Abstract:
A variable cutoff printing press is provided. The printing press includes a first plate cylinder rotating at a constant angular velocity and printing on a web during each revolution about a first plate cylinder axis and a first blanket cylinder rotating at varying angular velocities during each revolution about a first blanket cylinder axis. The first blanket cylinder comes in and out of contact with the first plate cylinder during operation. A method of variable cutoff printing is also provided.

Description:
[0001]    The present invention relates generally to printing presses and more particularly to variable cutoff printing presses. 
       BACKGROUND OF INVENTION 
       [0002]    U.S. Pat. No. 5,950,536 discloses a variable cutoff offset press unit wherein a fixed cutoff press is adapted to a variable cutoff press while maintaining the size of the blanket cylinders. A plate cylinder sleeve has a variable outer diameter, whereby a length of an image to be printed is varied proportionally to a variable outer diameter while maintaining an outer diameter of the gapless blanket cylinder sleeve constant. The size of a plate cylinder is changed by using a sleeve mounted over the plate cylinder or adding packing under a plate to increase the diameter of the plate cylinder. 
         [0003]    U.S. Pat. No. 6,327,975 discloses a method and apparatus for printing elongate images on a web. A first printing unit prints a first image portion on the web at prescribed spacings, by moving the impression cylinder away from the blanket cylinder each time one first image portion is printed. A second printing unit prints a second image portion on the spacings left on the web by the first printing unit, also by moving the impression cylinder away from the blanket cylinder each time one second image portion is printed. A variable velocity motor rotates each blanket cylinder, while each time the associated impression cylinder is held away to create a space on the web for causing printing of the first or the second printing portion at required spacings. 
         [0004]    U.S. Pat. No. 7,066,088 discloses a variable cut-off offset press system and method of operation which utilizes a continuous image transfer belt. The offset printing system comprises at least two plate cylinders adapted to have thereon respective printing sleeves. Each of the printing sleeves is adapted to receive colored ink from a respective ink source. The system further comprises at least a impression cylinder, wherein the image transfer belt is positioned to contact each of the printing sleeves at respective nips formed between respective ones of the plate cylinders and the at least one impression cylinder. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A variable cutoff printing press is provided. The printing press includes a first plate cylinder rotating at a constant angular velocity during each revolution about a first plate cylinder axis and a first blanket cylinder rotating at varying angular velocities and printing on a web during each revolution about a first blanket cylinder axis. The first blanket cylinder comes in and out of contact with the first plate cylinder during operation. 
         [0006]    A method of variable cutoff printing is also provided. The method includes, during a single rotation of a first blanket cylinder about a first blanket cylinder axis, rotating the first blanket cylinder and bringing the first blanket cylinder into contact with a first plate cylinder carrying a first image and rotating at a first constant velocity, the blanket cylinder contacting the first plate cylinder and receiving the first image from the first plate cylinder; rotating the first blanket cylinder and bringing the first blanket cylinder out of contact with the first plate cylinder; varying a rotational velocity of the first blanket cylinder after the first blanket cylinder is brought out of contact with the first plate cylinder; rotating the first blanket cylinder and bringing the first blanket cylinder into contact with a web traveling at a second constant velocity, the first blanket cylinder contacting the web and printing the first image on the web; rotating the first blanket cylinder and bringing the first blanket cylinder out of contact with the web; and varying the rotational velocity of the first blanket cylinder again after the first blanket cylinder is brought out of contact with the web. 
     
    
     
       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 printing unit of a printing press according to an embodiment of the present invention; 
           [0009]      FIG. 2   a  shows a table including predicted results for a printing section of the embodiment shown in  FIG. 1 ; 
           [0010]      FIG. 2   b  shows a graph illustrating a surface velocity of a contacting portion of a blanket cylinder, for each revolution of the blanket cylinder, according to the predicted results shown in the table of  FIG. 2   a;    
           [0011]      FIG. 3  shows a printing unit of a printing press according to an embodiment of the present invention; 
           [0012]      FIG. 4  shows a schematic side view of a four color offset printing press including one central impression cylinder according to an embodiment of the present invention; and 
           [0013]      FIG. 5  shows a schematic side view of a four color offset printing press according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  shows a printing unit  10  of a printing press according to an embodiment of the present invention. Printing unit  10  includes a first printing section  20  and a second printing section  30  printing images on a web  14  as web  14  passes over a central impression cylinder  16 . A nip roll  18  guides web  14  as web  14  comes into contact with impression cylinder  16 . Each printing section  20 ,  30  includes inkers  22 ,  32 , a plate cylinder  24 ,  34 , and a blanket cylinder  26 ,  36 , respectively, and prints images on web  14 . Inkers  22 ,  32  provide the same color ink to plate cylinders  24 ,  34 , respectively. Blanket cylinders  26 ,  36  print images on web  14  at areas  42 ,  44 , respectively, where nips are formed when blanket cylinders  26 ,  36 , respectively, contact web  14 . 
         [0015]    Inkers  22  disperse ink to plate cylinder  24 , which rotates about an axis of plate cylinder  24  and transfers a first inked image to blanket cylinder  26 . Blanket cylinder  26  rotates about an axis of blanket cylinder  26  and prints the first inked image on web  14 . Axes of blanket cylinder  26  and plate cylinder  24  remain stationary during printing. Inkers  22  and plate cylinder  24  are being rotated so that inkers  22  each have a constant surface velocity that is equal to the surface velocity of plate cylinder  24 . Impression cylinder  16  and web  14  also travel at constant velocities so that a surface velocity of impression cylinder  16  equals a velocity of web  14 . 
         [0016]    The surface velocity of plate cylinder  24  may vary from the surface velocity of impression cylinder  16  and the velocity of web  14 . However, while blanket cylinder  26  is receiving a first image from plate cylinder  24  the surface velocity of blanket cylinder  26  is equal to the surface velocity of plate cylinder  24  and while blanket cylinder  26  is printing the first images on web  14  the surface velocity of blanket cylinder  26  is equal to the surface velocity of impression cylinder  16  and the velocity of web  14 . Thus, during each  360  degree revolution, if the surface velocity of plate cylinder  24  varies from the surface velocity of blanket cylinder  26 , then blanket cylinder  26  accelerates and decelerates during each revolution. 
         [0017]    Printing section  30  operates in a manner similar to printing section  20  to print second images on web  14 , with inkers  32  and plate cylinder  34  having constant equal surface velocities that may vary from the velocity of web  14  and the surface velocity of impression cylinder  16 . As with blanket cylinder  26 , blanket cylinder  36  may accelerate and decelerate during each 360 degree revolution when the surface velocity of plate cylinder  34  varies from the surface velocity of impression cylinder  16  and the velocity of web  14 . 
         [0018]    In this embodiment, a position where blanket cylinder  26  contacts web  14  and a position where blanket cylinder  26  contacts plate cylinder  24  are separated by 180 degrees with respect to the axis of blanket cylinder  26 . Also, a position where blanket cylinder  36  contacts plate cylinder  34  and a position where blanket cylinder  36  contacts web  14  are separated by 180 degrees with respect to an axis of blanket cylinder  36 . In other embodiments, different angles of separation may be used. 
         [0019]    As shown in  FIG. 1 , blanket cylinders  26 ,  36  may include relieved portions  25 ,  35 , respectively, to allow blanket cylinders  26 ,  36  to accelerate and decelerate during each revolution without disrupting the rotation of plate cylinders  24 ,  34 , respectively, or impression cylinder  16  or disrupting the travel of web  14 . Relieved portions  25 ,  35  do not come into contact with plate cylinders  24 ,  34  or web  14  during normal printing operations. The portions of each blanket cylinder  26 ,  36  that are not relieved contact plate cylinders  24 ,  34 , respectively, during each revolution and may be referred to as contacting portions  27 ,  37 . Blanket cylinders  26 ,  36  receive respective first and second images and print the images using respective contacting portions  27 ,  37 . Each contacting portion  27 ,  37  has a pitch radius Rc that is greater than a pitch radius Rr of each respective relieved portion  25 ,  35 . 
         [0020]    In this embodiment, which is a preferred embodiment, printing sections  20 ,  30  are configured in the same manner, with plate cylinder  24  being the same size as plate cylinder  34 , blanket cylinder  26  being the same size as blanket cylinder  36 , and contacting portions  27 ,  37  being the same size. In an alternative embodiment, printing sections  20 ,  30  may be configured differently from each other. 
         [0021]    In operation, blanket cylinder  26  contacts plate cylinder  24  with contacting portion  27  and receives a first image from plate cylinder  24 . After contacting portion  27  receives the first image from plate cylinder  24  and contacting portion  27  is no longer in contact with plate cylinder  24 , blanket cylinder  26  may be accelerated or decelerated so that contacting portion  27  has a surface velocity that is equal to the velocity of web  14  when contacting portion  27  contacts web  14 . When contacting portion  27  prints the first image on web  14  and is no longer in contact with web  14 , blanket cylinder  26  may be accelerated or decelerated so that the surface velocity of contacting portion  27  is equal to the surface velocity of plate cylinder  24  when contacting portion  27  comes into contact with plate cylinder  24  again to receive a next first image. As blanket cylinder  26  contacts plate cylinder  24 , blanket cylinder  26  is aligned with respect to plate cylinder  24  so that a first inked image carried by plate cylinder  24  is properly transferred to contacting portion  27 . After blanket cylinder  26  receives the next first image and comes out of contact with plate cylinder  24 , blanket cylinder  26  may be accelerated or decelerated so that contacting portion  27  has a surface velocity that is equal to the velocity of web  14  as contacting portion  27  contacts web  14  and so that contacting portion  27  is properly aligned to print the next first image on web  14 . 
         [0022]    After blanket cylinder  26  prints a first image on web  14  and the first image passes by area  44 , blanket cylinder  36  prints a second image on web  14  directly behind the first image. As blanket cylinder  36  prints the image, blanket cylinder  36  is being rotated so that the surface velocity of blanket cylinder  36  equals the velocity of web  14  and the surface velocity of impression cylinder  16 . After blanket cylinder  36  finishes printing the second image on web  14 , blanket cylinder  36  may be accelerated or decelerated so that contacting portion  37  has a surface velocity that equals the surface velocity of plate cylinder  34 , and is in proper image receiving position when contacting portion  37  contacts plate cylinder  34  to receive a next second image. After blanket cylinder  36  contacts plate cylinder  34  and receives the next second image and contacting portion  37  is out of contact with plate cylinder  34 , blanket cylinder  36  may need to be accelerated or decelerated so that the surface velocity of contacting portion  37  equals the velocity of web  14  and so that contacting portion  37  is in a proper position as blanket cylinder  36  prints the next second image on web  14 . 
         [0023]    Blanket cylinder  26  prints first images on web  14  that are separated from one another by a distance that is equal to the length of each second image printed by blanket cylinder  36 . Blanket cylinder  36  prints second images on web  14  that are separated from each other by a distance that is equal to the length of each first image printed by blanket cylinder  26 . Thus, blanket cylinders  26 ,  36  are phased so that each blanket cylinder  26 ,  36  prints every other image on web  14  and no unprinted space is left between adjacent first and second images printed by blanket cylinders  26 ,  36 , respectively, on web  14 . 
         [0024]    In one embodiment, each first image printed on web  14  by blanket cylinder  26  may be a first image portion and each second image printed on web  14  by blanket cylinder  36  may be a second image portion, so that the each first image portion and each second image portion form a single continuous image. Thus, together blanket cylinders  26 ,  36  may act together to print a single image on web  14 . 
         [0025]    Each cylinder  16 ,  24 ,  26 ,  34 ,  36  may be driven by a motor  101 ,  102 ,  103 ,  104 ,  105 , respectively. Motors  101 ,  102 ,  103 ,  104 ,  105  may be controlled by a controller  110 , which acts to ensure that blanket cylinders  26 ,  36  are traveling at appropriate surface velocities when blanket cylinders  26 ,  36  contact plate cylinders  24 ,  34 , respectively, and web  14  and that blanket cylinders  26 ,  36  print images on web  14  at appropriate locations. Motors  102 ,  104  may also drive inkers  22 ,  32 , respectively. In an alternative embodiment, plate cylinders  24 ,  34  may be driven by a single motor. 
         [0026]    In order to vary a cutoff of images printed by printing unit  10 , plate cylinders  24 ,  34  may be altered so that plate cylinders  24 ,  34  transfer respective first and second replacement images to blanket cylinders  34 ,  36 . This may be accomplished by removing plates, which may be disposed about plate cylinders  24 ,  34  and carry the respective first and second images, from plate cylinders  24 ,  34  and replacing the plates with replacement plates that carry the respective first and second replacement images. When the first and second replacement images are of a length that varies from the length of contacting portions  27 ,  37 , respectively, the velocity that blanket cylinders  26 ,  36  are rotated and the phasing of blanket cylinders  26 ,  36  may be adjusted so that blanket cylinders  26 ,  36  properly receive the first and second replacement images from plate cylinders  24 ,  34 , respectively, and print the first and second replacement images in proper alignment on web  14 . 
         [0027]      FIG. 2   a  shows a table including predicted results for printing section  20  of the embodiment shown in  FIG. 1 , under five scenarios  201 ,  202 ,  203 ,  204 ,  205 , where the velocity of web  14  is constant. Because printing sections  20 ,  30  operate in the same manner, the predicted results may also apply to printing section  30 . 
         [0028]    For scenario  201 , blanket cylinder  26  prints first images on web  14  during 180 degrees of each revolution. The surface velocity of plate cylinder  24  is equal to the velocity of web  14  and blanket cylinder  26  travels at a constant speed during each revolution, with a surface velocity of contacting portion  27  equal to the velocity of web  14 . Blanket cylinder  26  does not accelerate or decelerate throughout each revolution. 
         [0029]    For scenario  202 , blanket cylinder  26  prints first images on web  14  during 120 degrees of each revolution and contacting portion  27  makes up one third of the circumference of blanket cylinder  26 . The surface velocity of plate cylinder  24  is more than twice the velocity of web  14 . Blanket cylinder  26  accelerates for 60 degrees after printing a first image on web  14  and decelerates for 60 degrees after receiving a first image from plate cylinder  24 . After printing a first image on web  14 , blanket cylinder  26  rotates 240 degrees in the time it takes web  14  to travel a distance that equals a length of a second image printed by contacting portion  37 , in order to be back in proper printing position. While not printing on web  14 , contacting portion  27  has an average surface velocity that equals twice the velocity of web  14 . 
         [0030]    For scenario  203 , blanket cylinder  26  prints first images on web  14  during 90 degrees of each revolution. The surface velocity of plate cylinder  24  is more than three times the velocity of web  14 . Blanket cylinder  26  accelerates for 90 degrees after printing a first image on web  14  and decelerates for 90 degrees after receiving a first image from plate cylinder  24 . After printing a first image on web  14 , blanket cylinder  26  rotates 270 degrees in the time it takes web  14  to travel a distance that equals a length of a second image printed by contacting portion  37 , in order to be back in proper printing position. While not printing on web  14 , contacting portion  27  has an average surface velocity that equals three times the velocity of web  14 . 
         [0031]    For scenario  204 , blanket cylinder  26  prints first images on web  14  during 72 degrees of each revolution. The surface velocity of plate cylinder  24  is more than four times the velocity of web  14 . Blanket cylinder  26  accelerates for 108 degrees after printing a first image on web  14  and decelerates for 108 degrees after receiving a first image from plate cylinder  24 . After printing a first image on web  14 , blanket cylinder  26  rotates 288 degrees in the time it takes web  14  to travel a distance that equals a length of a second image printed by contacting portion  37 , in order to be back in proper printing position. While not printing on web  14 , contacting portion  27  has an average surface velocity that equals four times the velocity of web  14 . 
         [0032]    For scenario  205 , blanket cylinder  26  prints first images on web  14  during 60 degrees of each revolution. The surface velocity of plate cylinder  24  is more than five times the velocity of web  14 . Blanket cylinder  26  accelerates for 120 degrees after printing a first image on web  14  and decelerates for  120  degrees after receiving a first image from plate cylinder  24 . After printing a first image on web  14 , blanket cylinder  26  rotates 300 degrees in the time it takes web  14  to travel a distance that equals a length of a second image printed by contacting portion  37 , in order to be back in proper printing position. While not printing on web  14 , contacting portion  27  has an average surface velocity that equals five times the velocity of web  14 . 
         [0033]      FIG. 2   b  shows a graph illustrating the surface velocity of contacting portion  27  for each 360 degree revolution of blanket cylinder  26  for scenarios  202 ,  203 ,  205  shown in the table of  FIG. 2   a.  The graph assumes uniform acceleration and deceleration of blanket cylinder  26  between printing on web  14  and receiving images from plate cylinder  24 . Web  14  is traveling at a constant velocity of 100 fpm and equals a minimum surface velocity of blanket cylinder  26  in scenarios  202 ,  203 ,  205 . Each scenario  202 ,  203 ,  205  has a different maximum surface velocity, which equals a surface velocity of plate cylinder  24  for the respective scenario  202 ,  203 ,  205 . For scenario  202 , blanket cylinder  26  has a maximum surface velocity of 300 fpm. For scenario  203 , blanket cylinder  26  has a maximum surface velocity of 500 fpm. For scenario  205 , blanket cylinder  26  has a maximum surface velocity of 900 fpm. 
         [0034]      FIG. 3  shows a printing unit  310  of a printing press according to an embodiment of the present invention. Printing unit  310  includes printing sections  320  and  330  that operate in essentially the same manner as printing sections  20 ,  30  except that blanket cylinders  326 ,  336  of printing unit  310  do not include relieved portions and contacting portions and the axes of blanket cylinders  326 ,  336  do not remain stationary during operation. Inkers  22 ,  32  feed ink to plate cylinders  24 ,  34 , which transfer inked images to blanket cylinders  326 ,  336 . 
         [0035]    Blanket cylinder  326  is translated between two positions  326   a,    326   b  by an actuator  130  during each revolution. In position  326   a,  blanket cylinder  326  receives first images from plate cylinder  24  and a surface velocity of blanket cylinder  326  equals the surface velocity of plate cylinder  24 . In position  326   b,  blanket cylinder  326  prints first images on web  14  and the surface velocity of blanket cylinder  326  equals the velocity of web  14 . As blanket cylinder  326  is translated between positions  326   a,    326   b  blanket cylinder  26  may be accelerated or decelerated to ensure that blanket cylinder  326  is traveling at an appropriate velocity when blanket cylinder  326  comes into contact with plate cylinder  24  or web  14 . 
         [0036]    Blanket cylinder  336  is translated between two positions  336   a,    336   b  by an actuator  132  during each revolution. In position  336   a,  blanket cylinder  336  receives second images from plate cylinder  34  and a surface velocity of blanket cylinder  336  equals the surface velocity of plate cylinder  34 . In position  336   b,  blanket cylinder  336  prints second images on web  14  and the surface velocity of blanket cylinder  336  equals the velocity of web  14 . As blanket cylinder  336  is translated between positions  336   a,    336   b  blanket cylinder  336  may be accelerated or decelerated to ensure that blanket cylinder  336  is traveling at an appropriate velocity when blanket cylinder  336  comes into contact with plate cylinder  34  or web  14 . 
         [0037]    In order to vary a cutoff of images printed by printing unit  310 , plate cylinders  24 ,  34  may be altered so that plate cylinders transfer first and second replacement images to blanket cylinders  34 ,  36 . This may be accomplished by removing plates, which may be disposed about plate cylinders  24 ,  34  and carry the respective first and second images, from plate cylinders  24 ,  34  and replacing the plates with replacement plates that carry the respective first and second replacement images. The velocity that blanket cylinders  326 ,  336  are rotated and the phasing of blanket cylinders  326 ,  336  may be adjusted so that blanket cylinders  326 ,  336  properly receive the first and second replacement images from plate cylinders  24 ,  34 , respectively, and print the first and second replacement images on web  14  so the first and second replacement images are properly aligned and there are no unprinted spaces between the first and second replacement images. The translation of blanket cylinders  326 ,  336  between respective positions  326   a,    336   a  and respective positions  326   b,    336   b  may also be adjusted so that blanket cylinders  326 ,  336  contact plate cylinders  24 ,  36  and web  14  for the proper amount of time to receive and print the replacement images on web  14 . 
         [0038]      FIG. 4  shows a schematic side view of a four color offset printing press  400  including one central impression cylinder  405  according to an embodiment of the present invention. Four printing units  402 ,  404 ,  406 ,  408  are disposed about central impression cylinder  405  and print on a web  410  that passes over an outer surface of central impression cylinder  405 . Each printing unit includes two plate cylinders  424 ,  434  and two blanket cylinder  426 ,  436 , as well as a set of inkers for each plate cylinder  424 ,  434 . Printing units  402 ,  404 ,  406 ,  408  may be configured the same as and operate in essentially the same manner as printing unit  10  shown in  FIG. 1  or printing unit  310  shown in  FIG. 3 . Blanket cylinders  426 ,  436  may include contacting and relieved portions or blanket cylinders  426 ,  436  may be translated between positions of contacting web  410  and plate cylinders  424 ,  434 , respectively. Each printing unit  402 ,  404 ,  406 ,  408  prints in a different color on web  410 , so that printing units  402 ,  404 ,  406 ,  408  print images that overlap and form four color images on web  410 . 
         [0039]      FIG. 5  shows a schematic side view of a four color offset printing press  500  according to an embodiment of the present invention. Printing press  500  includes four printing units  502 ,  504 ,  506 ,  508  printing images on a web  510 . Each printing unit  502 ,  504 ,  506 ,  508  includes two plate cylinders  524 ,  534 , two blanket cylinder  526 ,  536 , and one impression cylinder  516 , as well as a set of inkers for each plate cylinder  524 ,  534 . Printing units  502 ,  504 ,  506 ,  508  may be configured the same as and operate in the same manner as printing unit  10  shown in  FIG. 1  or printing unit  310  shown in  FIG. 3 . Blanket cylinders  526 ,  536  may include contacting and relieved portions or blanket cylinders  526 ,  536  may be translated between positions of contacting web  510  and plate cylinders  524 ,  534 , respectively. Each printing unit  502 ,  504 ,  506 ,  508  prints in a different color on web  510 , so that printing units  502 ,  504 ,  506 ,  508  print images that overlap and form four color images on web  510 . In one alternative embodiment each printing unit  502 ,  504 ,  506 ,  508  may include two impression cylinders in place of impression cylinder  516 , with each blanket cylinder  526 ,  536  contacting one impression cylinder. In another alternative embodiment printing press  500  may be a perfecting printing press with printing units  502 ,  504 ,  506 ,  508  printing on both sides of web  510 . 
         [0040]    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.