System and method for printing system process magnification adjustment

Document processing systems and duplex printing methods are presented in which side 1 to side 2 process magnification errors are compensated for by selective use of two raster output scanner clocks for latent image generation of images destined for first and second sides of a printed substrate, with the second clock speed being increased to compensate for substrate shrinkage due to fusing station heating for two-sided printing.

BACKGROUND

The present exemplary embodiment relates to document processing systems such as printers, copiers, multi-function devices, etc., and more particularly to mitigation of side1to side2process magnification errors (sometimes referred to as “show-thru” or “see-thru error) in printing engines and duplex printing methods for printing images on two sides of a printed substrate. This form of magnification error is seen as a difference in the image size for images printed on two different sides of a printed substrate, and is unacceptable in many customer applications. Show-thru errors are mainly cause by the substrate shrinking when fed through a fusing station after the image is transferred to the first side of the substrate and before an image is transferred to the second side. In particular, conventional duplex printing systems include a duplex routing station and media inverter downstream of the fusing station that reintroduce a printed sheet into the transfer path before the once-printed sheet has had time to be reacclimated to the ambient temperature. The side2image is then transferred to the shrunken paper and becomes larger relative to the side1image once the paper resumes the original size. This results in a process magnification error evident as a show-thru discrepancy between the image sizes on either side of the substrate, with the side2image appearing larger than the side1image in the process direction. The error can be addressed somewhat by shifting the margin for the side2image in order to evenly distribute the magnification error equally on both sides. However, this approach does not reduce the process magnification error, but instead makes it less apparent upon visual inspection. Image data may be manipulated to artificially shrink the side2image, for instance, by removing certain data, but this leads to image defects. Consequently, a need remains for improved printing systems and duplex printing techniques by which the adverse effects of side1to side2process magnification errors can be mitigated.

BRIEF DESCRIPTION

The present disclosure provides document processing systems and printing methods that may be employed to address the above mentioned shortcomings of conventional duplex printing systems by selective use of different scanning speeds for generating latent images on a photoreceptor for images destined for different sides of a printed substrate. The concepts of the disclosure can be advantageously employed to compensate for show-thru error without image distortion effects by selectively operation using two different raster output scanner (ROS) clocks for latent image generation of images destined for different sides of a printed sheet, with the second clock speed used on side2images being increased to compensate for substrate shrinkage during fusing for two-sided printing. This concept can be implemented to accurately correct show-thru errors due to paper shrinkage or any other process magnification effect while avoiding image defects associated with image data manipulation techniques.

In accordance with one or more aspects of the present disclosure, a document processing system is provided, which is comprised of a photoreceptor, such as a belt or drum that continuously moves along a closed path, with two or more raster output scanners (ROSs) located along the path of the photoreceptor, where each ROS is operable to generate a latent image on a portion of the photoreceptor based on a clock input. Corresponding developers are provided downstream of the associated ROSs to develop toner of a given color on the latent image and a transfer station is located downstream of the ROSs for transfer of developed toner from the photoreceptor directly or indirectly to a substrate traveling along a first substrate path. The system also includes a fusing station for fixing the transferred toner to the substrate, a duplex router to selectively direct the substrate along a second path, and a media inverter to invert the substrate and to return it to the first path upstream of the transfer station for two-sided printing operation. The system further comprises first and second clocks providing corresponding output signals to the ROSs, and a controller coupled with the ROSs to selectively operate a given ROS according to the first clock signal if the latent image being generated by the given ROS is to be fixed to a first side of the substrate or according to the second clock signal if the latent image being generated by the given ROS is to be fixed to a second side of the substrate.

In further aspects of the disclosure, the second clock is adjustable, and is preferably adjusted such that the frequency ratio of the first and second clocks corresponds to a side1to side2process magnification for the system measured using the first clock. In this manner, the adverse effects of side1to side2magnification error can be mitigated or avoided, whether attributable to substrate shrinkage in the fuser or other causes. In certain embodiments, moreover, the photoreceptor may include two or more image panel zones in which the ROSs generate latent images, with successive panel zones separated by inter panel zones. In this case, the controller may provide the individual ROSs with a control parameter indicating whether a latent image to be generated on an upcoming panel zone is to be ultimately fixed to a first side or a second side of the substrate. The individual ROSs then select one of the two clock output signals for use in generating a latent image on the upcoming panel zone based on the control parameter.

In accordance with other aspects of the disclosure, a raster output scanner (ROS) is provided for generating a latent image on a portion of a photoreceptor traveling along a closed path. The ROS is comprised of a light source, such as an LED laser, that generates light according to image data, a scanning mechanism that directs light from the light source toward a photoreceptor according to a selected clock input, a first clock input, a second clock input, and a clock select component that selectively connects one of the first and second clock inputs to the selected clock input according to a select input. In certain embodiments, the ROS scanning mechanism is a motor polygon assembly (MPA) having a plurality of facets rotating about an axis at a speed set by the selected clock input for scanning light from the light source across a portion of the photoreceptor.

In accordance with still further aspects of the present disclosure, a duplex printing method is provided, which includes receiving image data for print job pages and selectively generating latent images on panel zone portions of a photoreceptor that continuously moves along a closed path using a plurality of ROSs positioned along the path. The latent image is generated by a given one of the ROSs by selectively operating the given ROS according to the first clock signal if the latent image is to be fixed to a first side of a substrate or according to the second clock signal if the latent image is to be fixed to a second side of the substrate. The method also includes developing toner of a given color on the latent images on the photoreceptor, transferring developed toner to a substrate traveling along a first substrate path, fixing the transferred toner to the substrate, and for two-sided printing, selectively directing the substrate along a second path, inverting the substrate, and returning the inverted substrate to the first path upstream of the transfer station.

Certain embodiments of the disclosed method may further include measuring a side1to side2process magnification using the first clock and adjusting the second clock based on the measured side1to side2process magnification. In one preferred implementation, the second clock is adjusted such that a frequency ratio of the first and second clocks corresponds to the measured side1to side2process magnification. In addition, where the photoreceptor includes a number of image panel zones in which the ROSs generate latent images, the method may also include providing a first clock output signal from the first clock to each of the ROSs, providing a second clock output signal from the second clock to each of the ROSs, providing the individual ROSs with a control parameter indicating whether a latent image to be generated on an upcoming panel zone is to be fixed to a first side or a second side of the substrate, and selecting one of the clock output signals for use at individual ROSs in generating a latent image in the upcoming panel zone based on the control parameter. The control parameter is preferably provided prior to the end of the inter panel zone preceding the upcoming panel zone, and the method may include allowing the selected clock output signal to settle before generating the latent image in the upcoming panel zone.

DETAILED DESCRIPTION

Referring now to the drawing figures, several embodiments or implementations of the present disclosure are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features, structures, and graphical renderings are not necessarily drawn to scale. The disclosure relates to correction of process magnification errors in document processing systems and is hereinafter illustrated in the context of an exemplary multi-color document processing system having five raster output scanners and corresponding developers situated around a photoreceptor belt traveling at a generally constant speed along a circuitous closed path, although the various aspects of the disclosure can be implemented in association with systems employing any number of ROSs and using any form of intermediate transfer medium, including without limitation photoreceptor belts, drums, and the like. Moreover, the concepts of the present disclosure find utility in association with printing systems that include multiple transfer stages prior to printing on a final print media, wherein implementations of the disclosed concepts in any such alternate systems are contemplated as falling within the scope of the present disclosure and the appended claims.

FIG. 1illustrates an exemplary multi-color xerographic document processing system2including a continuous photoconductive (e.g., photoreceptor) imaging belt4having first and second lateral sides4aand4b(FIG. 2below). The photorecptor belt4traverses a closed path4p(counterclockwise in the view ofFIG. 1) of a drive assembly80having a series of rollers68and70or bars8at a substantially constant speed to move successive portions of its external surface sequentially beneath the various xerographic processing stations disposed about the path4pin the system2. Beginning on the right side inFIG. 1, the belt4passes through a first charging station10that includes a charging device such as a corona generator20that charges the exterior surface of the belt4to a relatively high, and substantially uniform potential. The charged portion of the belt4advances to a first raster output scanner (ROS) type exposure device22which image-wise illuminates the charged belt surface to generate a first electrostatic latent image thereon, whereFIG. 3schematically illustrates further details of the exemplary first ROS device22. The first electrostatic latent image is developed at a development station by developer unit24that deposits charged toner particles of a selected first color on the first electrostatic latent image.

Once the toner image has been developed, the photoreceptor belt4advances to a recharging station12that recharges the belt surface, and a second ROS28image-wise illuminates the charged portion of the belt4selectively to generate a second electrostatic latent image corresponding to the regions to be developed with toner particles of a second color. The second latent image then advances to a subsequent developer unit30that deposits the second color toner on the latent image to form a colored toner powder image of that color on the belt4. The belt4then continues along the path4pto a third image generating station14that includes a charging device32to recharge the belt4and a ROS exposure device34which illuminates the charged portion to generate a third latent image. The belt4proceeds to the corresponding third developer unit36which deposits toner particles of a corresponding third color on the belt4to develop a toner powder image, after which the belt4continues on to a fourth image station16. The fourth station16includes a charging device38and a ROS exposure device40at which the belt4is again recharged and a fourth latent image is generated, respectively, and the belt4advances to the corresponding fourth developer unit42which deposits toner of a fourth color on the fourth latent image. The belt4then proceeds to a fifth station18that includes a charging device44and a ROS46, followed by a fifth developer48for recharging, generation of a fifth latent image, and development thereof with toner of a fifth color.

Thereafter, the photoconductive belt4advances the multi-color toner powder image to a transfer station50at which a printable medium or substrate, such as paper52in one example is advanced from a stack or other supply via suitable sheet feeders (not shown) and is guided along a first substrate media path P1. A corona device54sprays ions onto the back side of the substrate52that attracts the developed multi-color toner image away from the belt4and toward the top side of the substrate52, with a stripping axis roller60contacting the interior belt surface and providing a sharp bend such that the beam strength of the advancing substrate52strips from the belt4. A vacuum transport or other suitable transport mechanism (not shown) then moves the substrate52along the first media path P1toward a fusing station58. The fusing station58includes a heated fuser roller64and a back-up roller62that is resiliently urged into engagement with the fuser roller64to form a nip through which the substrate52passes. In the fusing operation and the station58, the toner particles coalesce with one another and bond to the substrate to affix a multi-color image onto the upper side thereof.

While the multi-color developed image has been disclosed as being transferred from the photoreceptor belt4to the substrate52, in other possible embodiments, the toner may be transferred to an intermediate member, such as another belt or a drum, and then subsequently transferred and fused to the substrate52. Moreover, while toner powder images and toner particles have been disclosed herein, one skilled in the art will appreciate that a liquid developer material employing toner particles in a liquid carrier may also be used, and that other forms of marking materials may be employed, wherein all such alternate embodiments are contemplated as falling within the scope of the present disclosure.

For single-side printing, the fused substrate52continues on the first path P1to be discharged to a finishing station (not shown) where the sheets are compiled and formed into sets which may be bound to one another and can then be advanced to a catch tray for subsequent removal therefrom by an operator of the document processing system2.

For two-sided printing, the system2includes a duplex router82that selectively diverts the printed substrate medium52along a second (e.g., duplex bypass) path P2to a media inverter84in which the substrate52is physically inverted such that a second side of the substrate52is presented for transfer of marking material in the transfer station50. Absent one or more countermeasures of the present disclosure, the heat introduced into the substrate52by the fusing station58may cause the substrate52to shrink, and if two-sided printing is performed, the duplex router diversion to the second path P2and media inversion in the apparatus84may return the inverted substrate52to the transfer station50before the substrate52can be again acclimated to the ambient temperature, whereby the image is transferred to the second side of the substrate52before the substrate52returns to its original size, and process magnification error results.

In order to combat this, the system2provides multiple ROS clocks including a first clock101providing a first clock output signal101ato the ROSs22,28,34,40, and46, and a second clock102providing a second clock output signal102ato the ROSs. The system2further includes a controller100coupled with the ROSs22,28,34,40, and46, which selectively operates a given ROS according to the first clock signal101aif the latent image being generated by the given ROS is to be fixed to a first side of the substrate52or alternatively according to the second clock signal102aif the latent image being generated by the given ROS is to be fixed to a second side of the substrate52. The controller100may be any suitable form of hardware, software, firmware, programmable logic, or combinations thereof, whether unitary or implemented in distributed fashion in a plurality of components, wherein all such implementations are contemplated as falling within the scope of the present disclosure and the appended claims. The first and second clocks101and102may directly couple their output signals101aand102ato the individual ROSs22,28,34,40, and46or local ROS interface modules (RIMs) thereof as shown, or alternatively, the clocks101and/or102can be connected indirectly to the ROSs22,28,34,40, and46via one or more intervening components such as the controller100, or the controller100may include one or both of the clocks101,102, wherein all such variant implementations as contemplated as falling within the scope of the present disclosure.

The second clock102, moreover, is preferably adjustable to allow for calibration of the second clock speed to counteract the amount of shrinkage-related side1to side2process magnification error in a given document processing system2. In particular, the illustrated embodiments provide for adjustment of the second clock102such that a frequency ratio of the first and second clocks101,102corresponds to a side1to side2process magnification for the system2as measured during setup using the first clock101, where the side1to side2process magnification is quantified as the ratio of the side1image size divided by the side2image size using clock1to perform two-sided printing of the same image data size to both sides of a substrate52.

Referring also toFIGS. 2 and 3, the exemplary photoreceptor belt4includes a plurality of image panel zones102(FIG. 2) in which the ROSs22,28,34,40, and46generate latent images, where three exemplary panel zones106a,106b, and106care illustrated in the partial view ofFIG. 2. Any number of panels106may be defined along the circuitous length of the photoreceptor4, and the number may change dynamically based on the size of the printed substrates52being fed to the transfer mechanism50, where the illustrated belt4includes about 11 such zones106for letter size paper sheet substrates52. The panel zones106are separated from one another by inter panel zones IPZ, where two exemplary inter panel zones IPZ1and IPZ2are shown inFIG. 2, with IPZ1being defined in a portion of the belt4that includes a belt seam4s. In operation, the controller100provides the individual ROSs22,28,34,40, and46with one or more control signals via connections104, including a control parameter associated with each upcoming image panel zone106to indicate whether a latent image to be generated on the upcoming panel zone106is to be fixed to a first side or to a second side of the substrate52. Based on this control parameter, the ROSs22,28,34,40, and46individually select one of the clock output signals101a,102afor use in generating a latent image on the upcoming panel zone106.

As best shown inFIG. 3, further details are schematically illustrated for the first ROS22, wherein the other ROSs28,34,40, and46in the exemplary system2are similarly constructed. The ROS system22includes a data input104afrom the controller100to a driver112of a diode laser114, as well as a clock select parameter input104afrom the controller100to a clock select component105for selecting between first and second clock inputs105aand105bconnected to the first and second clocks101and102, respectively. The clock select component105selectively couples the output of one of the clocks101,102to a selected clock input connection128bthat is operatively coupled to the clock input of a polygon motor speed control128a.

In operation of the ROS22, a stream of image data is provided to the driver112associated with a single color portion of a panel image, and the driver112modulates a diode laser114to produce a modulated light output122in conformance with the input image data. The laser beam light output122passes into conditioning optics124and then illuminates a facet126of a rotating polygon128having a number of such facets126(eight in one example). The light122is reflected from the facet126through a lens130to form a spot on the photosensitive image plane of the passing photoreceptor belt4. The rotation of the facet126causes the spot to sweep across the image plane forming a succession of scan lines oriented in a “fast scan” direction (e.g., generally perpendicular to a “slow scan” or process direction4palong which the belt4travels). Movement of the belt4in the slow scan direction4pis such that successive rotating facets126of the polygon128form successive scan lines that are offset from each other in the slow scan direction. Each such scan line in this example consists of a row of pixels produced by the modulation of the laser beam122as the laser spot scans across the image plane, where the spot is either illuminated or not at various points as the beam scans across the scan line so as to selectively illuminate or refrain from illuminating individual locations on the belt4in accordance with the input image data.

In the illustrated example, the ROS system22includes the driver112and clock select component105which together constitute a ROS interface module (RIM) that receives the first and second clock signals from the clocks101and102, where the controller100provides the parameter104ato the RIM in order to indicate to the RIM whether the upcoming panel image is destined for side1or side2on the final printed substrate52. This parameter allows the RIM of a given ROS to determine whether or not to switch clocks, and this selective employment of the faster second clock102facilitates adaptation of side2images to the preshrunk substrate52resulting from the duplex routing and inversion following the high temperature fusing in two-sided printing in the document processing system2. In this regard, the speed of the ROS motor polygon assembly (MPA)128, along with the speed of the photoreceptor belt4determine the overall process magnification of the latent image on the belt, where the belt speed is held substantially constant in the system2, and the process magnification error is susceptible to substrate size variation resulting from thermal shrinking in the fuser58absent the selective dual speed MPA operation of the present disclosure.

It is noted that since there may be multiple panels106having images for different substrate sides at any given time, the speed of the belt4cannot be changed to address the side1to side2process magnification errors caused by substrate shrinkage in the fuser58. Moreover, there are typically more than one ROS generating latent images concurrently, and thus simply changing the speed of a single ROS clock does not provide a solution, since the concurrently generated latent images may be destined for both side1and side2of the substrate52at any given time.

The presently disclosed techniques employ two separate clocks101and102, with the higher speed second clock102being used by the ROSs while generating latent images destined for side2of the substrate52. The transition to the second clock102in the illustrated embodiment is done during the time when an IPZ is traveling past the ROS, with each ROS being selectively adapted to the appropriate clock101,102independently as the belt4continues at a generally constant controlled speed. In the system2, moreover, the image data synchronization is maintained by providing the first clock signal101ato the driver112. Once a ROS has switched to the second clock102for driving the MPA128, the ROS operates to rephase the MPA128when a sync signal is received from the first clock101.

Referring toFIGS. 4 and 5, the second clock102is preferably adjustable, and its frequency is preferably set relative to that of the first clock101to counteract a measured process magnification error performed using the first clock101.FIG. 4illustrates an exemplary setup procedure200in which the speed of the belt4and the first ROS master clock (RMC)101may be adjusted at202. A side1to side2process magnification is then measured at204. The measurement at204can be any suitable show-thru error measurement in which images are printed onto two sides of a single substrate, preferably by printing the same image data on both sides, such that the process magnification error attributable to fuser shrinkage of the substrate52can be quantified. In one embodiment, the process magnification error is characterized at204as the side1image size divided by the side2image size for images printed using image data representing the same image size, to yield a unitless error ratio. At206, the second clock102(RMC2) speed is adjusted based on the measured process magnification. In one implementation, the clock speed of the second clock102is adjusted at206such that the frequency ratio of the first and second clocks101,102corresponds to the side1to side2process magnification for the system2measured using the first clock. Thus, for example, a 2% measured process magnification error would yield a side2image that is 2% larger than that of side1, and the second clock102would be adjusted at206to be 2% faster than the first clock101.

FIG. 5illustrates an exemplary process300in which the adjusted second clock102(and the preset first clock101) are used in performing duplex printing in the system2. At302, print job page image data is received in the system2, such as in the controller100. This data can include latent image data for one or more colors (e.g., corresponding to the ROSs22,28,34,40, and46inFIG. 1), where each page data is ultimately destined for printing onto either side1or side2of the substrate52. At304, the controller100determines this from the data and sends image control information to each of the ROSs22,28,34,40, and46relating to latent images to be generated in upcoming image panel zones106of the photoreceptor belt4. The individual ROSs receive next image control parameters at304that include a panel side parameter indicating whether a latent image to be generated by a given ROS on an upcoming panel zone106is to be fixed to a first side or a second side of the substrate52. The control parameter is preferably provided prior to the end of the IPZ preceding the upcoming panel zone106, and the method300may include allowing the selected clock output signal to settle at304prior to generating the latent image in the upcoming image panel zone106. The RIM of each ROS determines at306whether the next image is for the second side, and if not (NO at306), the first clock (RMC1)101is selected at311. Otherwise, if the next image is for side2(YES at306), the second clock102is selected at312. The ROS then uses the selected clock at314to generate the latent image in the current image panel zone106of the photoreceptor belt.

The above examples are merely illustrative of several possible embodiments of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications, and further that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.