Abstract:
A device is provided for feeding sheets of a sheet stack pressing against front edge stops to a printing cylinder using transport suction devices, which engage a particular uppermost sheet in the area of the sheet rear edge and bring it in a conveyance direction, sheet transport means and sheet acceleration means downstream therefrom being provided between the front edge stops and the printing cylinder. The object of the invention is to provide a device for feeding sheets which occupies little installation space, maybe implemented using simple means, and does not disadvantageously influence the productivity of the machine which processes sheets. The object is achieved according to the invention in that the sheet acceleration means ( 43 ) are directly downstream from the front edge stops ( 7 ).

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims priority to German patent application no. 102008014812.1 filed Mar. 18, 2008, the entirety of which is incorporated herein by reference thereto. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a device for feeding sheets of a sheet stack, pressing against front edge stops, to a printing cylinder, having transport suction devices, which engage a particular uppermost sheet in the area of the sheet rear edge and bring it in a conveyance direction, sheet transport means and sheet acceleration means downstream therefrom being provided between the front edge stops and the printing cylinder. 
       BACKGROUND 
       [0003]    In machines which process rapidly running sheets, it is generally typical to position a sheet stack having the front side on front edge stops in a sheet feeder and to provide a sheet separator in the rear edge area. A presser foot and separation and transport suction devices are accommodated in the sheet separator. The separation suction devices execute a vertical movement and engage the particular uppermost sheet upon their movement toward the top side of the sheet stack and separate it from the following sheet by their movement into the starting position in the rear edge area. An air cushion is built up between the two sheets by additionally provided fans and the sheet held by the separation suction devices is thus completely separated from the following sheet. The sheet held by the separation suction devices is accepted by transport suction devices, which move back and forth, and transported in a conveyance direction. The front edge area of the sheet thus reaches the front edge stops of immediately downstream sheet transport means. A first sheet transport means, which comprises a continuously revolving transport roll and padded rollers assigned thereto, engages the sheet guided by the transport suction devices and conveys it to a second sheet transport means, the sheet being released by the transport suction devices. The transport suction devices move back into their starting position after releasing the sheet to accept the following sheet accommodated by the separation suction devices in the meantime and associate it underlapping with the sheet guided by the first sheet transport means. 
         [0004]    The second sheet transport means is typically implemented as a belt table, preferably as a suction belt table. The second sheet transport means guides the sheets arriving for processing in staggered form onto a laying table, where the particular uppermost sheet of the staggered sheets is transported having the front edge against perceptible laying marks in the path of the sheet, brought to rest, and thus oriented according to the front edge. The stationary sheet is then oriented according to the side edge. The oriented and stationary sheet is grasped by sheet acceleration means, accelerated to printing cylinder velocity, and fed to the printing cylinder. The sheets are typically accelerated by a first sheet acceleration means, which is implemented as a rotating or oscillating pre-gripper, to a fraction of the printing cylinder velocity, and then transferred to a second sheet acceleration means, which implements the printing cylinder velocity and feeds the sheet to the printing cylinder. 
         [0005]    Furthermore, not implementing the target position of the sheets guided to the laying table thereon, but rather performing the orientation according to the front edge and/or side edge on the first and/or second acceleration means is known (DE 3305219 A1, DE 614107). 
         [0006]    The sheet transport means provided between the front edge stops of the sheet stack and the sheet acceleration means are complex and require a large installation space. Furthermore, it is disadvantageous that the sheets held in a defined way in the rear edge area by the transport suction devices are transferred to sheet transport means and transported thereby using friction on the laying table and with the front edge against the laying marks. The danger thus exists that the position of the sheets to one another and/or their position to the machine cycle will be changed, which results in productivity losses. In addition, it is disadvantageous to guide the sheets in staggered form on the laying table and to guide the particular frontmost sheet of the staggered sheets having the front edge against the laying marks, because the danger exists that the drawing sheet, i.e., the sheet grasped by the sheet acceleration means, will entrain the underlapping following sheet at its free end, which results in malfunctions. 
         [0007]    If the second sheet transport means is implemented as a suction belt table, as is generally typical in machines which process sheets, it is problematic and only possible with great effort to meticulously adapt the partial vacuum holding the sheets to be transported to the sheet material arriving for processing. Moreover, additional means must be provided which allow the first sheet of staggered sheets to be reliably accepted from the suction belt table and the last sheet of staggered sheets to be laid having the front edge on the laying marks without interference. 
         [0008]    A sheet feeder according to the species having a specially implemented device for isolating and transporting away flat objects is described in DE 19511296 A1. To be able to adapt the control characteristic of the transport suction devices, in particular the route to be covered in the sheet transport direction and the transport velocity, to the formats of the sheets arriving for processing, it is suggested that the transport suction devices be provided as movable back and forth on linear guides using a drive unit. The route over which the transport suction devices are activated and/or the velocity of the transport suction devices may be varied using a control unit associated with the drive unit. To implement a high number of sheets transported away per unit of time, first and second transport suction devices are provided, to which separate drive units are assigned. The transport suction devices alternately engage an isolated sheet and transport it in the conveyance direction up to the transfer to the sheet transport means. After the sheet transfer, the transport suction devices run back to the sheet acceptance position opposite to the conveyance direction, by pivoting of the guides, the transport suction devices following a path which lies above the path which is described by the transport suction devices during the transport of the sheets in the conveyance direction. 
         [0009]    Furthermore, a device for feeding the sheets of a sheet stack pressing against front edge stops to a printing cylinder is known from EP 0939 738 B1, in which suction devices, which engage the particular sheet to be fed in the area of the sheet front edge above the sheet stack, separate the sheet from the sheet stack, and transport it over a laying table to laying marks, are provided. An oscillating drive is associated with the suction devices and a pre-gripper, which engages the sheet to be fed, accelerates the sheet, and transfers it to the printing cylinder, is situated above the plane of the laying table. 
         [0010]    This device for feeding sheets is only suitable for small-format machines and machines of lower performance, because the suction devices, which separate the particular uppermost sheet from the sheet stack and transport it to the laying marks, may always only engage the following sheet when the free end of the drawing sheet has left the front edge area of the sheet stack. In addition, it is disadvantageous that the sheets isolated from the sheet stack and guided in the area of the front edge by the suction devices into a defined position are guided against the front marks for orientation and released, by which the productivity of the machine which processes sheets is disadvantageously influenced. 
       SUMMARY 
       [0011]    The object of the invention is to provide a device for feeding sheets which occupies a small installation space, is to be implemented using simple means, and does not disadvantageously influence the productivity of the machine which processes sheets. 
         [0012]    The object is achieved according to the invention by a device for feeding sheets ( 2 ) of a sheet stack ( 3 ) pressing against front edge stops ( 7 ) to a printing cylinder ( 49 ) having transport suction devices ( 13 ,  14 ), which engage a particular uppermost sheet ( 2 ) in the area of the sheet rear edge ( 2 . 2 ) and bring it in a conveyance direction ( 18 ), sheet acceleration means ( 43 ) being provided between the front edge stops ( 7 ) and the printing cylinder ( 49 ), characterized in that the sheets ( 2 ) may be fed to the sheet acceleration means ( 43 ) by the transport suction devices ( 13 ,  14 ). 
         [0013]    The achievement of the object according to the invention allows the sheet feeder to be situated directly upstream from the sheet acceleration means and thus to implement a cost-saving and compact construction. In addition, it is advantageous that the sheets isolated in the sheet feeder are fed to the sheet acceleration means in a defined position, by which excess sheets are avoided, a high sheet throughput is made possible, and thus a high working productivity is ensured. 
         [0014]    The invention is explained in greater detail on the basis of an exemplary embodiment and associated drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows the partial illustration of a sheet feeder in the side view. 
           [0016]      FIG. 2  shows the schematic gearing diagram of a mechanism associated with the transport suction device. 
           [0017]      FIG. 3  shows a view along line A-A in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0018]    A sheet feeder  1  having a sheet stack  3  comprising sheets  2  is shown in  FIG. 1 . The sheet stack  3  is built up on a stack plate  4 , on which traction means  5  engage, which are connected to a drive, which is associated with a frame  6  of the sheet feeder  1 . The sheets  2  of the sheet stack  3  have a sheet front edge  2 . 1  pressing against stop faces  7 . 1  of front edge stops  7  situated distributed spaced apart from one another over a maximum format width. A sheet flap  8 , which also extends over the format width and which is mounted using a flap shaft  9  and may be pivoted clockwise or counterclockwise by means (not shown), is provided at the upper end of the front edge stops  7 . Separation suction devices  10 , which execute a movement directed up and down in the machine cycle, and a presser foot  11 , which also executes a movement directed up and down, which has a pivot movement superimposed, are provided in the area of the sheet rear edges  2 . 2  of the sheets  2  of the sheet stack  3 . Furthermore, fans  12  directed toward the sheet rear edges  2 . 2  are provided. 
         [0019]    First transport suction devices  13  are situated downstream from the separation suction devices  10  in a conveyance direction  18 . The first transport suction devices  13  are each situated using a sliding block  15  on a first guide rail  16  and are provided distributed spaced apart over the format width of the sheets  2  arriving for processing. The first guide rails  16  extend parallel to the surface of the sheet stack  3  and run in the conveyance direction  18 . A first pushrod  21 , which is connected to a first push crank  23 , engages on a first suction device rod  19  connecting the first transport suction devices  13 . The first push crank  23  is associated rotationally fixed with a first driveshaft  25 , which is driven at a single speed in the operating cycle. For this purpose, the first driveshaft  25  is connected via a toothed belt  29 , for example, to a first motor  27  ( FIGS. 1 and 3 ). 
         [0020]    To allow the first transport suction devices  13 , which describe a sheet conveyance plane  30  upon the movement in the conveyance direction  18 , to be guided above this sheet conveyance plane  30  during a movement opposite to the conveyance direction  18 , the first guide rails  16  may be accommodated so they are pivotable by a bearing shaft  31  situated in the area of the sheet rear edges  2 . 2 . A first roller lever  34 , which runs using a first cam roller  36  on a first cam disk  38 , which is connected rotationally fixed to the first driveshaft  25 , engages on the free end of a guide rail  16  via a first connecting rod  32 , by which the first guide rails  16  may be raised and lowered in the operating cycle. 
         [0021]    It is also possible to provide second transport suction devices  14  in addition to the first transport suction devices  13  and use the transport suction devices  13 ,  14  alternately. For this purpose, second guide rails  17 , which are assigned pivotably at one end to the bearing shaft  31 , are provided between the first guide rails  16 . A second transport suction device  14  is provided on each second guide rail  17  using a sliding block  15 . The second transport suction devices  14  are connected by second suction device rods  20 , on which a second pushrod  22  engages, which is connected to a second push crank  24 . The second push crank  24  is associated rotationally fixed with a second driveshaft  26 , which is driven at half speed by a second motor  28  via a toothed belt  29 . If second transport suction devices  14  are provided, it is necessary to also drive the first driveshaft  25  at half speed by the first motor  27 . 
         [0022]    If second transport suction devices  14  are used, they must be guided above the sheet conveyance plane  30  described by the transport suction devices  13 ,  14  during the movement opposite to the conveyance direction  18 . For this purpose, a second connecting rod  33 , which is connected to a second roller lever  35 , engages on a free end of the second guide rail  17 . A second cam roller  37 , which runs on a second cam disk  39 , is mounted in the second roller lever  35 . The second cam disk  39  is connected rotationally fixed to the second driveshaft  26 , which is connected via the toothed belt  29  to the second motor  28 . 
         [0023]    A sheet routing device  40 , which comprises upper sheet routing means  41  and lower sheet routing means  42 , is associated with the sheet conveyance plane  30  in the front area. The sheet routing device  40  extends up to sheet acceleration means  43  immediately downstream from the front edge stops  7 . The sheet acceleration means  43  are implemented in such a way that they accelerate the sheet  2 , i.e., increase its transport velocity, and transfer it accelerated to a downstream system. The downstream system is implemented in the exemplary embodiment as a laying drum  45 . In the exemplary embodiment, an oscillating pre-gripper  44  and a laying drum  45  are provided as the sheet acceleration means  43 . However, a revolving pre-gripper drum may also be provided instead of the pre-gripper  44 . The pre-gripper  44 , which has a sheet holding means, which comprises grippers  47  working together with an impact strip  46 , is additionally equipped with laying marks  48 . The laying drum  45  downstream from the pre-gripper  44  is provided with sheet holding systems, which are implemented as displaceable in the axial direction to implement a lateral edge orientation. A printing cylinder  49  is downstream from laying drum  45 . 
         [0024]    In a known way, the sheets  2  are situated on the stack plate  4  to form the sheet stack  3 , the sheet front edge  2 . 1  of the sheets  2  pressing against the stop faces  7 . 1  of the front edge stops  7 . The top side of the sheet stack  3  is continuously kept at an operating level by a drive engaging on the traction means  5 . The uppermost sheet  2  is grasped by the separation suction devices  10 , which are positioned in the area of the sheet rear edge  2 . 2  and controlled toward the surface of the sheet stack  3 , and separated from the following sheet by the movement of the separation suction devices  10  into their starting position in the area of the sheet rear edge  2 . 2 , the presser foot  11  being pivoted out of the profile of the sheet stack  3 . Using the fans  12  and the presser foot  11 , which is pivoted back into the profile of the sheet stack  3 , an air cushion is built up between the sheet  2  held by the separation suction devices  10  and the following sheet, the sheet flap  8  forming a linear extension of the front edge stops  7 , so that the sheet  2  is separated from the following sheet over its entire area. The upper sheet routing means  41  of the sheet routing device  40  ensure the position of the free end of the sheet  2 . The first transport suction devices  13  then engage the sheet  2  held by the separation suction devices  10 , and are directly associated with the separation suction devices  10 . The sheet  2  is released by the separation suction devices  10  and the sheet flap  8  is pivoted counterclockwise, the sheet flap  8  forming an inlet funnel with the lower sheet routing means  42  and the upper sheet routing means  41 . The first transport suction devices  13 , which are situated on the first guide rails  16  by sliding blocks  15 , are then displaced via the first pushrod  21  and the first push crank  23 , which engages on this pushrod and is connected rotationally fixed to the first driveshaft  25 , in the conveyance direction  18 . The route implemented by the first transport suction devices  13  in the conveyance direction  18  is so large that the sheet front edge  2 . 1  of the sheet  2  held by the first transport suction devices  13  is guided against the laying marks  48  of the pre-gripper  44 , which is in a detent position. The sheet  2  is then accepted by the pre-gripper  44 , in that the grippers  47  are guided against the stop strip  46 , and released by the first transport suction devices  13 . The pre-gripper  44  is accelerated and the sheet  2  is fed to the laying drum  45  for transfer to the printing cylinder  49 . 
         [0025]    After the laying of the sheet  2  with the front edge  2 . 1  on the laying marks  48  and the release by the first transport suction devices  13 , after passing through a reversal position, the boxes are returned back to the separation suction devices  10  to accept a sheet  2  which has been isolated in the meantime. If a pre-gripper  44  is provided, which passes through a detent position to accept a sheet  2 , this sheet  2  is laid on the laying marks  48  by the first transport suction devices  13  immediately before passing through the reversal position. If a pre-gripper drum which rotates continuously at an alternating velocity is provided, the sheet  2  conveyed by the first transport suction devices  13  is then laid on the laying marks  48  when its velocity is slightly higher than the peripheral velocity of the laying marks  48 . 
         [0026]    If, in the event only first transport suction devices  13  are used, it is desirable for the first transport suction devices  13  to be returned to the separation suction devices  10  on a path which runs above the sheet conveyance plane  30 , the first guide rails  16  associated pivotably with the bearing shaft  31  may be raised and lowered by the first roller lever  34 , which is controlled by the first cam disk  38  and is connected to the first guide rails  16  using the first connecting rod  32 . 
         [0027]    If a high sheet throughput is to be implemented, it is possible to provide the second transport suction devices  14  in addition to the first transport suction devices  13 , the transport suction devices  13 ,  14  being driven at half speed by the motors  27 ,  28  and the mode of operation of the second transport suction devices  14  and their drive occurring similarly to that of the first transport suction devices  13 . If the first and second transport suction devices  13 ,  14  are used, it is necessary, to allow an interference-free transport of the sheets  2  and/or avoid a collision of the transport suction devices  13 ,  14 , to implement the movement of the transport suction devices  13 ,  14  after the laying of the sheets  2  with the sheet front edge  2 . 1  on the laying marks  48  on a path toward the separation suction devices  10  which runs above the sheet conveyance plane  30 . In addition, to allow collision-free operation of the device, it is necessary for the first suction device rods  19  connecting the first suction devices  13  and the second suction device rods  20  connecting the second suction devices  14  to be implemented in such a way that an interference-free return of the transport suction devices  13 ,  14  on the path situated above the sheet conveyance plane  30  is possible during the transport of the sheets  2  by the first transport suction devices  13  or second transport suction devices  14 . 
         [0028]    To allow a secure contact of the sheet front edges  2 . 1  on the laying marks  48  independently of the longitudinal format of the sheets  2  arriving for processing within a format range, the separation suction devices  10 , the presser foot  11 , the transport suction devices  13 ,  14 , and possible further operating elements as well as the associated drives are assembled into a functional unit, which may be displaced in or opposite to the conveyance direction  18 . 
         [0029]    In the exemplary embodiment, to be able to implement such a stroke of the transport suction devices  13 ,  14 , which allows the sheets  2  located on the sheet stack  3  and isolated by the separation suction devices  10 , to be fed directly to the sheet acceleration means  43  without additional sheet transport means using the transport suction devices  13 ,  14 , a first push crank gear  50  and a second push crank gear  51  are associated with the transport suction devices  13 ,  14 . The push crank gears  50 ,  51  comprise the sliding blocks  15 , guide rails  16 ,  17 , pushrods  21 ,  22 , push cranks  23 ,  24 , and driveshafts  25 ,  26 . The transport suction devices  13 ,  14  may also be driven by other mechanisms which generate a sufficient stroke to feed the sheets  2  grasped in the area of the rear edge  2 . 2  from the sheet stack  3  directly to the sheet acceleration means  43 . Thus, for example, the transport suction devices  13 ,  14  situated on the guide rails  16 ,  17  may also be directly associated with drives which generate a translational movement, such as linear motors, hydraulic drives, or pneumatic drives, the transport suction devices  13 ,  14  also being able to take over the additional function of separating the sheets  2  from the sheet stack  3 . 
         [0030]    To ensure the processing of taller sheet stacks in spite of the direct feed of sheets  2  held by the transport suction devices  13 ,  14  in the area of the sheet rear edge  2 . 2  to the sheet acceleration means  43 , it is advantageous to situate a tall version add-on assembly according to DE 4343614 B4 having three drums situated offset in height and an oscillating facility upstream from the printing cylinder  49 . 
         [0031]    Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be applied therein by one skilled in the art without departing from the scope or spirit of the invention.