Patent Publication Number: US-6705786-B2

Title: Duplex printing of print sheets

Description:
TECHNICAL FIELD 
     This invention relates to systems and methods for duplex printing of print sheets. 
     BACKGROUND 
     Printing on two sides of a print sheet (or print media or image substrate), referred to as duplex printing, is a desirable feature in printing systems because, for example, it allows the amount of paper needed for a particular print task to be reduced as compared with one-sided (simplex) printing. Duplex printing also allows print sets with layouts resembling that of professionally printed books to be generated. Conventional duplex printing devices often employ complex paper handling mechanisms. For example, in accordance with one duplexing method, an extra tray is used for temporary storage of a stack of pre-cut print sheets having printing on a first side. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned with an odd number of inversions along a duplex path to receive second side imaging. Alternatively, the first side copies may be returned along a second paper path to receive second side printing without stacking. 
     High speed printing by xerographic, ionographic, ink jet or other copiers, printers, plotters or other reproduction apparatus (encompassed herein by the terms “printer” and “printing apparatus”) has become increasingly important and increasingly demanding in terms of quality, reliability, and other enhanced features, including full color and black and white printing functionality, and simplex and duplex printing functionality. High-speed printing machines typically print onto a web of sheet material, rather than using cut sheets as the copy sheets. The web of sheet material may be advanced from a roller through a printing module, which applies markings to the web of sheet material. Such roll feeding and printing systems may provide “two up” or “four up” (duplex signature) printing, in which dual page images are printed in side by side pairs on one or both sides of a wide web (or large format) dual page width web of sheet material. 
     In general, duplex printing on continuous web substrates is much more difficult than printing on cut sheets. One continuous web duplex printing approach uses multiple opposing print engines for respectively printing on opposite sides of the web (see, e.g., U.S. Pat. Nos. 3,940,210, 5,701,565, and 5,455,668). Such multiple print engine web printing duplex systems, however, typically are characterized by substantial size, cost, complexity and maintenance requirements. In another approach, U.S. Pat. No. 5,970,304 has proposed a continuous web substrate duplex printing system that utilizes a single xerographic print engine. Separate first and second image transfer stations are positioned in line with one another in the direction of movement of the endless surface imaging member. The second image transfer station is positioned downstream of the first image transfer station. Each image transfer station respectively transfers print images to the first and second sides of the continuous web sequentially without requiring a dual width imaging member or dual imaging members. The two inline transfer stations may be part of a dockable web printing module that is configured to feed the continuous web into the print engine for image transfers to both sides of the web with web inversion. The system includes a web loop in between the two transfer stations for transferring the page print images onto both sides of the web in the proper sequence and positions. 
     Still other duplex printing systems and methods have been proposed. 
     SUMMARY 
     The invention features systems and methods for duplex printing of print sheets in which print sheets may be controllably and reliably re-introduced into the print module in an orientation that is suitable for marking the second side of the print sheet without requiring a support structure that spans the entire width of the print sheet. In large format printing applications, the invention avoids large and heavy support structures, such as feed rollers, that otherwise would be needed to support the print sheets, as well as their own weight. In this way, the invention enables duplex printing apparatus of relatively light weight and a relatively small overall footprint to be implemented readily and in a cost effective manner. 
     In one aspect, the invention features a printing apparatus for marking first and second sides of a print sheet. The printing apparatus comprises a print module, a simplex module, and a duplex module. The print module is configured to mark one side of the print sheet at a time. The simplex module is configured to move the print sheet along a simplex feed path and to introduce the print sheet into the print module in an orientation suitable for marking the first side of the print sheet. The duplex module is configured to receive the print sheet from the print module. The duplex module also is configured to move the print sheet along a duplex feed path while clamping side edge regions of the print sheet and lo tensioning unsupported print sheet regions between the clamped side edge regions. In addition, the print module is configured to re-introduce the print sheet into the print module in an orientation suitable for marking the second side of the print sheet. 
     As used herein, the term “module” is intended to refer to a functional feature of a printing apparatus and is not intended to connote any particular structural implementation. For example, various modules of a printing apparatus may be incorporated into a single, unitary structure or they may be implemented as separable structural units that cooperate to perform one or more printing tasks. 
     Embodiments of the invention may include one or more of the following features. 
     In some embodiments, the duplex module comprises a print sheet handling assembly with sheet clamps mounted on respective rotatable arms. The rotatable arms may be configured to rotate about a common shaft. A first rotatable arm may have a fixed lateral position on the common shaft, and a second rotatable arm may have an adjustable lateral position on the common shaft to accommodate a width dimension of the print sheet. 
     In some embodiments, the print handling assembly of the duplex module comprises a cam surface system that is configured to control action of the sheet clamps during movement of the print sheet along the duplex feed path. The cam surface system may comprise a cam surface controlling separation of the sheet clamps during movement of the print sheet along the duplex feed path. The cam surface system also may comprise a cam surface controlling clamping of the sheet clamps when the print sheet is received from the print module and controlling unclamping of the sheet clamps from the side edge regions of the print sheet before the print sheet is re-introduced into the print module. 
     In some embodiments, the printing apparatus may be characterized by a footprint that is substantially smaller than the print sheet size. 
     The print module may comprise a sensor system that is configured to detect one or more holes in or edges of the print sheet for registering the first and second sides of the print sheet. 
     In another aspect, the invention features a printing apparatus having a duplex module that is configured to re-introduce the print sheet into the print module trailing edge first in an orientation suitable for marking the second side of the print sheet. 
     In another aspect, the invention features a printing method for marking first and second sides of a print sheet. In accordance with this inventive method, the print sheet is moved along a simplex feed path. The print sheet is introduced into a print module in an orientation suitable for marking the first side of the print sheet. The print sheet is received from the print module. The print sheet is moved along a duplex feed path while clamping side edge regions of the print sheet and tensioning unsupported print sheet regions between the clamped side edge regions. The print sheet is re-introduced into the print module in an orientation suitable for marking the second side of the print sheet. 
     In another aspect, the invention features a printing method for marking first and second sides of a print sheet. In accordance with this inventive method, the print sheet is moved along a simplex feed path. The print sheet is introduced into a print module in an orientation suitable for marking the first side of the print sheet. The print sheet is received from the print module. The print sheet is reintroduced into the print module trailing edge first in an orientation suitable for marking the second side of the print sheet. 
     Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic perspective view of a printing apparatus that includes a print module, a simplex module, and duplex module. 
     FIG. 2A is a diagrammatic side view of a print sheet web moving along a simplex feed path and being introduced into a print module in an orientation suitable for marking a first side of the print sheet. 
     FIG. 2B is a diagrammatic side view of the print sheet web of FIG. 2A having a trailing edge formed by cutting the print sheet web in a transverse direction while being clamped at side edge regions. 
     FIG. 2C is a diagrammatic side view of the cut print sheet of FIG. 2B being moved along a duplex feed path with unsupported regions between the clamped side edge regions being tensioned. 
     FIG. 2D is a diagrammatic side view of the print sheet of FIG. 2C being reintroduced into the print module in an orientation suitable for marking the second side of the print sheet. 
     FIG. 3A is a diagrammatic cross-sectional front view of a print sheet handling assembly of the printing apparatus of FIG. 1 with sheet clamps mounted on respective rotatable arms. 
     FIG. 3B is a diagrammatic side view of a print sheet handling assembly with rotatable arms and sheet clamps shown at different points along a duplex feed path. 
     FIG. 4A is a diagrammatic front view of a print sheet handling assembly with rotatable arms and sheet clamps shown at different points along a duplex feed path defined by a cam surface system. 
     FIG. 4B is a diagrammatic view of the cam surface system of FIG.  4 A. 
     FIG. 5A is a diagrammatic front view of a print sheet handling assembly with sheet clamps shown at different points along a duplex feed path defined by a cam surface system. 
     FIG. 5B is a diagrammatic view of a sheet clamp and a rotatable arm of the print sheet handling system of FIG.  5 A. 
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
     Referring to FIG. 1, in one embodiment, a printing apparatus  10  includes a print module  12 , a simplex module  14 , and a duplex module  16  that are configured to cooperatively provide simplex and duplex printing functionality, which enables one or both sides  18 ,  20  of a print sheet  22  to be marked. Printing apparatus  10  may be implemented as any one of a wide variety of different printing machines, including xerographic, ionographic, ink jet or other copiers, printers, plotters or other reproduction apparatus. In the illustrated embodiment, printing apparatus  10  is shown as a large format, high performance graphics printer. Print sheet  22  may be introduced into printing apparatus as a pre-cut sheet of print media or it may be introduced from a roll of web sheet media. In the illustrated embodiment, print sheet  22  is shown as a large format sheet of material. As used herein, the term “large format” is intended to refer broadly to print sheets having a width (w) that is greater than approximately 28 cm (11 inches). Conventional large format print sheets have typical widths in the range of about 46 cm (18 inches) to about 61 cm (24 inches); although some large format print sheets have widths up to about 152 cm (60 inches), or greater. 
     In a simplex mode of operation, print sheet  22  is moved along a simplex feed path and introduced into print module  12  in an orientation that is suitable for marking the first side  18  of print sheet  22 . In a duplex mode of operation, after the first side  18  of print sheet  22  has been marked, print sheet  22  is moved along a duplex feed path and re-introduced into print module  12  in an orientation that is suitable for marking the second side  20  of print sheet  22 . The print sheet  22  may be fed into printing apparatus  10  through an input feed slot (not shown) and may be fed out printing apparatus  10  through an output feed slot  24 . In other embodiments, print sheet  22  may be fed into and out of the same feed slot. 
     As explained in detail below, duplex module  16  is configured so that print sheets may be controllably and reliably re-introduced into the print module  12  in an orientation that is suitable for marking the second side  20  of print sheet  22  without requiring a support structure that spans the entire width of the print sheet. In large format printing applications, this feature avoids large and heavy support structures, such as feed rollers, that otherwise would be needed to support the print sheets, as well as their own weight. In this way, printing apparatus  10  may provide duplex printing functionality with a structure that has a relatively light weight and a relatively small overall footprint. 
     As explained in connection with FIGS. 2A-2D, in one embodiment, duplex module  16  is configured to receive a print sheet from the print module  12 , and to re-introduce the print sheet into the print module  12 , trailing edge first and in an orientation that is suitable for marking the second side  20  of the print sheet. 
     Referring initially to FIG. 2A, print sheets are fed into printing system  10  from a web of sheet material (or print sheet web)  32  that is mounted on a roller  30 . Simplex module  14  may include a conventional feed mechanism (e.g., conventional friction rollers, pinch wheels, and overdrive wheels; not shown) that engages with a main drive roller  34  to feed the web of sheet material  32  along a simplex feed (or guide) path  36 . The simplex feed path  36  guides the web of sheet material  32  to a print zone  38  inside print module  12 . One side edge of the web of sheet material  32  preferably is registered against a reference edge (not shown). As the first side  18  of the web of sheet material  32  is being marked by print module  12 , the web of sheet material is guided to a print sheet handling assembly  40  of duplex module  16 . Print sheet handling assembly  40  includes sheet clamps  42  that are configured to receive the web of sheet material  32  from print module  12 . Sheet clamps may include conventional pinch rollers or other conventional sheet clamping mechanisms. 
     As shown in FIG. 2B, after the first side  18  of the web of sheet material  32  has been marked by print module  12 , the web of sheet material  32  is advanced into the print sheet handling assembly  40 . Sheet clamps  42  hold onto side edge regions of the web of sheet material. A cutter  44  (or slitter) cuts the web of sheet material  32  to a specified length to form a trailing edge  46  of print sheet  22 . After the web of sheet material  32  has been cut, the simplex feed mechanism may retract the web of sheet material  32  out of the print zone  38  and into simplex module  14 . 
     Referring to FIG. 2C, sheet clamps  42  are mounted on respective rotatable arms (not shown), which carry sheet clamps  42 —and print sheet  22 —along a first duplex feed path  48 . While print sheet  22  is being moved along first duplex feed path  48 , sheet clamps  42  tension unsupported print sheet regions between the clamped side edge regions. In this way, print sheet  22  may be controllably and reliably re-introduced into the print module  12  in an orientation that is suitable for marking the second side  20  of print sheet  22  without requiring a support structure that spans the entire width of the print sheet. Print handling assembly  40  introduces the trailing edge  46  of print sheet  22  into a second duplex feed (or guide) path  50  of duplex module  16 . 
     Referring to FIG. 2D, duplex module  16  may include a conventional feed mechanism (e.g., conventional friction rollers, pinch wheels, and overdrive wheels; not shown) that engages with main drive roller  34  to feed print sheet  22  along second duplex feed path  50 . After the feed mechanism of duplex module  16  has engaged the trailing edge  46  of print sheet  22 , sheet clamps  42  release print sheet  22  so that the duplex feed mechanism may feed print sheet  22  along duplex path  50 . The second duplex feed path  50  guides the trailing edge  46  of print sheet  22  to print zone  38 , where the second side  20  of print sheet  22  is marked. The second side  20  of print sheet  22  may be registered with the first side  18  by measuring the skew of the trailing edge  46  and the position of a side edge of print sheet  22  as it is being fed into second duplex feed path  50 . Conventional optical sensors may be used to measure the edge skew and edge position of print sheet  22 . Some embodiments may include a sensor system that is configured to detect one or more holes in print sheet  22  for registering first and second sides  18 ,  20  of print sheet  22 . The holes may be formed by a hold punch mechanism in printing apparatus  10 . Holes may be located in pre-designated side margin areas of print sheet  22  or in a center region of print sheet  22 , or both. 
     As shown in FIGS. 3A and 3B, sheet clamps  42  of print handling assembly  40  may be mounted on a pair of rotatable arms  52 ,  54 . Each rotatable arm  52 ,  54  may be mounted on a spline shaft  56 . In the illustrated embodiment, the lateral position of one arm  52  may be fixed adjacent to the reference edge (not shown) against which one side of print sheet  22  preferably is registered, and the lateral position of the other arm  54  may be moved to different locations along spine shaft  56  to accommodate different widths of the web of sheet material  32 . In other embodiments, both arms  52 ,  54  may be adjusted laterally to accommodate center-justified rolls. As shown in FIG. 3B, rotatable arms  52 ,  54  may rotate about spline shaft  56  to controllably position sheet clamps  42  along first duplex feed path  48 . Rotatable arm  54  may be positioned and driven from any point across the length of spline shaft  56 . Rotatable arms  52 ,  54  may each may include a spring or other biasing member that is configured to balance tension as rotatable arms  52 ,  54  move sheet clamps  42  and print sheet  22  along first duplex feed path  48 . By providing a flexure against tension, the springs reduce risk of tearing or scratching print sheet  22  as it is moved along first duplex feed path  48 . 
     Duplex module  16  may be configured so that a single motor and drive apparatus may control the duplexing functionality of printing apparatus  10 . In particular, an existing internal motor, such as the motor powering main drive roller  34 , may be engaged by the feed mechanism  58  and the spline shaft  56  of duplex module  16  through conventional clutching mechanisms. Sheet clamps  42  may be opened and closed by a special position of the print head of print module  12  or by a separate armature assembly. 
     Referring to FIGS. 4A and 4B, in another embodiment, a respective cam surface system  60  may be used to control action of each sheet clamp  42  during movement of print sheet  22  along first duplex feed path  48 . In this embodiment, each sheet clamp  42  includes a tensioning member  62  and a clamping member  64  that is coupled to a follower wheel  66  by a shaft  68 . Shaft  68  may rotate about a pivot pin  69 , which is attached to tensioning member  62 . Each sheet clamp  42  also includes a biasing member (e.g., a spring; not shown) that is configured to urge clamping member  64  away from tensioning member  62  (i.e., an open position). Each cam surface system  60  includes a tensioning cam surface  70  and a clamping cam surface  72 . The tensioning cam surface  70  includes a tensioning ramp  74  and a relaxation ramp  76 . The clamping cam surface  72  includes a clamping ramp  78  and an unclamping ramp  80 . The clamping cam surface also includes a pair of follower ramps  82 ,  84 , which track the surface variations of tensioning ramp  74  and relaxation ramp  76 , respectively. 
     In operation, tensioning member  62  slides over tensioning cam surface  70  and the follower wheel  66  of clamping member  64  slides over clamping cam surface  72 . Sheet clamps  42  initially receive print sheet  22  from print module  12  in an open position on cam surface systems  60  (position A). In this position, the spring force of the biasing member of each sheet clamp is sufficient to hold clamping member  64  in an open position and, thereby, enable print sheet  22  to pass between tensioning member  62  and clamping member  64 . In large format print sheet applications, the relatively large width of print sheet  22  tends to cause unsupported regions near the center of the print sheet to sag slightly, as shown. As rotatable arms  52 ,  54  drive sheet clamps  42  along duplex path  48 , the follower wheel  66  associated with each clamping member  64  first engages clamping ramp  78 . This causes shaft  68  to rotate about pivot pin  69  and clamping member  64  to close down on a side edge region of print sheet  22 , holding it in place against tensioning member  62  (position B). Next, tensioning member  62  engages tensioning ramp  74  and follower wheel  66  engages follower ramp  82 . This causes the sheet clamps to separate and, thereby, tensions unsupported print sheet regions between the sheet clamps (position C). As the sheet clamps  42  approach the unloading station near the entrance to the second duplex feed path  50 , tensioning member  62  engages relaxation ramp  76  and follower wheel  66  engages follower ramp  84 . This causes the sheet clamps to move closer together and, thereby, relaxes unsupported print sheet regions between the sheet clamps (position D). Print sheet  22  may be unloaded after the duplex feed mechanism engages trailing edge  46  of print sheet  22  and the follower wheel  66  engages unclamping ramp  80 , enabling the spring force of the biasing member of each sheet clamp  42  to place clamping member  64  in an open position (position E). 
     Referring to FIGS. 5A and 5B, in another embodiment, the tensioning of print sheet  22  may be controlled by a cam surface system  90  and the clamping action of each sheet clamp  42  may be controlled by a stop  92 . Cam surface system  90  includes a tensioning ramp  94  and a relaxation ramp  96 , and is similar in construction to tensioning cam surface  70  of cam surface system  60 . Each sheet clamp  42  includes a tensioning member  98 , a clamping member  100  and a biasing member (not shown), and is similar in construction to the sheet clamp in the embodiment of FIGS. 4A and 4B, except that the associated shaft  102  is configured to engage stop  92  and the biasing member is configured to urge clamping member  100  into a closed position. In this embodiment, rotatable arms  52 ,  54  include a four-bar linkage mechanism  104 , which is configured to maintain the alignment of sheet clamps  42  over the entire range of duplex feed path  48 . Stop  92  is located at the loading and unloading positions along duplex feed path  48 . 
     In operation, tensioning member  98  slides over cam surface system  90 . Sheet clamps  42  initially receive print sheet  22  from print module  12  in an open position on cam surface systems  90  (position A). In this position, the engagement between shaft  102  and stop  92  is sufficient to overcome the spring force of the biasing member of each sheet clamp and hold clamping member  100  in an open position, enabling print sheet  22  to pass between tensioning member  98  and clamping member  100 . In large format print sheet applications, the relatively large width of print sheet  22  tends to cause unsupported regions near the center of the print sheet to sag slightly, as shown. As rotatable arms  52 ,  54  drive sheet clamps  42  along first duplex path  48 , shaft  102  disengages from stop  92  and the spring force of the biasing member of each sheet clamp is sufficient to cause clamping member  100  to close down on a side edge region of print sheet  22 , holding it in place against tensioning member  98  (position B). Next, tensioning member  98  engages tensioning ramp  94 . This causes the sheet clamps to separate and, thereby, tensions unsupported print sheet regions between the sheet clamps (position C). As the sheet clamps  42  near the unloading station near the entrance to the duplex feed path  50 , tensioning member  98  engages relaxation ramp  96 . This causes the sheet clamps to move closer together and, thereby, relaxes unsupported print sheet regions between the sheet clamps (position D). Print sheet  22  may be unloaded after the duplex feed mechanism engages trailing edge  46  of print sheet  22  and shaft  102  engages stop  92 , which overcomes the spring force of the biasing member of each sheet clamp  42  and places clamping member  100  in an open position (position E). 
     Other embodiments are within the scope of the claims. For example, in some embodiments, the leading edge of print sheet  22  may be re-introduced into print module  12  rather the trailing edge  46 . In these embodiments, sheet clamps  42  may hold onto side edge regions near the leading edge of print sheet  22 . After the first side  18  of the web of sheet material  32  has been marked by print module  12  and the web of sheet material  32  has been cut to a specified length by cutter  44 , sheet clamps may move the print sheet over an inverting duplex feed path. The inverting duplex feed path is configured so that print sheet  22  may be reintroduced into print module  12  leading edge first and in an orientation that is suitable for marking the second side  20  of print sheet  22 . In some embodiments, the inverting duplex feed path may extend, for example, over the top of printing apparatus  10 . In other embodiments, the inverting duplex feed path may extend within the housing of printing apparatus  10 . 
     Still other embodiments are within the scope of the claims.