Abstract:
A web handling module has been developed for horizontally transporting a web under a printer having at least one print head. The web handling module includes a plenum, an air vent coupled to the plenum, the air vent being coupled to an air handler and configured to generate a negative air pressure inside the plenum, a support plate sealingly coupled to the plenum, the support plate having a plurality of apertures configured to allow air to pass through the plurality of apertures, and a porous belt wound about the support plate to form a continuous loop, the porous belt enabling the negative air pressure to couple the porous belt to a web moving over the support plate to rotate the porous belt about the support plate without relative motion occurring between the web and the porous belt.

Description:
TECHNICAL FIELD 
     The devices and methods disclosed below generally relate to web transport systems, and, more particularly, to a modular web transport system used in the field of web printing. 
     BACKGROUND 
     Web transport systems are used in a variety of applications to transport a web from one location to another. In printing applications, a printing assembly including one or multiple print heads positioned near the web prints patterns onto the web. As the ink is ejected on to the web, the web must remain flat and a predictable distance away from the printing assembly. Web unevenness or variations in distance from the printing assembly can result in poor printing quality. 
     To ensure web flatness, one solution often implemented in the prior art is to stretch the web between two rollers. The distance between the rollers affects the flatness of the web. For example, if the two rollers are placed a long distance from each other the web can unpredictably flutter up and down. To prevent this fluttering action more rollers can be added to the web path to reduce the distance between adjacent rollers and the rollers are positioned to provide an arcuate path for the web. Both the addition of the rollers and the arcuate positioning of the rollers are required to reduce the fluttering action. 
       FIG. 9  shows a prior art implementation of a web transport system with a series of printing print heads. In order to implement an extended web printing station  10 , rollers  20  are provided for print heads  30 . The required flatness of the web  40  is maintained by placing a roller  20  under each print head  30  and positioning the rollers to provide an arc. By placing the rollers in an arcuate path, as shown in  FIG. 9 , the web  40  is ensured to maintain contact with each roller  20 . For example, three degrees of contact between each roller and the web may be achieved by the arcuate path shown in  FIG. 9 . 
     One challenge with the web transport system of  FIG. 9  is that the arcuate path requires print heads to be positioned at different angles. The angular placement of the print heads is necessary to enable the print heads to be perpendicular to the surface of the web. If the print heads are angularly oriented with respect to the web surface poor quality printing may result. 
     In the web transport system of  FIG. 9 , a one-to-one correspondence exists between the rollers and the number of print heads. As the number of print heads increases in longer printing systems, so does the number of rollers. Because each roller makes sliding contact with the web, the rollers can dislodge dust and other particulate matter from the web. This particulate matter may affect print quality, require more frequent system cleaning, or necessitate ventilation and removal of the dust from the system. 
     SUMMARY 
     A web handling module has been developed for horizontally transporting a web under a printer having at least one print head. The web handling module includes a plenum, an air vent coupled to the plenum, the air vent being coupled to an air handler and configured to generate a negative air pressure inside the plenum, a support plate sealingly coupled to the plenum, the support plate having a plurality of apertures configured to allow air to pass through the plurality of apertures, and a porous belt wound about the support plate to form a continuous loop, the porous belt enabling the negative air pressure to couple the porous belt to a web moving over the support plate to rotate the porous belt about the support plate without relative motion occurring between the web and the porous belt. 
     A method has also been developed for horizontally moving a web in a printing device with at least one print head above the web. The method includes applying a vacuum through a plurality of apertures in a support plate and through a porous belt positioned over the support plate to couple the porous belt to a web of material, driving the web to rotate the porous belt about the support plate, and ejecting ink from at least one print head onto the web as the web is moving over the support plate. 
     A printing production environment has also been developed for printing onto a moving web. The printing production environment includes a plurality of web handling modules, each web handling module of the plurality having a plenum, an air vent coupled to the plenum, the air vent being coupled to an air handler and configured to generate a negative air pressure inside the plenum, a support plate sealingly coupled to the plenum, the support plate having a plurality of apertures configured to allow air to pass through the plurality of apertures, a porous belt wound about the support plate to form a continuous loop, the porous belt enabling the negative air pressure to couple the porous belt to a web moving over the support plate to rotate the porous belt about the support plate without relative motion occurring between the web and the porous belt, a web feeder configured to receive the web from a web source and to provide the web to the plurality of the web handling modules, a web stacker configured to receive the web from the plurality of the web handling modules and provide the web to a downstream web handling unit, and a plurality of print heads assigned to each of the plurality of web handling modules disposed above the web and configured to eject ink onto the web as the web is moving over the support plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of the present disclosure are explained in the following description, taken in connection with the accompanying drawings. 
         FIG. 1  is a perspective view of a web handling module with the web positioned above the web handling module and cutouts provided to reveal different features. 
         FIG. 2  is a perspective view of the web handling module depicted in  FIG. 1  without the web. 
         FIG. 3  is a perspective view of a support plate used in the web handling module. 
         FIG. 4  is schematic diagram of the web handling module. 
         FIG. 5  is a schematic diagram of the web handling module with the web positioned above the web handling module and print heads positioned above the web. 
         FIG. 6  is a schematic diagram of print heads positioned over a web. 
         FIG. 7  is a schematic diagram of the web handling module at one end of the module providing a detailed view of a print head in relationship to the web. 
         FIG. 8  is a schematic diagram of a series of web handling modules positioned side by side each module having the web over the module and print heads over the web as well as a web feeder and a web stacker. 
         FIG. 9  is a schematic diagram of a web transport system according to the prior art. 
     
    
    
     DETAILED DESCRIPTION 
     The term “printer” as used herein refers, for example, to reproduction devices in general, such as printers, facsimile machines, copiers, and related multi-function products. While the specification focuses on a web transport system that controls the transport of a web under a series of print heads, the transport system may be used with any web transport system that transports a web from one location to another. 
     A web handling module  100  is illustrated in  FIG. 1 . The main components shown in  FIG. 1  are a housing  110 , two rollers  130  and  140 , a support plate  120 , a series of apertures  124  on the support plate  120 , a web  150  positioned over a porous belt  160  which is over the support plate  120  and partially spans the width of the support plate  120 , and a sealing cover  180  positioned over the portion of the width of the support plate  120  not covered by the porous belt  160 . Referring to  FIG. 2 , the web handling system  100  is depicted without the web to demonstrate the relationship between the porous belt  160 , the sealing cover  180  and the support plate  120 . The housing  110  provides a structure for mounting features that are described below. Rollers  130  and  140  are mounted about roller shafts  132  at the two ends of the housing  110 . Momentum of the web rotates the rollers  130  and  140  about the roller shafts  132 . The support plate  120  is mounted on the top of the housing  110 . Fastening and locating holes  122  are provided for aligning and securely mounting the support plate  120  to the housing  110 . A series of apertures  124  are provided on the support plate  120 . These apertures  124  are provided in different angular relationship with respect to the support plate  120 . The apertures  124  are distributed over an area that covers most of the support plate  120 . The support plate  120  is configured to have a low friction surface. The low friction surface can be achieved by coating the support plate  120  with an appropriate coating material. A typical coating material used in such applications is Teflon. Alternatively, the low friction surface of the support plate can be achieved by choosing a support plate material that ensures a smooth surface. The apertures  124  and the support plate  120  are described in more detail below. 
     The porous belt  160  is provided on the top surface of the support plate  120 . The porous belt  160  is wound around the rollers  130  and  140  in a tight manner to provide a continuous loop around the rollers  130  and  140 . Therefore, moving the porous belt  160  over the support plate  120  causes the rollers  130  and  140  to rotate. As discussed below, a vacuum is applied in the housing to the underside of the support plate  120 . The vacuum is pulled through the apertures  124  to couple the porous belt  160  to the web  150 . Therefore, while the vacuum is applied, moving the web over the web handling module  100  rotates the porous belt  160  about the support plate  120 . While rollers  130  and  140  are shown in  FIG. 1 , in one embodiment rollers can be substituted with stationary ends having rounded surfaces, in which case the porous belt rotates about the stationary ends. In embodiments in which the porous belt  160  is mounted about rollers  130  and  140 , these rollers and any other rollers mounted in contact with the porous belt  160  are driven by the movement of the web  150  coupled to the porous belt  160  by the vacuum. Therefore, the web handling module  100  shown in  FIG. 1  advantageously eliminates the need for actuators, e.g., electric motors, to rotate rollers in order to move the web. This advantage, as discussed below, can be used to build up a series of web handling modules  100  in a modularized printing environment. 
     The porous belt  160  is made of a resilient material and the porous belt  160  has a high level of porosity. The porosity may be a characteristic of the material used for the belt  160  or a series of holes, slits, and the like may be formed in a non-porous material to provide the porosity. The material of the porous belt  160  should be chosen so that the porous belt  160  can slide over the support plate  120  with minimal friction force. That is, the coefficients of friction associated with the porous belt material and the coating of the support plate, or the material of the support plate if no coating is present, should enable a smooth sliding action between the porous belt  160  and the support plate  120 . 
     The material of the porous belt should also be sufficiently pliable such that the porous belt  160  conforms easily to the shape of the support plate  120 , even when the porous belt  160  is sliding over the support plate  120 . The porous belt  160  needs to conform to the shape of the support plate  120  even when the porous belt is moving over the support plate  120 . Furthermore, the material and the thickness of the porous belt should preclude the porous belt from being pulled through the apertures  124  of the support plate  120  because entry of the porous belt  160  into the apertures  124  would prevent or impede the sliding action of the porous belt  160  over the support plate  120 . Moreover, the material of the porous belt  160  should be chosen to avoid giving off dust particles as the porous belt  160  slides over the support plate  120  and the rollers  130  and  140 . In one embodiment a loop of sheet-metal with small holes may be used as the porous belt  160 . 
     In one embodiment, the width of the porous belt  160  is smaller than the width of the support plate  120 . This relationship is shown in  FIGS. 1 and 2 , where the support plate  120  spans the entire width of the web handling module  100 , while the porous belt  160  spans only a portion of the width. Referring to  FIG. 1 , the support plate  120  and the apertures  124  can be seen on the far left hand side in the cutout of the web  150  and in the cutout of the porous belt  160 . The support plate and the apertures can also be seen on the right hand side in the cutout of the sealing cover  180 . The sealing cover  180  covers the portion of the support plate  120  that is not covered by the porous belt  160 . The area of the support plate  120  that is covered by the sealing cover  180  is hereinafter referred to as the unused portion of the support plate. The unused portion of the support plate exists because in certain applications the width of the web  150 , and hence the porous belt  160 , is smaller than the width of the support plate  120 , as the support plate  120  is provided to handle the largest web width in a class of web applications. 
     The sealing cover  180  is made of a sufficiently resilient non-porous material to prevent the sealing cover  180  from being pulled through the apertures  124  of the support plate  120  when a vacuum is applied to the underside of the support plate  120 . The pliable material needs to flex in order to seal the apertures  124  of the support plate  120  but yet have sufficient thickness so that the sealing cover  180  cannot be pulled through the apertures. An exemplary material for the sealing cover  180  can be rubber. In one embodiment the porous belt  160  covers the entire width of the support plate  120 , or at least the portion of the support plate  120  where apertures  124  are present. In this embodiment the sealing cover  180  can be omitted. 
     The web  150  is transported over the web handling module  100  along the direction of arrows  170 . The web is positioned over the porous belt  160 . The cutouts shown in  FIG. 1  reveal the porous belt  160  under the web  150  and the support plate  120  under the porous belt  160 . The width of the web  150  is substantially the same as the width of the porous belt  160 . Therefore, the web  150  is configured to be substantially over the porous belt  160  and not over the unused portion of the support plate  120 . 
     In operation, a vacuum is coupled to a plenum (not shown in  FIG. 1 ) in the housing  110  and to the underside of the support plate  120 . The vacuum pulls air through the apertures  124  of the support plate  120  and through the porous belt  160 . The sealing cover  180  ensures vacuum does not escape through uncovered apertures  124  of the support plate  120  in cases where the web  150  and the porous belt  160  do not cover the entire span of the support plate  120 . The vacuum that is pulled through the porous belt  120  pulls the web  150  against the porous belt  160  and toward the support plate  120 . The vacuum force exerted on the web applies sufficient normal force to the porous belt and the web to enable the porous belt  160  to move along with the web  150  when the web  150  is moved in the direction of arrows  170 . The vacuum also enables the web  150 , along with the porous belt  160 , to conform to the shape of the support plate  120  to provide a rigid and flat surface for the web  150 . Thus the vacuum prevents any fluttering of the web  150 . Therefore, the web handling module  100  enables superior printing quality to be achieved as compared to the web handling system of the prior art shown in  FIG. 9 . 
     While the web  150  is configured to be substantially over the porous belt  160  and not over the unused portion of the support plate  120 , there may be cases where a printing-width of the web, i.e., the portion of the width of the web where the print heads deposit ink, is smaller than the width of the web. In these cases portions of the web which are outside of the printing-width, can be positioned over the sealing cover  180 , as any minor fluttering action that may occur in these areas would not affect the print quality. 
     The configuration of the web handling module  100  shown in  FIG. 1  advantageously does not require sliding contact between the web and any surfaces, thereby substantially eliminating production of web dust. The sliding action of the porous belt  160  over the support plate  120  is different than the sliding of the web over the rollers of the web handling system of the prior art shown in  FIG. 9  in several ways. First, the porous belt  160  and the support plate  120  are configured to provide low levels of friction. Second, the material of the porous belt  160  is chosen to avoid giving off dust particles. Therefore, the sliding action of the porous belt  150  over the support plate  120  does not generate debris as the previously known webs do as they slide over the rollers. 
     Referring to  FIG. 3 , the support plate  120  is depicted. The support plate  120  has a plurality of apertures  124  that are provided through the support plate. These apertures  124  are formed in the shape of slits that are placed at varying angular positions with respect to the support plate  120 . The apertures  124  are provided with different sizes, e.g., different widths and lengths. Although apertures  124  are shown as slits, other shapes, e.g., circular patterns may be used. The design criteria for these apertures  124  are twofold. First, the apertures  124  should be sized and frequently positioned to provide sufficient vacuum to the porous belt  160  to achieve the required coupling with the web  150 . Secondly, formation of these apertures  124  should not remove excessive material from the support plate  120  as to weaken the support plate  120 , thereby necessitating a thicker support plate  120 . Moreover, the apertures  124  should have rounded edges to prevent damaging the porous belt  160  or impeding the movement of the porous belt  160  as the porous belt  160  is sliding over the support plate  120 . 
     As previously discussed the support plate  120  is configured to have low frictional qualities. In particular, the support plate  120  can be made of a material with few surface irregularities or be coated by an appropriate coating material. The objective is to provide a low frictional surface between the porous belt and the support plate  120  for unencumbered sliding of the porous belt  160  over the support plate. 
     Referring to  FIG. 4 , a schematic of the web handling module  100  is provided. The rollers  130  and  140  are found at the opposite ends of the web handling module  100 . In one embodiment, the rollers can be replaced with stationary arcuate structures that allow the porous belt  160  to slide over the structures. However, to reduce wear on the porous belt  160  rollers  130  and  140  may be used to rotate along with the porous belt  160 . Guiding rollers  210  and  220  define the shape the porous belt  160  assumes as it continuously travels around the web handling module  100 . Although two guiding rollers  210  and  220  are shown, a single guiding roller or three or more guiding rollers may be used to accomplish the same function. The porous belt  160  travelling around rollers  130  and  140  and around guiding rollers  210  and  220  can provide a pattern that is similar to the shape of the plenum  240 . For example, the plenum  240  and the porous belt  160  both are shaped according to a trapezoid. However, both the plenum and the shape that the porous belt  160  assumes could be a conical shape, in which only one guiding roller would be used on the porous belt  160 . 
     Inside the plenum  240 , a vacuum shown by arrows  230  is generated. The vacuum can be generated by an air pump positioned inside the plenum  240  pulling in air through the support plate  120  and pumping the air to the outside of the plenum  240  through air vents (not shown in  FIG. 4 ). Alternatively, the vacuum can be generated outside of the plenum and applied to the plenum  240  by way of ducts which then provide the vacuum to the supporting plate  120 . In either case, the plenum  240  is coupled to the support plate  120  to provide an airtight interface. 
     Referring to  FIG. 5 , a printing module  300  is depicted. The printing module  300  has a web handling module  100  and a plurality of print heads  310   a - 310   d , or as discussed below a plurality of print head arrays  312   a - 312   d . As the vacuum  230  is applied to the support plate  120 , the vacuum pulls the web  150  and the porous belt  160  against the support plate  120 . The support plate provides a flat and consistent surface for the web. While the web  150  is moved, the porous belt  160  moves with the web  150  around the rollers  130  and  140  and guide rollers  210  and  220 . A series of print heads  310   a - 310   d  are provided over the web  150  at a distance away from the web that allows for proper application of ink from the print heads onto the web. Four print heads  310   a - 310   d  are shown in  FIG. 5 . 
     Each of the print heads  310   a - 310   d  can be a member of an array having multiple print heads which are positioned in series along the width of the web. An exemplary embodiment of arrays of print heads  312   a - 312   d  is shown in  FIG. 6 . A series of print heads  310   a  form an array  312   a . The print heads of each array are positioned in a staggered fashion above the web  150 . The pattern of arrays of print heads  312   a - 312   d  shown in  FIG. 6  provides a configuration such that a length of the web that spans the distance between arrays  312   a - 312   d  can be printed at once. This simultaneous printing capability improves efficiency of printing of the web in high speed printing applications. In one embodiment, each array  312   a - 312   d  of print heads can be configured to print a different color. In this embodiment, a full color image can be printed on the web each time the web passes through a single printing module  300 . Alternatively, in another embodiment, all arrays  312   a - 312   d  of each printing module are configured to print the same color. In this embodiment, a full color image is printed on the web after the web has passed through multiple printing modules  300 , as part of a printing environment. 
     Referring to  FIG. 7 , a close up of the schematic of  FIG. 5  at the end close to the roller  130  is provided. The vacuum pulls the web  150  and the porous belt  160  on to the support plate  120 , thereby providing a flat and consistent web surface onto which the print head  310  is able to eject ink. The web, therefore, is positioned at a consistent distance  320  away from the print head  310 , as required to achieve high quality printing. Therefore, the print heads  310  can all be positioned vertically at the same distance  310  away from the web  150 . This arrangement advantageously eliminates the requirement of arcuate placement of the print heads shown in  FIG. 1 . A consistent vertical placement of the print heads  310  is advantageous since such a placement configuration allows for a modular implementation of the web handling module  100  as compared to the implementation of the prior art, depicted in  FIG. 9 , where the arcuate path prevented a long modular implementation. In  FIG. 7  reference numeral  250  represents the point where the porous belt and the web are no longer in contact. 
     Referring to  FIG. 8 , a printing production environment  400  is shown. There are six printing modules  300   a - 300   f , each printing module  300  has a plurality of arrays  312 , as described above with reference to  FIG. 6 , and a single web handling module  100 . The printing module  300   a , on the right, receives the web  150  from a web feeder  340 . Upon being printed, the web  150  exits the last printing module  300   f , on the left hand side of  FIG. 8 , and enters the web stacker  350 . The web stacker  350  drives the web  150  over a series of rollers and processes the web  150  to other processing units downstream (not shown). 
     As previously discussed, the printing production environment  400  takes advantage of the moving web to rotate the rollers  130  and  140  of the web handling module  100 . Because the web  150  rotates the porous belt  160  and the rollers  130  and  140 , actuators are not required to drive the rollers  130  and  140 . Thus, the web movement does not need to be synchronized with the rotation of rollers driven by actuators. Elimination of this synchronization requirement by avoiding actuator rollers improves motion quality of the web  150 , which is important in a web printing application. 
     The capability to provide additional printing modules  300  in a modular fashion is clearly demonstrated in  FIG. 8 . Each web handling module  100  is placed next to another web handling module  100  so that the porous belt  160  of each module is at the proximity of another module. The proximity of each module to the next is not a critical design consideration. Close proximity allows for a smaller floor space. However, the modules should not be placed so close that the porous belts  160  make contact with one another, as this condition may prevent proper operation and/or shorten the life of the porous belts  160 . 
     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. A few of the alternative implementations may comprise various combinations of the methods and techniques described. 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.