Abstract:
A method for driving a satellite offset press, and a satellite offset press which, with little expenditure, permits multicolor printing in one pass. A satellite offset press, in which form cylinders and associated transfer cylinders are driven synchronously, while in each case segments located in the circumferential direction of the form cylinders and of the transfer cylinders and also of the transfer cylinders and of an impression cylinder interacting with the latter roll on one another in accurate register with a sheet held thereon, following each full revolution. The speed of the impression cylinder is reduced and increased again, so that the transfer cylinders lead by at least one segment length in the circumferential direction.

Description:
BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0001]     The invention relates to a method for driving a satellite offset press, in which form cylinders and associated transfer cylinders are driven synchronously, while in each case segments located in the circumferential direction of the form cylinders and of the transfer cylinders and also of the transfer cylinders and of an impression cylinder interacting with the latter roll on one another in accurate register with a sheet held thereon. The invention further relates to a satellite offset press having an impression cylinder which interacts with at least two satellite printing units in order to print on sheets. Each of the printing units contains at least one transfer cylinder and a form cylinder having an inking unit. The impression cylinder, the transfer cylinder and the form cylinder have equally long segments located in the circumferential direction. A device for leading the sheets to and from the impression cylinder, and at least one drive device for the cylinders, are provided.  
         [0002]     Published, non-prosecuted German patent application DE 102 59 496 A1 discloses an offset press for multicolor printing on a printing material, in which an impression cylinder, a transfer cylinder and a printing form cylinder each have at least three equally long segments located in the circumferential direction. The number of segments on the transfer cylinder corresponds to an-integer multiple of the number of segments on the impression cylinder plus one segment. All the cylinders can conventionally be driven by a gear wheel mechanism. Likewise, individual cylinders or groups of cylinders can be provided with individual drives. In any case, the cylinders are driven such that the segments roll on one another in accurate register. In the case of four-color printing, the result is press configurations with voluminous cylinders, which are expensive in terms of material and costs.  
       SUMMARY OF THE INVENTION  
       [0003]     It is accordingly an object of the invention to provide a method for driving a satellite offset press, and a satellite offset press which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which, with little expenditure, permit multicolor printing in one pass.  
         [0004]     With the foregoing and other objects in view there is provided, in accordance with the invention,  
         [0005]     According to the invention, a central impression cylinder is provided with an individual drive and is braked and accelerated during a revolution such that the transfer cylinders driven in synchronism with the printing form cylinder lead by one segment length in the circumferential direction.  
         [0006]     Given a specific geometric configuration of double-size transfer cylinders and likewise double-size printing form cylinders, the width in the circumferential direction of a channel in the impression cylinder is in each case so large that, as the channel on the transfer cylinder passes, the rotational speed of the impression cylinder is reduced by a servo drive such that, in the intervening time, the transfer cylinder and printing form cylinder rotate one printing area further. At the correct time in relation to the printing start of the following printing areas of the transfer cylinders, the impression cylinder is accelerated to the circumferential speed of the transfer cylinders.  
         [0007]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0008]     Although the invention is illustrated and described herein as embodied in a method for driving a satellite offset press, and a satellite offset press, 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.  
         [0009]     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 DRAWINGS  
       [0010]      FIG. 1  is a diagrammatic, illustration of a satellite offset press according to the invention;  
         [0011]      FIGS. 2 . 1 - 2 . 15  are schematic phase drawings of the satellite offset press according to  FIG. 1  in 90 degree steps; and  
         [0012]      FIG. 3  is a graph showing a curve of the speed of an impression cylinder as a function of a machine angle.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a schematic drawing of a satellite offset press having an impression cylinder  1 , two transfer cylinders  2 ,  3  and two printing form cylinders  4 ,  5 . The cylinders  1 - 5  can be rotated in the direction of arrows  6 , an axes of rotation of the impression cylinder  1  and of the transfer cylinders  2 ,  3  lying in parallel in a horizontal plane h and the axes of rotation of the printing form cylinders  4 ,  5  and of the transfer cylinders  2 ,  3  each lying in a vertical plane v. Each cylinder  1 - 5  has two segments A-J with equally long printing areas in the circumferential direction. Between the segments A-J, the cylinders  1 - 5  have channels  7 . In the channels  7  of the impression cylinder  1  there are gripper systems  8  for holding sheets  9 . In the channels  7  of the transfer cylinders  2 ,  3  there are holding and clamping devices  10  for an elastic cover  11  on each segment A-D. Drawn onto the segments G-J of the printing form cylinders  4 ,  5  is a printing film  12 , which is in each case stored on an unwind roller  13  and tensioned via a rewind spool  14 . During printing, the covers  11  are in rolling contact with a sheet  9  held on the segments E, F. Likewise, there is contact between a printing film  12  and a respective cover  11 . The printing form cylinders  4 ,  5  are assigned rolls  15  of inking units, in each case it being possible for an ink applicator roll  16  to be thrown onto and off the printing film  12 . Furthermore, each printing form cylinder  4 ,  5  is assigned an imaging configuration  17 , which contains laser diode arrays, with which image points accepting printing ink can be produced on the printing films  12 .  
         [0014]     The satellite offset press further contains a feeder  18  for separating sheets  9  from a stack  19  and for feeding the sheets  9  into the gripper system  8 . In detail, the feeder  18  includes a suction head  20 , a feed table  21  with tape transport system, a swinging gripper  22  and a feed drum  23 .  
         [0015]     Furthermore, the satellite offset press includes a deliverer  24  having a chain gripper system  27  led over deflection rollers  25 ,  26  for conveying the sheets  9  from the gripper system  8  onto a stack  28 . A dryer  29  is disposed on the conveying path of the sheets  9 .  
         [0016]     In order to drive the satellite offset press, two motors  30 ,  31  are provided, which are connected to a control device  32 . The motor  30  is connected via a gear mechanism  33  to a gear train which is used to drive the transfer cylinders  2 ,  3 , the printing form cylinders  4 ,  5  and the inking unit rolls  15 ,  16 . The motor  31  is connected via a gear mechanism  34  to a gear train for driving the impression cylinder  1 , the feed drum  23  and the deflection roller  25 . The rotational position of the transfer cylinders  2 ,  3  and of the printing form cylinders  4 ,  5  is registered by a rotary encoder  35 . The rotational position of the impression cylinder  1  is obtained by a rotary encoder  36 . The rotary encoders  35 ,  36  are connected to a control device  32 .  
         [0017]     By using  FIGS. 2 . 1 - 2 . 15 , the functioning of the satellite offset press is to be explained in more detail. Using the imaging configurations  17 , partial images in the primary colors cyan, yellow, magenta and black are produced on the printing films  12 . For this purpose, the impression cylinder is brought by the motor  31  into the rotational position shown in  FIG. 1  and fixed, in which position the channels  7  are opposite the transfer cylinders  2 ,  3 . Using the motor  30 , the printing form cylinders  4 ,  5  are driven for the purpose of imaging. The imaging rotational speed depends on the characteristics of the printing film  12  and on the power and number of laser diodes of the laser diode array in the imaging arrangements  17 . During imaging, the transfer cylinders  2 ,  3  and the ink applicator rolls  16  are thrown off the printing form cylinders  4 ,  5 .  
         [0018]     During printing, the transfer cylinders  2 ,  3  are thrown onto the printing form cylinders  4 ,  5 . The printing form cylinders  12  are inked by the ink applicator rolls  16 , an ink applicator roll  16  in each case inking a printing film  12  in that, during one revolution of a printing form cylinder  4 ,  5 , it is thrown cyclically onto the relevant printing film  12  and lifted off again. During printing, the transfer cylinders  2 ,  3  and the printing form cylinders  4 ,  5  rotate synchronously and continuously with an approximately equal circumferential speed, ink being transferred from the printing films  12  to the covers  11 .  
         [0019]      FIG. 2 . 1  shows the satellite offset press at a machine angle of 0 degrees. A sheet  9  has been transferred into the gripper system of the segment E of the impression cylinder  1 . The impression cylinder  1  has the same circumferential speed as the adjacent transfer cylinders  2 ,  3 . When the impression cylinder  1 , the transfer cylinders  2 ,  3  and the printing form cylinders  4 ,  5  rotate synchronously onward, then the sheet is printed with the color black. The segments A, E of the transfer cylinder  2  and of the impression cylinder  1  roll on one another, which is shown at a machine angle of 90 degrees in  FIG. 2 . 2 . In  FIG. 2 . 3 , at a machine angle of 180 degrees, it is shown that a second sheet  9  has been transferred into the gripper system  8  of the segment F of the impression cylinder  1 . During synchronous onward rotation of the impression cylinder  1  and of the adjacent transfer cylinders  2 ,  3 , as shown in  FIG. 2 . 4  at a machine angle of 270 degrees, the second partial image is printed on the sheet  9  in the color cyan on the second segment E, and the first partial image in the color magenta is printed on the segment F. As soon as these partial images of the colors cyan, magenta have been printed, the impression cylinder is braked, while the adjacent transfer cylinders continue to revolve uniformly. The transfer cylinders  2 ,  3  then lead by one printing area, which is shown in  FIGS. 2 . 5 - 2 . 7  at a machine angle of 360 degrees to 540 degrees. At the correct time in relation to the printing start of segments A, C of the transfer cylinders  2 ,  3 , the impression cylinder  1  has been accelerated again to the uniform speed of revolution of the transfer cylinders  2 ,  3 . As shown in  FIG. 2 . 8  at a machine angle of 630 degrees, the sheet  9  then receives the second partial image in the color yellow in segment F, and the sheet  9  receives the third partial image in the color magenta in segment E. During synchronous onward rotation of the impression cylinder  1 , transfer cylinders  2 ,  3  and printing form cylinders  4 ,  5 , as shown in  FIGS. 2 . 9  and  2 . 10  at a machine angle of 720 and 810 degrees, the fourth partial image in the color yellow is printed on the sheet  9  in segment E, and the third partial image in the color black is printed on the sheet  9  in segment F. When the sheet  9  has been printed completely in segment E, the impression cylinder  1  is braked again after the printing end, while the transfer cylinders  2 ,  3  and printing form cylinders  4 ,  5  rotate synchronously onward. As illustrated in  FIG. 2 . 11  at a machine angle of 900 degrees, the sheet  9  is transferred to the chain gripper system  27  of the deliverer  24 , while a still unprinted sheet  9  is fed to the gripper system  8  on segment E. Therefore, in order to finish a sheet  9 ,  2 . 5  revolutions of the impression cylinder  1  are needed.  FIGS. 2 . 12  and  2 . 13  show the onward rotation of the transfer cylinders  2 ,  3  by one printing area at a machine angle of 990 degrees and 1080 degrees. At the machine angle of 1080 degrees, the impression cylinder  1  has been accelerated to the speed of revolution of the adjacent transfer cylinders  2 ,  3  again, so that the third revolution of the impression cylinder  1  begins. The second sheet  9  then receives a print with the fourth partial image in the color yellow in segment F. The third sheet  9  receives a first partial image in the color black in segment E. This phase is illustrated at a machine angle of 1170 degrees in  FIG. 2 . 14 . During the synchronous onward rotation of the impression cylinder  1  and of the transfer cylinders  2 ,  3  and printing form cylinders  4 ,  5 , the second sheet  9  is printed out completely in segment E. As illustrated in  FIG. 2 . 15  at a machine angle of 1260 degrees, the second sheet is transferred to the chain gripper system  27  of the deliverer  24 , while a next unprinted sheet  9  is fed to the gripper system  8  on segment E.  
         [0020]     The inking units of such a satellite offset press can be constructed with conventional zonal ink metering elements or else as anilox inking units.  
         [0021]      FIG. 3  shows a curve of the circumferential speed of the impression cylinder  1 . The control device  32  is used to set the motor  31  in such a way that, in addition to phases  37  with synchronous running of impression cylinder and adjacent transfer cylinders  2 ,  3 , there are also braking phases  38  and acceleration phases  39  of the impression cylinder  1 . In order to produce the actuating signals for the motor  31 ; the signals from the rotary encoders  35 ,  36  are processed in the control device  32 . The control device  32  and the motor  31  are configured in such a way that the braking phase  38  and the acceleration phase  39  expire in a short time.