Abstract:
A device for producing print images of varying lengths in offset printing, said device comprises replaceable, cylindrical format sections with differing cylinder diameters. Each format section includes a support shaft with which the format section forms a single unit. The units are replaceable with one another to change print image length.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority of European Patent Application No. 04405119.1-1251, filed on Feb. 27, 2004, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a device for producing print images of varying lengths in offset printing, the device comprising format sections with different cylinder diameters which can be exchanged for changing the print image length. 
   A device for producing print images of varying lengths in offset printing is known from German patent document DE 199 55 084 A. This device uses printing sleeves with a changeable diameter which are fitted onto cylinder cores and/or base cylinders for a full-rotation offset printing machine. The cylinder cores are positioned with both ends inside a frame, wherein one side of the frame is provided with a drive unit for the cylinder cores. The other side of the frame is used for the removal of the printing sleeves. The cylinder cores must take the form of air shafts, so that the printing sleeves can be fitted over the cylinder cores. The printing sleeves, which form the format sections, must be provided with a compressible layer on the inside surfaces, allowing the sleeves to be expanded somewhat and fitted over the air shaft. The disadvantage of these elastic and/or compressible layers, however, is that the high line forces generated in offset printing push the printing sleeves from the concentric position. This leads to changes in the adjustments and thus considerable printing problems. Air shafts and/or printing sleeves of this type have long been known in flexographic printing. However, since considerably lower pressure forces occur in the printing gap during flexographic printing, the aforementioned problems do not arise. 
   A further difficulty with this device is the torque transmission. The air shaft of known print units in offset printing has a specific diameter that is based on the smallest print length to be produced. For example, if this print length must start at approximately 350 mm (13.8″ circumference), then the air shaft should have a maximum diameter of 105.158 mm. The same air shaft is also used for a print length of approximately 609 mm (24″, D=194.04 mm). In that case, the air shaft diameter is not favorable and can lead to considerable problems in the printing sleeve composition and the torque transmission. 
   European patent document EP 1 101 611 A also relates to a device for producing print images of varying lengths in offset printing, wherein this device also has replaceable printing sleeves. These printing sleeves are positioned on pivoting arms. For the printing sleeve replacement, openings are worked into one of the two bearing plates through which the printing sleeves can be exchanged. However, the aforementioned problems also exist with this method and/or device. 
   German patent document DE 35 43 704 A relates to a device for imprinting a web. The sleeves in this case are also attached so as to be replaceable on a rotating body. A bearing plate can be folded down on the operating side for replacing the sleeves. However, producing such a fold-down bearing plate for an offset press is costly. 
   German patent document DE 19 53 4651 relates to a printing unit for indirect printing. For this, respectively one form cylinder and one transfer cylinder can be fitted for a variable circumference with so-called sleeves having variable outer diameters. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to create a device where the aforementioned disadvantages are avoided. 
   The above and other objects are accomplished according to the invention by the provision of a device for producing print images of varying lengths in offset printing, the device comprising: replaceable, cylindrical format sections with differing cylinder diameters, each format section including a support shaft with which the format section forms a single unit, the units being exchangeable with one another to change print image length. 
   Thus, the foregoing object is solved in that the aforementioned format sections form a single unit together with respectively one support shaft and that the complete units are replaced for changing the print image length. To change the print image length for the device according to the invention, respectively a unit comprising a format section and a support shaft is therefore replaced, instead of only replacing the printing sleeve and/or the format section as has been the case so far. The main advantage of this design is that the support shaft can be very low-weight and that the elastic layer used so far on the inside of the format section can be omitted. In this way, the format sections can be fixedly connected to the support shaft to ensure a secure torque transmission and high form stability. 
   To change the print image length for the device according to the invention, at least one rigid unit that cannot be separated is replaced, wherein this unit consists of a format section and a support shaft. 
   The aforementioned units are preferably designed as either rubber blanket cylinders or plate cylinders. The invention furthermore has the advantage that the paper web is not interrupted for the change in the print image length. 
   According to a modification of the invention, the units can be installed and uninstalled essentially perpendicular to the rotational axis of a unit for such a replacement. The units are not inserted from the side through openings in a bearing plate, but rather are moved between the bearing plates, perpendicular to the rotational and/or the drive shafts. The main advantage of this design is that the bearing and drive parts can be positioned easier on the bearing plates and no pivoting bearing arms or fold-down bearing plates are required. The units can furthermore be exchanged manually since the support shafts, as previously mentioned, can be more light-weight, wherein the unit has a particularly low weight if the support shaft is hollow. 
   Yet another embodiment of the invention calls for the aforementioned units to be provided at the support shaft ends with respectively one pivot bearing with a separate outer bearing shell which can be replaced jointly with the unit. Since the units also comprise the respective pivot bearings which are provided with separate bearing shells, the replacement is particularly easy. For example, the pivot bearings can be fitted into shell halves which are respectively arranged on the inside of a bearing plate and can be clamped in. A particularly good rotational movement can be achieved with this type of positioning. 
   Additional advantageous features follow from the dependent patent claims, the specification, as well as the drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One exemplary embodiment is explained in the following with the aid of the drawing. 
       FIG. 1  shows a schematic perspective view of a device according to the invention, wherein known parts that are not essential to the invention are omitted. 
       FIG. 2  is a section through the device according to  FIG. 1 . 
       FIG. 3  is a view from the side of a unit with a holding device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , there is shown a device according to the invention, designed as slide-in unit  1  for a print unit, not shown herein, of an offset press. This slide-in unit  1  comprises a plate cylinder  2  and a rubber blanket cylinder  3  which are arranged between two bearing plates  19  and  20 , arranged at a distance to each other. The plate cylinder  2  and rubber blanket cylinder  3  are positioned between bearing plates  19  and  20  with housings  22 . Housings  22  positioned on either side of rubber blanket cylinder  3  are displaceable along guide slots  25  and  26  of bearing plates  19  and  20 . The standard inking unit  29  and the counter pressure cylinder  28  are indicated in  FIG. 2  with dashed lines. The counter pressure cylinder  28  and the inking unit  29  can have a known design and are therefore not described in further detail herein. 
   The plate cylinder  2  and the rubber blanket cylinder  3  respectively form a single unit, comprising a format section  6  and  7  and respective support shafts  4  and  5 . For this, the format sections  6 ,  7  are provided with respectively one through bore  8  for accommodating the respective support shaft  4 ,  5 .  FIG. 2  shows an endless paper web  27  which normally moves between the rubber blanket cylinder  3  and the counter pressure cylinder  28  and is imprinted by both cylinders. 
   The support shafts  4  and  5  are respectively provided with a pivot bearing  10  on a journal  30  ( FIG. 2 ), projecting outward on the side, for example a ball bearing or roller bearing or a different type of bearing with respectively one upright outer bearing shell  10   a . The pivot bearings  10  are preferably fixedly mounted on the support shaft  4  and  5 , thus also forming a fixed unit together with the respective support shafts  4  and  5  and the respective format sections  6  and  7 .  FIG. 2  shows that each pivot bearing  10  is positioned inside respective holding devices  11  on the right in  FIG. 2  and respective holding devices  12  on the left in  FIG. 2 . The holding devices  11  and  12  for the plate cylinder  2  are positioned to be displaceable inside approximately horizontally extending guide slots  33  in the bearing plates  20  and  19 , respectively, and can be displaced during a replacement, to adapt the axial spacing. However, these holding devices do not have to be displaceable. The two holding devices  11  and  12  for the rubber blanket cylinder  3  are positioned displaceable inside the respective guide slots  26  and  25  in the respective bearing plate  20  and  19 . The rubber blanket cylinder  3  thus can be displaced inside guide slots  25  and  26 . As a result, the axial spacing between the plate cylinder  2  and the rubber blanket cylinder  3  can be adjusted. 
   Drive shafts  31  are provided for the rotating operation of plate cylinder  2  (drive  23 ) and rubber blanket cylinder  3  (drive  24 ), having respectively one gearwheel  31  mounted thereon, which is not depicted. The drive shafts  34  are respectively positioned in roller bearings  35  in separate housings  36 . For the torque transfer, the drive shafts  34  are connected via coupling mechanisms  32  to the respective support shafts  4  and  5 . 
   The holding devices  11  and  12  respectively consist of a lower half shell  13  and an upper half shell  15  as shown in  FIG. 3 . The lower half shells  13  are each securely connected by means of fastening screws  17  to one of the two bearing plates  19  and/or  20  and are each provided with a semicircular depression  14 , which is open on the top and into which a pivot bearing  10  can be inserted from the top. The upper half shells  15  can respectively be tilted away or otherwise removed from the lower half shell  13 . If the two upper half shells  15  are tilted away, then the plate cylinder  2  and the rubber blanket cylinder  3  with the corresponding pivot bearings  10  can be inserted from the top into the lower half shells  13 . The outer bearing shells  10   a  are secured in place by screwing the upper half shells  15  with screws  18  to the lower bearing shells  13 . Recesses  16  are provided in the shell halves  15  for the screws  18 . As shown in  FIG. 1 , the screws  18  can respectively be provided with a tension lever  21 . Prior to securing the pivot bearing  10  in place, the plate cylinder  2  and the rubber blanket cylinder  3  in  FIG. 2  are moved in an axial direction somewhat to the right, so that the support shafts  4  and  5  are connected to the corresponding drive shaft  34 . 
   For the removal of the plate cylinder  2  and/or the rubber blanket cylinder  3 , the cylinder is displaced somewhat to the left for releasing the respective coupling mechanism  32  and for removing the upper half shell  15 , as shown in  FIG. 2 . Once the half shells  15  are tilted away, the plate cylinder  2  and/or the rubber blanket cylinder  3  can be lifted out by means of the recessed grips  9 . 
   The support shafts  4  and  5  are respectively connected securely to format sections  6  and  7  to ensure in each case a safe torque transfer from the support shafts  4  and  5  to the respective format sections  6  and  7  as well as high form stability. The connection between support shaft  4  and  5  and the respective format section  6  and  7  in particular can be form-locking, e.g. if the support shafts  4  and  5  are non-round and are inserted into a correspondingly non-round passage of the format section  6  and  7 . However, other types of connections are conceivable as well. 
   The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention.