Abstract:
The invention relates to a sheet guide element for use in an apparatus for transporting sheets by means of a gripper system having at least two grippers spaced apart from each other and a sheet guide surface defined by the sheet guide element. Here, the sheet guide element is provided with depressions in the sheet guide surface, running parallel to the transport direction, at least in some sections, in order at least partially to accommodate the grippers, so that the sheet guide surface described by the sheet guide element in the transport direction runs, at least in some sections, at the same height as the movement path of the sheet leading edge fixed in the gripper system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of application Ser. No. 10/504,488, which is the National Stage of International Application No. PCT/DE03/00136, filed Jan. 20, 2003, the entire disclosures of which are incorporated herein by reference. 
         [0002]    The invention relates to an apparatus for transporting sheets with a sheet guide element according to the preamble of claim  1 ,  4  or  5 . 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    EP 08 92 754 B1 discloses apparatuses for transporting and guiding sheets by means of a gripper system and a sheet guide element in combination with an assessment system for quality control in sheet-fed rotary presses for printing securities. 
         [0004]    A sheet to be assessed is clamped by its sheet leading edge in grippers of the gripper system and moved by the latter along a transport direction into a position in which the quality control is carried out. The transport path of the sheet leading edge is in this case defined by the movement path of the gripper system. In order to guide the sheet, use is made of a sheet guide element, on which the part of the sheet to be inspected is intended to come to lie, as completely and flatly as possible, with no corrugations or folds, at the time of the qualitative assessment. 
         [0005]    DE 697 01 173 T2 shows a paper guide apparatus for a sheet-fed offset press, with a guide plate. This guide plate has depressions which extend in the transport direction and into which the grippers dip. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is based on the object of providing an apparatus for transporting sheets with a sheet guide element. 
         [0007]    According to the invention, the object is achieved by the features of claim  1 ,  4  or  5 . 
         [0008]    The advantages that can be achieved with the invention are in particular that the sheet guide element is provided with depressions running parallel to the transport direction, at least in some sections, in order at least partially to accommodate the grippers. This achieves the situation where the sheet guide surface described by the sheet guide element runs, at least in some sections, at the same height as the transport path of the sheet leading edge defined by the gripper movement path, and therefore the sheet leading edge also comes to lie flatly on the sheet guide surface. The depressions machined into the sheet guide surface are configured in particular such that, at the recording time, that is to say in the sheet transport position in which the quality control of the sheet is carried out by the inspection system, the sheet comes to lie completely flatly and without corrugations on the sheet guide surface defined by the sheet guide element. This means that, at the recording time, the sheet is arranged reproducibly in its position opposite the inspection system. This ensures that the inspection system, whose mode of action is matched to the distance from the sheet guide element, can carry out the quality control of the entire printed sheet reproducibly and without faults. 
         [0009]    In principle, the manner in which the depressions are formed in the sheet guide surface is arbitrary. According to a preferred exemplary embodiment of the invention, the depressions in the sheet guide surface, viewed in the transport direction, begin only from a specific position and run as far as the end of the sheet guide surface. This means that, from the transport position, in which the sheet leading edge clamped in the grippers and the sheet guide surface are at the same height, the part of the sheet which is located in the region of overlap with the sheet guide surface comes to lie on the latter completely and flatly, with no corrugations or folds. 
         [0010]    Likewise, it is possible to provide the sheet guide surface along the entire transport direction with depressions running in parallel for the partial accommodation of the grippers of the gripper system. This has the advantage that, along the entire transport movement, the grippers of the gripper system can dip into the plane of the sheet guide surface to such an extent that the sheet leading edge clamped in the grippers is located at the same height as the sheet guide surface along the entire movement path. This again means that, during the entire transport movement, the part of the printed sheet which overlaps the sheet guide surface comes to lie over its entire area and flatly on the latter. 
         [0011]    One preferred embodiment is for the sheet guide surface formed by the sheet guide element to approach the transport path of the sheet leading edge continuously. For this purpose, the sheet guide surface of the sheet guide element is provided, at least in some sections, with depressions to accommodate the grippers of the gripper system. From the sheet transport position at which the grippers have dipped into the depressions of the sheet guide surface to such an extent that the transport path of the sheet leading edge is located at the same height as the sheet guide surface, all of the part of the printed sheet guided by the sheet guide surface comes to lie on the sheet guide surface completely and flatly, with no corrugations or folds. 
         [0012]    Whether the sheet guide surface of the sheet guide element is curved in the transport direction or not is not important in the basic function of the invention. In a preferred exemplary embodiment, the sheet guide surface is curved concavely or describes a concave circular arc segment in the transport direction. If, in particular, the printed sheet comes to lie completely and flatly on the circular arc-shaped sheet guide surface, each point of the sheet is at the same distance from the center of the circular arc segment along the transport direction. If, for the quality control of sheets, an inspection system is used which needs a constant distance between inspection system and printed sheet for fault-free operation, then it is particularly advantageous to arrange the inspection system at the center of the circular arc segment described by the sheet guide surface. 
         [0013]    In constructional terms, the sheet guide element can be designed as a sheet guide plate and the depressions can be formed by cutouts in the sheet guide plate. In this way, a sheet guide surface can be produced in an economical manner. 
         [0014]    In order to increase the stability of the sheet guide element designed as a sheet guide plate, it is expedient to provide the sheet guide plate on the rear side, at least in some sections, with reinforcing ribs running longitudinally and/or transversely. 
         [0015]    In principle, it is also possible to form the sheet guide element as a sheet guide board, in which the depressions are formed by grooves in the sheet guide board. 
         [0016]    One advantageous embodiment of the existing invention consists in providing the sheet guide element, at least in some sections, with cutouts shaped like holes for the passage of air and to assign to the sheet guide element configured in this way a suction apparatus, using which a negative pressure can be produced on the sheet guide surface. The flat position of the printed sheet on the sheet guide surface is assisted by means of the negative pressure prevailing on the sheet guide surface. In particular, the printed sheet can be transported and guided on the sheet guide surface counter to its inherent gravitational force, that is to say in a hanging manner. 
         [0017]    If the sheet guide element is provided with an adjusting apparatus for position control, accurate fine positioning of the sheet guide element in the apparatus for transporting and guiding sheets can be carried out as a result. This is advantageous in particular when the apparatus for transporting and guiding sheets is arranged opposite an inspection system, for whose fault-free function the distance between inspection system and sheet and also the curvature of the sheet to be examined has to be set very accurately. 
         [0018]    In a preferred embodiment, an optical inspection system for the quality control of sheets is arranged opposite the sheet guide surface. 
         [0019]    Exemplary embodiments of the invention are illustrated in the drawings and will be described in more detail in the following text. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    In the drawings: 
           [0021]      FIG. 1  shows an apparatus for transporting and guiding sheets with a sheet guide element and an inspection system arranged opposite for the quality control of printed sheets in the schematically illustrated cross section; 
           [0022]      FIG. 2  shows the apparatus according to  FIG. 1  in plan view from the position of the opposite inspection system; 
           [0023]      FIG. 3  shows the apparatus according to  FIG. 1  in front view; 
           [0024]      FIG. 4  shows a longitudinal section through a sheet guide element formed as a sheet guide board in the region of a depression with a gripper dipped partly into the plane of the sheet guide surface. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]    In  FIG. 1 , a quality control system with a sheet guide element  02  is shown in the sheet transport position, in which the assessment of the sheet  01  is carried out. For the purpose of qualitative assessment of sheets  01 , at least at the assessment time, the part of the sheet  01  to be tested must be arranged reproducibly in terms of distance and curvature and with no corrugations or folds opposite the inspection system  04 . Furthermore, the sheet guide surface  03  of the sheet guide element  02  has to be designed in such a way that it is matched to the requirements of transmitter and receiver of the inspection system  04  in terms of position and shape. A quality control system for the qualitative assessment of sheets  01  substantially comprises a sheet guide surface  03  formed by a sheet guide element  02 , a transport device, which is assembled from a gripper system  07  (see  FIG. 2 ) with grippers  06  and a chain conveyor  08 , and an inspection system  04 . Such a quality control system is used, inter alia, in the quality control of printed sheets in a rotary press, such as in a sheet-fed rotary press for securities. 
         [0026]    A sheet  01  to be inspected is clamped in the grippers  06  of the gripper system  07  at its leading edge and transported in the transport direction  09 . The gripper system  07  is fixed to circulating chains of a chain conveyor  08  known per se. In the present exemplary embodiment, the movement path of the sheet leading edge fixed in the grippers  06  of the gripper system  07  is described by a circular arc segment with radius Rg. The guidance of the sheet  01  moved in the transport direction  09  is accomplished by a sheet guide element  02 , on whose sheet guide surface  03  the sheet  01  comes to lie. In the present exemplary embodiment, the sheet guide element  02  is designed as a sheet guide plate  02 . The sheet guide surface  03  of the sheet guide element  02  describes a circular arc segment with radius Ra, whose concave side faces the inspection system  04 . Furthermore, the inspection system  04  is arranged at the center of the circular arc segment of the sheet guide surface  03 . It follows from this that, in the present exemplary embodiment, the shape of the sheet guide surface  03  and the position of the sheet guide surface  03  in relation to the inspection system  04  is matched to the requirements of a scanning system  04 , which, for fault-free functioning, needs a constant distance from the sheet  01  to be examined. 
         [0027]    In the plan view (see  FIG. 2 ), the sheet guide surface  03  of the sheet guide plate  02  shows depressions  11  running parallel to the transport direction  09  for the partial accommodation of the grippers  06 , which depressions begin only from a specific position on the sheet guide surface  03  and run as far as the end of the sheet guide surface  03 . Likewise, the sheet guide surface  03  of the sheet guide plate  02  is designed with cutouts  12  shaped like holes for the passage of air. 
         [0028]    On the rear side, the sheet guide plate  02  is assigned a suction apparatus comprising suction box  13  and fans  14  (see  FIGS. 1 and 3 ). By means of the suction apparatus, a negative pressure is produced on the sheet guide surface  03  of the sheet guide plate  02 . 
         [0029]    The sheet guide plate  02  is arranged in such a way that the sheet guide surface  03  continuously and progressively approaches the movement path of the sheet leading edge clamped in the grippers  06 . As viewed in the transport direction  09 , the sheet guide plate  02  at its start rests on a surface of the suction box  13  that faces the sheet guide plate  02  and moves away from said surface in the transport direction  03 . This means that the end of the sheet guide plate  02  has no direct contact with the suction box  13 . In order to increase the dimensional stability of the sheet guide element  02  designed as a sheet guide plate  02 , reinforcing ribs  16  are fitted to the rear side of the sheet guide plate  02 . It is also entirely possible for the reinforcing ribs  16  shown in  FIG. 1  to function simultaneously as spacers between suction box  13  and sheet guide plate  02  or, in addition to the reinforcing ribs  16  or instead of the reinforcing ribs  16 , for spacers to be fitted to the rear side of the sheet guide plate  02 , in order to achieve the desired course of the sheet guide surface  03 . 
         [0030]    The exact position of the sheet guide surface  03  in relation to the inspection system  04  can be accomplished by means of an adjusting apparatus for position control  17 . This can be an important feature, in particular when the apparatus for transporting and guiding sheets  01  is assigned an inspection system  04  which, in terms of its function, reacts sensitively to the distance and curvature of the sheet  01  to be examined. 
         [0031]    Once the sheet leading edge, as viewed in the transport direction  09 , is in the initial or central region of the sheet guide surface  03 , the sheet leading edge clamped in the grippers  06  is at a different height than that part of the sheet  01  resting on the sheet guide surface  03 . It follows from this that a certain part of the sheet  01 , which adjoins the sheet leading edge, does not come to lie on the sheet guide surface  03 . 
         [0032]    As can be seen from  FIG. 1 , at the end of the transport movement, the movement path of the sheet leading edge in the transport direction  09  is described by a circular arc segment with radius Rg, at the same height as the sheet guide surface  03 , which in the transport direction  09  is described by a circular arc segment with radius Ra. At this point, the sheet guide surface  03  and movement path of the sheet leading edge intersect. In the present exemplary embodiment, this point of intersection is the same as the end edge of the sheet guide surface  03  of the sheet guide plate  02 . 
         [0033]    In this transport position, the sheet  01  rests on the sheet guide surface  03  completely and flatly, with no corrugations or folds, from the start of the sheet guide surface  03  as far as the end of the latter. This is the transport position, in which a qualitative inspection of the sheet  01  can be carried out by the inspection system  04 , since the sheet  01  now rests reproducibly on the sheet guide surface  03  with no corrugations or folds opposite the inspection system  04 . This means that, by means of the inspection system  04 , which, in terms of its mode of action, is matched to the curvature and distance from the sheet guide surface  03 , the qualitative inspection of the sheet  01  can be carried out reproducibly and without faults. 
         [0034]    During the transport movement of the sheet  01  along the transport direction  09 , the grippers  06  of the gripper system  07  approach the sheet guide surface  03  and, on account of depressions  11 , can dip into the plane of the sheet guide surface  03  without collision. The depressions  11  in the present exemplary embodiment are formed by cutouts in the sheet guide surface  03  of the sheet guide plate  02 .  FIG. 2  shows a plan view of the sheet guide plate  02  and the sheet  01  clamped in the grippers  06  of the gripper system  07  from the position of the inspection system  04  arranged opposite. 
         [0035]    A front view of the apparatus can be seen in  FIG. 3 . In the transport position illustrated, the grippers  06  of the gripper system  07  have dipped into the cutouts  11  in the sheet guide surface to such an extent that the leading edge of the sheet  01  clamped in the grippers  06  comes to lie on the entire sheet guide surface  03 . 
         [0036]      FIG. 4  reveals a longitudinal section in the transport direction  09  through a sheet guide element  18  formed as a sheet guide board  18 . The depressions  19  are formed in the shape of grooves  19 . A gripper  06  of the gripper system  07  has dipped partly into the groove  19  to such an extent that the sheet leading edge clamped in the gripper  06  is at the same height as the sheet guide surface  03  of the sheet guide board  18  and therefore all of the part of the sheet  01  guided by the sheet guide surface  03  comes to lie completely and flatly on the latter. 
         [0037]    The sheet guide element  02 ;  18  can also be designed as a perforated plate. 
       LIST OF DESIGNATIONS 
       [0000]    
       
           01  Sheet 
           02  Sheet guide element, sheet guide plate 
           03  Sheet guide surface 
           04  Inspection system, scanning system 
           05  - 
           06  Gripper 
           07  Gripper system 
           08  Chain conveyor 
           09  Transport direction 
           10  - 
           11  Depression to accommodate the gripper 
           12  Cutout shaped like a hole 
           13  Suction box 
           14  Fan 
           15  - 
           16  Reinforcing ribs 
           17  Adjusting apparatus for position control 
           18  Sheet guide element, sheet guide board 
           19  Depression, groove 
         Ra Radius 
         Rg Radius