Abstract:
A printing press is provided including a plate cylinder having an outer perimeter of a first length. A removable flexible continuous tubular plate having an inner perimeter of a second length is disposed about the plate cylinder. The second length is greater than the first length so that the inner perimeter of the removable flexible continuous tubular plate and the outer perimeter of the plate cylinder define a first gap during a printing mode. A method for varying cutoff in a printing press is also provided.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to a printing press and more specifically to a variable cut off printing press having flexible plates and blankets. 
         [0002]    U.S. Pat. No. 5,950,536 discloses a variable cut off offset press unit including a blanket cylinder with a fixed diameter and a plate cylinder of a variable diameter. The diameter of the plate cylinder is varied by mounting plate cylinder sleeves of various sizes on the plate cylinder. Each sleeve is proportional to the length of the image to be printed. 
         [0003]    U.S. Pat. No. 6,327,975 discloses using a printing press with two or more printing units to print an image on a web. Each printing unit includes a blanket cylinder, a plate cylinder, and an impression cylinder. Each printing unit prints a portion of the image, leaving no unprinted space between the portions of the image. This allows the press to print an image whose dimension in the longitudinal direction of the web is longer than the circumference of each plate cylinder. To eliminate unprinted spaces, each impression cylinder moves into and out of rolling engagement with the associated blanket cylinder, via the web, and the web is only printed on when the blanket cylinder and impression cylinder are engaged. The plate and blanket cylinders of each printing unit are driven at the same speed as the web when the unit is printing on the web and a different speed when the unit is not printing. 
         [0004]    U.S. Pat. No. 7,066,088 discloses a variable cut off offset press including at least two sources of ink of at least two different colors, at least two plate cylinders, at least two impression cylinders, and a continuous image transfer belt. Each plate cylinder is adapted to receive printing sleeves of different diameters, enabling the effective length of the printing plate to be changed and allowing images of multiple dimensions to be printed. The image transfer belt is positioned to contact the printing sleeves at respective nips formed with respective impression cylinders. A web passes through a nip formed by the image transfer belt and an impression roller. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A printing press is provided including a plate cylinder having an outer perimeter of a first length. A removable flexible continuous tubular plate having an inner perimeter of a second length is disposed about the plate cylinder. The second length is greater than the first length so that the inner perimeter of the removable flexible continuous tubular plate and the outer perimeter of the plate cylinder define a first gap during a printing mode. 
         [0006]    A method for varying cutoff in a printing press is also provided. The steps include printing an image having a first cutoff using a first removable flexible continuous tubular plate having a first inner perimeter disposed about a plate cylinder, removing the first removable flexible continuous tubular plate from the plate cylinder, placing a second removable flexible continuous tubular plate having a second inner perimeter different from the first inner perimeter so that the second removable flexible continuous tubular plate is disposed about the plate cylinder, and printing an image having a second cutoff different from the first cutoff using the second removable flexible continuous tubular plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention is described below by reference to the following drawings, in which: 
           [0008]      FIG. 1  shows a schematic side view of a four color perfecting offset printing press according to an embodiment of the present invention; 
           [0009]      FIG. 2  shows an enlarged schematic side view of a printing unit of the perfecting offset printing press from  FIG. 1  with inker form rollers; and 
           [0010]      FIG. 3  shows an enlarged view of a printing unit of a nonperfecting offset printing press according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Variable cut off printing presses have been developed to allow for printing products of different sizes on the same printing press without having to change plate and blanket cylinders. Changing plate and blanket cylinders to correspond to the size of the image that needs to be printed can be a time consuming and difficult process. It also may require purchasing and storing cylinders of multiple sizes. 
         [0012]      FIG. 1  shows a schematic side view of a four color perfecting offset printing press  8  according to an embodiment of the present invention. Printing press  8  may include four printing units  10 , a cutter  102 , a folder  104 , a delivery fan  106 , and a transport belt  108 . Each printing unit  10  prints on both sides of a web  20 . In each printing unit  10 , inkers supply ink to plates  22 ,  24  on plate cylinders  12 ,  14 , which transfer respective inked images to blankets  26 ,  28  on blanket cylinders  16 ,  18 . Blankets  26 ,  28  print images on web  20  moving in the direction of arrow B. 
         [0013]      FIG. 2  shows an enlarged schematic side view of printing unit  10  of perfecting offset printing press  8  from  FIG. 1  with inker form rollers  27 . Printing unit  10  includes first plate cylinder  12 , first blanket cylinder  16 , second blanket cylinder  18 , and second plate cylinder  14 . Web  20  passes between blanket cylinders  16 ,  18  in a direction of an arrow A. Each cylinder  12 ,  14 ,  16 ,  18  has a constant circumference that is less than a smallest potential printed image cutoff. Continuous tubular plates  22 ,  24  are placed on plate cylinders  12 ,  14 , respectively. Similarly, continuous tubular blankets  26 ,  28  are placed on blanket cylinders  16 ,  18 , respectively. Plates  22 ,  24  and blankets  26 ,  28  are composed of flexible materials. Inkers supply ink to plates  22 ,  26 , which transfer inked images to blankets  26 ,  28 , respectively. Blankets  26 ,  28  then print the respective inked images on web  20  as blanket cylinders  16 ,  18  are rotated. 
         [0014]    Each plate,  22 ,  24 , has an inner perimeter length that is more than nominally greater than an outer perimeter length of the respective associated plate cylinder,  12 ,  14 . Each blanket,  26 ,  28 , has an inner perimeter length that is more than nominally greater than an outer perimeter length of the respective associated blanket cylinder,  16 ,  18 . Therefore, plates  22 ,  24  and blankets  26 ,  28  have excess perimeters  32 ,  34 ,  36 ,  38  in relation to respective associated cylinders  12 ,  14 ,  16 ,  18 . Nip points  15 ,  17 ,  19  are formed between plate cylinder  12  and blanket cylinder  16 , between blanket cylinder  16  and blanket cylinder  18 , and between blanket cylinder  18  and plate cylinder  14 , respectively. During a printing mode, in which printing unit  10  is in operation, cylinders  12 ,  14 ,  16 ,  18  rotate and the excess perimeters  32 ,  34 ,  36 ,  38  traverse away from respective associated cylinders  12 ,  14 ,  16 ,  18  when not passing through respective nip points  15 ,  17 ,  19 , and come into contact with the respective outer perimeters of cylinders  12 ,  14 ,  16 ,  18  at nip points  15 ,  17 ,  19 . The amount of excess perimeter  32 ,  34 ,  46 ,  38  traversing away from cylinders  12 ,  14 ,  16 ,  18  is a function of the perimeters of plates  22 ,  24  and blankets  26 ,  28 , which are selected to achieve a given cutoff. 
         [0015]    To maintain correct radial positioning, and prevent slipping between the surfaces of the outer perimeters of cylinders  12 ,  14 ,  16 ,  18  and surfaces of the inner perimeters of respective plates  22 ,  24  and blankets  26 ,  28  as cylinders  12 ,  14 ,  16 ,  18  are rotated, surfaces of the inner perimeters of plates  22 ,  24  and blankets  26 ,  28  and surfaces of the outer perimeters of cylinders  12 ,  14 ,  16 ,  18  may be splined. The splined surfaces, as shown in detail in  FIG. 3 , maintain positioning by mating in a manner similar to gears in a harmonic drive. Inker form rollers  27  may be utilized to cause portions of the splined surface of blankets  26 ,  28  to mate with portions of the splined surface of blanket cylinders  16  and  18  at certain desired locations. Alternatively, a spring-loaded tensioner equivalent device could be added to keep excess perimeters  32 ,  34 ,  36 ,  38  under control. 
         [0016]    In a preferred embodiment, surface speeds of cylinders  12 ,  14 ,  16 ,  18 , inkers, plates  22 ,  24 , and blankets  26 ,  28  remain essentially equal. The inkers may be geared together if desired, eliminating the requirement for individual shaftless drives. 
         [0017]    Changing over to a new printed image cutoff requires only replacing plates  22 ,  24  with replacement plates, each replacement plate having a new image, and replacing blankets  26 ,  28  with replacement blankets. The replacement plates and replacement blankets can have respective inner perimeters that vary in length from the inner perimeters of plates  22 ,  24  and blankets  26 ,  28 , respectively. The replacement plates and replacement blankets are sized to correspond to a new desired image cutoff length. The replacement plates and blankets can also be thicker or thinner than the respective plates  22 ,  24  and blankets  26 ,  28  the replacement plates and blankets are replacing. In a preferred embodiment, the images on plates  22 ,  24  and the replacement plates should cover the entire outer perimeter of continuous plates  22 ,  24  and the replacement plates, respectively. 
         [0018]    Before plates  22 ,  24  and blankets  26 ,  28  are removed and replaced with replacement plates and blankets, during a printing mode web  20  will be printed with images having a cutoff essentially equal to the length of the perimeter of each plate  22 ,  24 . After plates  22 ,  24  and blankets  26 ,  28  are removed and replaced with replacement plates and blankets, web  20  will be printed with images having a cutoff essentially equal to the length of the perimeter of each replacement plate. Cylinders  12 ,  14 ,  16 ,  18  will not need to be changed to vary the cutoff. Additionally, the positioning of cylinders  12 ,  14 ,  16 ,  18  may not need to be moved when printing in a new cutoff. Replacement plates and blankets, although having different respective perimeters than plates  22 ,  24  and blankets  26 ,  28  and therefore providing for a new cutoff, may be of the same thickness as plates  22 ,  24  and blankets  26 ,  28 , which the replacement plates and blankets are replacing. 
         [0019]      FIG. 3  shows an enlarged schematic side view of a printing unit  40  of a nonperfecting offset printing press according to another embodiment of the present invention. Printing unit  40  includes an impression cylinder  42 , a blanket cylinder  44 , and a plate cylinder  46 . A plate  56  is traversely disposed about plate cylinder  46  and a blanket  54  is traversely disposed about blanket cylinder  44 . Plate  56  and blanket  54  are each continuous and are composed of flexible material. Inkers supply ink to plate  56 , which transfers an inked image to blanket  54 , which prints the image on a passing web  50 . 
         [0020]    The surfaces of the inner perimeters of plate  56  and blanket  54  and the surfaces of the outer perimeters of plate cylinder  46  and blanket cylinder  44  are splined. The length of the inner perimeter of blanket  54  is greater than the outer perimeter of blanket cylinder  44 . The length of the inner perimeter of plate  56  is also greater than the length of the outer perimeter of plate cylinder  46 . As cylinders  44 ,  46  are rotated, a surface of the inner perimeter of plate  56  is pressed against a surface of the outer perimeter of plate cylinder  46  at a nip  51  formed by plate  56  and blanket  54 . Inkers contacting plate  56  may also cause the surface of the inner perimeter of plate  56  to contact the surface of the outer perimeter of plate cylinder  46 . A surface of the inner perimeter of blanket  54  is pressed against a surface of the outer perimeter of blanket cylinder  44  at nip  51  and at a nip  53  formed by blanket  54  and impression cylinder  42 . At nips  51 ,  53 , the splined surfaces of blanket  54  and plate  56  mate with the respective splined surfaces of blanket cylinder  44  and plate cylinder  46 , forming spline mating positions. These spline mating positions  57  act to maintain correct radial positioning of blanket  54  and plate  56  as cylinders  44 ,  46  rotate. Splined surfaces of plate cylinder  46  and plate  56  may also mate at positions other than nips  51 ,  53 , depending on the amounts of force applied by inkers and cylinders  44 ,  46  to plate  56  and a speed at which cylinders  42 ,  44 ,  46  are rotated. Similarly, splined surfaces of blanket cylinder  44  and blanket  54  may also mate at positions other than nips  51 ,  53 , depending on the amounts of force applied by cylinders  42 ,  44 ,  46  and web  50  and a speed at which cylinders  42 ,  44 ,  46  are rotated. 
         [0021]    The surface of the inner perimeter of blanket  54  not contacting the surface of the outer perimeter of blanket cylinder  44  during printing mode traverses away from blanket cylinder  44  and may form a gap  55  on a side of blanket cylinder  44  if forces cause substantially an entire side of the surface of the outer perimeter of plate cylinder  46  to mate with the surface of the inner perimeter of plate  56 , as shown in  FIG. 3 . The surface of the inner perimeter of plate  56  may interact with the outer surface of plate cylinder  46  in a similar manner and also form a gap  59  on a side of plate cylinder  46 . Alternatively, tensioners may be employed to act on plate  56  and blanket  54  to produce a similar result. 
         [0022]    The embodiment shown in  FIG. 3  may allow plate cylinder  46  and blanket cylinder  44  to be in close proximity to one another, but at the same time may allow larger cutoffs than would be possible if the lengths of the inner perimeters of plate  56  and blanket  54  were substantially equal to the lengths of the outer perimeters of plate cylinder  46  and blanket cylinder  44 , respectively. Blanket  54  and plate  56  can be replaced with replacement blankets and plates that have greater inner perimeters than blanket  54  and plate  56 , but are the same thickness as blankets  54 ,  56 , thus allowing a larger cutoff, yet maintaining the positional relationship between plate cylinder  46  and blanket cylinder  44 . 
         [0023]    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.