Abstract:
A printing machine for multicolor printing which includes a plurality of printing units and a system for transporting and guiding either sheet-type or web-type printable matter through the printing units. The guiding system includes means, such as adhesive, contact pressure, or retaining belts, for maintaining the printable matter on a transfer belt in proper registry during transfer through the successive printing units.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to multicolor printing machines, and more particularly, to a system for guiding and transporting printable matter through a plurality of printing units of such printing machines. 
     BACKGROUND OF THE INVENTION 
     PRIOR ART 
     In printing machines for various printing methods, it is common practice to provide sheet transport means that allow a linear transport of substrates to be printed through the printing units from the feed station to the delivery station. Some of these methods and devices utilize grippers. Other methods and devices utilize conveyor belts that are linearly guided through the printing units for transporting the sheet-like materials. 
     DE 19527264 A1 discloses a printing machine with a linear substrate guide. In this case, the transport path of the substrates should extend linearly from the feed stack to the transport means in the plane of the transport path through the printing units. A conveyor belt is provided which transports the substrates between the cylinders of the printing units, e.g., by means of a frictional engagement. However, this publication contains no information regarding retention of the sheets on the conveyor belt with correct registration. 
     DE 19921271 A1 discloses a method for transporting sheets through a printing machine, as well as a device for carrying out said method. In this case, instead of grippers, regions that are coated with an adhesive are provided on the sheet guiding elements, with said adhesive-coated regions making it possible to guide the sheets while they are secured in position. This publication also describes a printing machine in which printable matter is linearly transported through the printing machine by means of a conveyor belt. This publication also contains a reference to the fact that retention of the sheet by means of electrostatic charges is not sufficient for transport of the sheets. 
     The present invention aims to develop a variable transport device that can be used in different printing machines. In addition, a holding device for the printable matter need be provided that makes it possible to always realizing the same conditions for transport of the printable matter. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a versatile printable matter transport system that can be used in different types of printing machines. 
     Another object is to provide a printing machine having a sheet transport and guiding system which maintains the printable matter in proper condition for transport and printing through a multiplicity of printing units. 
     A further object is to provide a printing machine as characterized above in which printable matter can be linearly transferred through a plurality of printing units without the use of mechanical grippers. 
     The foregoing objects are attained by a machine configuration that is adaptable for reliably transporting printable matter that may vary broadly with respect to shape, size, and material composition. In this case, renewable holding regions preferably are provided on a conveyor belt as the holding means for sheet-like printable matter. This makes it possible to always realize the same conditions for all sheets to be transported through the printing machine. In addition, it is no longer necessary to generate electrostatic charges. The device also is suitable for various types of printable matter. Advantageous embodiments of the invention include holding means in the form of adhesive films, melt-on adhesive regions, variably applicable adhesive strips, offset pressing devices, rolling devices, or timed transport movements of the rollers. 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially diagrammatic depiction of a web-fed rotary printing machine with which sheet conveying systems in accordance with the invention may be used. 
       FIG. 2  is diagrammatic depiction of a printing machine of a similar configuration as that shown in  FIG. 1  with a conveyor belt and holding band printable matter transfer and guiding system in accordance with the invention; 
       FIG. 3  is a diagrammatic depiction of a printing machine with an alternative embodiment of sheet transport and guiding system in accordance with the invention, in this case utilizing pressing rollers; 
       FIG. 4  is a diagrammatic depiction of a printing machine with still another alternative embodiment of sheet transport and guiding system, in this case using pneumatic pressing devices; and 
       FIG. 5  is a top view of the printing machine shown in FIG.  2 . 
    
    
     While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more particularly to  FIG. 1 , there is shown a web-fed rotary printing machine with several printing units  1 - 4 , the basic configuration of which comprises an impression cylinder  7 , a blanket cylinder  6  and a plate cylinder  5 . The web  8  of printable matter is unwound from a supply roll  10  and transported to the impression cylinder  7  of the printing unit  1 , with the web being printed in this printing unit by means of the blanket cylinder  6  and then transported to the next printing unit  2  via a deflection roller  20 . This process continues similarly until all print images are printed on the web in the printing units  1 - 4 . In the described embodiment, the web  8  of printable matter is transported to a take-off roller  11  and wound up again. 
     While the described printing machine is an offset printing machine it does not contain so-called blanket-to-blanket printing units. In this case, each printing unit  1 - 4  is respectively provided with an impression cylinder  7  that merely serves to press the printable matter against the printing cylinder, in this case, the blanket cylinder  6 . Such a configuration of a web-fed rotary printing machine is relatively simple in contrast to printing units that normally are equipped for a double-sided printing process. For reasons of simplicity, the impression cylinders  7  have a smaller diameter than the blanket cylinders  6  and the plate cylinders  5 . This is possible because each impression cylinder  7  merely serves a support function. The proper registration of the print images in the various printing units  1 - 4  can be achieved with the aid of deflection rollers  20  or other devices, e.g., so-called web tensioning devices, which preferably are appropriately mounted for adjustable positioning. 
       FIG. 2  shows a printing machine that has the same basic configuration as that shown in FIG.  1 . In this case, a known type of conveyor belt  40  for printable matter is guided over the region of the impression cylinders  7 . The conveyor belt  40  extends along a plane path through the printing zones of all printing units  1 - 4 , namely between the respective blanket cylinders  6  and the impression cylinders  7 . Printable matter in the form of webs or sheets can be laced on this conve or belt  40 . 
     Sheets of printable matter are fed to the conveyor belt  40  from a feed station  41  arranged in front of the printing unit  1 , with said sheets being removed from the feed stack by means of a sheet feeder  30 . The sheets are removed from the conveyor belt  40  at a delivery station  48  and placed onto a stack by means of a sheet delivery mechanism  31 . The sheets of printable matter are held on the conveyor belt  40  with suitable means while they pass through the printing zones of the printing units  1 - 4 . 
     Webs of printable matter can be processed similarly. When printing a web of printable matter by means of one-sided printing units, e.g., as in the embodiment shown, problems in guiding the printable matter may arise because the printable matter only adheres to a printing cylinder with one side in the printing zone. This problem can be eliminated by providing a suitable guide on the conveyor belt  40 . 
     In  FIG. 2 , the printable matter is held on the conveyor belt  40  by means of holding bands  42 . For this purpose, the conveyor belt  40  and the holding bands  42  are guided parallel to one another in the region in which the printable matter passes through the printing units. The holding bands  42  are returned above the printing units  1 - 4 , in a closed circuit. Tensioning devices  43  may be provided in the region of the holding bands  42 . The printable matter is transported by providing a timed catch roller for the holding bands  42  that can be moved in the vertical direction at the beginning of the conveyor belt  40 . This makes it possible to produce an inlet gap  44  at the feed station  41  for the printable matter to be transported such that the printable matter can be inserted between the holding bands  42  and the conveyor belt  40  in a controlled and adjustable fashion. After the printable matter is inserted sufficiently far, the holding bands  42  are lowered and take hold of the printable matter such that it is held onto and transported along with the conveyor belt  40  due to the frictional engagement. A guide roller  45  arranged at the end of the inlet gap  44  feeds the printable matter to the conveyor belt  40  correctly and places the printable matter on the conveyor belt  40  such that it can be printed. The holding band or the holding bands  42  can be in the form of magnetic bands. These magnetic bands cooperate with corresponding counter surfaces of the conveyor belt  40 . A secure frictional engagement between the printable matter and the conveyor belt  40  is achieved in this fashion. The printable matter is fixed on the conveyor belt  40  and can then be safely guided through the printing units  1 - 4  along a straight and planar transport path. The rollers  41 , 45  preferably are appropriately mounted for relative movement to each other, either linearly relative to each other or for movement for defining an arc. 
     A station  46  is provided in order to influence the transport of the printable matter. This station can be in the form of a measuring device and/or aligning device  46  or in the form of an electrostatic device. The position of the printable matter is detected at this station with the printable matter being aligned or electrostatically charged or discharged. All of these measures promote an orderly printing process. 
       FIG. 5  shows a top view of the transport path of the sheets  50  of printable matter through the printing machine shown in FIG.  2 . The holding bands  42  are placed laterally on the sheets  50  of printable matter. In this case, the sheets  50  are held on edges  47  that are not provided with a print image, while the regions to be printed in the center of the sheets  50  of printable matter remain uncovered. Alternatively, the holding bands  42  could be located in the center of the transport path if non-printed regions are situated at this location in the print image. 
       FIG. 3  shows a printing machine of the same basic configuration as that shown in FIG.  1 . In this case, special conveyor belts  40  are provided with pressing rollers  60  being arranged opposite these conveyor belts. The printable matter is roiled onto the conveyor belts  40  by means of the pressing rollers  60  and fixed thereon in this fashion. The holding force of the conveyor belts  40  relative to the printable matter can be advantageously influenced by choosing the material of the conveyor belts  40  accordingly. Depending on the printable matter, different materials can be used for the conveyor belts  40 . The pressing rollers  60  cooperate with a rigid counter or guide surface  61  and serve to exhaust any air situated between the printable matter and the conveyor belt  40 . When using film-like materials, it usually suffices to provide an equally smooth conveyor belt  40 . In this case, sufficient adhesion is achieved when pressing the printable matter onto the conveyor belt by means of the pressing rollers  60 . When processing paper-like printable matter, it is advantageous to provide an adhesive film on the conveyor belt  40  in order to additionally increase the holding force. 
     With respect to the described configuration, it can be advantageous to effect a charge equalization of the printable matter or to charge the printable matter before it is fed to the first printing unit  1 . An electrostatic charging device can be used for this purpose. Before being fed to the first printing unit  1 , the position of the printable matter must first be detected and corrected if required. This can be achieved by means of the guidance of the conveyor belt  40 . By appropriate belt adjusting means, conveyor belt  40  can be adjusted in the longitudinal and in the lateral direction as it passes through the printing units  1 - 4 . 
     In order to ensure adhesion to the conveyor belt  40 , the printable matter also can be pressed onto the conveyor belt  40  in a correctly registered fashion between the printing units  1 - 4  by means of additional pressing rollers  62 . The guide surfaces  61  provided underneath the conveyor belt  40  serve to achieve an intimate contact with the printable matter. The pressing rollers  62  should be provided with an ink-rejecting surface in this case. However, it also would be possible by means of the pressing rollers  62 , to introduce drying substances onto the print image produced on the printable matter. 
       FIG. 4  shows another printing machine of the same configuration as that shown in FIG.  1 . In this case, the printable matter is held on the conveyor belt  40  by means of an air current. For this purpose, a pneumatic pressing device  70  is provided upstream of the printable matter inlet into the printing zone of the first printing unit  1 . This pneumatic pressing device can be in the form of a slot-shaped blower that extends over the entire width of the printable matter. The pneumatic pressing device  70  should be able to generate a very high pressure. It also would be possible for the pneumatic pressing device  70  to move over the printable matter outward from the center. In this case, it may be advantageous to contour the pneumatic pressing device  70  in the transport direction of the printable matter such that, for example, an approximately arrow-shaped arrangement pointing opposite to the transport direction is provided. 
     Additional pneumatic pressing devices  71 ,  72  and  73  also are provided for maintaining adhesion between the printing units  1 - 4 . These pressing devices  71 - 73  make it possible to restore the possibly-diminished adhesion in the printing zones. This is particularly advantageous because the pneumatic pressing devices  71 - 73  operate in a contactless fashion and consequently cannot smear the fresh print images. An intermediate drying of the print images also can be effected by means of the pneumatic pressing devices  71 - 73 . In this case, it is practical to supply the pneumatic pressing devices  71 - 73  with pre-heated air. 
     The adhesion of the printable matter to the conveyor belt  40  can also be increased with additional means, e.g., a detachable adhesive. In this respect, it would be possible to arrange a station for joining the printable matter to the conveyor belt  40  in the feed region of the printable sheets, wherein regions provided with an adhesive bond are arranged in the conveyor belt  40 . These regions can be melted with the aid of a heating station to take hold of the surface of the printable matter such that the printable matter adheres particularly well to the conveyor belt. The delivery of the printable matter at the delivery station is achieved by heating the-adhesive regions once again. This type of adhesive bond advantageously makes it possible to join the printable matter and the conveyor belt  40  under conditions that are practically always identical. The alternative and cost-efficient utilization of conventional adhesive strips from which paper-like printable matter can, for example, easily be removed again, is variable as a function of time, and cannot be easily renewed. The option of melting on adhesive regions always provides the same adhesive conditions during transport of the printable matter. 
     The devices shown also make it possible to process sheet-type printable matter in a printing machine that is configured for web-type printable matter. All variations of attaching the printable matter to the conveyor belt  40  are advantageous with respect to the fact that they always provide identical adhesive conditions. When utilizing electrostatic charges, or if only regions coated with an adhesive are provided, the adhesive conditions cannot be easily renewed. In addition, these options are not suitable for certain printing methods, e.g., the wet offset printing method. The renewability of the adhesive conditions is accomplished, for example, by constant cleaning the adhesive films, thus keeping them free of paper dust. The melt-on adhesive also provides identical adhesive conditions at all times. Adhesion of the printable matter can be constantly monitored, and restored if so required, by means of the pressing rollers  60 ,  62  and the pneumatic pressing devices  70 - 73 . 
     The printing machine described can be used for all known printing methods. This means that, in particular, limitation to conventional offset printing does not apply in this case. Also, the transport of the printable matter is not limited to conventional printing methods. On the contrary, it can be utilized in all methods including planographic printing, rotogravure printing and letterpress printing. In this respect, it is possible to carry out direct and indirect printing methods. Digital printing methods in which printing plates are produced in the machine also can be used. Various inking methods can be used in the printing machine, with the orientation taking place according to the required printing quality. Inking methods used in the field of sheet printing can be used with equal success as inking methods known from the field of a web-fed printing. The utilization of special inking methods that are based on toners in dry or liquid form would also be possible, in particular, in digital printing machines. 
     The printing machine can also be designed in accordance with current construction principles, wherein the utilization of sleeve-shaped printing plates or blankets or other cylinder linings are used. 
     With respect to the machine configuration, it also would be possible for the cylinders that form the printing gaps to be adjusted relative to one another linearly or in the shape of an arc. This provides the advantage that assignment of the printing elements can be easily effected. In this case, the printing units do not have to be refitted when the printing method or the type of printable matter is changed. 
     In this context, the utilization of individual drives for all known printing unit elements is particularly advantageous. It would be possible to drive the sheet feeder  30  separately. This enables the transport of sheets of printable matter to the printing machine in a much more targeted fashion. 
     Printing processes for web-type printable matter that are not dependent on the format can also be used in this case. Printing processes with a not-completely-covered plate cylinder can be controlled in such a way that the web of printable matter is printed over its entire length. In this case, the printable matter can simply be moved in cycles. Although the plate cylinders rotate steadily, the conveyor belt is moved only when a print image needs to be transferred. The conveyor belt is at a standstill when the circumferential sections of the plate cylinder that are not covered with print images rotate past the printable matter. This means that no gaps that would unnecessarily increase the consumption of printable matter are formed between the print images. This method is particularly suitable for a printing process carried out on the previously described printing machine with a conveyor belt. The web of printable matter can be guided very precisely and controlled almost arbitrarily once it is placed onto the conveyor belt. The registration stability of the print images in the individual printing units is always ensured because the conveyor belt guides the web of printable matter. When processing web-type printable matter, the described auxiliary means for producing the connection between the printable matter and the conveyor belt during transport of printable matter can be utilized as described above with reference to sheet-type printable matter. 
     List of Reference Symbols 
     
         
         Printing unit  1   
         Printing unit  2   
         Printing unit  3   
         Printing unit  4   
         Plate cylinder  5   
         Blanket cylinder  6   
         Impression cylinder  7   
         Web of printable matter  8   
         Feed roller  10   
         Take-off roller  11   
         Deflection roller  20   
         Sheet feeder  30   
         Sheet delivery mechanism  31   
         Conveyor belt  40   
         Feed station  41   
         Holding bands  42   
         Tensioning device  43   
         Inlet gap  44   
         Guide roller  45   
         Measuring and aligning device  46   
         Electrostatic device  46   
         Edge of printable matter  47   
         Delivery station  48   
         Sheet of printable matter  50   
         Pressing rollers  60   
         Guide surface  61   
         Pressing roller  62   
         Pneumatic pressing device  70   
         Pneumatic pressing device  71   
         Pneumatic pressing device  72   
         Pneumatic pressing device  73   
         Guide surface  74