Abstract:
A noncontact web stabilizer is provided in which members located on opposite sides of a web reduce out-of-plane web vibrations. Specifically, a first member is located on one side of a web and a second member is located on the opposite side of the web. Both members are positioned so that the distance between the web and the members decrease in the direction that the web is moving, creating opposing regions of high pressure that force the web toward its nominal running position, thereby reducing out-of-plane web instability.

Description:
BACKGROUND  
       [0001]     The present invention relates to printing presses and more particularly to a web stabilization apparatus.  
         [0002]     In a web fed rotary printing press having multiple printing units, it may be desired to stop printing one or more printing units by throwing the blanket cylinders away from the web. This can permit, for example, a plate or blanket change. Automatic plate changes can occur using an automatic transfer printing unit. Such a printing press is for example manufactured by Goss International as the Sunday 2000 Autotransfer Press.  
         [0003]     When the blanket cylinders are separated from the web, the web can pass freely between the two blanket cylinders. As the web passes between the separated blanket cylinders the web may demonstrate out-of-plane vibrations. More specifically, these out-of-plane vibrations occur when the auto transfer unit blankets are off impression and when the web is passing through at normal printing speeds.  
         [0004]     When the web experiences out-of-plane vibrations, unintentional web contact can occur with the blanket cylinders. Unintentional web contact with the blanket cylinders could result in print defects on the web or web breakage. It is known in the printing industry to use rollers located upstream and downstream from a printing unit in an attempted to stabilize a moving web. However, rollers can produce marking or damage to the web. U.S. Pat. No. 5,924,619 describes an apparatus for passing a printed web between separated cylinders of a deactivated printing unit.  
         [0005]     Referring to  FIG. 1 ( a ), a prior art printing press  100  is shown with a web  110  and without a web stabilization device. Printing press  100  has printing units  105 - 1  through  105 - a , where a is a predetermined value, preferably 5 or 8 for an automatic transfer press with 5 units having two black printing units and 8 having two printing units each for magenta, cyan, yellow and black. The printing units  105 - 1  through  105 - a  each have 4 cylinders, 2 blanket cylinders, 2 plate cylinders and 2 automatic plate changers. Printing unit  105 - 1  has blanket cylinders  115 - 1   a,b , plate cylinders  120 - 1   a,b , and automatic plate changers  160 - 1   a,b . Print unit  105 - 2  has blanket cylinders  115 - 2   a,b  and plate cylinders  120 - 2   a,b , where all 4 cylinders are rolling without contact, which can permit, for example, automatic plate transfer by automatic plate changers  160 - 2   a,b . As shown in  FIG. 1 ( a ), as web  110  moves in the direction denoted by arrow  125 , web  110  experiences out-of-plane vibrations (denoted by arrow  130 ) where unintentional web contact can occur with blanket cylinders  115 - 2   a,b.    
         [0006]      FIG. 1 ( b ) shows the prior art printing press  100  of  FIG. 1 ( a ) with rollers  130 - a  and  130 - b  located upstream and downstream from printing unit  105 - 2  which is off impression. Web  110  runs over roller  130 - a  and under  130 - b  in an attempt to provide out-of-plane web stability. The problem with this configuration is that rollers  130 - a,b  can produce unacceptable damage to web  110 , such as such as damage to the wet printed surface and web breakage.  
         [0007]      FIG. 1 ( c ) shows the prior art printing press  100  of  FIG. 1 ( a ) with rollers  140 - a  and  140 - b  located upstream and downstream from the deactivated printing unit  105 - 2 , in an attempt to provide out-of-plane web stability. In  FIG. 1 ( c ), the cylinders of print unit  105 - 2  are inclined away from the vertical angle by an angle of inclination, for example, of 10 to 15 degrees. Like in  FIG. 1 ( b ), web  110  runs over roller  145 - a  and under roller  145 - b  in an attempt to stabilize moving web  110 . As mentioned above above, rollers  140 - a,b  can produce unacceptable damage to web  110 , such as damage to the wet printed surface and web breakage.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with an embodiment of the present invention, a web automatic transfer print unit includes a first plate cylinder, a first blanket cylinder, a second blanket cylinder, a second plate cylinder, and a first and second member. The members are located on opposite sides of a web. The first member is positioned so that the distance between the web and the first member decreases in the direction that the web is moving. The second member is positioned so that the distance between the web and the second member decreases in the direction that the web is moving. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1 ( a ), illustrates a prior art automatic transfer printing press having multiple printing units without stabilizing a web;  
         [0010]     FIGS.  1 ( b ) and  1 ( c ) illustrate prior art rollers for stabilizing a web in an automatic transfer unit;  
         [0011]     Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 2  illustrates a printing press with noncontact stabilizers  230 ,  235  in accordance with an embodiment of the present invention;  
         [0013]      FIG. 3  illustrates general air velocity profiles and pressures in accordance with an embodiment of the invention;  
         [0014]      FIG. 4 a  printing press with noncontact stabilizers  330 ,  335  in accordance with a further embodiment of the present invention;  
         [0015]      FIG. 5  illustrates noncontact stabilizers  330 ,  335  positioned past the center-line of the blanket cylinders in accordance with a further embodiment of the present invention; and  
         [0016]      FIG. 6  illustrates noncontact stabilizers  330 ,  335  in accordance with a further embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]     In accordance with embodiments of the present invention, a noncontact web stabilization apparatus is provided. In accordance with the embodiments of the present invention, the noncontact web stabilization apparatus causes changes in air pressure to provide out-of-plane web stability.  
         [0018]      FIG. 2  illustrates the printing press of the present invention with noncontact stabilizers  230  and  235  for improving out-of-plane web stability of moving web  210 . As shown in  FIG. 2 , a printing press  200  has print units  205 - 1  through  205 - n , where n is a predetermined value. Each print unit  205 - 1  through  205 - n  is shown with 4 cylinders: blanket cylinders  215 - 1   a,b  through  215 - na,b  and plate cylinders  220 - 1   a,b  through  220 - na,b.    
         [0019]     As show in  FIG. 2 , print units  205 - 1  and  205 - n  have all four cylinders rolling and blanket cylinders  215 - 1   a,b  and  215 - na,b  in contact with web  210 . In contrast, print unit  205 - 2  has blanket cylinders  215 - 2   a,b  and plate cylinders  220 - 2   a,b  rolling without contact with web  210 . Web  210  moves from print unit  205 - 1  to print unit  205 - n  in the direction denoted by arrow  225 . Web  210  passes between print unit  205 - 1  and through noncontact stabilizers  230  and  235  before passing through print unit  205 - 2 , without experiencing out-of-plane vibrations and without contacting blanket cylinders  215 - 2   a  and  215 - 2   b  in accordance with an embodiment of the present invention. Each print unit can have an automatic plate change unit  221 - 1   a,b  through  221 - na,b.    
         [0020]     In this particular embodiment of the present invention, noncontact stabilizers  230  and  235  are rigid plates, for example made of metal, that are positioned on both sides of web  210 . Preferably, noncontact stabilizers  230  and  235  are as wide as, or wider than, web  210 , but do not have to be as wide as web  210 . Noncontact stabilizers  230  and  235  are positioned before the blanket-to-blanket nip of blanket cylinders  215 - 2   a  and  215 - 2   b . Noncontact stabilizers  230  and  235  are also tilted so that the distance between web  210  and noncontact stabilizers  230  and  235  decreases in the direction that web  210  travels, as shown in  FIG. 2 . The decreasing gap between web  210  and noncontact stabilizer  230  creates a high pressure on the top side of web  210 . Similarly, the decreasing gap created between web  210  and noncontact stabilizer  235  creates a high pressure on the bottom side of web  210  which balances the pressure created by noncontact stabilizer  230  located on the opposite side of web  210 . The opposing pressures created by noncontact stabilizers  230  and  235  prevent out-of-plane vibrations of web  210  and stabilizes web  210  as it passes through print unit  205 - 2 . Further, as web speed increases, the opposing pressures created by noncontact stabilizers  230  and  235  increase, thus providing greater stabilization of web  210 .  
         [0021]     For example,  FIG. 3  shows the air velocity profiles of air entering and exiting noncontact stabilizer  235 . At the entrance, air at the tip  236  is at zero velocity due to the no slip boundary condition, while air at the web, is traveling at web speed V web , due to the same boundary condition. At point  211  an air velocity profile as shown is created. At tip  237 , the air velocity is also zero, while the air velocity at point  212  is also V web . Since, however, the exit distance between tip  237  and the web  210  has decreased, a bulge velocity profile may occur at the exit of noncontact stabilizer  235  to satisfy the physical law of conservation of momentum. A pressure P will result due to the bulge profile,even if some air escapes sideways By placing a similar device  230  on the opposite side of the web, two high pressure regions are created, one on either side of the web, which together force the web into an equilibrium position thereby eliminating the undesired out of plane vibration.  
         [0022]      FIG. 4  illustrates noncontact stabilizers  330  and  335  embodying the principles of the present invention for improving out-of-plane web stability of moving web  310 , in accordance with another embodiment of the present invention. As shown in  FIG. 4 , a printing press  300  has print units  305 - 1  through  305 - n , where n is a predetermined number. For the purpose of clarity, each print unit  305 - 1  through  305 - n  is shown with 4 cylinders: blanket cylinders  315 - 1   a,b  through  315 - na,b , plate cylinders  320 - 1   a,b  through  320 - na,b  and actuators  336 - a,b.    
         [0023]      FIG. 4  shows that print units  305 - 1  and  305 - n  each have all four cylinders rolling and blanket cylinders  315 - 1   a,b  and  315 - na,b  in contact with web  310 . In contrast, print unit  305 - 2  has blanket cylinders  315 - 2   a,b  and plate cylinders  320 - 2   a,b  rolling without contact with web  310 . Web  310  moves from print unit  305 - 1  to print unit  305 - n  in the direction denoted by arrow  325 . As shown in  FIG. 4 , web  310  passes between print unit  305 - 1  and through stabilizers  330  and  335  before passing through print unit  305 - 2 , without experiencing out-of-plane vibrations and without contacting blanket cylinders  315 - 2   a  and  315 - 2   b , in accordance with the present invention.  
         [0024]     In this particular embodiment of the present invention, noncontact stabilizers  330  and  335  are sheets of material which are thin and flexible and positioned on both sides of web  310 . Noncontact stabilizers  330  and  335  are configured so that the distance between web  310  and noncontact stabilizers  330  and  335  decreases in the direction that web  310  travels, as shown in  FIG. 4 .  
         [0025]     Noncontact stabilizers  330  and  335  are positioned on the inlet side of blanket cylinders  315 - 2   a  and  315 - 2   b . One end of each noncontact stabilizer  330  and  335  is moved in between web  310  and blanket cylinders  315 - 2   a  and  315 - 2   b  which improves out-of-plane web stability. Actuators  336  are used to move noncontact stabilizers  330  and  335  in and out of position. For example, when print unit  305 - 2  is in use and in contact with web  310 , actuators  336 - a  and  336 - b  move noncontact stabilizers  330  and  335  away from blanket cylinders  315 - 2   a  and  315 - 2   b  so that blanket cylinders  315 - 2   a  and  315 - 2   b  can be clear to engage web  310 . When print unit  305 - 2  is off impression, blanket cylinders  315 - 2   a  and  315 - 2   b  are moved away from web  310  and actuators  336 - a  and  336 - b  move noncontact stabilizers  330  and  335  in between web  310  and blanket cylinders  315 - 21  and  315 - 2   b , as shown in  FIGS. 4 .  
         [0026]     Referring back to  FIG. 4  when placed near blanket cylinders  315 - 2   a  and  315 - 2   b  or between web  310  and blanket cylinders  315 - 2   a  and  315 - 2   b , the no slip boundary condition at the interface of the air and the surfaces of noncontact stabilizers  330  and  335  force the air velocity at the surfaces to go to zero. This lowers the average velocity and flow rate of air entering the nip region of blanket cylinders  315 - 2   a  and  315 - 2   b  which disrupts the destabilizing forces that would cause web  310  to vibrate out-of-plane. By disrupting the destabilizing forces, greater stabilization is provided and web  310  is able to return to its nominal running position, i.e. without out-of-plane vibrations.  
         [0027]     Referring to  FIG. 5 , noncontact stabilizers  330  and  335  are positioned past the center-line of blanket cylinders  315 - 2   a  and  315 - 2   b . Thus, this embodiment requires actuators  336 - a  and  336 - b  to move noncontact stabilizers  330  and  335  in and out of position. In  FIG. 6 , noncontact stabilizers  330  and  335  are positioned near the nip of blanket cylinders  315 - 2   a  and  315 - 2   b  while web  310  passes through blanket cylinders  315 - 2   a ,  2   b . In this embodiment of the present invention, actuators are not needed because noncontact stabilizers  330  and  335  are fixed and outside the space between blanket cylinders  315 - 2   a  and  315 - 2   b . Sensors  340  can be provided to measure web fluctuation and can be used to fine tune the position of the actuators in  FIG. 6  to reduce fluctuations.  
         [0028]     The surfaces of noncontact stabilizers  330  and  335  force the air velocity at the surfaces to go to zero. As mentioned above, this lowers the average velocity and flow rate of air entering the nip region of blanket cylinders  315 - 2   a  and  315 - 2   b  which disrupts the destabilizing forces that would cause web  310  to vibrate out-of-plane. By disrupting the destabilizing forces, greater stabilization is provided and web  310  is able to return to its nominal running position without out-of-plane vibrations.  
         [0029]     The noncontact stabilizers illustrated in  FIGS. 5 and 6  can be made from flexible materials, such as Mylar, paper or thin sheet metal. Preferably, the noncontact stabilizers are as wide as, or wider than, the web, but do not have to be as wide as web.  
         [0030]     Based on the above disclosure, it is apparent that the principles of the invention can be incorporated into existing printing structures, such as guards and automatic blanket wash systems to achieve the benefits of the invention. In addition, based on the disclosure, it is apparent that the noncontact stabilizers can be located anywhere along the web and anywhere in the printing press where out-of-plane vibrations may occur.