Abstract:
In an apparatus for feeding printing plates to a plate cylinder of a printing press, the printing plate is prealigned on stops outside the plate cylinder with a lateral offset and with an oblique skew. Then the printing plate is fed, in the thusly aligned position to the register pins of the plate cylinder, wherein the printing plate is finally aligned by lateral displacement and by a pivoting movement about the first register pin, until the printing plate bears with its receptacles against both register pins.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German patent application DE 10 2008 016 225.6, filed Mar. 27, 2008; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method and apparatus for feeding printing plates to a plate cylinder of a processing machine, in particular a printing press, having aligning means for the prealignment and final alignment of the printing plates. 
     An apparatus of this generic type is described in the commonly assigned German published patent application No. DE 198 03 723 A1 and its counterpart U.S. Pat. No. 6,571,708 B1. There, there is disclosed an apparatus for feeding printing plates to a plate cylinder of a printing press, having aligning means for the prealignment and final alignment of the printing plate. The aligning means for the prealignment have an offset as viewed in the printing plate feed direction. The offset is identical to an offset of the aligning means on the plate cylinder. This measure is intended to avoid the printing plate being fed with the sides reversed. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a printing plate feed method and a printing plate feed apparatus, which overcome certain disadvantages of the heretofore-known devices and methods of this general type and which use aligning means that ensure tautening of the printing plate. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for feeding a printing plate to a plate cylinder of a processing machine, such as a printing press. The method comprises the following steps: 
     prealigning the printing plate on stops outside the plate cylinder in an obliquely and laterally offset position relative to a final alignment position; 
     subsequently feeding the printing plate to register devices of the plate cylinder with an oblique orientation and with a lateral offset; and 
     aligning the printing plate laterally upon coming into contact with a first register device and pivoting the printing plate about the first register device until the printing plate is aligned in the final alignment position. 
     It is a particular advantage of the invention that the printing plate can be tautened simply by a fixed arrangement of the aligning means. 
     In accordance with an added feature of the invention, the printing plate is first brought into engagement with the first aligning device and subsequently into contact with a second aligning device by pivoting the printing plate about the first aligning device. 
     With the above and other objects in view there is provided, in accordance with the invention, an apparatus for feeding a printing plate to a plate cylinder of a processing machine, such as a printing press. The apparatus comprises: 
     an aligning assembly formed with an aligning device for a prealignment of the printing plate and an aligning device for a final alignment of the printing plate; 
     the aligning device for the prealignment of the printing plate having a lateral offset with respect to the aligning device for the final alignment of the printing plate on the plate cylinder; 
     the aligning device for the prealignment of the printing plate having a first stop and a second stop and the aligning device for the final alignment of the printing plate having a first register pin and a second register pin; and 
     wherein a spacing between the first stop and the first register pin is greater than a spacing between the second stop and the second register pin. 
     In accordance with an added feature of the invention, there are provided transport means for transporting the printing plate from the first and second stops to the first and second register pins. 
     In accordance with an added feature of the invention, the stops for the prealignment of the printing plate are disposed on a protective device of the processing machine, such as on a cover of a cylinder and roll region of the printing press. 
     In accordance with an added feature of the invention, the first and second register pins (i.e., the final alignment register pins) are disposed on the plate cylinder. 
     The invention is particularly suited for implementation in the context of a rotary printing press. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a method and apparatus for feeding printing plates to a plate cylinder of a processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic sectional illustration of a sheet-fed rotary printing press; 
         FIG. 2  shows the printing plate feed apparatus in an operating position and in a printing plate receiving position; 
         FIG. 3  shows the printing plate feed device in the operating position; and 
         FIG. 4  is a diagrammatic plan view of the printing plate feed path with prealignment and final alignment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a sheet-processing machine, for example a printing press  1 . The assembly includes a feeder  2 , at least one printing unit  3  and/or  4  and a delivery  6 . Sheets  7  are removed from a sheet stack  8  and are fed in a separated or overlapping manner to the printing units  3  and  4  via a feed table  9 . The printing units  3  and  4  comprise in a known manner in each case one plate cylinder  11 ,  12  and blanket cylinders  15 ,  20  which interact in each case with the latter. The plate cylinders  11  and  12  have in each case one clamping apparatus  13 ,  14  for fastening flexible printing plates. Moreover, each plate cylinder  11 ,  12  is assigned an apparatus  16 ,  17  for changing printing plates in a semiautomatic or fully automatic manner. 
     The sheet stack  8  rests on a stack board  10  which can be raised in a controlled manner. The sheets  7  are removed from the upper side of the sheet stack  8  by means of a so-called suction head  18  which has, inter alia, a number of lifting and dragging suckers  19 ,  21  for separating the sheets  7 . Moreover, blowing devices  22  are provided for loosening the upper sheet layers and sensing elements  23  are provided for tracking the stack. A number of lateral and rear stops  24  are provided for aligning the sheet stack  8 , in particular the upper sheets  7  of the sheet stack  8 . 
     The apparatuses  16 ,  17  are structurally identical and will therefore be described using primarily by reference to the apparatus  16 . The apparatus  16  has a guide element  27  for a printing plate  28 . The guide element  27  is arranged pivotably on a protective means  29  which covers the cylinder and roll region in front of the printing unit  3 . The guide element  27  is arranged such that it can be pivoted from a receiving position “A” for the printing plate  28 , in which it is prealigned by means of provided stops  30 ,  31 , into an operating position “B” for feeding the printing plate  28  to the plate cylinder  11 . The guide element  27  has a guide plane  32  which, in the operating position “B”, forms an extension of a printing plate clamping pad  33  of the clamping device  13  of the plate cylinder  11  and is arranged on the guide element  27  such that it can be pivoted on a lever  37 . Furthermore, two transport rollers  34 ,  36  are arranged on the guide element  27 , which transport rollers  34 ,  36  are jointly in working contact, in order to transport the printing plate  28  or to fix it in the receiving position “A”. Here, the transport roll  34  which is in contact with the rear side of the printing plate  28  is arranged directly on the guide element  27 , and the transport roll  36  which is in contact with the imaged printing plate front edge is mounted on the pivotably arranged lever  37 . A printing plate flexing roller  41  is mounted rotatably at one end which is remote from the bearing point  38  of the lever  37 . In the operating position “B”, the printing plate flexing roller  41  lies between one end of the guide face  32  and the printing plate clamping pad  33 . Here, the printing plate flexing roller  41  presses onto a defined location on the printing plate  28 . The defined location corresponds to the bent location which a used printing plate has when it is reused. This bent location is produced by the transition from the clamping device  13  to the circumference of the plate cylinder  11 . 
     In order to feed a new printing plate  28  or one which has already been used to the plate cylinder  11 , the printing plate  28  is first of all prealigned on the stops  30 ,  31  in the receiving position “A”. The guide element  27  then pivots about its bearing point  42  into the operating position “B” for feeding the printing plate. Here, the printing plate flexing roller  41  optionally presses onto the bent location of the used printing plate  28 . The printing plate flexing roller  41  is then pivoted in the direction of the plate cylinder  11  until the printing plate front edge is aligned parallel to the printing plate clamping pad  33 . As soon as the printing plate front edge is parallel to the clamping pad  33 , the transport rolls  34 ,  36  transport the printing plate  28  into the clamping device  13 . 
     The printing plate is prealigned on the stops  30 ,  31  in such a way that the printing plate is positioned obliquely in relation to its front edge by a small angular offset a and is prealigned by a lateral offset S with respect to the register pins  43 ,  44 , also referred to as a first register device  43  and a second register device  44 . The printing plate  28  is then fed to the register pins  43 ,  44  obliquely and with the lateral offset S. 
     A spacing a between the stop  30  for the prealignment of the printing plate  28  and the register pin  43  of the plate cylinder  11  is smaller than a spacing b between the stop  31  for the prealignment of the printing plate  28  and the register pin  44  of the plate cylinder  11 . 
     At its front edge, the printing plate has two receptacles  46 ,  47  which, for prealignment, are first of all brought into bearing contact with the stops  30 ,  31  of the printing plate feed apparatus (in the direction of arrow C in  FIG. 4 ) and later with the register pins  43 ,  44  on the plate cylinder  11 . 
     The stop  30  and the register pin  43  have a circular cross section and, for example as viewed in the printing plate feed direction, are arranged on the right hand side of the printing plate. 
     The receptacle  46  which can be brought into contact with said aligning means  30 ,  43  likewise has a contour which is adapted to the circular shape, run up slopes  48  being provided which are arranged in a funnel shape and facilitate the engagement of the register pin  43  into the receptacle  46 . 
     The stop  31  and the register pin  43  have a square or rectangular cross section and, as viewed in the printing plate feed direction, are correspondingly arranged on the left hand side of the printing plate. 
     The receptacle  47  which can be brought into contact with said aligning means  31 ,  44  likewise has a contour which is adapted to the cross sectional shape, with run up slopes  49  which are arranged in a funnel shape. 
     When the printing plate  28  is fed to the plate cylinder  11 , said printing plate  28  is first of all prealigned on the stops  30 ,  31 . Here, the printing plate  28  assumes an oblique position in relation to its aligned position on the plate cylinder and is arranged to the side by the offset S in the printing plate feed direction, for example to the left. 
     The printing plate is then fed in this position to the register pins  43 ,  44  of the plate cylinder  11 . Here, the printing plate  28  first of all comes into contact by way of the run up slope  48  of the receptacle  46  with the circular register pin  43 . 
     As a result of the run up slope  48 , the printing plate is displaced laterally to the right, as viewed in the printing plate feed direction, until the register pin  43  engages into the circular receptacle  46 . The printing plate is then pivoted about the register pin  43  until the register pin  44  also engages into the receptacle  47 . The printing plate is then aligned on the plate cylinder with regard to the register pins  43 ,  44  and can be clamped by means of the provided clamping elements  13 . 
     After the printing plate  28  has been gripped and clamped fixedly, the lever  37  is pivoted away with the printing plate flexing roller  41 , the guide plane  32  and the transport roller  36 . 
     As a result of this measure, the printing plate  28  can be wound up by rotation of the plate cylinder  11 , without the guide elements being in contact with the imaged side of the printing plate  28 . 
     The printing plate is fed by means of the transport rollers  34 ,  36  and the pivoting movements of the guide element  27  and the lever  37  take place by way of actuating means which can be actuated remotely, preferably in an automatically controlled manner.