Patent Document

FIELD OF THE INVENTION 
     The present invention relates to methods and devices for transporting sheets. A sheet to be transported or conveyed in a sheet processing machine with at least one conveying cylinder is fed to the conveying cylinder in two successive passes. 
     DESCRIPTION OF THE PRIOR ART 
     The document “Sheet Feed System” Research Disclosure, December 1997, XP000735770, page 944, describes a method for conveying sheets in a sheet processing machine having a conveying cylinder and the following steps: 
     a sheet is fed to the conveying cylinder, 
     this sheet is removed from the conveying cylinder by means of a pair of rollers and a belt conveyor system, 
     a position of this sheet is checked, 
     the sheet is thereafter conducted to the conveying cylinder a second time for perfecting. 
     FR-A-2 401 027 describes a device for conveying sheets in a sheet processing machine, having a conveying cylinder, to which a first sheet feeding device and a first sheet removal device, as well as a second sheet feeding device and a second sheet removal device are assigned. 
     DE 29 55 96 C1 shows two conveying drums assigned to a conveying cylinder, which are used as sheet feeding and removing device. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of providing a method and devices for transporting sheets. 
     In accordance with the invention, this object is attain ed by using a sheet processing machine having at least one conveying cylinder. The sheet to be processed is fed to the conveying cylinder. This sheet is removes from the conveying cylinder and is then fed a second time to the conveying cylinder. The sheet may be conveyed by a chain or by a belt conveying system. The sheet is typically processed on the conveying cylinder. 
     With the method of the present invention and with the associated device, it is possible, in an advantageous manner, to retrofit existing presses with a device for executing a further processing step, in particular for performing an inspection. 
     If an inspection is performed prior to further processing steps, for example prior to numbering or printing, further processing can be controlled as a function of the inspection result, i.e. numbering can be omitted, for example. 
     In the present preferred exemplary embodiment, a first side of a sheet is checked and its second side numbered. In contrast to an inspection later, damage to the numbered side is avoided because of the inspection performed prior to numbering. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention is represented in the drawings and will be described in greater detail in what follows. 
     The sole drawings show a schematic representation of a sheet processing machine in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A sheet processing machine  01 , which may be, for example a sheet-fed rotary printing press, has, as seen in the sole drawing figure, an installation  02  placed downstream of a feeding device, not specifically represented. This installation  02  essentially consists of, for example, a feed table  03 , a suction drum  04 , a first conveying drum  06  and a second conveying drum  07 . 
     A first processing cylinder  08 , for example an impression cylinder  08 , is situated downstream of the second conveying drum  07 . Viewed in the direction P of production, a third conveying drum  09  is assigned to the impression cylinder  08  and is located downstream of the second conveying drum  07 . This third conveying drum  09  acts in cooperation with chain wheels  11  carried on a first chain wheel shaft  12  of a first chain conveying system  13 . This first chain conveying system  13  has two endlessly rotating chains  14  lying next to each other in the axial direction. Chain gripper systems, which are not specifically represented, are arranged on these chains  14  and extend in the axial direction. The chains  14  of the first chain conveying system  13  are reversed by means of chain wheels  16  carried on a second chain wheel shaft  17  and are conducted back to the chain wheels  11  of the first chain wheel shaft  12 . A fourth conveying drum  18  is arranged between this first chain wheel shaft  12  and the impression cylinder  08 . 
     Two additional processing cylinders  19 ,  21  are connected downstream, viewed in the direction P of production, of this fourth conveying drum  18 . In the present preferred embodiment these second and third processing cylinders  19 ,  21 , respectively are embodied as numbering cylinders  19 ,  21 . But these second and third processing cylinders  19 ,  21  can also be transfer cylinders, varnishing rollers, perforating rollers or formed cylinders of a print unit. 
     Downstream of the second and third processing cylinders  19 ,  21 , viewed in the direction P of production, a second chain conveying system  22 , which may be a sheet removal device of a delivery device, which is not specifically represented, is assigned to the impression cylinder  08 . 
     A processing device  23 , for example an inspection device  23 , is arranged in the path of the chains  14  between the two chain wheel shafts  12 ,  17  of the first chain conveying system  13 . This inspection device  23  essentially consists of an illumination device and a photoelectric sensor, for example a CCD area camera. 
     A suction box  24 , extending in both the axial direction and in the production direction, is arranged opposite this inspection device  23  and outside of the path of the chains  14 . 
     One or several other processing stations or devices, for example ink jet printers, laser printers, perforating devices or other printing devices can also be arranged in place of the inspection device  23 . 
     In the present preferred embodiment, each conveying drum  06 ,  07 ,  09 ,  18  has one gripper system, and the impression cylinder  08  has two gripper systems. Thus, in reference to the nominal diameters of the conveying drums  06 ,  07 ,  09 ,  18 , the impression cylinder  08  is double-turning. The chain wheels  11  of the first chain wheel shaft  12  are also embodied to be double-turning. 
     The impression cylinder  08 , the first chain wheel shaft  12  and the third,  09 , and fourth conveying drum  18  interposed between the first chain wheel shaft  12  and the impression cylinder  08  are arranged in such a way that circumferential lengths  31 ,  32 ,  33 ,  34  of the cylinders, which are prescribed by the center lines  26 ,  27 ,  28 ,  29  of adjoining cylinders, are of the same length. This means that a circumferential length  31  of the third conveying drum  09  between the impression cylinder  08  and the chain wheel shaft  12  is defined by a center line  26 , which is described by an axis of rotation of the impression cylinder  08  and an axis of rotation of the third conveying drum  09 , and by a center line  27 , which is described by an axis of rotation of the chain wheel shaft  12  and the axis of rotation of the third conveying drum  09 . 
     A circumferential length  32  of the path of the chains  14  in the area of the first chain wheel shaft  12  between the third and fourth conveying drums  09 ,  18  is defined by a center line  27 , which is described by an axis of rotation of the third conveying drum  09  and the axis of rotation of the chain wheel shaft  12 , and by a center line  28 , which is described by an axis of rotation of the fourth conveying drum  18  and the axis of rotation of the chain wheel shaft  12 . 
     A circumferential length  33  of the fourth conveying drum  18  between the first chain wheel shaft  12  and the impression cylinder  08  is defined by a center line  29 , which is described by the axis of rotation of the impression cylinder  08  and an axis of rotation of the fourth conveying drum  18 , and by a center line  28 , which is described by an axis of rotation of the chain wheel shaft  12  and the axis of rotation of the fourth conveying drum  18 . 
     A circumferential length  34  of the impression cylinder  08 , between the third,  09 , and fourth transfer cylinder  18 , is defined by the center line  29 , which is described by the axis of rotation of the impression cylinder  08  and an axis of rotation of the fourth conveying drum  18 , and by a center line  26 , which is described by the axis of rotation of the impression cylinder  08  and the axis of rotation of the third conveying drum  09 . 
     In a simplifying manner, each circumferential length  31 ,  32 ,  33 ,  34  was defined in the above mentioned description, as a length of the path from the gripper feed devices of the gripper systems of the cylinders  08 ,  09 ,  18 , or respectively the gripper systems of the chains  14 . 
     In place of the above-described first chain conveying system  13 , preferred embodiments with other numbers of chain wheels or a different guidance of the paths are possible. For example, a different number of conveying cylinders can be interspersed between the impression cylinder  08  and the first chain conveying system  13 . 
     It is also possible to employ further drums or cylinders, or belt systems, in place of the first chain conveying system  13 . 
     The operation of the sheet processing machine in accordance with the present invention is as follows: 
     A sheet to be processed by the sheet processing machine  01  is fed, in a known manner, to the first conveying drum  06  via the feed table  03  by means of the suction drum  04 . 
     The first conveying drum  06  transfers the sheet to the second conveying drum  07 , and the second conveying drum  07 , which may also be called a first sheet guide device, passes the sheet on to the impression cylinder  08 . The impression cylinder  08  conveys the sheet to the third conveying drum  09 , which acts as a sheet delivery device, and which conveys the sheet to the first chain conveying system  13  and transfers the sheet to it. 
     The first chain conveying system  13  conveys the sheet to the inspection device  23 . The sheet is steadied during its inspection by the suction box  24 . The inspection takes place while the first chain conveying system  13  is running. 
     The first chain conveying system  13  conveys the checked sheet on to the fourth conveying drum  18  which acts as a sheet feeding device, and which returns the sheet to the impression cylinder  08 . 
     The impression cylinder or first processing cylinder  08  conveys the checked sheet to the second processing cylinder  19 . Following processing there, the checked and processed sheet is conveyed, by means of the impression cylinder  08  to the third processing cylinder  21  and is printed there. 
     Processing of the checked sheet can selectively take place using both of the second and third processing cylinders  19 ,  21 , or only by use of one of the two selectable processing cylinders  19 ,  21 . 
     For example, the processing cylinders  19 ,  21  can each be actuated depending on the result of the inspection done by the inspection device  23 . 
     It is common to all of the preferred embodiments, that initially a sheet is conveyed to a sheet processing and conveying cylinder  08 , which conveys the sheet during both first and second processing operations. The sheet is conveyed away by this sheet processing and conveying cylinder  08  for conveying the sheet to a second, or respectively to a first processing operation. 
     Following this processing operation, the sheet is again conveyed to this sheet processing and conveying cylinder  08  and is moved on. 
     The removal of the sheet from the sheet processing and conveying cylinder  08  can take place preferably prior to or also following a processing operation. 
     While preferred embodiments of methods and devices for transporting a sheet in accordance with the present invention have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that various changes in, for example, the type of printing press used, the drives for the various cylinders, and the like could be made without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the following claims.

Technology Category: b