Abstract:
A method for processing lenticular foil in sheet-fed printing presses is provided, the lenticular foil having lens strips adjacently disposed and extending transversely to the running direction of the sheets. The method ensures that the lens strips proceed parallel to the sheet&#39;s front edge For determining the actual position of a sheet aligned according to a front edge, the position of a contact line between two adjacent lens strips is determined, and compared with a nominal position. If the actual position deviates from the nominal position, an adjusting value is generated for realizing a leading or trailing movement of plate cylinders making possible the nominal position, of a gripper sheet-holding system of a sheet-accelerating device mounted in a drum.

Description:
FIELD OF THE INVENTION 
   The invention relates to a method for processing lenticular foil in sheet-fed printing presses, the lenticular foil having lens strips, which are disposed next to one another and extend transversely to the running direction of the sheets, the sheets of lenticular foil being aligned in the running direction of the sheets as well as transversely to the running direction of the sheets. 
   BACKGROUND 
   Lenticular foil, which is also referred to as lens raster foil, is a clear, transparent foil, on the front side of which there is a plurality of curvatures, which are disposed next to one another. The curvatures extend parallel to one another and act as optical lenses. These foils are used to produce lenticular products, for example, for realizing image sequences or three-dimensional image impressions. For this purpose, the back of the lenticular foil is imprinted with a subject. Subsequently, opaque white is applied or the foil is laminated on cardboard. 
   In order to be able to realize image sequences or three-dimensional image impressions, it is necessary to divide different images into strip-shaped image parts and to combine these sequentially into a single subject. In this connection, each strip sequence of all the images that are to be combined has exactly the same width as a lens strip and must be printed exactly underneath it. Only in this way, depending on the viewing angle selected, does the desired image effect come about, that is, the becoming visible of image sequences or of the 3-dimensional impression of the image. The product is useless if the strip sequences are not printed directly under the lens strip. 
   In sheet-processing machines, it is generally customary to align the sheets for processing according to their front edge in that these are guided with the front edge against feeding marks. Subsequently, the sheet, which has been aligned according to the front edge, is aligned according to the side edge. For this purpose, the sheet is shifted transversely to its running direction and transported with its side edge against a side stop (DE 100 47 314 A1). 
   From the DE 102 05 630 A1, it is furthermore known that, after the sheet is aligned in its running direction, the actual position of the side edges is determined by measuring means and compared with the nominal value. If the actual value deviates from the nominal value, a control signal is generated and supplied to a control device. The control device is connected with a gripper system, which is mounted in a feed cylinder so that it can be displaced in the axial direction. The nominal position of the side edge is then realized by shifting the gripper system. 
   If the sheets of lenticular foil reach the processing stage so that the lens structure extends transversely to the running direction of the sheets and, with that, parallel to the front edge of the sheets, they are aligned according to the front edge at the front marks. Subsequently, they are aligned according to the side edge and afterwards transported in the gripper bite by the sheet-processing machine. Since the front edge of the sheet of lenticular foil does not necessarily always proceed precisely with the lens structure of the lenticular foil, qualitatively bad or useless products cannot be excluded. In addition, it is necessary, by manual adjustment manipulations, to assign the strip sequences accurately to the lens strip. As a result, the productivity of the machine as a whole is also affected disadvantageously. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to develop a method, which ensures that the strip sequences are assigned accurately to the lens strips of the lenticular foil, extending parallel to the front edge. 
   Pursuant to the invention, the objective is accomplished by a method including: adjusting a front edge of a sheet of lenticular foil having lens strips to a known position on a feeder table of a printing press: sensing a position of a contact line formed between adjacently disposed lens strips; generating a first signal in response to sensing the position of the front edge; generating a second signal in response to sensing the position of the contact line; comparing the first and second signals to determine a correction value corresponding to a misalignment between the contact line and the front edge; feeding the sheet to the plate cylinders; and adjusting a leading or trailing movement of the plate cylinders in accordance with said correction value, thereby aligning the plate cylinders with an actual position of the lens strips. 
   Due to the inventive method, it is possible to supply sheets of lenticular foil to a sheet-fed printing machine positionally correctly independently of the position of the front edge of the sheet to form the lens structure. With that, the productivity of the plant as a whole and the quality of the lenticular products can be increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in greater detail by means of an example which is described in reference to the drawings. 
       FIG. 1  shows an enlarged representation of a section of a sheet of lenticular foil in plan view. 
       FIG. 2  shows a section through A-A in  FIG. 1 . 
       FIG. 3  shows a sheet-feeding apparatus, downstream for which there are printing units. 
       FIG. 4  shows a feeder table in plan view. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , the section of a sheet  1 , consisting of lenticular foil, is shown with a view of the back side  2 . A front edge  3  and a side edge  4  of the sheet  1  are shown. The sheet  1  has lens strips  6 , which extend transversely to the running direction  5  of the sheets  1 . A contact line  7  is formed in each case by two lens strips  6 , which are provided next to one another. In the sectional representation of  FIG. 2 , it is shown that in each case a first image strip  8 , a second image strip  9  and a third image strip to is assigned to each lens strip  6 . The image strips  8 ,  9 ,  10  represent a strip sequence  11 , which must be assigned accurately to the individual lens strips  6 . It is shown in  FIG. 2  that the front edge  3  is not identical with a contacting line  7 . 
   In  FIG. 3 , a sheet feeder with a feeder table  12 , a sheet-accelerating device  14 , which is constructed as a swing feeder  15 , and a drum  17  are shown. At the feeder table  12 , feeding marks  13  are shown in a working position. They can be brought out of their working position into a position at rest below the feeder table  12 . The swing feeder  15  is equipped with a sheet-holding system  16  and the drum  17  is provided with a gripper system  18 . Adjoining the drum  17  there are the printing units  19 , the drum  17  being disposed directly behind a first printing unit  19 . 1 , adjoining which there may be further printing units  19 . In  FIG. 3 , an nth printing unit  19 . n  is shown. The first printing unit  19 . 1  consists of a first printer cylinder  20 . 1 , to which a first offset cylinder  21 . 1  is assigned, which is connected with a first plate cylinder  22 . 1 . Correspondingly, the nth printing unit  19 . n  has an nth printing cylinder  20 . n  with an nth offset cylinder  21 . n  and an nth plate cylinder  22 . n . The printing units  19  are connected by transfer drums  23 . A first circumferential register control device  24 . 1  is assigned to the first plate cylinder  22 . 1  and an nth circumferential register control device  24 . n  is assigned to the nth plate cylinder  22 . n . The circumferential register control devices  24 . 1  to  24 . n  may be constructed as known devices, which can be actuated independently of one another. The circumferential control devices  24 . 1  to  24 . n  may also be designed so that an individual driving mechanism is assigned at least to the plate cylinders  22 . 1  to  22 . n . The individual driving mechanisms can be controlled in such a manner, that they revolve in a leading or trailing manner, by means of which the circumferential register is changed. A sheet  1 , held by the gripper system  18 , and a sheet  1 , lying with the front edge  3  at the feeding marks  13 , are shown on the feeder table  12 . The feeder table  12  has channels  25 , which are disposed transversely to the running direction  5  of the sheets  1  and in which the pull-type side guides  26  are mounted, which have a side stop  27  ( FIG. 4 ). A measuring unit  28  extends in the running direction  5  of the sheet  1  in the feeder table  12 . The measuring unit  28  is provided in the feeder table  12  so that the front edge region of the sheet  1 , contacting the feeding marks  13 , can be detected. For this purpose, the measuring unit  28  in the example is constructed as an optoelectronic measuring unit. However, any other measurement principal can also be used. 
   The measuring unit  28  is disclosed in a recess extending in the running direction  5  of the sheet  1  in the feeder table  12 . The recess is closed off with a transparent covering strip  29 , so that the surface of the feeder table  12  and the covering strip  29  form a common plane. The measuring unit  28  is connected with an evaluating and controlling device  30 , in which the nominal values can be entered and stored. The evaluating and controlling device  30  is connected with the circumferential register control devices  24 . 1  to  24 . n  and with a machine-controlling device  31 . The sheets  1 , consisting of lenticular foil, are transported by a belt table, which is not shown, to the feeder table  12  and with the front edge  3  against the feeding marks  13  positioned in the working position at the feeder table  12  and, with that, aligned according to the front edge  3 . The sheet  1 , brought to a rest, is taken hold of by the pull-type side guide  26 , passed against the side stop  27  and aligned according to the side edge  4 . The front edge position of the aligned sheet  1  is determined by the measuring unit  28 . At the same time, signals, characterizing the position of the front edge  3  and the position of the adjacent contact lines  7  are generated by the measuring unit  28  and supplied to the evaluating and controlling device  30 . In the evaluating and controlling device  30 , the signal, generated by the front edge  3  in the measuring unit  28 , is gated. In addition, all the signals, which are generated in the measuring unit  28  by the contact lines  7  extending parallel to the front edge  3 , are gated out. Only a signal, generated by a contact line  7  is not gated out and used for a nominal/actual comparison in the evaluating and controlling unit  30 . In an advantageous manner, the signal is always used for this purpose, which is generated by the contact lines  7 , which is adjacent to the front edge  3  of the sheet  1 . Any other signal, which is generated by a contact line  7 , can also be used. The aligned sheet  1 , which is detected with respect to the position of its front edge, is taken over by the sheet-holding system  16  of the swing feeder  15 , the feeding marks  13  are brought from their working position into the position at rest and the sheet  1  is transported to the drum  17  and transferred by this to the first printing cylinder  20 . 1 . If a deviation from the nominal position was recorded in the evaluating and controlling device  30  when the nominal value was compared with the actual value, an adjusting value is realized, which corresponds to a correction value, by which the circumferential register control device  24 . 1  to  24 . n  must adjust the plate cylinders  21 . 1  to  21 . n , in order to achieve an exact assignment, starting out from the contact line  7 , fixed as the nominal value, of the individual strip sequences  11  to the lens strip  6 . Since the adjusting value or correcting value, which was determined for a sheet  1  on the feeder table  12 , must be taken into consideration during the transport through each of the printing units  19 . 1  to  19 . n , the individual circumferential register control devices  24 . 1  to  24 . n  are driven synchronously with the passage of a measured sheet  1  with the corresponding adjusting or correcting value. This is realized by the evaluating and controlling device  30 , the rotational speed of the machine or the printing speed, converted by the machine control system  31 , being taken into consideration. 
   Basically, it is possible to align sheets  1  of lenticular foil, detected with respect to the position of their front edge, according to one of the contact lines  7 , in that the sheet holding system  16  of the sheet-accelerating device  14  or the gripper system  18  of the drum  17 , under the influence of the evaluating and controlling device  30 , are driven in a leading or trailing manner by additional regulating units.