Abstract:
Described is a transport device for paper which includes a metal conveyor belt through which air can flow and which is guided over at least two rollers, with the upper section of the belt forming the transport section and its lower section forming the returning section. A vacuum generator is arranged below the upper section. The conveyor belt is a metal mesh so as to be easy to produce and install.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The invention relates to a transport device for paper, as disclosed in the preamble to claim  1 , as well as to a paper processing device according to claim  16 . 
       PRIOR ART 
       [0002]    According to the prior art, so-called suction belts are known for moving paper elements that must be precisely positioned. Suction belts of this type generally are made of rubber or a similar material and are provided with a multitude of holes. The transport device comprises at least two rollers over which this suction belt moves, while a so-called suction box that can be subjected to a vacuum or low pressure is installed below the upper section of this suction belt which functions as conveyor belt (meaning below the transport section of the conveyor belt). The top surface of the suction box contains numerous openings, so that the vacuum effective in the suction box on the one hand pulls the transport section against the suction box and, on the other hand, pulls the paper located on the surface of the transport section against this surface. 
         [0003]    Laser cutting systems are furthermore known in the art which can be used to cut extremely precise contours from paper, for example to create letters, numbers or other symbols in the form of cutouts. Of course, with these systems the paper must also be placed and/or transported precisely positioned, relative to the laser, so that the use of corresponding suction belts make sense as well. As a result of the high thermal stresses caused by the laser, however, the use of conventional suction belts, in particular those made of rubber or a rubber-type material, is not possible and/or would result in extremely high wear. The use of a thin sheet metal strip for the conveyor belt is known for laser cutting systems of this type. This sheet metal is provided with an extremely high number of small, laser-cut holes prior to the ends being welded together to form a continuous belt, so that this metal belt can be guided in the conventional manner over a suction box. The disadvantages of such a metal belt are the extremely high costs for producing and installing it. 
       SUBJECT MATTER OF THE INVENTION 
       [0004]    Starting therefrom, it is the object of the present invention to further improve a generic transport device which can also be used at permanently high or occasionally high temperatures and which is noticeably easier to produce and preferably also easier to install. 
         [0005]    This object is solved with a transport device having the features as disclosed in claim  1 . 
         [0006]    The conveyor belt according to the invention is also composed of metal. However, it does not consist of a metal sheet with holes, but of a metal mesh. Metal meshes of this type are produced for different purposes in large amounts and at very reasonable cost. It has turned out that a metal mesh of this type serves the same purpose over a wide range of mesh widths and wire strengths as the above-mentioned metal belt with laser-cut holes. It has furthermore turned out that metal meshes of this type can be easily welded together to form continuous belts, using the plasma or laser welding technique, and are extremely suitable for use as continuous conveying belts because of their mechanical features (in particular the tensile strain). Another advantage is that compared to the standard metal belts with laser-cut holes, they can be cleaned easier in many cases. This is important for the above-described and presently preferred area of use in laser cutting systems (claim  16 ) since burning residues from the paper (ash and the like) remain on the conveyor belt as a result of the laser cutting and preferably should be removed constantly during the continuous operation. 
         [0007]    A further advantage is that the metal mesh scatters rather than reflects the laser light, which greatly reduces the negative influences of the reflections. The undesirable reflections can be reduced even more with the aid of sand blasting and/or by Nano coating of the metal mesh. 
         [0008]    Additional advantages and preferred embodiments of the invention follow from the dependent claims as well as the exemplary embodiments which are explained further with reference to the Figures. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0009]    Shown are in: 
           [0010]      FIG. 1  A strongly schematic cross sectional view through a laser cutting system, using a transport device according to the invention; 
           [0011]      FIG. 2  The detail D from  FIG. 1 , also shown in a strongly schematic sectional view which is not true to scale; 
           [0012]      FIG. 3  A plan view from the direction R 1  onto the representation in  FIG. 2 ; 
           [0013]      FIG. 4  The transport device shown in  FIG. 1 , in a somewhat more detailed representation, wherein the conveyor belt is not shown; 
           [0014]      FIG. 5  A plan view from the direction R 2  in  FIG. 4 ; 
           [0015]      FIG. 6  A plan view from the direction R 3  in  FIG. 5 ; 
           [0016]      FIG. 7  A perspective view of the representation shown in  FIGS. 4 to 6 ; 
           [0017]      FIG. 8  The representation shown in  FIG. 7  with the conveyor belt installed; 
           [0018]      FIG. 9  The representation shown in  FIG. 8 , showing a cut-open view; 
           [0019]      FIG. 10  A variation of the view of what is shown in  FIG. 1 ; 
           [0020]      FIG. 11  A preferred embodiment of a cleaning station; and 
           [0021]      FIG. 12  A variation of the view of what is shown in  FIG. 11 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]      FIG. 1  schematically shows a cross-sectional view of a device for producing laser cuts in flat paper blanks, such as greeting cards or the like. This device comprises four elements, namely a feed unit  40 , a transport device  10 , a laser  30  arranged above the transport device and a removal unit  50 . The paper is transported in the direction T, and the device can operate continuously, meaning the laser generates the cutout contours during a continuous transport movement of the transport device  10 . 
         [0023]    The feed unit  40  can have a standard configuration, namely consisting of a table  42  with smooth surface and a number of transport rolls  44  which supply the paper blanks with a sliding movement across the table to the transport device  10 . The angle of the transport rolls  44  can deviate slightly from a 90 degree angle, relative to the transport direction T (see  FIG. 1   a ) and can press the paper blanks in such a way against an end stop that a more precise positioning of the paper blanks is achieved. The removal unit  50  can also have a standard configuration and, for example, can consist of a connecting piece  52  and a conveying belt  54 . However, it would also be possible to provide a stacker or the like immediately downstream of the transport device  10 . 
         [0024]    The essential elements of the transport device  10  according to the invention are two rollers  12   a,    12   b,  wherein at least one of the two rollers is driven, the rear roller  12   b  in this case, the conveyor belt  25 , as well as a plurality of axial fans  16  which are arranged below the upper section (meaning the transport section)  25   a  of the conveyor belt  25 . A support  14  that is positioned in the horizontal plane and essentially extends from the front roller  12   a  to the rear roller  12   b  serves to position these axial fans  16  (the axial fans  16  in principle can be designed in the same way as conventional fans used in computer casings). The support  14  is provided with a plurality of openings. The axial fans  16  are arranged at these openings, as shown only very schematically in  FIG. 1 . In praxis, the support  14  can also be embodied considerably thinner (as shown in the following with reference to  FIGS. 4 to 9 ). The axial fans  16  are preferably positioned relatively close to the underside of the upper section  25   a  of the conveyor belt. 
         [0025]    The conveyor belt  25  according to the invention consists of a metal mesh, generally a mesh composed of warp wires  27  and weft wires  26 , as shown schematically in  FIGS. 2 and 3 . The wire strength of the woven wires advantageously ranges from 0.25 to 0.4 mm and the mesh width is preferably between 0.4 and 0.6 mm. Stainless steel or high-grade steel is advantageously used for the metal mesh, for example V2A. A so-called “normal wire mesh” is preferably used, meaning a wire mesh in smooth weave, a wire mesh in plain weave, or a wire mesh in twill weave. If a wire mesh in twill weave is used, the warp wires  27  preferably extend in transport direction. To produce the conveyor belt, a piece of metal mesh having the required length and width is cut and the edges of the two ends (as a rule the short edges) are welded together, preferably with the aid of plasma welding or laser welding, so that an endless conveyor belt is created. 
         [0026]    The transport device  10  can optionally also comprise the following elements shown herein: intake or feed rollers  23 , a delivery roller  20  and a lower cleaning brush  22  or a cleaning station. A preferred embodiment of such a cleaning station is explained later on with reference to  FIGS. 11 and 12 , wherein the delivery roller  20  can also have a cleaning function in this case. Providing at least one cleaning roller or cleaning brush is preferred for the described use of the transport device since the burning residues generally must be removed from the transport device  10 . Insofar as a delivery roller  20  is provided as shown at the end of the upper section  25   a  of the conveyor belt  25  (meaning the transport section), it must be driven counter to the rollers  12   a,  b. A cleaning brush  22  or a cleaning roller acting upon the lower, meaning the returning section, of the conveyor belt can also be driven in the same direction as the rollers  12   a , b, meaning in the direction counter to the lower section  25   b,  which can result in improving the cleaning effect. Since the delivery roller  20  also acts upon the paper blanks to be processed, it must be made of a relatively soft material, while the lower cleaning brush  22  can consist of a relatively hard material. The lower cleaning brush  22  could, of course, also act upon the conveyor belt  25  in the region of one of the two rollers (respectively already in the lower half). 
         [0027]    It has furthermore proven extremely advantageous to clean the lower section  25   b  with a “chainsaw-type” cleaning device for which the movement direction is perpendicular to the transporting direction. With a cleaning device of this type, the cleaning brushes circulate in the manner of a chainsaw between two rollers. In the effective section, the cleaning brushes move along a straight line. 
         [0028]    For most application cases, a slightly wet cleaning is preferable. 
         [0029]    The cutting laser  30  is arranged above the transport device  10 . 
         [0030]    The device preferably operates continuously, as previously mentioned, and at a constant transporting speed. As a result of the axial fans  16 , which suction in air through the upper section  25   a  of the conveyor belt  25 , the paper blanks which are supplied by the feed unit  40  in a precise position are held in this position. The air ejected by the axial fans  16  exits through the lower section  25   b  of the conveyor belt and thus also contributes to a cleaning of the returning section of the conveyor belt  25 . Providing axial fans instead of a suction box furthermore has the additional great advantages of requiring considerably less energy and resulting in a noticeably lower noise development (traditional suction boxes generally use radial compressors for the vacuum generators). 
         [0031]    The laser  30  cuts the paper blanks, positioned on the upper section of the conveyor belt, which then leave the transport device  10  at the rear roller  12   b  and are discharged via the discharge unit  50 . 
         [0032]      FIGS. 4 to 9  show the above-described transport device  10  once more with further details, wherein the conveyor belt  25  is not shown in  FIGS. 4 to 7 . All elements are provided with references to match those in  FIG. 1 , so as to avoid repetitions if possible. It is easy to see in  FIGS. 4 and 9  that the horizontally extending support  14  can be embodied pretty thin and that the drive motors for the axial fans  16  can be positioned outside of the plane defined by the support  14 . The diameters for the openings in the support  14  substantially correspond to the diameters of the vanes on the axial fans that are used. In particular in  FIG. 6 , it is obvious that the support  14  extends between two side faces  18   a,    18   b,  so that the two sections of the conveyor belt  25 , the rollers  12   a,    12   b  and the side faces  18   a,    18   b  enclose an inside area in which the aforementioned support  14  is arranged. 
         [0033]    To be able to tension the conveyor belt  25 , at least one end of each side face comprises a slot  19  that extends in transport direction and through which the axis of a roller—in this case the front roller  12   a —extends, so that the distance between the rollers  12   a,    12   b  can be changed and the conveyor belt  25  can thus be tensioned. The conveyor belt  25  can therefore also be installed in the fully assembled state, meaning in the state where it is welded together to form an endless loop, wherein it is fitted on by pushing it from the side onto the rollers  12   a,    12   b.  For this, additional units such as the intake rollers  23  and the like may have to be dismantled if applicable. 
         [0034]    To achieve a further improvement in the flatness of the transported paper in a central segment of the upper section  25   a  of the conveyor belt  25 , it is possible to provide two crossbars  60   a,    60   b  that extend crosswise to the transporting direction, the upper points of which are located above the upper points of the rollers  12   a,    12   b,  so that a slightly higher and extremely flat central segment is formed, as shown schematically in  FIG. 10 . 
         [0035]      FIGS. 11 and 12  show a preferred embodiment of a cleaning station  70  which can be arranged below the return section  25   b  of the conveyor belt  25 , for example at the location of the above-mentioned cleaning brush  22 . This cleaning station  70  comprises a cleaning roller  71 , driven around an axis  73 , and a container  76  that is open on the top for holding cleaning liquid  77  (water in the simplest case). A strip roller  78  is preferably also provided, which is driven in the opposite direction as the cleaning roller. At least the shell of the cleaning roller  71  is embodied as a sponge (sponge shell  74 — FIG. 11 ) or in the form of a brush (brush shell  75 — FIG. 12 ). The cleaning roller  71  is advantageously driven to rotate in the same direction as the rollers  12   a,    12   b.    
         [0036]    The cleaning roller  71  is positioned such that it presses from below against the return section  25   b  of the conveyor belt  25  while a lower portion of this roller is submerged in the cleaning fluid  77 . As a result of the rotation of the cleaning roller, new cleaning fluid  77  is constantly absorbed and conveyed to the return section  25   b  of the conveyor belt. The degree of moistening of the return section can be adjusted with the strip roller which is arranged in rotational direction of the cleaning roller between the cleaning fluid and the conveyor belt. It is preferable in that case if the radial distance between the cleaning roller and the strip roller  78  is adjustable. 
         [0037]    The moist or wet cleaning (in particular with the aid of the above-described cleaning station) has several advantages. Above all, it is possible to achieve a good cleaning of the conveyor belt to remove burning residue, ash and the like. The moistening of the conveyor belt as such furthermore also has advantages. On the one hand, it generates cold by evaporation—which is additionally helped by the arrangement of the axial fans—meaning it results in a cooling of the conveyor belt, the upper section  25   a  of which is admitted with laser energy. The degree of moistening can furthermore be adjusted, such that a certain amount of liquid still adheres to the upper section  25   a  of the conveyor belt. This remaining liquid improves the adhesion of burn residue, ash and the like, thereby preventing these residues from dirtying the back side of the paper to be processed. The mesh structure of the metal conveyor belt strongly favors the desired adherence of liquid. 
         [0038]    A further option for using the conveyor belt according to the invention is for drying sections for drying paper, in particular paper imprinted by an inkjet printer.