Abstract:
A wide/super wide digital printer comprising a printer head box that reciprocates from left to right across a wide or super wide printing table having a length of up to 20 cm that is supported by a fixed support, and a feed roller and a guiding roller that are moveably coupled to the fixed support, wherein the wide/super wide digital printer is configurable as a roll to roll printer by lowering the feed roller and the guiding roller to a lowered configuration wherein uppermost parts of the feed roller and the guiding roller are below upper surface of printing table, or as a discontinuous sheet printer by raising the feed roller and the guiding roller to a raised configuration wherein the uppermost parts of the feed roller and the guiding roller are collinear with the upper surface of the printing table.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is directed to providing a printer; specifically a wide format digital printer that is capable of printing onto both roll stock and onto single sheets of discontinuous substrate and to providing a novel mechanism for moving the feed rollers of the printer to facilitate quality printing on both types of substrate. 
         [0003]    2. Brief Description of the Art 
         [0004]    Digital printing is widely used for printing posters, wall decorations, signs and the like. The material to be printed, if flexible, is typically provided on a continuous roll and is advanced roll to roll past the print head. Sometimes however, particularly when printing onto a rigid material, the material to be printed is provided in sheet form and the printing technique is then known as flat bed printing. The wider the sheet, the greater the tendency for it to be warped or misaligned whilst being fed past the printer head, and with wide/super wide printing, here the print are is 3 m wide or more, flat bed printing is only suitable or printing onto rigid substrates. 
         [0005]    In all printing technologies advancing systems are required to accurately position the material to be printed with respect to the printing head. Even a small deviation from the correct positioning results in noticeable printing defects. 
         [0006]    To save space and equipment costs, it is useful for a single machine to be able to operate as both a flat bed printer and as a roll to roll printer. The wider the material to be printed, the more difficult it is to obtain alignment, and providing a single printer, capable of both flat bed and roll to roll printing, though desirable, is not easily achieved. 
         [0007]    WO04037543 to Nur Macroprinters LTD., titled “Advancing System and Method for a Digital Printing Apparatus”, describes a printer apparatus comprising a printing head system and an advancing system. The printing head includes a print head assembly mounted for movement along at least one horizontal axis with respect to a printing area. The advancing system is configured and operable for enabling to selectively locate the printing area in either one of a first or a second printing plane arranged in vertically spaced-apart relationship, thereby selectively exposing the first or second printing plane to the print head assembly for printing. The first and second printing planes are defined by, respectively, a first flat-bed assembly and a second roll-to-roll assembly of the advancing system. 
         [0008]    Nur Macroprinter&#39;s solution requires moving the printer head from one printing plane to another. In each printing mode the printer head moves over a relatively long table in two directions. The two printing modes use different printing tables. Moving from one printing mode to another in this manner is likely to be time consuming. Furthermore, since the printer head may be moved in three directions with respect to the substrate to be printed, it is not easy to ensure accurate, repeatable alignment, particularly when moving from one printing type to the other. Because two printing tables are used, both require calibrating to attain planarity in a parallel plane to the movement of the printer head, and this is not easily achieved since the printing tables have a tendency to warp. Indeed movement of the printing table is best avoided. 
         [0009]    U.S. Pat. No. 6,296,403 to Scitex Vision describes a dual-mode printer for printing on both flexible and rigid substrates that includes a table for providing a substantially planar support surface for supporting a substrate thereupon. A flexible-substrate feed system is configured to feed a flexible substrate in a given feed direction across the support surface. The printer has a print head configured for depositing a printing medium on a substrate as part of a printing process. A motion system is configured to generate relative displacement between the print head and the support surface in at least a first direction parallel to the feed direction. This combination of components allows the printer to be used in both: (i) a flexible-substrate mode in which relative displacement between the substrate and the print head is generated at least in part by the flexible-substrate feed system, and (ii) in a rigid-substrate mode in which relative displacement between the substrate and the print head is generated exclusively by the motion system. 
         [0010]    The printing table of the dual mode printer used is a long table suitable for flat bed printing. Such a table is inherently unsuitable for roll-to-roll printing since the distance between the rollers is large, and the flexible substrate to be printed is likely to assume a wavy surface which adversely affects the resolution of the printing thereon. 
         [0011]    Russian Patent Number RU 2167063 relates to a method of printing wherein the substrate to be printed is fed roll to roll and the table moves as well. 
         [0012]    WO05074519 to L &amp; P Property Management Company describes an apparatus and a method of ink jet printing that use a system for feeding a substrate longitudinally relative to a support area, and a system for moving a print head parallel to the direction of the substrate feed. Indexing between transverse scan rows of a print head is carried out initially by the substrate feed system and the actual feed distance is measured using an encoder or other substrate position measurement device. A controller determines the amount of any error that occurs between the actual and the desired feed distances. The controller then sends signals to move the print head to compensate for any error in the feeding of the feed system. Compensating adjustments are then made to the next subsequent substrate indexing step so that the print head tends to move back toward its home or zeroed position with its next correction and does not walk away from this home position as a result of cumulative movements. For printers that have bridges that are moveable relative to the machine frame on which the print head is carried, print head motion is achieved by moving the bridge, for example, by actuating a linear servo bridge motion system. For fixed bridge roll-to-roll printers, the print head can be caused to shift longitudinally on the bridge to make the correcting movements. 
         [0013]    The controller for controlling the amount of error and the compensation thereof indicate the problems in obtaining accurate positioning where the bridgehead moves relative to the support area, the support area moves relative to the material to be printed, and the material to be printed is fed as well. 
         [0014]    Thus, despite the developments described above, there is a need for a simple, reliable printing machine that is capable of accurately printing onto continuous substrate roll-to-roll in a first mode, or onto single sheets in a second mode, where conversion of the machine from one mode to the other is relatively easy, and the present invention addresses this need. 
       SUMMARY OF THE INVENTION 
       [0015]    In a first aspect, the present invention is directed to providing a system for raising and lowering a pair of rollers between a raised configuration and a lowered configuration with respect to a fixed support, comprising mounting each of said pair of rollers on a spindle fixed to a rocker plate on each end, each rocker plate being movable about an axle fixed to the fixed support, the moving of each rocker between a first position and a second position being driven by a driving means, and the first and second positions being determined by peg in slot mechanisms, wherein each rocker comprises a slot therethrough through which a peg fixed to the fixed support passes, and each rocker can be moved from a first position where the peg contacts the upper edge of the slot and a lower position where the peg contacts the lower edge of the slot. 
         [0016]    In a preferred embodiment, the pair of rollers comprises a feed roller and a guiding roller of a digital printer, such that in the raised configuration, the feed roller and guiding roller are brought into alignment with a surface of a printing table and a rigid laminar substrate may be printed in a flat bed print mode by a printer head that travels from side to side across the digital printer over the printing table, whereas in the lowered configuration, the feed roller and guiding roller are positioned below the printing table and a flexible substrate may be printed in a roll to roll configuration. 
         [0017]    Typically the feed roller is coated with a high friction rubbery surface. 
         [0018]    Typically the digital printer is a wide or super-wide digital printer having an effective printing width of at least 2.5 m. 
         [0019]    Typically the digital printer is a wide or super-wide digital printer having an effective printing width of up to 10 m. 
         [0020]    Typically the driving means is selected from the list of pneumatic pistons, hydraulic pistons and worms, motors, springs and the like. 
         [0021]    The printer table may be a short printer table having a length of not more than 15% of effective printing width. 
         [0022]    Typically the printer table is less than 20 cm long. 
         [0023]    Preferably the feed roller is advanced by a motor that is in fixed alignment with the spindle of the feed roller such that the motor moves up and down with the feed roller as the feed roller is moved between its upper and lower positions. 
         [0024]    Typically the raising and lowering of the pair of rollers between the raised configuration and the lowered configuration with respect to the fixed support takes less than five minutes. 
         [0025]    Preferably the raising and lowering of the pair of rollers between the raised configuration and the lowered configuration with respect to the fixed support is actuated by a switch and takes less than one minute. 
         [0026]    In a second aspect, the present invention is directed to providing a wide/super wide digital printer comprising a printer head box that reciprocates from left to right across a wide or super wide printing table having a length of less than 20 cm that is supported by a fixed support, and a feed roller and guiding roller that are moveably coupled to the fixed support, wherein the wide/super wide digital printer is configurable as a roll to roll printer by lowering the feed roller and guiding roller to a lowered configuration, or, as a discontinuous sheet printer by raising the feed roller and guiding roller to a raised configuration that is collinear with the printing table. 
         [0027]    Preferably the printable width of the wide/super wide digital printer is at least 2.5 m wide. 
         [0028]    More preferably, the printable width of the wide/super wide digital printer is at least 3 m wide. 
         [0029]    Typically the table length of the wide/super wide digital printer is no more than 15% of printable width. 
         [0030]    In preferred embodiments, the wide/super wide digital printer further comprises a system for raising and lowering the feed roller and guiding roller between the raised configuration and the lowered configuration with respect to the fixed support; the system comprising a first spindle mount through the feed roller that is coupled to a first rocker plate at one end and a second rocker plate at other end, and a second spindle mount through the guiding roller that is coupled to a third rocker plate at one end and a fourth rocker plate at other end; each of said rockers being movable about an axle fixed to the fixed support, the moving of each rocker between a first position and a second position being driven by a driving means, and the first and second positions being determined by peg in slot mechanisms, wherein each rocker comprises a slot therethrough, through which a peg fixed to the fixed support passes, and each rocker can be moved from a first position where the peg contacts the upper edge of the slot and a lower position where the peg contacts the lower edge of the slot. 
         [0031]    The term substrate as used herein refers to any flat medium that is printed on, including, inter alia, paper, fabric, card, boards of various types, and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0032]    For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings. 
           [0033]    With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention; the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
           [0034]    In the accompanying drawings: 
           [0035]      FIG. 1  is a schematic cross-section through a prior art roll-to-roll wide or super-wide inkjet printing system showing the feed roller, guiding roller and printing table thereof; 
           [0036]      FIG. 2  is a schematic isometric projection of the tensioning system of  FIG. 1 , showing the wide/super-wide substrate in tension by means of the relatively short printing table being raised slightly above the plane of the feed roller and guiding roller; 
           [0037]      FIG. 3  is a schematic isometric projection of a prior art flat bed printing system with a vacuum table suitable for wide or super wide flat-bed printing wherein the table advances the substrate past the printing head; 
           [0038]      FIG. 4  is a schematic isometric projection of a prior art flat bed printing system wherein the printer head advances over the substrate to be printed; 
           [0039]      FIG. 5  is a schematic cross section of the double configuration feed roller system of the present invention, configured for roll to roll printing; 
           [0040]      FIG. 6  is a schematic cross section of the double configuration feed roller system of the present invention, configured for printing onto discontinuous and typically rigid substrates; 
           [0041]      FIG. 7  is an isometric projection of the drive system for interchanging between the configuration of  FIG. 5  and the configuration of  FIG. 6 , and 
           [0042]      FIG. 8  is a schematic cross section of the double configuration feed roller system of the present invention, configured for printing onto a rigid substrate with roller tables positioned adjacent to the printer. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    The present invention relates to a digital inkjet printer that can print onto material fed by two separate feed modes: either onto a continuous sheet material fed by a roll to roll system, or, onto discontinuous sheets, previously requiring flat bed printers. 
         [0044]    Specifically, to allowing printing onto a discontinuous laminar substrate, such as cardboard and the like, the upper rollers, i.e. the feed and guide rollers of the roll to roll system can be raised to the height of the printing table, and guide wheels can be lowered to apply a pressure onto the upper surface of the laminar substrate to keep it pressed onto the feed roller. 
         [0045]    Since the direction of travel of the printer head is generally referred to as from side to side, and printing as described herein is generally referred to as being wide or super-wide printing, the direction perpendicular to the length of the rollers is known herein as the length, despite it being appreciated that with regards to the following description and contrary to common usage, the term width relates to the longer direction. 
         [0046]    With reference to  FIGS. 1 and 2 , a schematic cross section of a fairly typical roll-to-roll feed system of the prior art is shown. It is noted that the printing table  10  is typically about 15 cm long, and has a similar length L to that of the printing head box  12  or carriage, and typically a width of from tens of centimeters to 5 or 6 meters, in accordance with the width of the substrates that can be accommodated. The substrate  14  to be printed is inherently flexible and is supplied on one roll, and is rolled past the printing table onto a second roll. The substrate  14  is threaded between a feed roller  16  and a pressure roller  18  and kept pressed onto the feed roller  16  by the pressure roller  18 . The feed roller  16  advances the substrate  14  incrementally in small steps between passes of the printing heads  12  as their carriage moves from side to side along a track (not shown) over the printing table  10 . The substrate  14  is fed over a guide roller  20  and around a tension roller  22  which keeps the substrate  14  flat. It will be noted that the feed roller  16  and guiding roller  20  are positioned slightly below the printing table  10 . This enables the flexible substrate  14 , which may be a fabric or a paper, to be kept taut and flat over the printing table  10 ; it being appreciated that unless the substrate  14  is kept flat during printing, the resolution and accuracy of the printing is adversely affected. 
         [0047]    The feed roller  16  and guiding roller  20  need only be positioned a couple of centimeters below the printing table  10  however. The height of the printing table above the workshop floor should not be too high to impede viewing of the surface of the substrate as it is being printed, which should, therefore, be below eye level. The pressure roller  18  is required to be repositioned below and away from the feed roller  16  to enable passage of the hand so that the substrate  14  can be threaded therebetween. The tensioning roller  22  and the rolls for the roll stock of the substrate are generally positioned therebelow. 
         [0048]    With reference to  FIG. 3 , a schematic isometric projection of a prior art flat bed printing system is shown. The printing head box  32  moves from side to side over a long table  36  that may be a vacuum table to securely hold a flat sheet  34  to be printed. The table  36  moves past the printing head box  32 , which typically only moves from side to side. Flat bed printing is suitable for printing onto wide or super wide sheets of material, particularly where the material is too thick or stiff to be provided as roll stock. 
         [0049]    In contrast with roll to roll printing systems, the length of the flat sheet  34  that can be printed by a flat bed system is determined by the dimensions of the table  36 , since movement of the sheet  34  with respect to the table will result in misalignment of the material  34  with respect to the printing head box  32 . 
         [0050]    As shown in  FIG. 4 , in another type of prior art flat bed printing system, the flat sheet  44  to be printed is rigidly held to the table  46 , and the track  47  of the printer head  40  may be advanced down the table  46  on rails  48 A,  48 B along the edges thereof. 
         [0051]    There have been attempts to convert flatbed printers to print onto roll stock, by setting up rollers around a long table designed for flatbed printing onto rigid substrates. This approach does not produce reasonable results when printing onto wide/superwide media, which may be 3 to 6 meters wide, or more. When printing onto such wide substrates, the rollers have to be substantive so as not to bend, and the roll stock substrate to be printed is stretched unevenly and develops a wavy surface. This adversely affects the resolution of the printing thereupon. 
         [0052]    The present invention takes an opposite approach and adapts a roll to roll wide/super wide printer having a short printing table, to allow printing onto rigid substrates. Thus a double configuration feed roller system and a wide/super wide digital printer is proposed that can be used for digital printing onto a continuous substrate supplied on a roll, in a roll to roll printing configuration, or onto a flat sheet in a flat substrate printing configuration. 
         [0053]    With reference to  FIGS. 5 to 8 , one embodiment of the digital printer  100  is schematically shown. The double configuration described hereinbelow enables the feed roller  116  and guiding roller  120  to be moved between (i) a lower configuration shown in  FIG. 5  wherein the upper part of the feed roller  116  and guiding roller  120  are below the level of the table  110 , and (ii) an upper configuration shown in  FIG. 6  wherein the feed roller  116  and guiding roller  120  are raised to the height of the table  110  and are collinear therewith. 
         [0054]    As shown in schematic cross section in  FIG. 5 , when configured for roll to roll printing, the feed roller  116  and guiding roller  120  are below the level of the table  110 , and the substrate to be printed  114  is stretched over the table  110  and thereby kept taut and ripple free. The spindles  115 ,  121  of the feed roller  116  and guiding roller  120  are fixedly mounted at each end thereof, onto rockers  122 ,  124  that are rotatably mounted on axes  126 ,  128  respectively. Slots  132 ,  134  are cut through the rockers  122 ,  124 , and pins  136 ,  138  are fixedly mounted to the support structure  125  to which axes  126 ,  128  are also fixed. 
         [0055]    A drive means of variable length, illustrated herein as a piston  130 , such as a hydraulic or pneumatic piston, is attached to lower parts  140 ,  142  of rockers  122 ,  124 , which, in the lower configuration shown in  FIG. 5 , is kept compressed, thereby pulling lower parts  140 ,  142  towards each other, and forcing the pins  136 ,  138  to the top edge of slots  132 ,  134  in which position, the feed roller  116  and guiding roller  120  are below the level of the table  110 , and the substrate to be printed  114 , is thereby kept taut and ripple free. 
         [0056]    It will be appreciated that other driving means, such as springs, worms, motors and the like (not shown) may be used instead of a piston  130 , to give an equivalent movement, driving the feed rollers between the two positions. 
         [0057]    As shown in  FIG. 6 , to print onto separate sheets of a discontinuous substrate  145 , which is typically a less flexible, more rigid, thicker material such as cardboard and the like, the piston is extended. This forces bottom parts  140 ,  142  of rockers  122 ,  124  apart, rotating rockers  122 ,  124  around axes  126 ,  128 , thereby bringing slots  132 ,  134  upwards around pins  136 ,  138 , so pins  136 ,  138  contact base of slots  132 ,  134  and are stopped thereby, preventing further rotation of rockers  122 ,  124 . In this position, the feed roller  116  and guiding roller  120  are at the level of the table  110 . A flatbed pressure system  150  is lowered onto the substrate  145  to be printed, pressing the substrate  145  onto the feed roller  116 . The flatbed pressure system  150  may be a row of individual idling wheels  154  which are attached to arms  156  that pivot down from a common support  158 , each arm  156  being pressed downwards by a pressure means  152 , which may be a Hookian element such as a helical spring, or a closed piston, for example. The purpose of the flatbed pressure system  150  is only to keep the discontinuous substrate  145  pressed onto the feed roller  116 , ensuring that rotation of the feed roller  150  advances the discontinuous substrate  145  over the table  110  so that it may be printed. In this manner, a feed roller  116  is used for incremental advancing of a discontinuous substrate  145  which may be a rigid or thick discontinuous substrate  145 , unsuitable for rolling, or simply a relatively short length of material supplied as roll stock, such as the end of a roll. 
         [0058]    As illustrated in  FIGS. 5 and 6 , the drive means may be a rod in cylinder type piston  130  that can be hydraulically or pneumatically powered. The cylinder can be coupled to the rocker  122  of the guiding wheel  120  and the rod may be coupled to the rocker  124  of the feed roller  116 . Alternatively and equivalently, the piston  130  may be reversed with the piston rod being coupled to the rocker  122  of the guiding wheel  120  and the cylinder being coupled to the rocker  124  of the feed roller  116 . Furthermore, other driving means such as a worm and/or a motor, for example, might be substituted without exceeding the scope of the invention. In preferred embodiments, a pair of driving means is used on similar rockers; one at each end of the feeding  116  and guiding  120  rollers. This helps ensure accurate, straight feeding of the substrate  114 ,  145 . Strictly speaking however, only one driving means is required. 
         [0059]    The feed roller  116  is usually rubber coated to provide a high friction surface. The rollers are rigid by their construction and resist bending. The table  110  often has a square profile and is typically less rigid than the rollers  116 ,  120 . It will be noted that for wide/super wide printing, the width of the table may be several meters. Preferably the table  110  is supported periodically by adjustable supports and the absolute height of the table  110  at each support point may be adjusted to ensure planarity. The rollers  116 ,  120  may be used as guides for this purpose. 
         [0060]    Since the feed roller  116  is moved upwards and forwards when moving from the roll-to-roll lower configuration of  FIG. 5  to the flat bed upper configuration of  FIG. 6 , the feed roller  116  is separated from the pressure roller  120 , which is not even shown in  FIG. 6  as it plays no part. This separation aids feeding of substrate  114  supplied as roll stock between pressure roller  118  and feed roller  116 . In the prior art, the pressure roller  118  is typically lowered to achieve this. In some embodiments of the invention, the pressure roller  118  may still be lowered, but in other embodiments, this is not necessary. Since the height of digital printing machines is effectively limited, and there is a need to accommodate further rolls and rollers, etc. such as the supply roll of the substrate  114  to be printed, and the take up roll for the printed substrate  114 , space and height is at a premium, and the fact that the feed roller  116  can be lifted and moved forwards, away from the pressure roller  118 , provides additional space between feed roller  116  and pressure roller  118  for feeding the substrate  114  therethrough. 
         [0061]    With reference to  FIG. 7 , the adjustable roller support system, one end of the feed roller  116  and one end of the guiding roller  120  are shown in isometric projection. It will be noted that the motor unit  160  is coupled directly to the spindle  115  of the feed roller  116  which is incrementally advanced in a stepwise fashion thereby. In the embodiment shown, the motor unit  160  is attached to the spindle  115  of the feed roller  116  in a fixed alignment therewith, and moves down and up with the feed roller  116  as the feed roller  116  is moved between its lower and upper configurations as shown in  FIG. 5  and  FIG. 6  respectively. 
         [0062]    Referring now to  FIG. 8 , since in the present invention the wide flat bed table previously required has been eliminated, with the substrate  145  to be printed being advanced past the printing head box  112  that moves from side to side along a single track, by a feed roller  116 , it is typically necessary to provide external support to a discontinuous sheet substrate  145  to be printed, even if the substrate  145  is fairly thick and rigid. A convenient way to provide such support is to bring a feeder roller table  170  and a collector roller table  180  into proximal alignment with the rollers of the printing unit  100 . A rigid laminar substrate  145  to be printed may be placed on feeder roller table  170  with its front edge resting on feed roller  116 , and with the flatbed pressure system  150  applying a pressure thereto, to keep the rigid laminar substrate  145  in contact with the feed roller  116 . The feed roller  116  is turned in small steps by the motor unit, and the substrate  145  to be printed is incrementally advanced over the printing table  110  onto guiding roller  120  and then onto the collector roller table  180 . 
         [0063]    Super wide printers may be 3 meters wide or more. Rigidity becomes important for high resolution printing. In contradistinction to the prior art, since the digital printer of the invention uses a feed roller for advancing discontinuous laminar substrates as well as when printing roll to roll, long printing tables are eliminated and a printing table that is not more than 20 cm long is used. One consequence of this is that the length of the machine  100  is typically well under a meter. Nevertheless accurate forwarding of large substrates  145 ,  114  to be printed is allowed. 
         [0064]    The roller tables  170 ,  180  shown in  FIG. 8  are optional, and the substrate  145  to be printed may alternatively be supported in other ways, such as manually supported by workers, for example. Additionally, where provided, roller tables  170 ,  180  are utility components that may find a wide range of alternative uses other than for supporting discontinuous substrates  145  when using the digital printer  100  of the inventor for flat bed type printing. 
         [0065]    Thus persons skilled in the art will appreciate that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description. 
         [0066]    In the claims, the word “comprise”, and variations thereof such as “comprises”, “comprising” and the like indicate that the components or processing steps listed are included, but not generally to the exclusion of other components.