Patent Publication Number: US-8538306-B2

Title: Web feed system having compensation roll

Description:
BACKGROUND 
     Embodiments herein generally relate to a web feed system in a printing device, and more particularly to a web feed system that includes a compensation roll that keeps a constant tension on the web of print media as the movable transfer roller moves relative to the photoreceptor belt. 
     Contiguous label presses require the marriage of the photoreceptor continuous polyimide belt with a label stock (paper release/paper label or polymer release/polymer label) open loop web. The transfer of the image from the photoreceptor belt to the paper occurs at the fixed transfer roller along the photoreceptor belt. The photoreceptor belt has a seam that cannot be imaged. Therefore, a periodic retraction/engagement-disengagement of the web is necessary to skip the seam. This requires the paper to reverse and be reengaged to maintain a uniform gap label pitch between labels. Otherwise, a significant amount of waste would occur in the final label product stream. When the web is retracted by disengaging the biased (moveable) transfer roll from the fixed photoreceptor transfer roll, the web length changes and this can lead to high web tension changes, which can cause motion quality and image registration errors. This error can make the product unacceptable in the market due to poor image quality. 
     SUMMARY 
     The following describes a simple and low-cost device that can automate tension compensation when a media web is retracted from a photoreceptor. In this disclosure, a compensational roll is hard linked with a biased (moveable) transfer roll. Thus, whenever the biased transfer roll is disengaged from the photoreceptor transfer roll, the web slack generated by the biased transfer roll movement is compensated by the movement of the compensation roll so that ultimately no slack is generated on the web and the constant web tension is maintained. 
     An exemplary apparatus herein includes a photoreceptor belt having a seam, a fixed transfer roller positioned on the inside (on a “first” side) of the photoreceptor belt, and a movable transfer roller positioned on the outside of the photoreceptor belt (on a “second” side of the photoreceptor belt that is opposite the first side). The fixed transfer roller and the movable transfer roller are positioned to form a nip, and the photoreceptor belt and a web of print media are positioned in the nip. 
     Further, an actuator is connected to the movable transfer roller. The actuator selectively moves the movable transfer roller to open the nip when the seam of the photoreceptor belt passes through the nip. Also, a support roller and a compensation roller contact the web of print media. The support roller is positioned between the compensation roller and the nip. A cam can be used to cause the support roller to move when the actuator moves the movable transfer roller. 
     A physical link is connected to the support roller and the compensation roller. The physical link moves the compensation roller with the support roller so as to keep constant tension on the web of print media as the movable transfer roller moves relative to the photoreceptor belt. In some embodiments, the physical link can also be connected to the movable transfer roller, eliminating the need for the cam. Alternatively, a second actuator can be connected to the physical link or the support roller, again eliminating the need for the cam. 
     Additionally, the support roller can be approximately centered between the compensation roller and the nip, the support roller and the compensation roller can be approximately the same size, and the support roller and the compensation roller can be positioned on opposite sides of the web of print media. 
     These and other features are described in, or are apparent from, the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments are described in detail below, with reference to the attached drawing figures, in which: 
         FIG. 1  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 2  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 3  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 4  is a side-view schematic diagram of a device according to embodiments herein; 
         FIG. 5  is a side-view schematic diagram of a device according to embodiments herein; and 
         FIG. 6  is a side-view schematic diagram of a device according to embodiments herein. 
     
    
    
     DETAILED DESCRIPTION 
     A goal of the label web press industry is to print a continuous stream of labels with a constant gap between labels. This gap could be as small as 3 mm. However, a skip pitch problem arises due to the photoreceptor belt seam. To eliminate excessive material waste due to the photoreceptor seam, the web periodically retracts via a movement that is sometimes referred to as a “pilgrim step” movement. In the pilgrim step, the biased transfer roll is disengaged from the photoreceptor belt, decelerated, reversed, accelerated, and then reengaged to the photoreceptor belt so that the seam will not be “printed” on the web. This coordinated motion ensures that the gap is constant between labels. The goal of the pilgrim step registration is the industry standard of +150 um in both process and cross track directions. In order to achieve the registration careful control of the tension is essential. The embodiments described below address the tension control by keeping the web span lengths the same during the pilgrim step motion. 
     One current configuration is shown in  FIG. 1 , which includes a photoreceptor belt  130  which is supported by various rolls (which are sometimes referred to herein as “rollers”) including a driver roller  134  and a fixed transfer roller  132 . The web of print media  146  is similarly supported by various rollers, including an idler roller  148 , a support roller  138 , a biased movable transfer roller  136 , and a vacuum pull roller  144 . During the pilgrim step movement the biased movable transfer roller  136  moves away from the photoreceptor  130  and the fixed transfer roller  132  and a cam  140  causes the support roller to move from position  138  to position  138 A. Whenever the web  146  is retracted in the pilgrim step movement, the web  146  becomes slacked due to length change. 
     The web tension is hard to control because of the speed at which the retract and engage occur (within approximately 30 to 40 ms). More specifically, the speed at which the cam  140  mechanism engages and retracts may create unmanageable tension variations leading to poor web registration during the pilgrim step motion. Additionally, it is difficult, if not impossible, to prevent tension variation during the pilgrim step movement by only changing the servo timing. The various structures herein address the tension control issues by maintaining equal length spans in both engaged and disengaged positions. Another feature of the designs presented herein is that they avoid any wrapping of the label stock web on the biased transfer roll foam roller  136  that could provide nip instability during steady state printing. 
     Therefore, as shown in  FIGS. 2-5 , a tension compensation roller  160  is hard linked and pivoted together with the biased movable transfer roller  136  and the support roller  142 . A physical link  164  causes the compensation roller  160  and support roller  142  to move together so the net web length is equal in both the engage and disengage movements. The physical link  164  moves the compensation roller  160  with the support roller  142  so as to keep a constant tension on the web of print media  146  as the movable transfer roller  136  moves relative to the photoreceptor belt  130 . 
     More specifically,  FIGS. 2-5  show a similar structure as is illustrated in  FIG. 1 , with some elements removed to more clearly illustrate the features herein. In these Figures, a fixed transfer roller  132  is positioned on the inside (on a “first” side) of the photoreceptor belt  130 , and a movable transfer roller  136  positioned on the outside of the photoreceptor belt  130  (on a “second” side of the photoreceptor belt  130  that is opposite the first side). The fixed transfer roller  132  and the movable transfer roller  136  are positioned to form a nip  150 , and the photoreceptor belt  130  and the web of print media  146  are positioned in the nip  150 . 
     Further, an actuator  152  is connected to the movable transfer roller  136 . The actuator  152  selectively moves the movable transfer roller  136  to open the nip  150  when the seam  154  of the photoreceptor belt  130  passes through the nip  150 . The cam  140  can be used to cause the support roller  142  to move when the actuator  152  moves the movable transfer roller  136 . 
     The support roller  142  and compensation roller  160  contact the web of print media  146  and are positioned on either the same side or the opposite sides of the web of print media  146  depending on the tension compensation requirement. In this example, the support roller  142  is positioned on the inside (first side) of the web of print media  146 , and the compensation roller  160  is positioned on the outside (second side) of the web of print media  146 . The support roller  142  is positioned between the compensation roller  160  and the nip  150 . Additionally, the support roller  142  can be approximately centered between the compensation roller  160  and the nip  150 , and the support roller  142  and the compensation roller  160  can be approximately the same size. 
     As shown in  FIG. 2  for example, during normal operation (when the biased movable transfer roller  136  is engaged with the photoreceptor transfer roll) the tension compensation roller  160  may only lightly touch the web of print media  146 . However, as shown in  FIG. 3 , when the photoreceptor seam  154  needs to pass through the nip  150  and the biased movable transfer roller  136  is pivoted or moved away from the fixed transfer roller  132 , the tension compensation roller  160  is engaged more with the web. 
     The compensation roller  160  is designed so that the web length is constant or near constant even though the compensation roller  160  and the biased movable transfer roller  136  are moved/pivoted. This allows the web tension to remain constant (or near constant) even as the movable transfer roller  136  is moved. Thus,  FIG. 3  demonstrates that embodiments herein provide a structure that keeps a constant tension on the web of print media  146  as the movable transfer roller  136  moves relative to the photoreceptor belt  130 . 
     As shown in  FIG. 4 , in other embodiments, the physical link  164  can also be connected to the movable transfer roller  136 , eliminating the need for the cam  140 . Alternatively, as shown in  FIG. 5 , a second actuator  170  can be connected to the physical link  164  or the support roller  142 , again eliminating the need for the cam  140 . 
       FIG. 6  illustrates a computerized printing device  100 , which can be used with embodiments herein and can comprise, for example, a printer, copier, multi-function machine, etc. The printing device  100  includes a controller/processor  124 , at least one marking device (printing engines)  110  operatively connected to the processor  124 , a media path  116  positioned to supply print media from a media supply  102  to the marking device(s)  110 , and a communications port (input/output)  126  operatively connected to the processor  124  and to a computerized network external to the printing device. The printing engines  110  shown in  FIG. 6  can include the structures shown in  FIGS. 1-5  above, and provide the advantages discussed above. 
     After receiving various markings from the printing engine(s), the print media can optionally pass to a finisher  108  which can roll, cut, fold, staple, sort, etc., the printed media. Also, the printing device  100  can include at least one accessory functional component (such as a scanner/document handler  104 , media supply  102 , finisher  108 , etc.) and graphic user interface assembly  106  that also operate on the power supplied from the external power source  128  (through the power supply  122 ). 
     The input/output device  126  is used for communications to and from the multi-function printing device  100 . The processor  124  controls the various actions of the printing device. A non-transitory computer storage medium device  120  (which can be optical, magnetic, capacitor based, etc.) is readable by the processor  124  and stores instructions that the processor  124  executes to allow the multi-function printing device to perform its various functions, such as those described herein. 
     Thus, a printer body housing  100  has one or more functional components that operate on power supplied from the alternating current (AC)  128  by the power supply  122 . The power supply  122  connects to an external alternating current power source  128  and converts the external power into the type of power needed by the various components. 
     As would be understood by those ordinarily skilled in the art, the printing device  100  shown in  FIG. 6  is only one example and the embodiments herein are equally applicable to other types of printing devices that may include fewer components or more components. For example, while a limited number of printing engines and paper paths are illustrated in  FIG. 6 , those ordinarily skilled in the art would understand that many more paper paths and additional printing engines could be included within any printing device used with embodiments herein. 
     Many computerized devices are discussed above. Computerized devices that include chip-based central processing units (CPUs), input/output devices (including graphic user interfaces (GUI), memories, comparators, processors, etc. are well-known and readily available devices produced by manufacturers such as Dell Computers, Round Rock Tex., USA and Apple Computer Co., Cupertino Calif., USA. Such computerized devices commonly include input/output devices, power supplies, processors, electronic storage memories, wiring, etc., the details of which are omitted herefrom to allow the reader to focus on the salient aspects of the embodiments described herein. Similarly, scanners and other similar peripheral equipment are available from Xerox Corporation, Norwalk, Conn., USA and the details of such devices are not discussed herein for purposes of brevity and reader focus. 
     The terms printer or printing device as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, etc., which performs a print outputting function for any purpose. The details of printers, printing engines, etc., are well-known by those ordinarily skilled in the art and are discussed in, for example, U.S. Pat. No. 6,032,004, the complete disclosure of which is fully incorporated herein by reference. The embodiments herein can encompass embodiments that print in color, monochrome, or handle color or monochrome image data. All foregoing embodiments are specifically applicable to electrostatographic and/or xerographic machines and/or processes. 
     In addition, terms such as “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”, “over”, “overlying”, “parallel”, “perpendicular”, etc., used herein are understood to be relative locations as they are oriented and illustrated in the drawings (unless otherwise indicated). Terms such as “touching”, “on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., mean that at least one element physically contacts another element (without other elements separating the described elements). Further, the terms automated or automatically mean that once a process is started (by a machine or a user), one or more machines perform the process without further input from any user. 
     It will be appreciated that the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. 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. The claims can encompass embodiments in hardware, software, and/or a combination thereof. Unless specifically defined in a specific claim itself, steps or components of the embodiments herein cannot be implied or imported from any above example as limitations to any particular order, number, position, size, shape, angle, color, or material.