Abstract:
A method of preparing cylinders for printing on a web during auto transfer operations is provided. The method includes the steps of printing images on a web with at least one first printing cylinder; accelerating at least one second printing cylinder so that the at least one second printing cylinder has a surface velocity that equals a velocity of the web; adjusting a phasing of the at least one second printing cylinder with respect to the web during the accelerating step and before the surface velocity of the at least one second printing cylinder equals the velocity of the web; moving the at least one first printing cylinder away from the web and moving the at least one second printing cylinder towards the web; and printing images on the web with the at least one second printing cylinder. A printing press configured for auto transfer is also provided.

Description:
[0001]    The present invention relates generally to printing presses and more specifically to a method of phasing and accelerating cylinders of a printing press during auto transfer. 
       BACKGROUND OF INVENTION 
       [0002]    In offset printing presses one or more printing units may be moved out of contact with, or thrown off of, a passing web as one or more additional printing units are moved into contact with, or thrown onto, the web for continuous printing. This operation, which may be referred to as auto transfer, may help minimize the time between printing job changes and may reduce paper waste. 
         [0003]    U.S. Publication No. 2007/0144370, which is hereby incorporated by reference herein, describes auto transfer. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    A method of preparing cylinders for printing on a web during auto transfer operations is provided. The method includes the steps of printing images on a web with at least one first printing cylinder; accelerating at least one second printing cylinder so that the at least one second printing cylinder has a surface velocity that equals a velocity of the web; adjusting a phasing of the at least one second printing cylinder with respect to the web during the accelerating step and before the surface velocity of the at least one second printing cylinder equals the velocity of the web; moving the at least one first printing cylinder away from the web and moving the at least one second printing cylinder towards the web; and printing images on the web with the at least one second printing cylinder. 
         [0005]    A printing press configured for auto transfer is also provided. The printing press includes at least one first printing cylinder for printing images on a web, at least one second printing cylinder for printing images on the web and a controller coupled to the at least one first printing cylinder and the at least one second printing cylinder. The controller is capable of rotating the at least one first printing cylinder and the at least one second printing cylinder during auto transfer. The controller simultaneously accelerating and phasing the at least one second printing cylinder before a surface velocity of the at least one second printing cylinder equals a velocity of the web as the at least one first printing cylinder print images on the web. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention is described below by reference to the following drawings, in which: 
           [0007]      FIG. 1  shows a schematic view of a printing press according to an embodiment of the present invention with a first group of printing units printing on a web and a second group of printing units thrown off of the web; 
           [0008]      FIG. 2  shows a schematic view of the printing press shown in  FIG. 1  with the second group of printing units printing on the web and the first group of printing units thrown off of the web; 
           [0009]      FIGS. 3   a  and  3   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is prepared to go on impression and as the printing unit is on impression according to a known method; 
           [0010]      FIGS. 4   a  and  4   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is being prepared to go on impression and as the printing unit moves on impression to print according to an embodiment of the present invention; and 
           [0011]      FIGS. 5   a  and  5   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is being prepared to go on impression and as the printing unit moves on impression to print according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    In order for the printing units that are thrown onto the web to be able to properly print on the web, cylinders of each printing unit may need to be properly accelerated and phased such that the cylinders have a surface velocity that matches the velocity of the web when the cylinders begin printing. 
         [0013]      FIG. 1  shows a schematic view of a printing press  10  including printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36 . Each printing unit  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  includes an upper plate cylinder  12 , an upper blanket cylinder  14 , a lower blanket cylinder  16  and a lower plate cylinder  18 . Printing press  10  may also include a dryer, a folder having a former for folding a web, cutting cylinders and folding cylinders. 
         [0014]    In  FIG. 1 , printing units  22 ,  26 ,  30 ,  34  are on impression and printing four color images of a first print job on a web  11 . In operation, an inking and dampening apparatuses provide ink and dampening solution to plate cylinders  12 ,  18  of each printing unit  22 ,  26 ,  30 ,  34 . Plate cylinders  12 ,  18  of each printing unit  22 ,  26 ,  30 ,  34 , which may be provided with imaged printing plates mounted thereon, transfer inked images to printing blankets on respective blanket cylinders  14 ,  16  of each printing unit  22 ,  26 ,  30 ,  34 . Blanket cylinders  14 ,  16  of each printing unit  22 ,  26 ,  30 ,  34  then transfer the images to web  11  passing between blanket cylinders  14 ,  16  of each printing unit  22 ,  26 ,  30 ,  34 . 
         [0015]    Printing units  24 ,  28 ,  32 ,  36  are in an off impression position with plate cylinders  12 ,  18  of printing units  24 ,  28 ,  32 ,  36  including plates carrying image information for a second print job. In a preferred embodiment, each printing cylinder  12 ,  14 ,  16 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  may be coupled to a respective individual motor  50 . For clarity, in  FIG. 1 , motors  50  are shown only for printing units  22 ,  36 . A controller  100  controls the rotation cylinders  12 ,  14 ,  16 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  via motors  50 . Controller  100  may also control movement of cylinders  12 ,  14 ,  16 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  toward and away from web  11 . Printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  may be thrown on and off of web  11  by respective throw off mechanisms. Each throw off mechanism may be for example the supporting mechanism disclosed in incorporated by reference U.S. Publication No. 2007/0144370. 
         [0016]      FIG. 2  shows printing press  10  shown in  FIG. 1  printing the second print job. Printing units  24 ,  28 ,  32 ,  36  are on impression printing four color images of the second print job on web  11  in the same manner that printing units  22 ,  26 ,  30 ,  34  printed the four color images of the first print job on web  11 . Motors  50  are rotating respective cylinders  12 ,  14 ,  16 ,  18  of printing units  24 ,  28 ,  32 ,  36 . For clarity, in  FIG. 2 , motors  50  are shown only for printing units  22 ,  36 , but a motor may be provided for each cylinder  12 ,  14 ,  16 ,  18  of each printing unit  24 ,  28 ,  32 ,  36 . Printing units  22 ,  26 ,  30 ,  34  are now in an off impression position and not printing on web  11 . Plate cylinders  12 ,  18  of printing units  22 ,  26 ,  30 ,  34  may be undergoing automatic plate changing operations in order to print a third print job after printing units  24 ,  28 ,  32 ,  36  complete the second print job. For clarity, in  FIG. 2 , motors  50  are shown only for printing units  22 ,  36 . 
         [0017]    In order to throw one of printing units  24 ,  28 ,  32 ,  36 , for example printing unit  24 , on impression, from the off impression position, controller  100  signals motors  50  to rotate respective cylinders  12 ,  14 ,  16 ,  18  so that when cylinders  14 ,  16  contact web  11  and printing unit  24  begins printing images on web  11 , cylinders  12 ,  14 ,  16 ,  18  are traveling at a surface velocity that equals the velocity of web  11  and are appropriately phased to print images in a proper alignment on web  11 . In this embodiment, cylinders  12 ,  14 ,  16 ,  18  of printing units  24 ,  28 ,  32 ,  36  are thrown on impression simultaneously. 
         [0018]    In other embodiments of the present invention, instead of moving both plate cylinders  12 ,  18  and blanket cylinders  14 ,  16  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  away from web  11  during throw off and toward web  11  for printing, plate cylinders  12 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  may remain stationary and only blanket cylinders  14 ,  16  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  are moved in relation to web  11 . This may be accomplished by swinging blanket cylinders  14 ,  16  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  toward and away from web  11 . Thus, plate cylinders  12 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  may not need to moved for printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  to moved from an off impression position to an on impression position or from an on impression position to an off impression position. 
         [0019]      FIGS. 3   a  and  3   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is prepared to go on impression and as the print on a web according to a known method. The plate cylinder and the blanket cylinder are rotated so both cylinders have a surface velocity v c .  FIG. 3   a  shows a graph of the surface velocity v c  of the plate and blanket cylinders versus time.  FIG. 3   b  shows a graph of the acceleration a c  of the plate and blanket cylinders versus time. 
         [0020]    In this known method, before the printing unit is moved into an on impression position to print on the web, the plate and blanket cylinders are accelerated until time t 1 , when the surface velocity v c  of the plate and blanket cylinders equals the velocity v w  of the web. Then, the plate and blanket cylinders are further accelerated to a maximum surface velocity v cmax  and then decelerated back down to the velocity v w  of the web so the plate and blanket cylinders are appropriately phased to print images on the web. At time t 2 , when the surface velocity v c  of the plate and blanket cylinders equals the velocity v w  of the web and the plate and blanket cylinders are appropriately phased, the printing unit is moved on impression and begins printing on the web. As printing unit is moved on impression, a second printing unit including a second pair of plate and blanket cylinders, which just finished printing on the web, is moved off impression. At time t 2 , when the printing unit is moved on impression and the second printing unit is moved off impression, the plate and blanket cylinders and the second pair of plate and blanket cylinders have the same phasing with respect to the web. As a result, the printing unit going on impression prints images on the web in locations corresponding to locations where the second pair of plate and blanket cylinders were phased to print images on the web. 
         [0021]    Because the plate and blanket cylinder are phased after the plate and blanket cylinder are accelerated to have a surface velocity v c  that equals the velocity v w  of the web, the plate and blanket cylinders are accelerated to the maximum velocity v cmax  just before the printing unit goes on impression. Driving the blanket cylinder to the maximum velocity v cmax  may cause the blanket cylinder to push air towards the web, resulting in web flutter. This web flutter may be quite dramatic and may cause the web to break. 
         [0022]      FIGS. 4   a  and  4   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is being prepared to go on impression and as the printing unit goes on impression and begins to print according to an embodiment of the present invention.  FIG. 4   a  shows a graph of the surface velocity v c  of the plate and blanket cylinders versus time.  FIG. 4   b  shows a graph of the acceleration a c  of the plate and blanket cylinders versus time. 
         [0023]    In this embodiment, instead of accelerating the plate and blanket cylinders to match the velocity v w  of the web and then phasing the plate and blanket cylinders by accelerating and decelerating the plate and blanket cylinders, the plate and blanket cylinders are phased as they are accelerated to match the velocity v w  of the web. Thus, the cylinders are not accelerated to a surface velocity v c  that is greater than the velocity v w  of the web, and advantageously, the pushing of air by the blanket cylinder just before the printing unit goes on impression may be reduced or eliminated and the associated web flutter may be reduced or eliminated. 
         [0024]    As shown in  FIGS. 4   a  and  4   b , the place and blanket cylinders are accelerated until a time t 3 , when the plate and blanket cylinders are both phased and accelerated simultaneously. The plate and blanket cylinders are phased and accelerated until a time t 4  when the plate and blanket cylinders are appropriately phased to print on the web and also have a surface velocity v c  that equals the velocity v w  of the web. At time t 4 , the printing unit is moved on impression and begins printing on the web. As the printing unit is moved to the on impression position, a second printing unit including a second pair of plate and blanket cylinders, which just finished printing on the web, is moved off impression. At time t 4 , when the printing unit is moved on impression and the second printing unit is moved off impression, the plate and blanket cylinders and the second pair of plate and blanket cylinders have the same phasing with respect to the web. 
         [0025]      FIGS. 5   a  and  5   b  show graphs illustrating the rotation of a plate cylinder and a blanket cylinder of a printing unit as the printing unit is being prepared to go on impression and as the printing unit goes on impression and begins to print according to another embodiment of the present invention.  FIG. 5   a  shows a graph of the surface velocity v c  of the plate and blanket cylinders versus time.  FIG. 5   b  shows a graph of the acceleration a c  of the plate and blanket cylinders versus time. 
         [0026]    In this embodiment, the plate and blanket cylinders are accelerated briefly until a time t 5 , when the plate and blanket cylinders are accelerated and initially phase adjusted at the same time. Then, at a time t 6 , when the surface velocity v c  of the plate and blanket cylinders equals the velocity v w  of the web, to correct a minor disparity between the phasing of the plate and blanket cylinder and the desired phasing of the plate and blanket cylinder, the plate and blanket cylinders are again phased by accelerating and then decelerating the plate and blanket cylinder by a minimal amount to appropriately phase the plate and blanket cylinders for printing on the web. At a time t 7 , when the plate and blanket cylinders are appropriately phased, surface velocity v c  of the cylinders equals the velocity v w  of the web and the printing unit is moved on impression and begins printing on the web. 
         [0027]    As the printing unit is moved on impression, a second printing unit including a second pair of plate and blanket cylinders, which just finished printing on the web, is moved off impression. At time t 7 , when the printing unit is moved on impression and the second printing unit is moved off impression, the plate and blanket cylinders and the second pair of plate and blanket cylinders have the same phasing with respect to the web. 
         [0028]    In this embodiment, the initial phasing of the plate and blanket cylinders before the surface velocity v c  of the plate and blanket cylinders reaches the velocity v w  of the web, helps to minimize the amount that the surface velocity v c  of the plate and blanket cylinders exceeds the velocity v w  of the web and minimizes the amount of acceleration necessary just before the cylinders are moved on impression. Thus, the initial phasing during acceleration of the plate and blanket cylinders may advantageously reduce or eliminate the pushing of air by the blanket cylinder just before the printing unit goes on impression and may reduce or eliminate the associated web flutter. 
         [0029]    The accelerating and phasing method discussed in regards to  FIGS. 4   a ,  4   b  and the accelerating and phasing method discussed in regards to  5   a ,  5   b  may be applied with each of the printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  shown in  FIGS. 1 and 2 . These methods allow printing press  10  to match the surface velocities of cylinders  12 ,  14 ,  16 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  to a velocity of the web and match the phase relationship between plate cylinders  12 ,  18  of printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  as the respective printing units  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34 ,  36  are moved on impression. As a result, registration reference, color bar and ribbon automated control search zones may be maintained and waste may be minimized. 
         [0030]    Before printing units  24 ,  28 ,  32 ,  36  shown in  FIGS. 1 and 2  are moved on impression to print the second print job, controller  100  may direct motors  50  coupled to each upper cylinder  12 ,  14  of each printing unit  24 ,  28 ,  32 ,  36  motors  50  and the lower cylinders  16 ,  18  of each printing unit  24 ,  28 ,  32 ,  36  to accelerate the printing units  24 ,  28 ,  32 ,  36  in accordance with the method discussed with respect to  FIGS. 4   a ,  4   b  or accordance with the method discussed with respect to  FIGS. 5   a ,  5   b . Printing units  24 ,  28 ,  32 ,  36  are all simultaneously moved on impression to begin printing the second print job on web  11 . As printing units  24 ,  28 ,  32 ,  36  are moved on impression, printing units  22 ,  26 ,  30 ,  34 , which finished printing the first print job, are moved off impression. 
         [0031]    Before printing units  24 ,  28 ,  32 ,  36  finish printing the second print job, and after new printing plates have been mounted on the plate cylinders  12 ,  18  of printing units  22 ,  26 ,  30 ,  34 , controller  100  may direct motors  50  coupled to each upper cylinder  12 ,  14  of each printing unit  22 ,  26 ,  30 ,  34  and motors  50  coupled to each lower cylinder  16 ,  18  of each printing unit  22 ,  26 ,  30 ,  34  to accelerate the printing units  22 ,  26 ,  30 ,  34  in accordance with the method discussed with respect to  FIGS. 4   a ,  4   b  or accordance with the method discussed with respect to  FIGS. 5   a ,  5   b . Printing units  22 ,  26 ,  30 ,  34  are all simultaneously moved on impression to begin printing the third print job on web  11 . As printing units  22 ,  26 ,  30 ,  34  are moved on impression, printing units  24 ,  28 ,  32 ,  36 , which finished printing the second print job, are moved off impression. 
         [0032]    In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.