Abstract:
An offset print unit includes a plate cylinder, a blanket cylinder having an end and a blanket gear coaxial with the blanket cylinder, a drive axle or pinion supporting a gear driving the blanket gear and a blanket lift arm for selectively supporting the end to cantilever the blanket cylinder, the blanket lift arm being rotatable about the drive axle or pinion. A method is also provided.

Description:
This application claims priority to U.S. Provisional Application No. 60/666,440 filed Mar. 30, 2005, and hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     The present invention relates generally to printing presses and more specifically to web offset printing presses having separable blankets. 
     U.S. Pat. No. 4,240,346 describes for example a printing press with two blanket cylinders separable from each other to permit a blanket throw off. In such presses, the blankets are offset from a vertical from each other, and in order to pass the web through the blankets when the blankets are offset, lead rolls or air bars are necessary to properly guide the web through the blankets. These guides can mark the printed product and also alter registration of the web between two printing print units, causing deteriorated print quality. 
     U.S. Pat. No. 6,343,547 describes a device to counterpoise a cylinder and a method for counterpoising a cylinder to be cantilevered on a printing press. U.S. Pat. No. 6,877,424 describes a counterpoise device for cantilevering at least one cylinder of a printing press having a movable counterpoise element for selectively contacting the cylinder and a stationary mount. 
     U.S. Pat. Nos. 6,216,592 and 6,019,039 describe printing units with throw-off mechanisms and are hereby incorporated by reference herein. 
     SUMMARY OF THE INVENTION 
     In a print unit in which blankets cylinders have a large displacement from on impression to off impression, interference between the optimal lifting arm pivot point and drive pinion locations may occur. Deviations from the optimal lifting arm pivot point cause increasingly difficult design of the lifting arm to accommodate lift loads. 
     By providing a blanket lift arm that resides independently around a rotating drive pinion, the lift arm pivot and drive pinion may occupy the same center while working independently of one another. 
     The present invention provides an offset print unit comprising: 
     a plate cylinder; 
     a blanket cylinder having an end and a blanket gear coaxial with the blanket cylinder; 
     a drive axle or pinion supporting a gear driving the blanket gear; and 
     a blanket lift arm for selectively supporting the end to cantilever the blanket cylinder, the blanket lift arm being rotatable about the drive axle or pinion. 
     The present invention also provides a method for cantilevering a blanket cylinder driven by an axle or pinion offset from the blanket cylinder and having an axis parallel to an axis of the blanket cylinder, the method comprising: 
     rotating a blanket lift arm about the axis of the axle or pinion to contact an end of the blanket cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will be elucidated with reference to the drawings, in which: 
         FIG. 1  shows a web offset printing press; 
         FIG. 2  shows bearer cams in a first printing position; 
         FIG. 3  shows bearer cams in a transition position; 
         FIG. 4  shows bearer cams in a first throw-off position with the plate and blanket cylinders in contact; 
         FIG. 5  shows bearer cams in a second throw-off position with the plate and blanket cylinders out of contact; and 
         FIGS. 6 ,  7  and  8  show the drive pinion and cantilever lift mechanism for the blanket cylinder. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a web offset printing press having eight offset print units  10 ,  12 ,  14 ,  16 ,  18 ,  20 ,  22 ,  24 , each having a plate cylinder  42 , blanket cylinder  44 , plate cylinder  48  and blanket cylinder  46 . Blanket cylinders  44  and  46  nip a web  30  in a printing mode, as shown for print units  10 ,  12 ,  14 ,  16 , which may print black, cyan, yellow and magenta, respectively for example. The web may enter the print units via nip rollers  32  (which may be infeed rollers for example) and may exit via exit rollers  34 , which may for example be located downstream of a dryer. 
     The blanket cylinders  44 ,  46  for each print unit may be thrown-off, as shown for units  22  and  24 , so as to separate from each other and from the respective plate cylinder  42 ,  48 . Plate cylinders  42 ,  48  may move back into contact with the blanket cylinders  44 ,  46 , respectively, during an automatic plate change operation, for example via automatic plate changers  40  and  50 , respectively. Automatic plate changers are described in U.S. Pat. Nos. 6,053,105, 6,460,457 and 6,397,751 and are hereby incorporated by reference herein. 
     A throw-off mechanism  60  is shown schematically for moving the blanket and plate cylinders  46 ,  48 . Blanket cylinder  44  and plate cylinder  42  may have a similar throw-off mechanism. Preferably, each print unit is driven by two motors  70 ,  72 , one driving one of the plate or blanket cylinders  46 ,  48 , and one driving one of the plate cylinder  42  and blanket cylinder  44 . The non-driven cylinder may be geared to the driven cylinder on each side of web  30 . Each print unit  10 ,  12  . . .  24  may be the same. 
     The web path length between the nip rollers  32 ,  34  advantageously need not change, even when one of the print units has blanket cylinders which are thrown off. Registration may be unaffected by the throw-off. In addition, no web deflectors or stabilizers are needed, such as lead rolls or air rolls to make sure the web does not contact the blanket cylinders  44 ,  46 , which could cause marking. 
     The throw-off distance D preferably is at least 0.5 inches and most preferably at least 1 inch, i.e. that the web has half an inch clearance on either side of the web. Moreover, the centers of the blanket cylinders  44 ,  46  preferably are in a nearly vertical plane V, which is preferably 10 degrees or less from perfect vertical. This has the advantage that the throw-off provides the maximum clearance for a horizontally traveling web. 
     The circumference of the plate cylinder preferably is less than 630 mm, and most preferably is 578 mm. 
     The creation of the large throw-off distance D is explained with an exemplary embodiment as follows: 
       FIG. 2  shows the throw-off mechanism  60  for the lower blanket  44 . A blanket cylinder support  102  supports a gear side axle  144  of the blanket cylinder  44  and a plate cylinder support  104  supports a gear side axle  142  of the plate cylinder  42 . The blanket cylinder support  102  is pivotable about an axis  116 , and the plate cylinder support about an axis  114 . A pneumatic cylinder  106  can move the plate cylinder support  104  via an arm  108 . 
     When blanket cylinder  44  is in contact with blanket cylinder  46  in a printing position, a first bearer surface  111  of support  102  is in contact with a second bearer surface  112  of support  104 , which another bearer surface  109  of the support  102  is not in contact with a bearer surface  110  of support  104 . Distance F thus is zero, while a distance G between surfaces  109  and  110  may be 0.0045 inches. Distance H between the axial centers of the axles  144  and  142  may be 7.2463 inches. 
     In  FIG. 3 , support  104  is moved downwardly so distance H may be for example 7.2416 inches, and the distances F and G both are zero. The cam surfaces  111 ,  112  and  109 ,  110  thus are transitioning the load between themselves. 
     As shown in  FIG. 4 , when support  104  moves downwardly more, blanket cylinder  44  is thrown-off the blanket cylinder  46 , bearer surface or cam  109  of support  102  contacts bearer surface  110  of the box  104  so that the blanket cylinder box  102  rests on the box  104  at surfaces  109 / 110 . A distance between the bearer surface  111  of box  102  and a bearer surface  112  of box  104  may be 0.1561 inches. The bearer surface  109  may have a same arc of curvature as blanket cylinder  44 , and bearer surface  110  may have a same arc of curvature as plate cylinder  42 , so that even in  FIG. 4  distance H still remains 7.2416 inches. At this point an extension  122  also just comes into contact with a fixed stop  120  on a frame. 
     As shown in  FIG. 5 , when support  104  is moved downwardly more, blanket support  102  rests on stop  120  while plate support  104  moves downwardly even more. Thus, distance G between bearer surfaces  109  and  110  increases and may be 1 mm, for example. Distance F also increases. In this position, access to plate cylinder  42  for removing or changing a plate may be possible. For autoplating, the plate cylinder  42  may be moved again against the blanket cylinder  44  as in  FIG. 4 , if the autoplating mechanism so requires. 
     The upper plate and blanket throw-off mechanism may move in a similar manner with dual bearer surfaces, but since the gravity effects differ, a link may be provided between holes  130 ,  132  so that the raising of the plate cylinder  48  also causes the blanket cylinder  46  to rise. 
     As shown in  FIG. 2 , a drive gear  280  may drive a blanket cylinder gear  260 . The blanket cylinder gear  260  may drive a similar plate cylinder gear. These gears  280 ,  260  may be axially inside the support  102 , i.e. into the page. Due to the tangential arrangement of the gears, the rotation of the support  102  does not cause the gear  260  to disengage from gear  280  (which has an axis which does not translate). In the  FIGS. 2 ,  3 ,  4 , and  5  positions, the blanket cylinder gear  260  and an interacting plate cylinder gear can be driven by gear  280 . The motor  72  thus can be used for auto-plating. 
       FIGS. 6 ,  7  and  8  show the drive pinion  200  driven by the motor  72  ( FIG. 1 ), and connected to gear  280  which interacts with the blanket gear  260 . A mounting bracket  210  supports the pinion  200  via bearings  220 . A lifting arm  230  is supported for rotation around the pinion  200  and may be pneumatically actuated via a pneumatic cylinder  234  to interact with an end of the blanket cylinder  44  to permit removal axially of a sleeve-shaped blanket. Each blanket cylinder for each print unit preferably has a sleeve-shaped axially-removable blanket. 
     An adjusting screw  222  connects the lifting arm  230  to a lift arm eccentric  232 , which has a circular inner surface a distance C from the drive pinion  200  and an eccentric outer surface. By adjusting the screw  222 , the location for the lift arm  230  to support the blanket cylinder  44  may be adjusted in direction E. 
     By having the lifting arm  230  coaxial with the drive pinion  200 , larger movements of the blanket cylinder  44  during throw-off may be accommodated. 
     The present invention thus provides for large movement of the blanket and plate cylinders while maintaining cantilevering for blanket sleeves and auto-plating capability.