Abstract:
A digital printing machine includes a printing material transport device, an inkjet print head having a nozzle plate, and a capping element. The inkjet print head is adjustable into a first print head position relative to the capping element and the capping element is adjustable into a capping position relative to the inkjet print head. The capping element temporarily covers the nozzle plate when the inkjet print head is in the first print head position and the capping element is simultaneously in the capping position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2015 226 234.0, filed Dec. 21, 2015; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a digital printing machine including a printing material transport device, at least one inkjet print head, and a capping element. 
         [0003]    International Publication WO 2006/060844 A1, corresponding to Canadian Patent CA 2 588 637, discloses a digital printing machine with a capping element. The capping element is configured to be adjustable into a first position and into a second position. In the second position, the capping element is in contact with the inkjet print head. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the invention to provide a digital printing machine, which overcomes the disadvantages of the heretofore-known machines of this general type. 
         [0005]    With the foregoing and other objects in view there is provided, in accordance with the invention, a digital printing machine comprising a printing material transport device, an inkjet print head having a nozzle plate, and a capping element. The inkjet print head is configured to be adjustable into a first print head position relative to the capping element, the capping element is configured to be adjustable into a capping position relative to the inkjet print head, and the capping element temporarily covers the nozzle plate when the inkjet print head is in the first print head position and the capping element is simultaneously in the capping position. 
         [0006]    An advantage of the digital printing machine of the invention is that it has a particularly compact construction. A mechanism for moving the inkjet print head is very simple in structural terms. 
         [0007]    In another development, the inkjet print head is configured to be adjustable from a second print head position into the first print head position, wherein the distance between the inkjet print head and the printing material transporting device is greater when the inkjet print head is in the first print head position than when the inkjet print head is in the second print head position. 
         [0008]    In a further development the printing material transport device is embodied as a drum or as an endless belt. In the case of a drum, the inkjet print head is configured to be adjustable into the first print head position in a radial direction relative to the drum. In the case of the endless belt alternative, the inkjet print head is configured to be adjustable into the first print head position in a direction perpendicular to the endless belt. 
         [0009]    In an added development, the inkjet print head is disposed in a row of print heads together with further inkjet print heads and fixed to a crossbar, wherein the crossbar is configured to be adjustable and wherein the inkjet print head is adjustable into the first print head position together with the further inkjet print heads by an adjustment of the crossbar, and wherein the capping element is embodied as a common capping element for temporarily covering the nozzle plate of the inkjet print head and of nozzle plates of the further inkjet print heads or as a common capping element for temporarily covering a common nozzle plate of the inkjet print head and of the further inkjet print heads. 
         [0010]    In an additional development the crossbar is configured to be adjustable in such a way as to have only a single degree of freedom of movement. 
         [0011]    In yet another development the capping element is configured to be adjustable from a passive position into the capping position and the capping element is a trough filled with a fluid that forms a fluid surface. 
         [0012]    In yet a further development the capping element is oriented to be horizontal or tangential to the printing material transport device in the passive position and oriented to be vertical or radial relative to the printing material transport device in the capping position. The tangential and radial orientations refer to the aforementioned embodiment of the printing material transport device as a drum. 
         [0013]    In again a further development, the trough has an inner profile that causes the fluid surface to have a greater surface area when the capping element is in the capping position than when the capping element is in the passive position. 
         [0014]    In still another development the inner profile is a hook profile. 
         [0015]    In a concomitant development the inkjet print head, the further inkjet print heads, the capping element, and the crossbar jointly form a printing unit. This printing unit and further printing units of this kind are disposed along the printing material transport device in a straight or arcuate printing unit row. The configuration in an arcuate printing unit row refers to the aforementioned embodiment of the printing material transport device as a drum, wherein the printing unit row extends along the circumference of the drum. 
         [0016]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0017]    Although the invention is illustrated and described herein as embodied in a digital printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0018]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0019]      FIG. 1  is a fragmentary, diagrammatic, side-elevational view of a digital printing machine with inkjet print heads that have been lowered; 
           [0020]      FIG. 2  is a side-elevational view of a digital printing machine with inkjet print heads that have been lifted; 
           [0021]      FIG. 3  is a side-elevational view illustrating the digital printing machine during an inkjet print head cleaning process; 
           [0022]      FIG. 4  is a front-elevational view illustrating the inkjet print head cleaning process; and 
           [0023]      FIG. 5  is a side-elevational view illustrating the digital printing machine in a print head change process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring now in detail to the figures of the drawings, in which mutually corresponding elements have identical reference numerals, and first, particularly, to  FIG. 1  thereof, there is seen a digital printing machine including a plurality of printing units  9 ,  90 . The printing units  9 ,  90  may be referred to as printing bars. The printing units  9 ,  90  successively print different colors onto printing material  11 . The printing material  11  is a sheet that is transported in a direction of transport T past the printing units  9 ,  90  by using a printing material transport device  1 . The printing units  9 ,  90  form a row  10  of printing units that is parallel to the direction of transport T (see  FIG. 5 ). The printing material transport device  1  is a revolving endless belt holding the printing material  11  by a vacuum. Every printing unit  9 ,  90  is movable along a vertical linear guide  12 . A capping element  4  that is pivotable about a joint  13  is disposed next to every printing unit  9 ,  90 . Every printing unit  9 ,  90  includes inkjet print heads  2 ,  20  disposed in a row  5  of print heads perpendicular to the direction of transport T (see  FIG. 4 ). Every inkjet print head  2 ,  20  has a nozzle plate  3  including nozzles for expelling ink. Every printing unit  9 ,  90  is selectively movable along its vertical linear guide  12  to move the inkjet print heads  2 ,  20  into a first print head position  2 . 1  and into a second print head position  2 . 2 . 
         [0025]    In  FIG. 2 , all of the printing units  9 ,  90  have been moved to an upper position, i.e. all of the inkjet print heads  2 ,  20  are in the first print head position  2 . 1 . In  FIG. 1 , all of the printing units  9 ,  90  have been moved to a lower position, i.e. all of the inkjet print heads are in the second print head position  2 . 2 . A distance A between the nozzle plate  3  of the respective inkjet print head  2 ,  20  and the printing material transport device  1  is greater in the first print head position  2 . 1  than in the second print head position  2 . 2 . The first print head position  2 . 1  is provided for covering (capping) the nozzle plates  3  of the inkjet print heads  2 ,  20  of the respective printing unit  9 ,  90 . In the second print head position  2 . 2 , the printing units  9 ,  90  print on the printing material  11 . 
         [0026]      FIG. 3  illustrates the associated capping elements  4  covering the inkjet print heads  2 ,  20  of the middle printing unit  9  and of the left-hand printing unit  90  to protect the nozzles against drying out and becoming blocked during an interruption of the printing operation. Each respective capping element  4  is a common capping element for covering the nozzle plates  3  of all of the inkjet print heads  2 ,  20  of the respective printing unit  9 ,  90 . When they are covered, the middle and left-hand printing units  9 ,  90  are in the first print head position  2 . 1 . The right-hand printing unit  90  has been moved upward through a distance B beyond the first print head position  2 . 1  into a position for cleaning the nozzle plates  3 . The capping elements  4  of the middle and left-hand printing units  9 ,  90  have been pivoted upward into a horizontally-oriented capping position  4 . 1 , while the capping element  4  of the right-hand printing unit  90  has been pivoted downward into a vertically-oriented passive position  4 . 2 . Every capping element  4  is embodied as a trough filled with a fluid that forms a fluid surface  7 . The interior of every capping element  4  has a hook-shaped profile  8  enclosing a fluid chamber on three sides. The hook profile  8  includes a side wall of the capping element  4 . In the passive position  4 . 2 , the entire fluid stored in the capping element  4  is located in the fluid chamber and the fluid only covers a section of a bottom of the capping element  4 . The size of the surface area of the fluid surface  7  is defined by the size of the surface of the side wall, which is covered by the fluid in its entirety. In the capping position  4 . 1 , the fluid only covers a section of the side wall, but the entire bottom of the capping element  4  and the size of the surface of the fluid level  7  is defined by the size of the surface of the bottom. The bottom has a greater surface area than the side wall of the capping element  4 . In the capping position  4 . 1 , a lot of the fluid may evaporate from the large fluid surface  7 , creating a humid atmosphere between the fluid surface  7  and the nozzle plate  3  that is to be kept humid. In the passive position  4 . 2 , the small fluid surface  7  allows only little fluid to evaporate, keeping fluid losses to the environment low and saving fluid. 
         [0027]      FIG. 4  illustrates the construction of the printing units  9 ,  90  based on the right-hand printing unit  90  of  FIG. 3  by way of example. The printing unit  90  includes a row of seats  18  for the inkjet print heads  2 ,  20 . The seats  18  are interconnected and together, they form a crossbar  6 . Every seat  18  is provided to receive and hold another inkjet print head  2 ,  20 . The printing unit  90  is a so-called page-width printing unit, i.e. it extends over the entire width to be printed on the printing material  11 . In accordance with the perspective on which  FIG. 4  is based, the direction of transport T is perpendicular to the plane of the image of  FIG. 4 . In  FIG. 4 , the printing material  11  and the capping element  4  are not shown for reasons of clarity. A horizontal linear guide  15  that extends in a direction parallel to the crossbar  6  is disposed on the printing unit  90 . The horizontal linear guide  15  may be composed of track elements, each of which is a part of a different inkjet print head  2 ,  20 . The horizontal linear guide  15  guides a cleaning device  14  along the row of inkjet print heads  2 ,  20  to clean the nozzle plates  3  thereof. The movement of the cleaning device  14  is driven by a motor  16  through a threaded spindle  17 . The cleaning device  14  may be moved from a park position  14 . 2 , in which it is not located opposite the inkjet print heads  2 ,  20 , into various cleaning positions  14 . 1 . In every cleaning position  14 . 1 , the cleaning device  14  is located opposite a different one of the inkjet print heads  2 ,  20  to clean ink residue and paper dust off the nozzle plate  3  of the respective inkjet print head  2 ,  20  by using a cleaning element  19 . The cleaning element  19  may be a pad or a roller made of felt or any other type of soft, absorbent material. 
         [0028]      FIG. 5  illustrates a situation or setting in which the two outer printing units  90  are in their respective first print head positions  2 . 1  and the capping elements  4  are closed. The middle printing unit  9  has been moved into a change position for changing a defective inkjet print head  2  and its capping element  4  has been opened. The change position is lower than the first print head position  2 . 1  by a distance C, i.e. it is an intermediate position between the first print head position  2 . 1  and the second print head position  2 . 2 . The defective inkjet print head  2  is shown to be released from its seat  18 . The removal and subsequent reattachment may be carried out by an operator because the seat  18  and the inkjet print head  2  may be coupled through a quick-change device. 
         [0029]    An advantage of the invention is the compact construction of the digital printing machine. This is achieved by the fact that the capping elements are always located above the printing material transport path as defined by the printing material transport device  1 . Through the use of the joints  13 , the capping elements  4  may be fixed directly to the machine frame in such a way as to be stationary. Neither a lateral movement of the printing unit  9 ,  90  nor a lateral movement of the capping elements  4  is required to move the capping elements  4  into the capping position  4 . 1  to cover the nozzle plates  3 . In this context, “lateral” is understood to be a direction of movement corresponding to that of the cleaning device  14  (see  FIG. 4 ). Tracks that protrude from the machine on the sides to move the printing units  9 ,  90  are not required. 
         [0030]    An additional advantage of the invention is that the mechanism for adjusting the printing units  9 ,  90  may have a simple construction because no lateral movement of the printing units  9 ,  90  is required. The mechanisms may be embodied as the vertical guide  12  and may be combined with drives. Each respective vertical linear guide  12  provides a single degree of freedom for the movement of the respective crossbar  6 .