Abstract:
A folder is adapted to fold sheets. A drum having a circumferential surface is adapted to withdraw sheets from a stack or from an overlapping flow and feed the sheets to the folder. A creasing apparatus is operatively arranged with the drum and includes: a first creasing wheel which cooperates with the drum to crease the withdrawn sheets that are fed to the folder, and a tracing wheel positioned at least axis parallel with the first creasing wheel and running on the circumferential surface of the drum to maintain a constant distance between the first creasing wheel and the circumferential surface of the drum.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
   This application claims the priority of European Patent Application No. EP 06405154, filed on Apr. 10, 2006, the subject matter of which is incorporated herein by reference in its entirety. 
   BACKGROUND 
   The present invention relates to a folder feeder provided with a drum and used, for example, for withdrawing sheets and in particular printed sheets from a stack to feed the withdrawn sheets to a folder. The folder feeder comprises a first creasing wheel and a second creasing wheel that is arranged on the drum, which operates jointly with the first creasing wheel to crease the withdrawn sheets. 
   A folder feeder of this type is disclosed, for example, in European patent document EP-A-1 247 775 the disclosure of which is incorporated herein by reference. Printed sheets are pulled individually from a stack with a suction device and grippers and are folded on a folding sword during the continuous operation. The folded sheets are then deposited on a gathering chain where they are picked up by pushers. To obtain a sharp and if possible complete and closed fold, the pulled-off sheets are creased prior to the folding operation. The creased sheets are folded during the continuous operation on a folding sword, along the groove formed by the creasing. The quality of the fold depends on the quality of the creased groove. A creased groove that is not uniformly deep or is interrupted can result in a fold that is not sharp, is not complete, or is not closed. The folded sheets are subsequently used for producing print products such as brochures, magazines, catalogues, or books, meaning that in the final analysis, the quality of these print products also depends on the sheet fold quality. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a folder feeder which allows producing a higher-quality fold while still ensuring a high output and operational safety. 
   The above object and other objects are accomplished according to the invention, which in one embodiment comprises a folder feeder, comprising: a folder adapted to fold sheets; a drum having a circumferential surface and adapted to withdraw sheets from a stack or from an overlapping flow and feeding the sheets to the folder; and a creasing apparatus operatively arranged with the drum and including: a first creasing wheel which cooperates with the drum to crease the withdrawn sheets that are fed to the folder, and a tracing wheel positioned at least axis parallel with the first creasing wheel and running on the circumferential surface of the drum to maintain a constant distance between the first creasing wheel and the circumferential surface of the drum. 
   The first creasing wheel is positioned on a tracing wheel, which moves on the second creasing wheel and is pressed with a spring force against a running surface of the second creasing wheel, thereby maintaining a uniform distance between the first creasing wheel and the circumferential surface of the second creasing wheel. A creasing wheel is understood to be a wheel used for creasing sheets. 
   The tracing wheel effectively balances out any untrue running of the second creasing wheel, which can be caused in particular by a high output by an unbalancing force, an untrue shape, or an eccentric movement of the drum. The first creasing wheel extends with its creasing edge to a uniform depth in the groove of the second creasing wheel, thereby ensuring that the formed crease has a uniform depth. The shaft of the first creasing wheel is thus at a constant distance to the circumferential surface of the second creasing wheel. Since the first creasing wheel is continuously pressed against the second creasing wheel, any untrue running or eccentricity of the second creasing wheel is balanced out immediately. As a result, it is possible to crease and fold sheets for which the weight varies considerably, for example ranging from 70 g/m 2  to 260 g/m 2 , wherein the groove depth can be 0.02 mm. As a result of the aforementioned balancing operation, the production tolerance requirements and thus the production costs for the folder feeder can be lowered. 
   According to one embodiment of the invention, the first creasing wheel is positioned so as to be adjustable on the tracing wheel. An eccentric cam may be used to position the first creasing wheel on the tracing wheel, thereby making it easy to adjust the spacing between the first creasing wheel and the circumferential surface of the second creasing wheel and thus the depth of the groove. 
   According to another embodiment of the invention, the first creasing wheel and the tracing wheel form an integral unit that is positioned via an arm on a rod, wherein the rod extends parallel and at a distance to the shaft of the second creasing wheel and/or the drum. As a result, the first creasing wheel and the tracing wheel are positioned substantially stable and operationally safe. 
   According to another embodiment of the invention, an adjustment device may be used for adjusting the contact pressure of the first creasing wheel, wherein the use of a Bowden wire that acts upon the aforementioned extension arm permits an easy and precise adjustment. 
   The sheets may be conveyed substantially vertically during the creasing operation, wherein the sheets are picked up with a gripper drum and are guided between belts. 
   Additional advantageous features follow from the following description, as well as the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the invention will be further understood from the following detailed description with reference to the accompanying drawings in which: 
       FIG. 1A  schematic view of a folder feeder according to an embodiment of the invention; 
       FIG. 2  A sectional view along the line II-II in  FIG. 3 ; 
       FIG. 3  A partial view of the folder feeder according to the invention, in particular illustrating the positioning of the creasing wheel; 
       FIG. 4  A partial sectional view of a portion of the folder feeder according to an embodiment of the invention, and 
       FIG. 5  A partial view of  FIG. 4  on an enlarged scale. 
   

   DETAILED DESCRIPTION 
   The folder feeder  1  shown in  FIG. 1  is provided with a drum  7 , which is driven by a shaft  9  in a clockwise direction. The drum  7  is provided with at least two drum wheels  57 , arranged at a distance to each other. Each drum wheel  57  is provided along the circumference with a respective movable gripper  8  and a suction device  34 , which are used for pulling the sheets  4  from a stack  3  positioned inside a magazine  5 . In one embodiment, the sheets are pulled form an overlapping flow. When the drum  7  rotates, the lowest sheet  4  in the stack  3  is gripped and moved downward in clockwise direction. The individually pulled-off sheets  4  are guided between conveying belts  23  (shown in  FIG. 2 ). 
   Each conveying belt  23  is guided by a roll bearing  22  around a rod  19  that is fixedly attached to a frame. The sheets  4  are printed sheets, for example, intended for producing magazines, brochures, or books. 
   The pulled-off sheets  4  are supplied individually to a folding device  6 , comprising a folding sword  39 , which extends at an angle and is tangential to the drum  7 . A round chord  36 , which is fitted around two spaced-apart rolls  37  and  38 , is positioned on the folding sword  39 . The round chord  36  operates jointly with a folding belt  35 , which is driven in the direction of arrow  42 . The pulled-off sheets  4  disposed on the folding sword  39  are taken over by the round chord  36  and the folding belt  35  from the conveying belts  23  and folded between folding rolls  44 . The individual folding locations are pressed again with pressing rolls  41 . The sheets  4  are released individually via a sword extension  40 , for example, to a conveying device  2  of a gathering and wire-stitching machine (not shown). The folded sheets are picked up by pushers  52  and moved in the direction of arrow  43 . The sheets  4  are positioned straddling on the conveying device of the gathering and wire-stitching machine, with the fold pointing upward. 
   Before the sheets  4  are individually guided onto the folding sword  39 , the sheets are creased in the transporting direction by a creasing apparatus that includes a first creasing wheel  17  and a creasing device  10 , as shown in  FIG. 4 . The creasing device  10  is fixedly mounted on the drum  7 . The first creasing wheel  17  is driven in a counterclockwise direction as shown in  FIG. 1 . The creasing device  10  includes a second creasing wheel  10   a  having a cylindrical circumferential surface  11  including a circumferential groove  13  as shown in  FIG. 5 . At a distance to the groove  13 , the circumferential surface  11  includes a running surface  12  for a tracing wheel  15 , which is positioned rotatingly on an arm  21 . According to  FIGS. 2 and 3 , the arm  21  is connected to the rod  19 , which is attached with its ends and the flanges  20  to a machine frame (not shown). The tracing wheel  15  is positioned via a roller bearing  26  on a shaft  28  which, in turn, is positioned via a bearing  27  on the extension arm  21 . The tracing wheel  15  has a cylindrical circumferential surface  45 , which is pressed resiliently against the running surface  12  with a tensioning device  30 .  FIG. 3  shows that the contact force is generated by a spring  33 , which sits on a nut  53  that is screwed onto a cylindrical screw  46 . The nut  53  is supported via a part  54  on a frame  55  that is only indicated herein. An elongated hole  56  makes it possible to adjust the tension of spring  33 . The tensioned spring  33  acts via a holder  31  of the tensioning device  30  onto the extension arm  21 . The holder  31  is fixedly connected to the extension arm  21  and extends approximately at a right angle thereto. As shown in  FIG. 3 , the contact force acts in the direction of arrow  47 , wherein the rod  19  forms the rotational shaft. As a result of the contact force, the tracing wheel  15  is pressed with an adjustable constant force against the second creasing wheel  10   a  of the creasing device  10 . 
   According to  FIG. 2 , the shaft  28  is connected via an eccentric connection  16  to a shaft  18  on which the tracing wheel  15  is positioned rotating with a roller bearing  25 . The first creasing wheel  17  is provided in the circumferential direction with a creasing edge  24 . As shown in  FIG. 5 , the creasing edge  24  extends at a uniform depth into the groove  13  when the tracing wheel  15  is pressed on running surface  12 . For example, the depth of the groove  13  is about 0.02 mm. In one embodiment, a ridge is used instead of the groove  13 . The first creasing wheel  17  is provided with a corresponding circumferential groove in place of the creasing edge  24 . The first and second creasing wheels  17 ,  10   a  may be embodied so that the sheets  4  that pass through are perforated. According to an alternative embodiment, a perforation device may be arranged adjacent at least the first creasing wheel  17 , to perforate the sheets parallel to a folding edge. 
   The pulled-off sheets  4 , which are conveyed substantially vertically, are creased while passing between the creasing device  10  and the first creasing wheel  17 . The tracing wheel  15  in the process runs off the respectively withdrawn sheet  4 , which is pressed against the circumferential surface  11  as a result of the pressure exerted by the tracing wheel  15 . The first creasing wheel  17  rotates passively around the shaft  18 , for which the distance to the circumferential surface  11  and/or the groove  13  is kept uniform by the tracing wheel  15 . The running surface  12  is the reference surface, which extends concentric to the groove  13 . As a result of the connection  16 , the first creasing wheel  17  follows the re-adjustment movements of the tracing wheel  15 , thereby balancing out any untrue movement or eccentricity occurring as a result of the production. The engagement of the first creasing wheel  17  in the groove  13  is thus kept constant. The formed groove and/or the perforation in the withdrawn sheet  4  is kept at a uniform depth. Because of the eccentric connection between the tracing wheel  15  and shaft  18 , the distance between the shaft  18  and the circumferential surface  11  may be adjusted, thereby making it possible to precisely adjust the creasing depth. 
   The creased sheets  4  are transferred to the folder  6 , as explained above, in which the sheets  4  are folded along the pre-formed crease by pressing between the folding rolls  44 . 
   The contact pressure of the tracing wheel  15  against the second creasing wheel  10   a  may be adjusted, as shown in  FIG. 3 , with an adjustment device  14  that comprises a Bowden wire  29 . The Bowden wire  29  acts with a chord  49  upon a spring  32 , which is connected to the holder  31 . The Bowden wire  29  is attached to a support  50 , mounted fixedly on a frame, and may be operated with a manual wheel (not shown). The guide sleeve  51  for the Bowden wire  29  is connected via a holder  48  to the arm  21 . A counter pressure is built up on the spring  33  for tensioning the spring  32  by the Bowden wire  29 , thereby reducing the contact pressure exerted by the tracing wheel  15  onto the second creasing wheel  10   a . The contact pressure may also be increased by reversing the steps. 
   The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.