Abstract:
A sheet-fed offset printing press for printing on both sides of sheets has a compact construction and permits a number of color separations to be printed over one another in recto printing or recto and verso printing in a flexible manner and with high print quality. A plurality of printing units, which are disposed behind one another, each include at least one form cylinder, a transfer cylinder, a first impression cylinder and an inking unit having at least one ink applicator roll associated with the form cylinder. A second impression cylinder, which interacts with the transfer cylinder and the first impression cylinder, is provided in at least one printing unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 049 473.9, filed Sep. 29, 2008; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a sheet-fed offset printing press for printing on both sides of sheets, including a plurality of printing units disposed behind one another and each having at least one form cylinder, a transfer cylinder, a first impression cylinder and an inking unit with at least one ink applicator roll associated with the form cylinder. 
         [0003]    It is known to place a plurality of homogeneous printing units behind one another in a sheet running direction in order to print sheets in multiple colors. The printing units have a high degree of repeated parts, so that manufacturing costs are low. A color separation is applied to one side of a sheet in each printing unit. 
         [0004]    The sheets can be printed on the front side in a first pass and on the rear side in a second pass in order to print in multiple colors on both sides of the sheets. A machine of that type having satellite printing units is disclosed in German Published, Non-Prosecuted Patent Application DE 197 56 796 A1, corresponding to U.S. Pat. No. 6,293,193. Printing in two passes is time and cost-intensive. 
         [0005]    In printing presses which print sheets in multiple colors on both sides in only one pass, a turning apparatus is provided between a final printing unit for printing on the front side and a first printing unit for printing on the rear side. The turning apparatus works and tumbles the sheets about a transverse axis or turns them over about a longitudinal axis. A turning apparatus increases the installation space of the printing press. Register errors are produced by multiple sheet transfers, as a result of which the prints on the front side and the rear side of the sheets have positional deviations with respect to one another. 
         [0006]    A printing press according to German Patent DE 197 56 990 C2 includes an inline configuration of double printing units. Two blanket cylinders are operatively connected in each printing unit for simultaneous printing on both sides of the sheets. The axes of the sheet guiding cylinders are disposed in a horizontal plane. In each printing unit, printing form cylinders and inking units are disposed above and below that plane. The printing form cylinders and the inking units below the plane are accessible with difficulty for changeover and service purposes. The ink transport to the blanket cylinders is different above and below the plane due to gravity. When processing a print job, the inking units and the printing form cylinders below the plane are unused for printing only on the front side of the sheets. The double printing units have a high configuration. 
         [0007]    German Patent DE 33 27 791 C1 describes a sheet-fed printing press having a plurality of printing units of inline construction, in which a plate cylinder, a blanket cylinder and an impression cylinder having identical diameters are provided in each printing unit. A sheet is fed in after every second revolution of a plate cylinder, in order to print on both sides of the sheets. The sheet is conveyed from the impression cylinder to the blanket cylinder in a printing unit and is given a verso print on the rear side in the nip between the plate cylinder and the blanket cylinder. Afterward, the sheet is again fed to the impression cylinder. During verso printing operation, the blanket cylinders and the plate cylinders can be raised up cyclically respectively from the impression cylinder and the blanket cylinder, with the result that a transfer of printing ink is interrupted when the relevant cylinder does not guide a sheet during every second revolution. The cyclical throwing on and off of cylinders impairs the print quality and leads to high wear of machine parts. 
         [0008]    Printing units of inline construction according to German Patent DE 31 08 806 C2, corresponding to U.S. Pat. No. 4,409,894, each have a plate cylinder, a blanket cylinder and an impression cylinder for carrying out recto and verso printing. The impression cylinder carries a rubber blanket. The blanket cylinders are raised up from the respective impression cylinder during every second revolution. The disadvantages of throwing a cylinder on and off cyclically have already been mentioned above. 
         [0009]    German Patent DE 437203 discloses a rotary printing press for printing both sides of a sheet in multiple colors. Printing is carried out on single size impression cylinders by way of double size plate and blanket cylinders. The blanket cylinders are integrated into the sheet guiding device. During verso printing operation, the impression cylinder is covered with a rubber blanket. During verso printing operation, the machine operates at half revolutions, with recto printing being carried out in the nip between two rubber blankets and verso printing being carried out conventionally in the nip between a blanket cylinder and an impression cylinder. The ink transfer in a rubber/rubber configuration is different from that in a rubber/impression cylinder configuration, which leads to varying color phenomena in the printed image that are not desired in any case. 
       SUMMARY OF THE INVENTION 
       [0010]    It is accordingly an object of the invention to provide a sheet-fed offset printing press for printing on both sides of sheets in one pass, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which has a compact construction and by way of which it is possible to print a number of color separations over one another in recto printing or recto and verso printing in a flexible manner and with high print quality. 
         [0011]    With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet-fed offset printing press for printing on both sides of sheets. The printing press comprises a plurality of printing units disposed behind one another. Each of the printing units includes at least one form cylinder, a transfer cylinder, a first impression cylinder and an inking unit having at least one ink applicator roll associated with the form cylinder. At least one of the printing units has a second impression cylinder interacting with the transfer cylinder and the first impression cylinder. 
         [0012]    According to the invention, in an offset printing press having a plurality of printing units which are disposed behind one another, an additional impression cylinder which interacts with a transfer cylinder and a first impression cylinder is disposed in at least one printing unit. The operating mode of a printing unit which is equipped in such a way can be switched over, with the result that recto printing operation or recto and verso printing operation is possible selectively. Depending on the switching position of the transfer cylinder and the additional impression cylinder, a sheet is turned during printing and is printed on its rear side, or not turned and printed only on the front side. In an inline configuration having a plurality of printing units which are equipped in this way, all of the printing units can be switched to recto printing operation and recto and verso printing operation. The number of prints can therefore be configured as desired on the front side and the rear side. For example, it would be possible, in a printing press having eight printing units, to process print jobs, in which eight colors are printed on one side or seven are printed over one, six over two, five over three or four colors over four are printed on the front side and the rear side of the sheet. During the pass, a sheet can be turned twice or multiple times. During pure recto printing operation, the sheets are fed at full revolutions. In verso printing operation, the sheets are fed at half revolutions, that is to say during every second revolution of a single size form cylinder. 
         [0013]    The printing units of the sheet-fed printing press can be set up in line as desired in a modular construction. The vertical direction of the ink flow is identical in all of the printing units, with the result that it is possible to provide identical inking units for recto printing operation and recto and verso printing operation. The printing units are readily accessible from above for service purposes. 
         [0014]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0015]    Although the invention is illustrated and described herein as embodied in a sheet-fed offset printing press for printing on both sides of sheets, 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. 
         [0016]    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 
         [0017]    FIGS.  1 . 1 - 1 . 4  are sheet running diagrams in fragmentary, diagrammatic, longitudinal-sectional views of an offset printing press having double size transfer cylinders; 
           [0018]    FIGS.  2 . 1 - 2 . 2  are enlarged, fragmentary, longitudinal-sectional views of one variant of an offset printing unit having a single size transfer cylinder in recto and verso printing operation; and 
           [0019]      FIG. 3  is a further enlarged, fragmentary, longitudinal-sectional view of a variant of an offset printing unit having double size transfer cylinders and separate inking units. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring now to the figures of the drawings in detail and first, particularly, to  FIGS. 1.1  to  1 . 4  thereof, there are seen four printing units  1  to  4  of a sheet-fed wet offset printing press, which are disposed horizontally behind one another. Each printing unit  1 - 4  includes a form cylinder  5 - 8  with a printing form  9 - 12 . The printing forms  9 - 12  each lie on a respective active diameter D. Furthermore, each printing unit  1 - 4  includes a double size transfer cylinder  13 - 16 . Two semicylindrical sectors  17 - 24  are each formed on a respective one of the transfer cylinders  13 - 16 . Elastic covers  25 - 28  are mounted on the transfer cylinders  13 - 16  in the sectors  18 ,  19 ,  21  and  24 . The covers  25 - 28  each lie on a respective active diameter 2×D. The transfer cylinders  13 - 16  do not have a surface  29 - 32  which transfers printing ink in the sectors  17 ,  20 ,  22 ,  23 . Furthermore, each printing unit  1 - 4  includes a double size impression cylinder  33 - 36  and a single size impression cylinder  37  to  40 . Two semicylindrical sectors  41 - 48  of the impression cylinders  33 - 36  each have circumferential faces which carry a sheet  49  and gripper systems  50 - 57  which hold the respective sheet  49  at the leading edge. The circumferential faces lie in each case on an active diameter 2×D. The impression cylinders  37 - 40  each have a circumferential face which carries a sheet  49  and gripper systems  58 - 61  which hold the sheet  49  at the leading edge. Triple size transfer drums  62 - 66  are provided for transporting the sheet  49  to the printing unit  1 , between the printing units  1 ,  2 ;  2 ,  3 ;  3 ,  4  and away from the printing unit  4 . Each of three sectors  67 - 81  of the transfer drums  62 - 66  have circumferential faces which carry the sheet  49  and gripper systems  82 - 96  which hold the respective sheet  49  at the leading edge. The circumferential faces of the transfer drums  62 - 66  each lie on a respective active diameter 3×D. An inking unit  97 - 100  and two dampening units  101 - 108  are provided in each printing unit  1 - 4 . Ink applicator rolls of the inking units  97 - 100  and dampening solution applicator rolls of the dampening units  101 - 108  can be thrown on and off the printing forms  9 - 12 . In the rotational direction of the printing forms  9 - 12 , the ink applicator rolls lie between the dampening solution applicator rolls of the dampening units  101 ,  103 ,  105 ,  107  and  102 ,  104 ,  106 ,  108 . The inking units  97 - 100  are configured as ductor inking units, with it being possible to connect an intermediate roll  117 - 120  in each case between a ductor roll  109 - 112  and an ink transfer roll  113  and  116 . The transfer cylinders  13 - 16  can be thrown on and off the printing forms  9 - 12  and optionally the impression cylinders  33 - 36  and/or  37 - 40 . All of the rolls, cylinders and drums of the printing units  1 - 4  can be driven in the direction of arrows  155  through the use of gear mechanisms and/or individual drives. 
         [0021]    The printing units  1  and  4  are configured for printing on the front side of the sheets  49 . In the printing units  1 ,  4 , the intermediate rolls  117  and  120  and the dampening units  102  and  108  are out of operation, with the dampening solution applicator rolls of the dampening units  102 ,  108  being thrown off or disengaged from the printing forms  9 ,  12 . Furthermore, the transfer cylinders  13 ,  16  are thrown on or engaged with the impression cylinders  33 ,  36  and are thrown off or disengaged from the impression cylinders  37 ,  40  in the printing units  1 ,  4 . The impression cylinders  37 ,  40  are out of operation. The impression cylinders  13 ,  16  rotate in the clockwise direction. 
         [0022]    The printing units  2  and  3  are configured for printing on the rear side of the sheets  49 . In the printing units  2 ,  3 , the intermediate rolls  118 ,  119  for ink transfer are connected between the ductor rolls  110 ,  111  and the ink transfer rolls  114 ,  115 . The dampening units  104 ,  106  are in operation. The dampening units  103 ,  105  are out of operation. The transfer cylinders  14 ,  15  are in rolling contact with the printing forms  10 ,  11  and the impression cylinders  38 ,  39  and are thrown off or disengaged from the impression cylinders  34 ,  35 . The transfer cylinders  14 ,  15  are driven counter to the clockwise direction. FIGS.  1 . 1 - 1 . 4  show a sheet transport in four phases. A sheet  49  is fed to a printing unit  1 - 4  during every second revolution of a form cylinder  5 - 8 . 
         [0023]    According to  FIG. 1.1 , a sheet  49 . 1  is conveyed in the gripper system  82  on the transfer drum  62 . A sheet  49 . 2  is printed on the front side with a first color separation  121  in a nip between the cover  25  and the circumferential face in the sector  42  and is transferred through the use of the gripper system  86  out of the grippers of the gripper system  51  from the impression cylinder  33 . A further sheet  49 . 3  is transferred out of the grippers of the gripper system  52  of the impression cylinder  34  to the grippers of the gripper system  59  of the impression cylinder  38 . A sheet  49 . 4  receives a print of a first color separation  122  on the rear side in the nip between the cover  26  and the impression cylinder  38 . In the printing unit  3 , a sheet  49 . 5  is guided in the gripper system  60  on the impression cylinder  39 . The end of the sheet  49 . 5  is guided on the circumferential face in the sector  46 . A sheet  49 . 6  is conveyed through the use of the gripper system  91  on the circumferential face of the sector  76 . The sheet  49 . 6  receives a print of a second color separation  123  on the rear side in the nip between the cover  27  and the impression cylinder  39 . A sheet  49 . 7  receives a print of a second color separation  124  on the front side in the nip between the cover  28  and the circumferential face in the sector  48  of the impression cylinder  36 . The sheet  49 . 7  is conveyed by way of the gripper system  95  of the transfer drum  66  to the next printing unit or to a stack. 
         [0024]      FIG. 1.2  shows the situation after one full revolution of the form cylinders  5 - 8 . The sheet  49 . 1  is transferred out of the grippers of the gripper system  82  of the transfer drum  62  to the grippers of the gripper system  51  of the impression cylinder  33 . The printing ink for a further front side color separation  121  is transferred by the printing form  9  on the cover  25 . The sheet  49 . 2  is conveyed further through the use of the gripper system  86  on the transfer drum  63 . In the printing unit  2 , the cover  26  receives the printing ink of a first color separation  122  for the rear side of the sheet  49 . 3  which is conveyed by way of the gripper system  59  on the impression cylinder  38 . The sheet  49 . 4  is conveyed by way of the gripper system  88  from the impression cylinder  34  to the impression cylinder  35 . The sheet  49 . 5  is conveyed through the use of the gripper system  60  through the press nip between the cover  27  and the impression cylinder  39 . The printing ink of the second color separation  123  is transferred from the cover  27  onto the rear side of the sheet  49 . 5 . The sheet  49 . 6  is conveyed further on the circumferential face of the sector  76  through the use of the gripper system  91 . In the printing unit  4 , the printing ink of the second color separation  124  for the front side is transferred from the printing form  12  onto the cover  28 . The sheet  49 . 7  is conveyed in the gripper system  95  on the transfer drum  66 . 
         [0025]      FIG. 1.3  shows a situation after a further revolution of the form cylinders  5 - 8 . The sheet  49 . 1  is conveyed on the impression cylinder  33  in the gripper system  51  into the press nip between the cover  25  and the circumferential face of the sector  42 , in order to receive the first color separation  121  on the front side. The sheet  49 . 2  is conveyed through the use of the gripper system  86  on the transfer drum  63 . In the printing unit  2 , the sheet  49 . 3  receives the first color separation  122  on the rear side in the press nip between the cover  26  and the impression cylinder  38 . The sheet  49 . 4  is transferred out of the grippers of the gripper system  88  to the grippers of the gripper system  55  of the impression cylinder  35 . Furthermore, the sheet  49 . 5  has been transferred from the gripper system  60  to the gripper system  54  of the impression cylinder  35 . In the nip between the impression cylinder  35  and the transfer drum  65 , the sheet  49 . 5  is transferred to the gripper system  93  in the sector  78  of the transfer drum  65 . The sheet  49 . 6  is conveyed by way of the gripper system  57  into the press nip between the cover  28  and the circumferential face in the sector  48  of the impression cylinder  36 . The sheet  49 . 7  is conveyed further through the use of the gripper system  95  in the sector  80  of the transfer drum  66 . 
         [0026]    According to  FIG. 1.4 , the transfer cylinders  13 - 16  are situated in rotational positions, in which the surfaces  29 - 32  are opposite the printing forms  9 - 12 , with the result that no printing ink is transferred from the printing forms  9 - 12  to the transfer cylinders  13 - 16 . The sheet  49 . 1  receives the first color separation  121  on the front side in the press nip between the cover  25  and the circumferential face in the sector  42 . The sheet  49 . 2  has been transferred out of the grippers of the gripper system  86  to the grippers of the gripper system  52 . While the end of the sheet  49 . 3  receives the first color separation  122  on the rear side in the nip between the cover  26  and the impression cylinder  38 , the sheet  49 . 3  is peeled from the circumferential face in the sector  44  of the impression cylinder  34  through the use of the gripper system  90 . The sheet  49 . 4  is conveyed through the use of the gripper system  55  on the impression cylinder  35  and is removed from the circumferential face in the sector  73 . The sheet  49 . 5  has received the second color separation  123  on the rear side and is conveyed by way of the gripper system  93  in the sector  78  of the transfer drum  65 . The leading sheet  49 . 6  receives the second color separation  124  on the front side in the press nip between the cover  28  and the circumferential face in the sector  48 . 
         [0027]    The configuration of the printing units  1 - 4  as recto printing units and as verso printing units is embodied in this case only by way of example. In principle, each printing unit can be configured for printing on the front side or rear side. During printing on the rear side, a single size impression cylinder  37 - 40  is included into the sheet run in any case. The printing press can be configured as a pure recto printing press if in each case both sectors  17 - 24  of the transfer cylinders  13 - 16  are equipped with covers which transfer printing ink. In pure recto printing operation, one sheet  49  can be fed to a printing unit  1 - 4  with every revolution of a form cylinder  5 - 8 . 
         [0028]    In one variant according to  FIGS. 2.1  and  2 . 2 , printing units  125  are equipped with transfer cylinders  126  which have the same active diameter D as respectively associated form cylinders  127 . As in the variant according to FIGS.  1 . 1 - 1 . 4 , in each case the transfer cylinder  126  interacts selectively with an impression cylinder  128  and  129  which have respective active diameters of 2×D and D. The configuration of inking units  130  and dampening units  131 ,  132  is as described with respect to FIGS.  1 . 1 - 1 . 4 . 
         [0029]    According to  FIG. 2.1 , a printing unit  125  is configured in recto printing operation. The transfer cylinder  126  is thrown off the impression cylinder  129  and is thrown on the impression cylinder  128 . The impression cylinder  129  is functionless during recto printing operation. Furthermore, the inking unit  130  and the dampening unit  131  are set in operation. The dampening unit  132  is out of operation. The cylinders and rolls can be driven in the direction of the arrows  133 . 
         [0030]    During each revolution of the form cylinder  127 , a printing form  134  is inked with an image by way of the dampening unit  131  and the inking unit  130 . The printing ink of the color separation is transferred onto an elastic cover  135  of the transfer cylinder  126 . The double size impression cylinder  128  has two sectors  136 ,  137 . If a sheet  49  is held in a gripper system  138  and is conveyed on the circumferential face of the impression cylinder  128  in the sector  136 , a color separation  139  is transferred to the front side of the sheet  49  in the nip between the cover  135  and the impression cylinder  128 . No sheet  49  is guided in the sector  137 . During passing of the sector  137  on the transfer cylinder  126 , the transfer cylinder  126  is thrown off the impression cylinder  128 . As an alternative, the circumferential face can stand back in the sector  137 , with the result that no printing ink is transmitted on the circumferential face. 
         [0031]    In one alternative embodiment, the circumferential face can be configured to carry printing ink in the sector  137  in pure recto printing operation. A sheet is then fed at single revolutions with each revolution of the form cylinder  127 . 
         [0032]    In verso printing operation according to  FIG. 2.2 , the rotational directions of the transfer cylinder  126  and the form cylinder  127  are changed with respect to recto printing operation. The transfer cylinder  126  is thrown off the impression cylinder  128  and is thrown on the impression cylinder  129 . The impression cylinder  129  is thrown on the impression cylinder  128 , in order to accept a sheet  49 . The dampening unit  131  is taken out of operation. The dampening solution applicator roll  140  of the dampening unit  132  is thrown onto the printing form  134 . In verso printing operation, a sheet  49  is transferred from the impression cylinder  128  to the impression cylinder  129 . The sheet  49  receives a first print on the rear side in the nip between the cover  135  and the impression cylinder  129 . During every second revolution of the impression cylinder  127 , the transfer cylinder  126  is raised up from the impression cylinder  129 , with the result that the circumferential face of the impression cylinder  129  is not inked in an undesired manner. 
         [0033]      FIG. 3  shows a variant with a printing unit  141  which includes two inking units  142 ,  143 , two dampening units  144 ,  145 , two form cylinders  146 ,  147  and two half revolution transfer cylinders  148 ,  149 . The transfer cylinder  148  interacts with an impression cylinder  150 . The transfer cylinder  149  interacts with an impression cylinder  151 . Furthermore, the impression cylinders  151  and  150  interact. The impression cylinder  150  is assigned transfer drums  152 ,  153 . The form cylinders  146 ,  147  and the impression cylinder  151  have an active diameter D. The transfer cylinders  148 ,  149  are twice as large with a diameter 2×D. The transfer drums  152 ,  153  and the impression cylinder  150  are triple size with an active diameter 3×D. 
         [0034]    A first color separation is transferred on the front side of a sheet in recto printing in the nip between the transfer cylinder  148  and the impression cylinder  150 . The sheet is transferred from the impression cylinder  150  to the impression cylinder  151 . The sheet receives a print of a color separation on the rear side in the nip between the transfer cylinder  149  and the impression cylinder  151 . Subsequently, the sheet is transferred to the impression cylinder  150  again. The sheet which is printed on both sides passes from the impression cylinder  150  to the transfer drum  153 . The transfer drum  153  conveys the sheet to a following printing unit or to an apparatus for conveying it onto a stack. 
         [0035]    The printing unit  141  can be configured in such a way that a sheet receives two prints on the front side. To this end, an elastic cover  154  is pulled onto the circumferential face of the impression cylinder  151 . In this configuration, a sheet is not transferred from the impression cylinder  150  to the impression cylinder  151 . The second print takes place in the nip between the impression cylinder  151  and the cover  154 . Before this, the second color separation is transferred from the form cylinder  147  onto the transfer cylinder  149  and onto the cover  154 .