Abstract:
The invention relates to an apparatus for image formation on cylindrical surfaces of printing machines. The object of the invention is to provide a compact image formation unit with a broad application rage regarding its usage, the sequence in time and variation in time of the process steps. The invention accomplishes this by processing units mounted on slides movable separately on a common cross bar. Each slide carries at least one processing unit. The cross bar is located in a gusset area between a plate cylinder and a blanket cylinder.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for image formation on cylindrical surfaces in printing machines comprising multiple processing units arranged side by side and allocated to the plate cylinder of the printing machine. The processing units can be moved axially to the plate cylinder. 
     BACKGROUND OF THE INVENTION 
     A printing machine with a printing unit having a gapless image cylinder,.which is coated with a dryable polymer by a direct image formation process, is known through DE 19612927 A1. The surface characteristic of this polymer layer on the image cylinder is changed completely or partially by a selective laser beam in order to change its affinity to printing ink. The image cylinder is used instead of a plate cylinder in a conventional offset press either in wet offset or dry offset printing. The image cylinder is cleaned from the image carrying layer after finishing printing. The layer must not be removed completely. The radiation source, the coating unit and the drying unit are arranged side by side on a spindle drive and moved by the spindle drive over the width of the cylindrical surface to be imaged. The cleaning unit is mounted separately. 
     The disadvantage of this solution is the lack of processing space caused by the number and fixed allocation of the processing units. The versatility of this apparatus is insufficient for many applications. 
     SUMMARY DESCRIPTION OF THE INVENTION 
     The object of the invention is to provide a compact image formation unit with a broad application range regarding its usage, the sequence in time and variation in time of the process steps. 
     The present invention accomplishes this by processing units mounted on slides movable separately on a common cross bar. Each slide carries at least one processing unit. The cross bar is located in a gusset area between the plate cylinder and a blanket cylinder. 
     An advantage of the present invention is the variability of using the process steps. It is also possible to adjust the processing intensity of the processing units according to the process requirements by the time effecting the surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described below in greater detail by exemplary embodiments of the invention and by reference to the drawings, wherein: 
     FIG. 1 is a schematic drawing illustrating the roller and cylinder scheme of a printing unit in a printing press with an embodiment of the apparatus of the present invention mounted on a cross bar; 
     FIG. 2 is a schematic drawing illustrating an embodiment of the apparatus of the present invention mounted on a fixed spindle; 
     FIG. 3 is a schematic drawing illustrating an embodiment of the apparatus of the present invention mounted on a linear motor drive; and 
     FIG. 4 is a schematic drawing illustrating the roller and cylinder scheme of a printing unit in a printing press with an embodiment of the apparatus of the present invention mounted on two cross bars. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a printing unit of a multi-color sheet fed offset press. The printing unit contains an impression cylinder  3  carrying the sheet and, as the image transferring cylinders, a plate cylinder  1  and a blanket cylinder  2 . 
     An inking unit  4  and a dampening unit  5  are allocated to the plate cylinder  1 . The plate cylinder  1  can also carry a printing form, which is not shown in the drawings. 
     A cross bar  71  is located in a gusset area  12  between the place cylinder  1  and the blanket cylinder  2 . The cross bar is located in such a manner that other elements in this area, for instance a cleaning unit  16 , are not obstructed in their operational space. The cross bar  71  carries processing units  9 ,  10  and  11  for image formation on the surface of the plate cylinder  1  with respect to a printing form mounted on the plate cylinder  1 . 
     FIG. 2 shows the details of this embodiment. The cross bar  71  is mounted in the side frame  6  of the printing machine. The cross bar  71  stretches parallel to the surface of the plate cylinder  1  over the entire width of the printing press (see also FIG.  3 ). Parallel to the cross bar  71  is a fixed spindle  8  which is supported in a pillow block  123  and does not rotate. 
     The cross bar  71  and the fixed spindle  8  extend over the side frame  6 . Therefore the side frame  6  has a cut out  61  covered by a housing  121 . The housing  121  is accessible by a coverable opening  124 . 
     The first processing unit  9  is mounted on a slide  91 . This slide  91  is connected with a first motor  92  driving a first spindle  93 . The first spindle  93  is in an operational connection to the fixed spindle  8 . The first slide  91  also carries an erasing unit with an erasing head  94  and a suction  95  with a suction hose  96 . The erasing head  94  is embodied as a high-energy laser. The erasing head  94  precedes the suction  95  in the moving direction of the first slide  91  (shown by an arrow in FIG.  2 ). 
     The first processing unit  9  precedes the second processing unit  10  in the moving direction of the processing units  9 ,  10  and  11 . This unit is also mounted on a slide  101  and has a motor  102  and a spindle  103  of the same configuration. The slide  101  carries a coating unit  104 . The coating unit is embodied as an ink jet printing head. 
     In this embodiment, the next and last processing unit in the processing sequence is the third processing unit  11 . It has a motor  112  and a spindle  113 , similar to the processing units  9  and  11  described above. A slide  111  carries an image formation unit and a fixation unit  115 . 
     FIGS. 1 and 2 do not show the supply cables and supply hoses to simplify these representations. 
     The Operation of the Above-described Embodiment is Explained Below: 
     The three processing unites  9 ,  10  and  11  are in their parking positions on the side frame  6  respectively at the beginning of the image formation process. They are partially or completely covered by the housing  121 . 
     The first processing unit  9  moves towards the plate cylinder  1  in the direction shown by the arrow in FIG. 2 for image formation. The motor  92  starts its operation and rotates the spindle  93 . The slide  91  is moved in the designated direction because the fixed spindle  8  is non-rotating. The plate cylinder  1  rotates with an appropriate speed for this process. 
     The erasing head  94  is activated if the plate cylinder  1  is reached. The laser of the erasing head  94  erases the image information and thus removes the image layer of the preceding printing job from the plate cylinder  1 . The suction  95  takes the loosened particles and removes them from the printing machine. The first processing unit reaches its parking position at the opposite side of the side frame  6  after complete removal of the old image layer. A housing  122  analogous to the housing  121  is provided for this purpose. 
     The surface of the plate cylinder  1  prepared in this manner is coated by the coating unit  104  in the second processing unit  10  with a layer to be imaged. The movement of this second processing unit  10  is similar to the first processing unit  9 . This process starts typically immediately after removal of the old layer for the old image information. The second processing unit  10  also reaches its parking position on the opposite side after finishing coating. 
     The third processing unit  11  is started as the last processing step after the applied layer hardens after a required period of time. The third processing unit  11  moves in the described manner over the surface of the plate cylinder  1 . The actual image information is applied by the laser of the imaging unit  114  and hardened by the fixation unit  115  during this movement. 
     The processing units  9 ,  10  and  11  take their park positions on the opposite side after image formation. The printing process can now start. It is advantageous to move the processing units  9 ,  10  and  11  back to their original positions before printing. The speed of the movement is a multiple of the processing speed. The processing units  9 ,  10  and  11  can be moved one after the other or together in concert. 
     The embodiment described above is only one possible embodiment. It is for instance also possible to insert or to integrate an additional processing unit after the second processing unit  10  to harden the layer if technically required. A unit for cleaning and developing can be also inserted after the third processing unit  11 . 
     FIG. 3 shows the parking positions of the processing units after image formation. FIG. 3 shows another embodiment of the invention. The processing units  9 ′,  10 ′ and  11 ′ are equipped with linear motors  131 ,  141  and  151  and are mounted on slides  91 ′,  101 ′ and  111 ′ respectively. They are connected to the cross bar  71  through the drive members  132 ,  142  and  152 . The first processing unit  9 ′ has an erasing head  94 ′ and a suction  95 ′ with a suction hose  96 ′. The second processing unit  10 ′ has a coating unit  104 ′. The third processing unit  11 ′ has an imaging unit  114 ′ and a fixation unit  115 ′. The cross bar  71  extends over a side frame  6 . The side frame  6  has a cut out  61 ′ covered by a housing  122 . The operation is the same as described above. 
     FIG. 4 shows an embodiment with two cross bars  72  and  73 . This arrangement has the advantage that in embodiments with more processing units these units can be distributed between the two crossbars  72  and  73 . This results in better space distributions and more room in the parking positions adjacent to the side frame  6 . Thus the processing units can be driven either by linear motors  131 ,  141  and  151  or the motors  92 ,  102  and  112 .