Abstract:
A printer ( 1 ) is provided having two spaced apart pinions ( 29 ) that intermesh with two racks ( 31 ) which form frame elements of a stereotype printing assist system or which are fastened to the bottom side of the frame elements of the stereotype printing assist system. The pinions ( 29 ) allow movement of the stereotype printing assist system forwards and backwards true to the real position thereby allowing a reproducible overprint or overprinting of small sized products ( 19 ) to be imprinted using an one-dimensionally mobile print head unit ( 3 ).

Description:
BACKGROUND 
       [0001]    The subject of the invention is a printer for printing sheets, plates, and endless roll materials according to the preamble of claim  1 . 
         [0002]    Printers of this class are known. They are used for printing on large surface-area plates made from metal, plastic, or wood, sheets or endless roll materials, such as paper, textiles, films, etc. 
         [0003]    The known printers comprise a housing with a printing table or a printing surface, above which a print head unit is supported so that it can be driven along a straight track and also so that it can be lowered onto or moved away from the work piece for printing. A printer of this class further comprises at most one or two transport cylinders, which advance the printing material through frictional contact. 
         [0004]    With such printers, endless roll material can be printed on. The printing direction or forward feed direction of the endless roll material is always the same. Instead of endless roll material, plates lying on the transport cylinder or cylinders can also be printed on. An overprint, for example, of a white pre-print with ink, is not possible with the necessary accuracy, because neither the endless roll material nor the plates lying on the transport cylinders can be guided with sufficient accuracy forwards and backwards under the print head unit. 
         [0005]    Printing systems that can move with positional accuracy are also known. In these systems, either the print head unit can be moved together with its guide over the work piece, which is held fixed on the printing table, or the entire printing table is constructed so that it can move under the print head unit. The latter devices are built for the most part as single-purpose machines and cannot be converted for printing on endless roll materials. In addition, the masses of the printing table or the print head unit together with their guides are relatively large, so that only small travel speeds are possible. 
       SUMMARY 
       [0006]    One objective of the present invention now consists in constructing a printer such that printing can be performed on this work piece with absolute positional accuracy, wherein, in particular, small-format objects and also overprints can be performed in a reproducible way. In addition, the printing of endlessly fed, web-shaped material, such as films, etc., should also be possible on the printer. 
         [0007]    This objective is met by a printer according to the features of claim  1 . Especially advantageous constructions of the printer are transcribed in the dependent claims. 
         [0008]    A holder frame, which is connected to a forward feed drive via a positive-fit connection and which is used as a plate printing aid, allows the printing material to be guided with absolute precision and reproducible overprints to be produced on a conventionally built printer used for printing on endlessly fed material. The holder frame can be moved not only precisely in a forward feed direction, but also in two directions, so that overprinting becomes possible. The driving means necessary for driving the holder frame do not interrupt the conventional printing of endless material webs or plate-shaped work pieces that lie on a transport roller and that can be advanced frictionally engaged only in one transport direction. Conventional printers can be converted or retrofitted with very minimal technical and financial expense by adding drive means entering into a positive fit with the holder frame at the end sides of the transport cylinder or at a different position and are used as printers for reproducible prints or printing on small-format print carriers. 
         [0009]    Through the arrangement of ink print heads with at least one white print head arranged in series with these other print heads, a prior white print or a subsequent white print or subsequent treatment of the area to be printed, for example, with a coating can be performed. With UV dryers arranged at the end relative to the print heads, prints can be produced economically and with low energy expense, because the UV dryer must cover only the width of one print head. The printing of small plates, which cannot be held by the transport cylinders, can be performed individually or simultaneously. 
         [0010]    The removal and the loading of objects to be printed on by the printer can always be performed from the same side of the machine (front or back). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention is explained in more detail with reference to an illustrated embodiment. Shown are 
           [0012]      FIG. 1  a schematic cross sectional view through a printer in an application as a roller printer for endless material, 
           [0013]      FIG. 2  a schematic cross sectional view through the printer in an application for single printing on plate-shaped material, 
           [0014]      FIG. 3  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials, after the registration of the plate printing aid and also the printing medium, 
           [0015]      FIG. 4  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials at the beginning of the printing process, 
           [0016]      FIG. 5  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials during the printing process, 
           [0017]      FIG. 6  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials shortly before the end of the printing process, 
           [0018]      FIG. 7  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials after the completion of the printing process, 
           [0019]      FIG. 8  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials for the removal of the printing material, 
           [0020]      FIG. 9  a schematic cross sectional view through the printer with a plate printing aid for precise printing of plate-shaped materials after the placement of a new printing material onto the plate printing aid and retracting into the starting position, 
           [0021]      FIG. 10  a perspective top view of the printer. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    In the perspective overview illustration according to  FIG. 10 , the entirety of the printer  1  is designated with the reference symbol  1 . This comprises—in addition to a number of additional parts that are not necessary for the understanding of the present invention and that are therefore not described in more detail—a print head unit  3 , in which a plurality of print heads  25  are installed in series. At the end on the print head unit  3  there are, for example, two UV dryers  5 , which cure the printing inks immediately after the printing process. Between the UV dryers  5  and the ink print heads  25 , there can also be a white print head  26 . The print head unit  3  is arranged so that it can move on a rail  7  in the direction of the arrows P. The print head unit  3  can also be moved vertically in the direction of the arrows Y. Underneath the rail  7 , which is also called a beam, two horizontal drive and transport cylinders  11  and  13  are arranged on a frame in the illustrated example. The two transport cylinders  11 ,  13  driven by a drive (not shown) are arranged underneath the print head unit  3  such that the nozzles of the print head  25  are directed towards the area between the two parallel transport cylinders  11 ,  13 . In the printing area between the two transport cylinders  11 ,  13 , there is a plate, preferably a vacuum plate  15  as a printing table, on which the material for printing is laid flat. The vacuum plate  15  comprises a box closed on the bottom and on the sides, which is covered by a perforated plate  17  and suctions the material  19  for printing guided by the vacuum plate  15  during the printing process ( FIG. 1 ). In the basic construction of the printer  1  according to  FIG. 1 , the printing material  19  is an endlessly fed web, which is guided from a feed roll (not shown) over a number of carrier rolls  21  over the first transport cylinder  11 . A spring-loaded hold-down roll  23  lies above the first transport cylinder  11 . The printing material  19  is guided by the first transport cylinder  11  over the vacuum plate  15  under the print heads  25  with nozzles that are arranged on the bottom side and that are directed towards the printing material  19  to the second transport roller  13 , above which a hold-down roll  23  can also be arranged. From there, the printing material  19  now with the print is guided directly or indirectly via carrier rolls  21  to the receiver roll (not shown). 
         [0023]      FIG. 2  represents the same printer  1 , wherein now the printing material  19  is not fed and transported as an endless web, but instead is composed of a rigid plate  27 , which is driven, in turn, by at least one of the transport cylinders  11 ,  13  under the print head unit  3 . Similarly to the endlessly fed printing material  19 , the plate  27  can also be transported in a reproducible way by the transport cylinders  11 ,  13  only in a frictionally engaged connection and only in the direction of the arrow T. Reversing the transport direction, in order to print over certain areas on the printing material  19  or on the plate  27 , is not possible due to the inevitable slippage and the associated loss of precision. 
         [0024]      FIGS. 3 to 9  show the same printer  1  with a plate printing aid according to the invention in the shape of a holder frame  28 . Toothed pinions  29 , which each engage in an intermeshing way with a toothed rack  31 , are placed at a distance α on the ends of the first transport cylinder  11 . The toothed rack  31  forms either two parallel frame elements  33  of the holder frame  28  lying at a distance α or they are attached to the bottom sides of the frame elements  33  of the holder frame  28 . In the schematic representations, the toothed racks  31  are integrated into the frame elements  33 . 
         [0025]    The holder frame  28  is used as a carrier for a rigid or loose printing material  19 , which can be positioned at a stop  35  on the holder frame  28 . It is formed as a closed plate, a grating, or the like. Instead of a stop  35 , for the positioning or registering of the printing material  19  with respect to the holder frame  28 , other means can also be used. The registration of the holder frame  28  with respect to the print heads  25  is performed on a tracer or sensor element  37 , which can be lowered after the registration of the position of the holder frame  28 . A hold-down roll, which presses onto the top side of the frame elements  33 , is not shown in the figures, but guarantees that the positive-fit connection between the toothed pinion  29  and the toothed rack  31  is maintained. The second transport cylinder  13  in this embodiment assumes just a load-bearing function. 
         [0026]    After the tracer element  37  is lowered, the holder frame  28  is guided under the print heads  25  together with the printing material  19  driven by the pinion  29 . The printing is performed by moving the print head unit  3  along the rail  7 , i.e., transverse to the forward feed direction T of the printing material  19  lying on the holder frame  28 . Immediately following the printing, the still wet printing ink is dried by one of the UV dryers  5 . The effective width of the UV dryers  5  corresponds to the narrow side of the print heads  25 , which are arranged one behind the other, i.e., in series, and which are each arranged in front of or behind the UV dryers  5  in the direction of travel P. 
         [0027]    In  FIG. 5 , the printing of the printing material  19  is performed by all of the nozzles of the print head unit  3 , i.e., with optimal output. In this figure, it is further visible that very small individual objects for printing, which cannot be guided and clamped tight without the holder frame  28 , can now also be printed on with the holder frame  28 . If the holder frame  28  is perforated in the contact area with the printing material  19 , then the printing material  19  on the holder frame  28  can also be held tight by the vacuum plate  15 . Obviously, other means for fixing small and large printing materials  19  can also be used. 
         [0028]      FIG. 6  shows the printing process shortly before completion. From the print heads  25 , only a narrow area at the end of the printing material  19  is still to be charged with ink. 
         [0029]    After the end of the printing process according to  FIG. 7 , the print head unit  3  is moved upwards, i.e., lifted away from the printing material  19 . Then the print material  19  can be taken away from the holder frame  28 , i.e., removed from the printer  1  and replaced by new printing material  19 , which, as soon as it is positioned on the holder frame  28 , is guided under the print head  25  towards the rear side of the printer  1 . Readjustments to the plate printing aid  28  with respect to the toothed pinion  29  are not necessary, because the engagement of the toothed pinion  29  in the toothed rack  31  has not been disconnected ( FIG. 9 ). Instead of the positive-fit connection between the toothed pinions and toothed racks, another positive-fit connection element can also be used. For example, a punched tape or a track of punched holes can be formed on the holder frame  28 , in which the knobs on a knobbed wheel engage. The toothed racks could also be replaced by toothed belts. It is also not absolutely necessary to form the toothed pinion  29  on the shaft of the transport cylinder  11 ; it could also be arranged at another suitable position. The printer  1  according to the invention can also be operated without transport cylinders for printing on endlessly fed material webs. 
         [0030]    All of the motion sequences are controlled by an electronic controller (not shown).