Abstract:
An apparatus for supplying a shingled or overlapping sheet stream from a stack of sheets of a sheet feeder to a feed table of a sheet-processing machine with a belt table. The belt table is provided with at least one revolvingly driven suction belt in operative connection with at least two suction chambers, which can be acted upon by negative pressure, as well as means for taking hold of the sheets. After the last sheet of the sheet stream is detected and the front edge of the last sheet has been placed against the front guide stop, the operation of the suction belt can be stopped. The apparatus allows the last sheet of a sheet steam be aligned without problems, regardless the material of the sheets to be processed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to an apparatus for supplying a shingled or overlapping sheet stream from a stack of sheets of a sheet feeder to a feed table of a sheet-processing machine.  
         [0002]     Such devices are generally known. The sheets, segregated from a stack of sheets by a sheet feeder, are transported as a shingled or overlapping sheet stream on a belt table having suction belts, are taken hold of there by the suction belts and are transported to the feed table. At the same time, in the region where the sheets are taken over, the suction belts are acted upon with a negative pressure by a suction chamber facing the sheet feeder. At the same time, in the region of sheet transfer on the feed table, the suction belts are acted upon with negative pressure by a suction chamber facing the machine. The front sheet of the sheet stream is guided on the feed table with the front edge against front guide stop and thus is aligned with the font edge. Subsequently, the sheet is aligned, for example, with the side edge. During the alignment of the front sheet, the latter must be guided by the suction belt by a holding force, so that the front edge is not damaged while the sheet is fed to the front guide stop and thus lateral alignment is possible without problems. This becomes feasible owing the fact that, due to the under-shingled subsequent sheet, the suction belts are covered completely or almost completely, so that the sheet, which is to be aligned, is guided only with a slight holding force in the transfer region. If there is no subsequent sheet, for example, when the sheet stream is interrupted, the holding force acting on the last sheet to be aligned, during the processing of paper, presents a potential danger of damage to the front end of the sheet and an accurate lateral alignment is not possible.  
         [0003]     In order to eliminate this disadvantage, it is proposed in EP 0 554 774 B1 that the supplying of the last sheet of the sheet stream be detected. When the final sheet in the stream reaches the alignment end, the supply of negative pressure to the suction chamber facing the machine is interrupted and this suction chamber is connected with a source of positive pressure. This device cannot be used for thin printing paper, since there is no defined guiding of the last sheet to the front guide stop.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the invention to change a generic device so that, independently of the material that is to be processed, the last sheet of a sheet stream can also be aligned without problems.  
         [0005]     Pursuant to the invention, this objective is accomplished by an apparatus for supplying a shingled or overlapping sheet stream from a stack of sheets of a sheet feeder to a feed table of a sheet-processing machine with a belt table, which is provided with at least one revolvingly driven suction belt, which is in operative connection with at least two suction chambers, which can be acted upon by negative pressure, as well as means for tag hold of the sheets, characterized in that, after a last sheet of the sheet stream is detected and the font edge of the last sheet has been placed against the front guide stop or stops, the operation of the suction belt can be stopped.  
         [0006]     The inventive solution enables the last sheet of a shingled sheet stream to be placed against the front guide stop or stops independently of the nature of the material. Thus, it is ensured that the entirety of the material reaching the processing stage is processed defect-free. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]     The FIGURE illustrates the apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]     The present invention can be better understood from the following description of preferred embodiments, taken in conjunction with the accompanying drawings. It should be apparent to those skilled in the art that the described embodiments of the present invention provided herein are merely exemplary and illustrative and not limiting. All features disclosed in the description may be replaced by alternative features serving the same or similar purpose, unless expressly stated otherwise. Therefore, numerous other embodiments of the modifications thereof are contemplated as falling within the scope of the present invention and equivalents thereto.  
         [0009]     The invention is explained in greater derail by means of an example. In the associated drawing, a belt table  1  with a downstream feed table  2  is shown diagrammatically in side view. The belt table  1  has at least one suction belt  3 , which is guided over an upper guide roller  4  and a lower guide roller  5  and tensioned by means of two rollers  6 . An upper suction chamber  7  facing a sheet feeder, which is not shown, and a lower suction chamber  8 , facing a sheet-processing machine, which is also not shown, are disposed in the belt table  1 . Further suction chambers may be disposed between suction chambers  7 ,  8 . The upper suction chamber  7  is connected over a suction connecting piece  9  with a first source of negative pressure, which is not shown and the lower suction chamber  8  is connected over a suction connecting piece  10  with a second source of negative pressure, which is not shown. A servo unit  11 , which opens or closes the suction connecting piece  10 , is disposed at the suction connecting piece  10 . Furthermore, an air-removing flap  12 , which can be actuated by means of a servo device  13 , is disposed at the lower suction chamber  8 .  
         [0010]     The feed table  2 , of which a table sheet  14  is shown, is downstream from the belt table  1 . A front guide stop  15  is shown in a position at the feeder table  2 . The front guide stop  15  can be brought in a working cycle from a position at the feed table  2  into a position swiveled away from the feed table  2 . A sheet  17 , which is to be aligned and which is followed by a sheet  18  as the last sheet  19 , is shown lying in contact with the front guide stop  15 . Furthermore, a double-sheet control  16  is provided ahead of the lower guide roller  5  and a sponging roller, operating at a time cycle, is assigned to the upper guide roller  4 . The suction belt  3  is driven in a sheet-transporting direction  25  by a driving unit  20 , which is assigned to the upper guide roller  5 . The driving unit  20  is connected with a control unit  21 , which is linked with the servo unit  11 , the servo device  13  and the double-sheet control  16 . The machine control  22  and an input unit  24  are also connected with the controlled unit  21 .  
         [0011]     The sheets, segregated by the sheet feeder, are supplied shingled to the belt table  1  and, supported by the sponging roller  23  guided in the working cycle against the upper guide roller  4 , taken hold of by the suction belt  3 . The holding force, acting on the sheets, is realized by the negative pressure, which is built up in the upper suction chamber  7  by means of the source of negative pressure connected with the suction connecting piece  9  The sheets are conveyed in the sheet-transporting direction  25  as a sheet stream by the suction belt  3 , driven by the driving unit  20 , the front sheet of the sheet stream being transported as a sheet  17 , which is to be aligned on the feed table  2  and with tie front edge against the front guide stop  15 . At the same time, the holding force, acting on the sheet  17  to be aligned and generated from the negative pressure existing in the lower suction chamber  8 , is minimized or eliminated completely by the underlapping of the following sheet  18 . Thus, the sheet  17 , which is to be aligned, can be placed without problems against the front guide stop  15  and, subsequently, likewise optionally aligned at the side edges. After it is aligned, the sheet  17  is pulled off by means not shown and transported downstream to the next sheet-processing machine. Simultaneously with the pulling off of the sheet  17  that is to be aligned, tie next sheet  18  is conveyed in the sheet-transporting direction  25 .  
         [0012]     Depending on the position on the belt table  1  as well as the staggered distances of the underlapped sheet stream, if a single sheet is detected instead of a double or triple sheet, the single sheet is recognized as the last sheet of the sheet stream and a signal is generated. Preferably, the double-sheet control  16  is assigned to the belt table  1  in such a manner that it takes hold of the sheet  17 /subsequent sheet  18  and/or a further sheet, to align the underlapping sheet(s).  
         [0013]     The signal, generated by the double-sheet control  16 , is supplied to the control unit  21 . Thus, the last sheet  19  is recognized and the number of sheets between the front guide stop  15  and the last sheet  19 , or the number of operating cycles which must be realized before the last sheet  19  lies against the font guide stop  15  as a sheet  17  to be aligned, is determined. If the sheet, referred to as the subsequent sheet  18  in the pictorial representation, is determined to be the last sheet  19 , the subsequent sheet  18 /last sheet  19  is transported against the front guide stop  15  by means of a sheet-supplying device, which is not shown, while the sheet  17  to be aligned, is pulled of. At the same tie, controlled by the control unit  21 , the drive unit  20  is stopped and, thus, the movement of the suction belt  3  is interrupted when the front edge of the subsequent sheet  18 , determined to be the last sheet  19 , is up against the front guide stop  15 . Moreover, the drive unit  20  can be stopped so that the last sheet  19  is up against the front guide stop with a slight excess pressure. Simultaneously as or immediately before the sheet  19  comes up against the front guide stop  15  or within an operating cycle, in which the last sheet  19  is transported, the supply of negative pressure to the lower suction chamber  8  by means of the servo unit  11  is interrupted by way of the control unit  21  and the air-removing flap  12  is opened by the servo device  13 . Thus, the last sheet  19  can be aligned with the side edge and, subsequently, pulled off.  
         [0014]     The interruption of the supply of negative pressure to the lower suction chamber  8  by means of the servo unit II and the opening of the air-removing flap  12  by the servo device  13  can be controlled by the input Unit  24  within the working cycle, in which the last sheet  19  is transported to the front guide stop  15 . With that, the release of the last sheet  19  can be adapted to the material to be processed or to the configuration of the sheet installation. For example, in the case of a sheet installation, wherein after the alignment with respect to the front edge, a side edge alignment is provided on the feed table  2 , the lower suction chamber  8  must be ventilated earlier than in the case of a sheet installation with the side edge alignment on a downstream cylinder.  
         [0015]     In the example, it is described that the last sheet  19  as well as its position on the belt table is detected by the double-sheet control  16 . It is also possible to detect the last sheet  19  by additional means. Moreover, the last sheet  19  and additionally the sheets on the feed table  1 /belt table  2  before the last sheet  19 , can be detected by the machine control system.  
         [0016]     While various embodiments and individual features of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the present invention. As will also be apparent to those skilled in the art, various combinations of the embodiments and features taught in the foregoing description are possible and can result in preferred executions of the present invention. Accordingly, it is intended that such changes and modifications fall within the scope of the present invention as defined by the claims appended hereto.