photoreceptor  206  in an image-wise fashion by exposing photoreceptor  206  to electromagnetic radiation to form a latent electrostatic image. The uniformly-charged photoreceptor  206  is typically exposed to actinic radiation provided by selectively activating particular light sources in an LED array or a laser device outputting light directed onto photoreceptor  206 . In embodiments using laser devices, a rotating polygon (not shown) is sometimes used to scan one or more laser beam(s) across the photoreceptor in the fast-scan direction. One pixel site is exposed at a time, and the intensity or duty cycle of the laser beam is varied at each dot site. In embodiments using an LED array, the array can include a plurality of LEDs arranged next to each other in a line, all dot sites in one row of dot sites on the photoreceptor can be selectively exposed simultaneously, and the intensity or duty cycle of each LED can be varied within a line exposure time to expose each pixel site in the row during that line exposure time. 
     As used herein, an “engine pixel” is the smallest addressable unit on photoreceptor  206  which the exposure subsystem  220  (e.g., the laser or the LED) can expose with a selected exposure different from the exposure of another engine pixel. Engine pixels can overlap (e.g., to increase addressability in the slow-scan direction). Each engine pixel has a corresponding engine pixel location, and the exposure applied to the engine pixel location is described by an engine pixel level. 
     The exposure subsystem  220  can be a write-white or write-black system. In a write-white or “charged-area-development” system, the exposure dissipates charge on areas of photoreceptor  206  to which toner should not adhere. Toner particles are charged to be attracted to the charge remaining on photoreceptor  206 . The exposed areas therefore correspond to white areas of a printed page. In a write-black or “discharged-area development” system, the toner is charged to be attracted to a bias voltage applied to photoreceptor  206  and repelled from the charge on photoreceptor  206 . Therefore, toner adheres to areas where the charge on photoreceptor  206  has been dissipated by exposure. The exposed areas therefore correspond to black areas of a printed page. 
     In the illustrated embodiment, meter  212  is provided to measure the post-exposure surface potential within a patch area of a latent image formed from time to time in a non-image area on photoreceptor  206 . Other meters and components can also be included (not shown). 
     A development station  225  includes toning shell  226 , which can be rotating or stationary, for applying toner of a selected color to the latent image on photoreceptor  206  to produce a developed image on photoreceptor  206  corresponding to the color of toner deposited at this printing module  31 . Development station  225  is electrically biased by a suitable respective voltage to develop the respective latent image, which voltage can be supplied by a power supply (not shown). Developer is provided to toning shell  226  by a supply system (not shown) such as a supply roller, auger, or belt. Toner is transferred by electrostatic forces from development station  225  to photoreceptor  206 . These forces can include Coulombic forces between charged toner particles and the charged electrostatic latent image, and Lorentz forces on the charged toner particles due to the electric field produced by the bias voltages. 
     In some embodiments, the development station  225  employs a two-component developer that includes toner particles and magnetic carrier particles. The exemplary development station  225  includes a magnetic core  227  to cause the magnetic carrier particles near toning shell  226  to form a “magnetic brush,” as known in the electrophotographic art. Magnetic core  227  can be stationary or rotating, and can rotate with a speed and direction the same as or different than the speed and direction of toning shell  226 . Magnetic core  227  can be cylindrical or non-cylindrical, and can include a single magnet or a plurality of magnets or magnetic poles disposed around the circumference of magnetic core  227 . Alternatively, magnetic core  227  can include an array of solenoids driven to provide a magnetic field of alternating direction. Magnetic core  227  preferably provides a magnetic field of varying magnitude and direction around the outer circumference of toning shell  226 . Development station  225  can also employ a mono-component developer comprising toner, either magnetic or non-magnetic, without separate magnetic carrier particles. 
     Transfer subsystem  50  includes transfer backup member  113 , and intermediate transfer member  112  for transferring the respective print image from photoreceptor  206  of imaging member  111  through a first transfer nip  201  to surface  216  of intermediate transfer member  112 , and then to a receiver  42  which receives respective toned print images  38  from each printing module in superposition to form a composite image thereon. The print image  38  is, for example, a separation of one color, such as cyan. Receiver  42  is transported by transport web  81 . Transfer to a receiver is affected by an electrical field provided to transfer backup member  113  by power source  240 , which is controlled by LCU  99 . Receiver  42  can be any object or surface onto which toner can be transferred from imaging member  111  by application of the electric field. In this example, receiver  42  is shown prior to entry into a second transfer nip  202 , and receiver  42   a  is shown subsequent to transfer of the print image  38  onto receiver  42   a . In the illustrated embodiment, the toner image is transferred from the photoreceptor  206  to the intermediate transfer member  112 , and from there to the receiver  42 . Registration of the separate toner images is achieved by registering the separate toner images on the receiver  42 , as is done with the NEXPRESS SX 3900. In some embodiments, a single transfer member is used to sequentially transfer toner images from each color channel to the receiver  42 . In other embodiments, the separate toner images can be transferred in register directly from the photoreceptor  206  in the respective printing module  31 ,  32 ,  33 ,  34 ,  25  to the receiver  42  without using a transfer member. Either transfer process is suitable when practicing this invention. An alternative method of transferring toner images involves transferring the separate toner images, in register, to a transfer member and then transferring the registered image to a receiver. 
     LCU  99  sends control signals to the charging subsystem  210 , the exposure subsystem  220 , and the respective development station  225  of each printing module  31 ,  32 ,  33 ,  34 ,  35  ( FIG.  1   ), among other components. Each printing module can also have its own respective controller (not shown) coupled to LCU  99 . 
     As discussed in the background section, one problem that can occur in electrophotographic printing systems is known as “image burn-in” which can occur when a sequence of the same or similar pages having similar image data or patterns are printed. In this case, the performance of various system components can change as a function of position due to the repeated printing of the similar image data or patterns. This can cause subsequently printed images to have characteristics that vary in accordance with the repeated image data or pattern (i.e., “image burn-in artifacts”). This can require that the affected system components be frequently serviced, or even replaced, to eliminate the artifacts which can add significant cost and system down-time. 
     One system component that has been found to be particularly susceptible to the formation of image burn-in artifacts is the fuser module  60  (see  FIG.  1   ). The toner stacks that form the print image  38  on the receiver  42  generally have a higher roughness than the receiver  42 . As a result, when the receiver  42  passes through the fuser module  60 , the roughness of the toner can affect the surface of the fusing roller  62 . If a large number of pages are printed that have high-density image content at the same cross-track position, the surface characteristics of the corresponding portion of the fusing roller  62  can be changed (e.g., roughened) relative to the portions of the fusing roller  62  that correspond to low-density image content. The spatially-dependent surface characteristics of the fusing roller  62  can then affect the image quality of subsequently printed pages. For example, the gloss of the printed image can be lower in the image regions corresponding to the roughened surface of the fusing roller  62 . 
     Other system components besides the fuser module  60  can also contribute to the formation of burn-in artifacts. For example, the response of the photoreceptor  206  ( FIG.  2   ) can become position dependent when the same image content is repeated imaged. 
       FIG.  3 A  shows an example of a page  250  that is susceptible to producing image burn-in artifacts when printed repeatedly. The page  250  includes dark image content  252  which occurs in a particular cross-track position together with light image content  254 . Over time, the dark image content  252  can modify the surface of the fusing roller  6 , producing a roughened surface  256  as shown in  FIG.  3 B , when many copies of the page  250  are printed. The roughened surface  256  can in turn produce image burn-in artifacts  260  in a subsequently printed page  251  (in this example a uniform gray field) as shown in  FIG.  3 C . In this case, the image burn-in artifacts  260  show up as a lower gloss level in the cross-track positions that correspond to the dark image content  252  in page  250 . 
     The present invention represents a method or system for reducing image burn-in artifacts by varying the image positions when printing a sequence of similar images.  FIG.  4    shows a flowchart of a method that can be used to implement the present invention in accordance with an exemplary embodiment. A print job  305  including image data a set of pages  310  is received using a receive print job step  300 . 
     In some cases, the print job  305  may contain a sequence of pages  310  that include image data or patterns (for example, image content) that are identical or substantially similar. For example, the print job  305  may contain multiple copies of the same page  310 , or may include a series of pages  310  that include similar image content (e.g., a form letter where the name and address of the recipient vary but the rest of the page content is identical). The similar pages may correspond to all of the pages  310  in the print job  305 , or may correspond to a subset of the pages  310  in the print job  305 . 
     An identify similar pages step  315  determines a sequence of similar pages  320  in the print job  305  that have the same or similar image content. In some embodiments, the identify similar pages step  315  identifies the similar pages  320  based on metadata  312  associated with the print job  305  which indicates that the print job  305  includes multiple copies of the same page  310 . For example, the print job  305  may include image data for a single page  310 , together with metadata  312  which instructs the printing system to print a specified number of copies of the page  310 . In this case, it will be known a priori that all of the pages  310  of the print job  305  are identical, and will therefore be included in the sequence of similar pages  320 . 
     In other embodiments, the identify similar pages step  315  determines that the image data for a sequence of pages  310  are similar by automatically analyzing the image data to compute a predefined image similarity metric, and designating sequential pages to be similar by comparing the image similarity metric to a predefined threshold. 
       FIG.  5    shows a flowchart of a method for evaluating the similarity of a first page  310   a  and a second page  310   b  by automatically analyzing the corresponding image data. This method by the identify similar pages step  315  ( FIG.  4   ) to evaluate the similarity of sequential images (e.g., the i th  image and the (i+1) th  images  310  in the print job  305 ). A compute cross-track image profile step  500  is used to analyze the first page  310   a  to determine a corresponding cross-track image profile  505 , and a compute cross-track image profile step  510  is used to analyze the second page  310   b  to determine a corresponding cross-track image profile  515 . 
     Generally, the compute cross-track image profile step  500  and the compute cross-track image profile step  510  will use the same process to determine the corresponding cross-track image profiles  505 ,  515 . In an exemplary embodiment, the compute cross-track image profile steps  500 ,  510  determine the corresponding cross-track image profiles  505 ,  515  by averaging all of the pixels at a particular cross-track position: 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       
                         i 
                           
                       
                     
                     ( 
                     x 
                     ) 
                   
                   = 
                   
                     
                       1 
                       
                         N 
                         y 
                       
                     
                     ⁢ 
                     
                       
                         
                           ∑ 
                           
                             y 
                             = 
                             1 
                           
                         
                         
                           N 
                           y 
                         
                       
                       
                         
                           I 
                           i 
                         
                         ( 
                         
                           x 
                           , 
                           y 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where I i (x,y) is the image data for the i th  page  310 , P i (x) is the corresponding cross-track image profile  505 , x and y are the cross-track and in-track pixel positions, respectively, and Ny is the number of rows in the image data (i.e., the pixels in the in-track dimension). 
       FIG.  6    shows a cross-track image profile  505  determined using Eq. (1) for the exemplary page  250  shown in  FIG.  3 A . It can be seen that toward the left edge of the image profile there is a large dip in the cross-track image profile  505  corresponding to the black bar in the image content which extends down the length of the page  250 . There is also a shallower dip in the cross-track image profile  505  corresponding to the horizontal lines of text in the page. 
     A compute image difference statistics step  520  ( FIG.  5   ) is used to analyze the cross-track image profiles  505 ,  515  to determine one or more image difference statistics  525 . In an exemplary embodiments, the image difference statistics  525  include an RMS difference between the image profiles  505 ,  515 , which is computed based on the profile difference ΔP i : 
       Δ P   i ( x )= P   i+1   −P   i ( x )  (2)
 
     The RMS difference can then be determined to provide the image difference statistic S i : 
     
       
         
           
             
               
                 
                   
                     S 
                     i 
                   
                   = 
                   
                     
                       
                         1 
                         
                           N 
                           x 
                         
                       
                       ⁢ 
                       
                         
                           
                             ∑ 
                             
                               x 
                               = 
                               1 
                             
                           
                           
                             N 
                             x 
                           
                         
                         
                           
                             ( 
                             
                               Δ 
                               ⁢ 
                               
                                 
                                   P 
                                   i 
                                 
                                 ( 
                                 x 
                                 ) 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     In other embodiments, other types of image difference statistics can be determined such as the mean absolute difference between the image profiles, the standard deviation of the profile difference or the variance of the profile difference. 
     A compute image similarity metric step  530  is used to determine an image similarity metric  535  responsive to the image difference statistics  525 . In the case where a single image difference statistic  525  is determined, the image similarity metric  535  can be equal to the image difference statistic  525 , or can be determined by applying a transformation to the image difference statistic  525 . In the case where a plurality of image difference statistics  525  are determined, they can be combined using a predefined function to determine the image similarity metric  535 . In an exemplary embodiment, the image difference statistic S i  determined using Eq. (3) is used directly as the image similarity metric  535  (S). 
     An image similarity test  540  compares the image similarity metric  535  to a predefined threshold  545  (T S ) to classify the pages to be either similar pages  550  or dissimilar pages  555 . If the image similarly metric  535  is less than the predefined threshold (S i &lt;T S ) then the pages are classified to be similar. In an exemplary configuration, a threshold  545  of T S =30 (in an 8-bit encoding having a maximum pixel value of 255) can be used when the image similarity metric  535  is determined using Eq. (3). 
     The burn-in artifacts that are being addressed by the method of the present invention are most visible where there are distinct transitions in the image density within the page which produce corresponding transitions in the response of the various system components (e.g., the fusing roller  62 ). Therefore, if the cross-track image profile  505  does not exhibit any distinct transitions in the image density, then it is generally not necessary to apply the pattern of page orientations  330  ( FIG.  4   ). Referring back to  FIG.  5   , an optional image transitions test  560  can be applied to determine whether there are any distinct transitions. For example, the image transitions test  560  can determine the local range R i (x) of the cross-track image profile  505  as a function of cross-track position: 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       i 
                     
                     ( 
                     x 
                     ) 
                   
                   = 
                   
                     
                       
                         max 
                         
                           x 
                           j 
                         
                       
                       ( 
                       
                         
                           P 
                           i 
                         
                         ( 
                         
                           x 
                           j 
                         
                         ) 
                       
                       ) 
                     
                     - 
                     
                       
                         min 
                         
                           x 
                           j 
                         
                       
                       ( 
                       
                         
                           P 
                           i 
                         
                         ( 
                         
                           x 
                           j 
                         
                         ) 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where the max(⋅) and min(⋅) functions return the maximum and minimum values, respectively, of the cross-track image profile  505  in a window of cross-track positions x j  around the cross-track position x: 
       ( x−W/ 2)≤ x   j ≤( x+W/ 2)  (5)
 
     where W is the window size. If the maximum local range across the page is less than a predefined threshold (max(R i (x))&lt;T R ) then the pages  310   a ,  310   b  are designated to be dissimilar pages  555  such that the pattern of page orientations  330  is not applied even if the image similarity test  540  determines that the pages  310   a ,  310   b  are identical or similar. 
     In some embodiments, the image transitions test  560  can be effectively combined with the image similarity test  540  by providing a single test which determines whether a set of images should be subject to the application of the image rotations. For example, in one such embodiment, an average cross-track profile B i (x) across a range of pages can be obtained by: 
     
       
         
           
             
               
                 
                   
                     
                       B 
                       i 
                     
                     ( 
                     x 
                     ) 
                   
                   = 
                   
                     
                       1 
                       K 
                     
                     ⁢ 
                     
                       
                         
                           ∑ 
                           
                             k 
                             = 
                             0 
                           
                         
                         
                           K 
                           - 
                           1 
                         
                       
                       
                         
                           
                             P 
                             ^ 
                           
                           
                             ( 
                             
                               i 
                               - 
                               k 
                             
                               
                             ) 
                           
                         
                         ( 
                         x 
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where: 
         {circumflex over (P)}   i ( x )= P   i ( x )− p   0   (7)
 
     p0 is the midpoint of the code range for the image data (e.g., 128), and K is the number of pages being averaged. In an exemplary embodiment, the value of K is the same as the number of repeated page orientations N1, N2, in the pattern of page orientations  330  as will be discussed below. For example, in some configurations K=N1=N2=50. 
     If the pages being averaged have a high degree of dissimilarity, then the value of B i (x) will generally have a small magnitude so that it provides a measure of image similarity. Therefore, large magnitudes are indicative of image similarity. Furthermore, sharp transitions in the value of B i (x) as a function of x will be indicative of image content that is susceptible to the formation of image burn-in artifacts. As before, a local range R i (x) of the average cross-track image profile B i (x) can be determined using: 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       i 
                     
                     ( 
                     x 
                     ) 
                   
                   = 
                   
                     
                       
                         max 
                         
                           x 
                           j 
                         
                       
                       ( 
                       
                         
                           B 
                           i 
                         
                         ( 
                         
                           x 
                           j 
                         
                         ) 
                       
                       ) 
                     
                     - 
                     
                       
                         min 
                         
                           x 
                           j 
                         
                       
                       ( 
                       
                         
                           B 
                           i 
                         
                         ( 
                         
                           x 
                           j 
                         
                         ) 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     The maximum of the local range values can then be treated as in image similarity metric: 
     
       
         
           
             
               
                 
                   
                     S 
                     
                       R 
                       , 
                       i 
                     
                   
                   = 
                   
                     
                       max 
                       x 
                     
                     ( 
                     
                       
                         R 
                         i 
                       
                       ( 
                       x 
                       ) 
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     If the maximum local range across the page is greater than a predefined threshold (S R,i ≥T R ), then it can be inferred that the page is similar to the nearby pages, and also that it contains distinct transitions, and it can therefore be designated to belong to the set of similar pages  320  ( FIG.  4   ). 
     In another exemplary embodiment, an image similarity metric is computed based on determining a difference image D i (x,y) between the image data for sequential pages: 
         D   i ( x,y )= I   i+1 ( x,y )− I   i ( x,y )  (9)
 
     where I i (x,y) is the image data associated with the i th  page of the print job  305 , I i+1 (x,y) is the image data associated with the next page, and (x,y) is the row and column pixel address. 
     An image similarity metric can then be determined from the difference image by computing image difference statistics such as the mean absolute difference, the RMS difference, the standard deviation of the difference image or the variance of the difference image. For example, an image similarity metric S D,i  for the i th  page based on the RMS difference can be determined using the equation: 
     
       
         
           
             
               
                 
                   
                     S 
                     
                       D 
                       , 
                       i 
                     
                   
                   = 
                   
                     
                       
                         1 
                         
                           
                             N 
                             x 
                           
                           ⁢ 
                           
                             N 
                             y 
                           
                         
                       
                       ⁢ 
                       
                         
                           
                             ∑ 
                             
                               x 
                               = 
                               1 
                             
                           
                           
                             N 
                             x 
                           
                         
                         
                           
                             
                               ∑ 
                               
                                 y 
                                 = 
                                 1 
                               
                             
                             
                               N 
                               y 
                             
                           
                           
                             
                               ( 
                               
                                 
                                   D 
                                   i 
                                 
                                 ( 
                                 
                                   x 
                                   , 
                                   y 
                                 
                                 ) 
                               
                               ) 
                             
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where N x  and N y  are the number of pixels in the image data in the cross-track and in-track directions, respectively. Two sequential pages are determined to be similar if the image similarity metric is less than a predefined threshold T S . 
     Returning to a discussion of  FIG.  4   , a print similar pages step  325  is used to print the identified set of similar pages  320 . In an exemplary embodiment, the print similar pages step  325  includes a rotate page orientations step  335 , which rotates the page orientations of the similar pages  320  according to a predefined pattern of page orientations  330 . In an exemplary configuration, the rotate page orientations step  335  can be performed in the DFE. The pattern of page orientations  330  preferably includes a first page orientation and a second page orientation where the image or image data to be printed is rotated 180 degrees relative to the first page orientation. The pattern of page orientations  330  specifies a page orientation that should be used for each of the similar pages. When the pattern of page orientations  330  indicates that a particular similar page should be printed with the first page orientation, the unmodified image data is stored in the reoriented similar pages. When the pattern of page orientations  330  indicates that a particular similar page should be printed with the second page orientation, the image data is rotated by 180 degrees and stored in the reoriented similar pages. 
     In an exemplary embodiment, the pattern of page orientations  330  is a repeating pattern which includes N 1  pages in the first orientation followed by N 2  pages in the second orientation, where N 1  and N 2  are predefined integers. Preferably, N 1  and N 2  are in the range of 10 to 500, and more preferably are in the range of 50 to 200. An exemplary pattern of page orientations  330  is shown in  FIG.  7    where N 1 =N 2 =50. The pattern of page orientations  330  indicates which pages should be printed with a first page orientation  331 , and which should be printed with a second page orientation  332 . In other embodiments, the pattern of page orientations  330  can take other forms including non-repeating patterns. 
     Returning to a discussion of  FIG.  4   , a print reoriented similar pages step  345  is used to print the reoriented similar pages  340 , providing a set of printed similar pages  350 . The printed similar pages  350  will include some pages printed with the first page orientation  331  and some pages printed with the second page orientation  332  in accordance with the pattern of page orientations  330 . 
     The printed similar pages  350  will typically be directed into a finishing system  70  ( FIG.  1   ) which includes an output tray  69 . The finishing system  70  is sometimes referred to as a finisher. Since the printed similar pages  350  in the first page orientation  331  will be intermixed with the printed similar pages  350  in the second orientation  332 , in some embodiments it can be desirable for the finishing system  70  to position the printed similar pages  350  differently depending on their page orientation. This can be accomplished using an optional adjust position of printed similar pages step  358  in which the finishing system  70  positions the pages printed in the first orientation  331  in a first position and the pages printed in the second orientation  332  in a second position. 
     In an exemplary embodiment of the adjust position of printed similar pages step  355 , the finishing system  70  deposits the pages printed in the first orientation  331  and the second orientation  332  into a single output tray  69  in first and second positions, respectively, wherein the second position is offset laterally relative to the first position in the output tray. This is illustrated in  FIG.  8    which shows a finishing system  70  having an output tray  69  with a stack of printed similar pages  400 . The stack of printed similar pages  400  includes pages printed in the first orientation  331  positioned in a first position  405  and pages printed in the second orientation  332  positioned in a second position  410 . The second position  410  is offset laterally from the first position  405  by a lateral offset  415 , enabling an operator to easily separate the pages printed in the first and second orientations  331 ,  332  so that they can be manually reoriented into a consistent orientation. 
     In another embodiment of the adjust position of printed similar pages step  355 , the finishing system  70  deposits the pages printed in the first orientation  331  into a first output tray  69   a  and deposits the pages printed in the second orientation  332  into a second output tray  69   b . This is illustrated in  FIG.  9    which shows a printer  100  with a finishing system  70  having two stacker modules  71   a ,  71   b  with respective output trays  69   a ,  69   b . The pages printed in the first orientation  331  are directed into the first stacker module and deposited in the first output tray  69   a  in first position  405 . The pages printed in the second orientation  332  pass through the first stacker module and are directed into the second stacker module  71   b  and deposited in the second output tray  69   b  in second position  410 . This configuration is particularly appropriate for scenarios where all of the similar pages  320  ( FIG.  4   ) are identical such that the order that they are stacked in the finisher  70  is not important. In this case, the operator can manually reorient the stack of printed pages from the second output tray  69   b  before combining it with the stack of printed pages from the first output tray  69   a  to form a single stack of pages with a consistent orientation. While the first and second output trays  69   a ,  69   b  in  FIG.  9    are shown in horizontally adjacent positions, it will be recognized that in other embodiments they can be arranged in other configurations. For example, some printers have a plurality of output trays at different vertical positions (i.e., one above the other) and the pages can be directed into the output trays using appropriate media guides or by raising or lowering the output trays within the finishing system  70  so that the appropriate output tray is aligned with the media path. 
     In another embodiment of the adjust position of printed similar pages step  355 , the finishing system  70  rotates the pages printed in the second orientation  332  using an orientation rotator  420  so that they match the orientation of the pages printed in the first orientation  331  before stacking them in the output tray  69  as illustrated in  FIG.  10   . The orientation rotator  420  can use any appropriate means known in the art to physically rotate the orientation of the pages printed in the second orientation  332 . This is typically accomplished using components such as roller, belts and media guides configured to provide a media transport path in which the orientation is rotated. In the illustrated configuration pages printed in the first orientation  331  are directed along a first paper path  431  (shown with dashed arrows) into the output tray  69 . Pages printed in the second orientation  332  are directed along a second paper path  432  (shown with solid arrows) which takes the printed page through the orientation rotator  420 . The orientation rotator  420  includes a first roller  421  and a second roller  422 . The second paper path  432  directs the printed pages around the first roller  421  which turns the printed pages over so that the front face is facing down and the leading edge is to the right in the figure. The printed pages are then directed around the second roller  422  which turns the printed pages over again so that the front face is now facing up but the page has been reoriented so that it is now in the first orientation  331 . The rotated pages in the first orientation  331  are then directed into the paper tray  69 . One skilled in the art will recognize that the paper paths  431 ,  432  will also include other components such as paper guides that are not shown in  FIG.  10    for clarity. 
     In a variation of the method described with reference to  FIG.  4   , rather than rotating the orientation of the similar pages  320  to reduce the burn-in artifacts, the image data can be repositioned on the page by applying a lateral translation to the image data in the cross-track direction and/or the in-track direction. This alternate embodiment is illustrated in  FIG.  11   . In this configuration, the print similar pages step  325  of  FIG.  4    is replaced by an analogous print similar pages step  365  which applies a pattern of page translations  370  using a translate page positions step  375  to provide a set of translated similar pages  380 . The translated similar pages  380  are then printed by a print translated similar pages step  385  to form the printed similar pages  350 . In an exemplary configuration, the pattern of page translations  370  are lateral translations in the cross-track (x) direction such as those illustrated in  FIG.  12   . In this example, the translations vary continuously within a range of +/−N T  pixels from the nominal position. The value of N T  is chosen such that the translated images don&#39;t have objectionably large changes in the image margins in the printed pages  350 . For example, translations of about ¼ inch may be acceptable in some applications. For a 600 dpi printer, this would correspond to N T =150 pixels. In the example of  FIG.  12   , the pattern of page translations  370  is a periodic pattern which repeats every 100 pages. In other embodiments, the pattern of page translations  370  can have other repeat periods or can take other forms such as random or pseudo-random patterns. 
     An advantage of the  FIG.  11    embodiment is that the printed pages  350  do not need to be reoriented since they will all have a consistent orientation. However, the reduction in the image burn-in artifacts may be less than with the method of  FIG.  4    because rather than shifting the dark image content to a completely different part of the printed page, it is merely shifted by a relatively small displacement. This will have the effect of blurring out any hard edges in the burn-in artifacts, thereby reducing the visibility of the artifacts. 
     Within the context of the present invention, lateral translations are defined to be translations within the plane of the page. In the example of  FIG.  12   , the lateral translations are in the cross-track direction. In other embodiments, the lateral translations can be in the in-track direction, or in both the cross-track and in-track directions. In this case, the pattern of page translations  370  will include a Δy component. For cases where the burn-in artifacts are primarily caused by the fuser module  60 , the cross-track translations will generally provide the most significant improvements, but for burn-in artifacts which originate in other subsystems the in-track translations can also provide significant improvements. 
       FIG.  13 A  shows an example of a printed similar page  350  having image content printed in a nominal content position  390 .  FIG.  13 B  shows an example of a printed similar page  350  where the image content has been translated to a translated content position  392  in accordance with the method of  FIG.  11   . The translated content position  392  is offset in the cross-track direction by a cross-track translation Δx and in the in-track direction by an in-track translation Δy relative to the nominal content position  390 . The result is that the image content is shifted relative to the page borders. In the illustrated example, the effect is to decrease the size of the left margin  394  and the top margin  296  and to increase the size of the right margin  396  and the bottom margin  397 . The cross-track translation Δx and the in-track translation Δy will be varied for each similar page  320  ( FIG.  11   ) in accordance with the pattern of page translations  370 . 
     In some embodiments, the similar pages can be modified by both the pattern of page orientations  330  as in  FIG.  4    and the pattern of page translations  370  in  FIG.  11   . This can further reduce the magnitude of the burn-in artifacts beyond what would be possible with the  FIG.  4    and  FIG.  11    embodiments alone. 
     In embodiments of the present inventions, a controller (such as the logic and control unit  99  in  FIG.  1   ) is used to implement the various operations such as the identify similar pages step  315  and the rotate page orientations step  335  of  FIG.  4   . In some embodiments the controller is a single processing unit operated by appropriate software. In other embodiments, the controller can include a plurality of different processing units each of which implement a portion of the operations. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations, combinations, and modifications can be effected by a person of ordinary skill in the art within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           31  printing module 
           32  printing module 
           33  printing module 
           34  printing module 
           35  printing module 
           38  print image 
           39  fused image 
           40  supply unit 
           42  receiver 
           42   a  receiver 
           42   b  receiver 
           50  transfer subsystem 
           60  fuser module 
           62  fusing roller 
           64  pressure roller 
           66  fusing nip 
           68  release fluid application substation 
           69  output tray 
           69   a  output tray 
           69   b  output tray 
           70  finishing system 
           71   a  stacker module 
           71   b  stacker module 
           81  transport web 
           86  cleaning station 
           99  logic and control unit 
           100  printer 
           111  imaging member 
           112  intermediate transfer member 
           113  transfer backup member 
           201  first transfer nip 
           202  second transfer nip 
           206  photoreceptor 
           210  charging subsystem 
           211  meter 
           212  meter 
           213  grid 
           216  surface 
           220  exposure subsystem 
           225  development subsystem 
           226  toning shell 
           227  magnetic core 
           240  power source 
           250  page 
           252  dark image content 
           254  light image content 
           256  roughened surface 
           260  image burn-in artifacts 
           300  receive print job step 
           305  print job 
           310  page 
           310   a  first page 
           310   b  second page 
           312  metadata 
           315  identify similar pages step 
           320  similar pages 
           325  print similar pages step 
           330  pattern of page orientations 
           331  first page orientation 
           332  second page orientation 
           335  rotate page orientations step 
           340  reoriented similar pages 
           345  print reoriented similar pages step 
           350  printed similar pages 
           355  adjust position of printed similar pages step 
           365  print similar pages step 
           370  pattern of page translations 
           375  translate page positions step 
           380  translated similar pages 
           385  print translated similar pages step 
           390  nominal content position 
           392  translated content position 
           394  left margin 
           395  right margin 
           396  top margin 
           397  bottom margin 
           400  stack of printed similar pages 
           405  first position 
           410  second position 
           415  lateral offset 
           420  orientation rotator 
           421  roller 
           422  roller 
           431  first paper path 
           432  second paper path 
           500  compute cross-track image profile step 
           505  cross-track image profile 
           510  compute cross-track image profile step 
           515  cross-track image profile 
           520  compute image difference statistics step 
           525  image difference statistics 
           530  compute image similarity metric step 
           535  image similarity metric 
           540  image similarity test 
           545  threshold 
           550  similar pages 
           555  dissimilar pages 
           560  image transitions test