Abstract:
A folder for a web printing press includes a cut cylinder cutting a web into signatures; a first transport belt having a first raised section; a second transport belt having a second raised section, the signatures being received from the cut cylinder so as to be located between the first and second raised sections; and at least one variable speed motor driving the first and second transport belts. A method is also provided.

Description:
[0001]    The present invention relates generally to folders for web printing presses. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many folders used in web printing presses use driven belts or tapes to transport signatures from the cut cylinder to the next operation, such as signature deceleration or folding. These tapes contact the web or ribbons before the signature is created and have a velocity higher than that of the ribbon. The velocity difference causes relative motion (scrubbing) between the ribbons and tapes. 
         [0003]    After a signature is created by the cut cylinder, the signature is accelerated by the tapes from ribbon or web speed, which generally matches the surface speed of the cut cylinder as well, to tape speed. The rate of signature acceleration depends on the mass of the signatures and on the normal force and coefficient of friction between the tapes and signatures. Variations in these factors cause position variations in the signatures when they reach the next device, such as a fan or jaw cylinder. Position variations include: signature-to-signature variation at a given press speed, variations due to press speed changes, and variations over time due to, for example, tape wear. Position variations cause the following problems: reduced maximum allowable press speed, increased need for manual phase adjustments, machine damage, and press downtime due to jammed signatures. Such problems are worse in variable cutoff applications and become worse as press speeds increase. 
         [0004]    U.S. Pat. No. 4,919,027 shows a sheet diverting system and U.S. Pat. No. 6,612,213 shows a belt diverter. Both are hereby incorporated by reference herein. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a folder for a web printing press comprising: a cut cylinder cutting a web into signatures; a first transport belt having a first raised section; and a second transport belt having a second raised section, the signatures being received from the cut cylinder so as to be located between the first and second raised sections; and at least one variable speed motor driving the first and second transport belts so as to accelerate the signatures. 
         [0006]    By providing raised belt sections and acceleration, head-to-tail spacing can be created while the signatures remain under positive control. 
         [0007]    The present invention also provides a method for delivering signatures cut from a web comprising: receiving the signatures at a ribbon speed under positive control between two belts; and accelerating the two belts to create a spacing between the signatures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    One embodiment of the present invention is shown with respect to the drawings in which: 
           [0009]      FIG. 1  shows a folder section including cut cylinders, a transport system, and slowdown fans; 
           [0010]      FIG. 2  shows an enlarged view of the transport system; and 
           [0011]      FIGS. 3A and 3B  are plots of belt pad velocity as a function of time. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  describes a folder section  10  according to the present invention, having an incoming web or ribbon  12 , nip rollers  14 , a first cut cylinder  16  interacting with a first anvil cylinder, a second cut cylinder  18  interacting with a second anvil cylinder, a transport system  20 , and slowdown fans  22 ,  24 . Transport system  20  includes tapes  26 ,  28  driven by a motor  30 , and positive control transport belts  32 ,  34  driven by motors  36 ,  38 . First cut cylinder  16  creates first perforations in ribbon  12 , and second cut cylinder  18  creates signatures by cutting between the perforations. Transport system  20  delivers the signatures to slowdown fans  22 ,  24 . 
         [0013]      FIG. 2  shows transport system  20  schematically in more detail. Perforated ribbon  12  enters transport system  20  traveling at velocity V 1 . The lead edge of ribbon  12  is guided loosely by belts  26 ,  28  traveling at a higher velocity V 2 , but is not positively gripped by the belts  26 ,  28 . 
         [0014]    Ribbon  12  then is contacted by belt pads  40 ,  42 . Belt pads  40 ,  42  are driven by motor  48  and, when belt pads first close on ribbon  12 , belt pads  40 ,  42  are also traveling at velocity V 1 . Cut cylinder  18  then cuts a signature from ribbon  12  with a knife blade  50 . Motor  48  then accelerates the signature and pads  40 ,  42  to velocity V 2  of tapes  26 ,  28 . The signature is then transported from pads  40 ,  42  to tapes  26 ,  28  for continued transportation to fans  22 ,  24 . Alternately, rather than being delivered to fans  22 ,  24 , signatures could be delivered to a jaw cylinder, for example. 
         [0015]    When a signature is first created by cut cylinder  18 , a trailing edge  52  of the new signature is contacting a leading edge  54  of ribbon  12 . By accelerating each signature in transport system  20  from V 1  to V 2 , a head-to-tail distance L between consecutive signatures is advantageously created for delivery of the signatures to fans  22 ,  24 . 
         [0016]    Pads  40 ,  42  have positive control over the signature to prevent slipping between pads  40 ,  42  and the signature. Positive control advantageously minimizes position variations in signatures at the exit of transport system  20 . 
         [0017]    Transport belts  32 ,  34  may contain two sets of pads  40 ,  42  and  44 ,  46 . Each set of pads  40 ,  42  and  44 ,  46  contacts every other signature and each belt  32 ,  34  can be driven by separate motors  48 ,  56 . The spacing of the pads is such that the pads  40 ,  42  do not influence the signature contacted by the pads  44 ,  46  (and visa versa). 
         [0018]    After releasing a signature and prior to contacting a subsequent signature, each set of pads  40 ,  42  and  44 ,  46  is decelerated on return paths  58 ,  60  to velocity V 1  by variable speed motors  48 ,  56 . Then pads  40 ,  42  and  44 ,  46  contact ribbon  12  again, and the process is repeated. 
         [0019]      FIGS. 3A and 3B  contain plots of velocity versus time for belt pads  40 ,  42  and belt pads  44 ,  46 , respectively, during the creation of two consecutive signatures. In these figures, belt pads  40 ,  42  contact and accelerate the first signature, and belt pads  44 ,  46  contact and accelerate the second signature. The first signature is created by cut cylinder  18  at time t 1  and the second is created by cut cylinder  18  at time t 3 . 
         [0020]    Variable speed motors, such as servo motors available from Siemens Corporation, can be used to provide such velocity variation. 
         [0021]    As shown in both  FIGS. 3A and 3B , the velocity of belt pads  40 ,  42  and  44 ,  46  oscillates between ribbon velocity V 1  and tape velocity V 2 . In  FIG. 3A , at time t 1 , the velocity of belt pads  40 ,  42  equals ribbon velocity V 1 . Belt pads  40 ,  42  then accelerate the first signature and reach tape velocity V 2  at time t 2 . Belt pads  40 ,  42  and signature A (SA) remain at velocity V 2  until time t 3  when belt pads  40 ,  42  deliver the first signature to tapes  26 ,  28  and begin to decelerate. Belt pads  40 ,  42  reach ribbon velocity V 1  at time t 4  and remain at velocity V 1  until time t 5  when a new signature is created and the process repeats. 
         [0022]    As shown in  FIG. 3B , the velocity of belt pads  40 ,  42  is the mirror image of the velocity of belt pads  44 ,  46 . At time t 1 , belt pads  44 ,  46  deliver a preceding signature to tapes  26 ,  28  at velocity V 2  and begin to decelerate. Belt pads  44 ,  46  reach velocity V 1  at time t 2 . When the second signature is created at time t 3 , belt pads  44 ,  46  accelerate the second signature and reach velocity V 2  at time t 4 . Belt pads  44 ,  46  and signature B (SB) remain at velocity V 2  until the second signature is delivered at time t 5 . 
         [0023]    Belt pad velocity profiles are not limited to those shown in  FIGS. 3A and 3B . Alternately, these velocity profiles could be sinusoidal or piece-wise linear, for example. Varying the velocity profiles can set the spacing between signatures. 
         [0024]    A single variable motor and gearing could also be used for the belts  32 ,  34 .