Abstract:
Disclosed is a clamping device ( 02 ) for fastening a plate ( 03 ) to the periphery of a cylinder ( 01 ). Said clamping device ( 02 ) comprises a first clamping element ( 04 ), a pivotally mounted second clamping element ( 06 ), a spring part ( 07 ), and a bracing element that is embodied as a pivotable spindle ( 08 ) and is movable between a clamping position in which the bracing element maintains the plate in a clamped state between the clamping elements and a released position in which the clamping elements release the plate. The spindle ( 08 ) is mounted in a groove so as to be displaceable, is fixed in an intermediate space between the spring part ( 07 ) and the second clamping element ( 06 ), and is pressed against the second clamping element by means of the spring part in the clamping position.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a clamping device for a printing plate on a cylinder according to the preamble of claim  1 .  
         [0002]     The subject of the invention is a cylinder having a clamping device for fastening a plate, in particular a printing plate, to the periphery of the cylinder, the clamping device comprising a first clamping element, a pivotably mounted second clamping element, a spring part and a tensioning element, which can be moved between a clamping position, in which it holds the printing plate clamped in between the clamping elements, and a released position, in which the clamping elements release the printing plate. With the cylinder for example incorporated in a rotary press, printing plates with different thicknesses, such as those which occur in what is known as the letterpress process, for example, can be fastened to the periphery of the cylinder.  
       PRIOR ART  
       [0003]     A clamping device for fastening a printing plate to a press cylinder is disclosed, for example, by DE 690 20 463 T2. The clamping device comprises a clamp W for an upper edge of the printing plate and a clamp S for a lower edge of the printing plate. The two clamps W and S each comprise two clamping bars, between which the corresponding edge of the printing plate is clamped.  
         [0004]     The necessary clamping force is respectively ensured by a tensioning spindle, which is rotatably mounted between the clamping bars. The tensioning spindle has a cross section which is substantially circular, apart from a flat. It can be rotated into a position in which it presses with a maximum diameter against the two clamping bars and, in the process, clamps the printing plate between them, or else rotated into a position in which, because of a width shortened by the flat, it can no longer exert any clamping force on the clamping bars and the printing plate is released. However, with the embodiment shown, it is not possible to set the clamping force optimally to a specific thickness of the printing plate in order to fasten printing plates of different thicknesses. For example, printing plates with a low thickness are not clamped in firmly enough or even not at all in a gap between the clamping bars, while printing plates with a greater thickness under certain circumstances cannot even be inserted into the gap between the clamping bars.  
         [0005]     In EP 04 35 410 B2, a clamping device that is configured differently is shown. In the case of this clamping device, too, an edge of the printing plate is clamped in between two clamping bars. One of the clamping bars is pivotably mounted and is pressed against the other clamping bar by a resilient spring. In order to open the two clamping bars, a spindle with an eccentric cross section is provided, with which the pressure of the resilient spring can be counteracted. Although, in the case of this device, in the event of different thicknesses of the printing plate, the resilient spring is pressed in to different extents, which leads to a correspondingly changed spring force and therefore to a changed clamping force for the printing plate, this clamping force is firstly weak, because the resilient spring can exert only small spring forces, as a result of which printing plates with an excessively high thickness cannot be held in this clamping device. Secondly, during the insertion of the printing plate between the clamping bars, care must be taken that the spindle acts permanently counter to the spring force. This requires a fixing mechanism for the spindle, which means increased mechanical complexity, since without such a fixing mechanism there is the risk that, during the insertion of the printing plate, the spindle will slip and release the pivotable clamping bar again, which will then be pressed immediately against the other clamping bar because of the spring force. However, even with such a fixing device for the spindle, the insertion of the printing plate is cumbersome and associated with a risk of injury, since, in particular when the printing plate has a great thickness, it has a certain stiffness, which has to be overcome when bending over the printing plate and introducing it between the two clamping bars.  
         [0006]     As a consequence of this stiffness, the printing plate continually attempts to bend back again, so that it has to be held between the clamping bars while the fixing device for the spindle is released, in order that the clamping bars are are able to grip the printing plate. In this case, there is the risk to a person holding the printing plate that his fingers will be clamped in between the clamping bars. If the printing plate is mounted by only one person, the risk of injury is increased considerably, since he has to hold the printing plate with one hand while he simultaneously has to operate the fixing device for the spindle with the other hand.  
         [0007]     DE 26 06 773 B2 discloses a device for fastening a printing plate on a cylinder, in which the printing plates are held between fixed clamping bars and movable clamping elements. The clamping elements are moved by a pivotable, flattened spindle by means of interposed disk springs.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention is based on the object of providing a clamping device for a printing plate.  
         [0009]     According to the invention, the object is achieved by the features of claim  1 .  
         [0010]     The advantages that can be achieved with the invention are in particular that printing plates with different thicknesses can be fastened to the cylinder. By means of the special design of the clamping device, it is ensured that each printing plate experiences a clamping force from the clamping device which corresponds to its thickness, and is gripped securely by the clamping elements. Furthermore, the play of the tensioning element between the clamping elements in the released position prevents the clamping elements inadvertently snapping shut and, as a result, reduces the risk of injury. In addition, the mounting of the printing plate is simplified considerably, since it can firstly be introduced carefully between the clamping elements and is held by the latter before it is acted on with a clamping force by moving the tensioning element into the clamping position.  
         [0011]     The spring part preferably comprises at least one disk spring. As opposed to tensioning springs, disk springs have a considerably greater spring constant with a compact design and are therefore capable of exerting a much higher spring force with less compression. This permits a more compact and space-saving design of the clamping device, which is additionally capable of holding printing plates with a thickness in which a clamping device designed with resilient springs could not supply the clamping force needed for this purpose.  
         [0012]     The clamping device is preferably arranged in an elongated groove in the cylinder. Because the clamping device is countersunk completely in the groove, the cylinder can be used, for example, as a plate cylinder in a rotary press without the clamping device impeding the printing operation.  
         [0013]     In this case, a clamping device which can be displaced within the groove is particularly preferred. Using such a clamping device, the printing plate held by the clamping device can be tensioned by displacing the clamping device in the peripheral direction within the groove, so that the printing plate rests closely on the periphery of the cylinder, or can be displaced as a whole in the peripheral direction. The clamping device can also be displaceable along the groove. In a machine which has a plurality of plate cylinders for multicolor printing, the individual printing plates can be adjusted in register with the aid of such clamping devices.  
         [0014]     In this case, at least one of the clamping elements is preferably a bar running parallel to the groove. By using such bars, a printing plate can be clamped in along an entire length of one of its end sections, which improves the clamping.  
         [0015]     One side of the first clamping element, with which the first clamping element clamps the printing plate, preferably has a curved profile in section transversely with respect to the axis of the cylinder. In this case, depending on the suitability, the curved profile can be curved in the shape of a circular arc or a section of an ellipse or in any other desired way. Such a configuration of the first clamping element benefits kink-free clamping of the printing plate.  
         [0016]     Likewise preferred is a tensioning element which is a spindle running parallel to the groove. In the case of bar-like clamping elements, by means of a tensioning element embodied in this way, a clamping force may be applied along an entire length of the clamping elements, which benefits the secure clamping of the printing plate.  
         [0017]     The spindle preferably has a cross section substantially in the form of a circular segment with a first flat. Such a spindle may be moved from the clamping position into the released position and vice versa by means of simple rotation. Here, in the released position, the flat is oriented substantially toward one of the two clamping bars, which results in the play of the spindle in the interspace between the clamping bars.  
         [0018]     A further embodiment of the spindle has a second flat and a third flat, which are arranged diametrically with respect to each other on the spindle, in the clamping position the second flat pressing against the second clamping element and the third flat being pressed by the spring part. The second and the third flat have the effect that the spindle latches in in the clamping position.  
         [0019]     There are advantageously pins in one of the clamping elements, on which pins the printing plate is hooked in. By virtue of the pins, the mounting of the printing plate is simplified further, since it is prevented from sliding out between the two clamping elements.  
         [0020]     As already mentioned, the cylinder is particularly preferably a part of a rotary press.  
         [0021]     An exemplary embodiment of the invention is illustrated in the drawings and will be described in more detail in the following text. 
     
    
     BREIF DESCRIPTION OF THE DRAWINGS  
       [0022]     In the drawings:  
         [0023]      FIG. 1  shows a cross section through a part of a cylinder and a clamping device;  
         [0024]      FIG. 2  shows a front view of a first clamping element. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]      FIG. 1  shows a cross section through a part of a cylinder  01  with an associated clamping device  02 . In this case, the clamping device  02  is arranged within a longitudinal groove  11  in the cylinder  01  and entirely accommodated in this groove  11 . Fastened to the periphery of the cylinder  01  is a plate  03 , for example a printing plate  03 , which is bent down in one end section and is clamped in the clamping device  02 .  
         [0026]     The clamping device  02  includes a first clamping element  04 , a second clamping element  06 , a bearing block  17  having a spring part  07  and a tensioning element  08 . The first clamping element  04  is an L-profile bar  04  extending through the length of the groove  11 . Arranged in a limb  18  of the L-profile bar  04  which is vertical in the drawing are pins  16 , which project with one end section out of the end of the limb  18  and reach with a form fit through holes in the edge of the printing plate  03 . In a limb  19  of the L-profile bar  04  which is horizontal in  FIG. 1 , on the side of the limb  18 , a recess  21  is provided in an end section of the limb  19  opposite the limb  18 . The L-profile bar  04  is arranged within the groove  11  in such a way that the limb  18  is oriented toward an aperture  22  of the groove  11  in the surface of the cylinder  01 , and the limb  19  points away from the aperture  22 .  
         [0027]     The bearing block  17  rests on the horizontal limb  19  of the L-profile bar  04  and on the vertical limb  18 . At an end section facing the vertical limb  18 , the bearing block  17  has a rotary bearing  23 . In an end section facing away from the vertical limb  18 , the bearing block  17  has a channel-like groove  24  running parallel to the groove  11 . The second clamping element  06  is attached to the rotary bearing  23 , while the groove  24  serves as a bearing  24  for the tensioning element  08 . At the lowest point of the bearing  24  an aperture  26  is provided as an engagement for the spring part  07 .  
         [0028]     The second clamping element  06  extends through the length of the groove  11  and is attached to the rotary bearing  23  such that it can pivot about a longitudinal axis. Thus, the clamping element  06  acts like a two-armed lever. A lever arm facing the aperture  22  forms a clamping bar  06 , which rests on the vertical limb  18  of the L-profile bar  04 . The clamping bar  06  has holes  27 , into which the pins  16  projecting from the limb  18  project.  
         [0029]     The tensioning element  08  is a spindle  08  which extends through the length of the groove  11 . The spindle  08  substantially has a cross section in the form of a circular segment with a wide first flat  12 . Provided on the spindle  08 , diametrically with respect to each other, are two further flats  13  and  14 , which are parallel to each other and are both arranged at right angles to the flat  12 . The flats  13  and  14  are much narrower than the flat  12 . The spindle  08  extends over the entire length of the bearing block  17  and is rotatably mounted in its groove  24 . The spacing of the flats  13 ,  14  from the axis of rotation of the spindle  08  corresponds to the radius of curvature of the part of the cross section that is in the form of a circular segment; the spacing of the flat  12  from the axis of rotation is smaller.  
         [0030]     The spring part  07  comprises a plurality of springs  09 , for example disk springs  09 , on which a plate  28  is mounted. The plate  28  has a protrusion  29  on a side facing away from the disk springs  09 . The disk springs  09  and the plate  28  are accommodated by the recess  21  in the horizontal limb  19  of the L-profile bar  04 . In this case, the protrusion  29  reaches through the aperture  26  in the bearing block  17  into the interior of the bearing  24  and presses against the spindle  08  located in the latter.  
         [0031]     When the spindle  08  is in a released position, it is oriented with the first flat  12  either toward a lever arm of the clamping bar  06  facing away from the aperture  22  or toward the protrusion  29  of the spring part  07 . It then has play within the bearing  24 , that is to say in an interspace between the spring part  07  or the protrusion  29  of the spring part  07  and the clamping bar  06 . The disk springs  09  press the plate  28  against the bearing block  17 . The clamping bar  06  can pivot freely about the rotary bearing  23  and can be pivoted back in order to release the pins  16 .  
         [0032]     In order to fasten the printing plate  03 , first of all an edge section of the printing plate  03  provided with holes is pushed through the aperture  22  in the groove  11  in the periphery of the cylinder  01  and hooked onto the pins  16  by means of the holes. The printing plate  03  is then bent around the cylinder  01  and an opposite edge section is hooked in a second groove  11  in the same way. In order to avoid the bending leading to permanent deformation of the printing plate  03 , the limb  18  of the L-profile bar  04  has a curved profile in section transversely with respect to an axis of the cylinder  01 , as shown in  FIG. 2 . In the embodiment of the L-profile bar  04  shown, the curvature has the form of a circular section.  
         [0033]     In order to clamp the printing plate  03  between the two clamping elements  04  and  06 , the spindle  08  is rotated into the clamping position shown in  FIG. 1 . In this position, it presses with its second flat  13  against the clamping bar  06  and with the third flat  14  against the protrusion  29  of the spring part  07 . In order to assume this position, an additional expenditure of force, which can easily be applied, is necessary so that the spindle  08  is latched in the clamping position by virtue of the flats  13  and  14 . The disk springs  09  are compressed by the spindle  08  via the protrusion  29 . They react to this with a spring force which, via the protrusion  29 , acts on the spindle  08  and on the second clamping element  06 . Since the second clamping element  06  acts like a two-armed lever as a result of its pivotable mounting on the rotary bearing  23 , the printing plate  03  is clamped in between the clamping bar  06  of the second clamping element  06  and the limb  18  of the L-profile bar  04 .  
         [0034]     Depending on the thickness of the printing plate  03  clamped in, the disk springs  09  are compressed either more or less and react with a correspondingly different spring force, that is to say the clamping force for the printing plate  03  increases with the thickness of the printing plate  03 , since the disk springs  08  are compressed to a greater extent with increasing thickness of the printing plate  03 . Thus, in this embodiment of the clamping device  02 , a clamping force corresponding to the thickness of the printing plate  03  is automatically established by itself.  
         [0035]     After the printing plate  03  has been clamped in between the L-profile bar  04  and the clamping element  06 , the clamping device  02  is pushed away from the aperture  22  within the groove  11 , in order to tension the printing plate  03  on the periphery of the cylinder  01 . For this purpose, a tensioning screw  31  is provided, which strikes a wall of the groove  11  and with which the clamping device  02  can be displaced toward the aperture  22  or away from the aperture  22  within the groove  11 .  
         [0036]     After printing has been carried out, the printing plate  03  is removed from the cylinder  01  by the spindle  08  being rotated into the released position again, in which said plate has play in the interspace between the spring part  07  and the second clamping element  06 , so that the second clamping element  06  can again be pivoted freely. Now, the clamping bar  06  of the second clamping element  06  can easily be pivoted back, as a result of which the pins  16  are exposed and the printing plate  03  can be unhooked from the pins  16 .  
         [0037]     The invention is not restricted to the embodiment described. Instead, alternative configurations of the clamping device  02  shown are possible without departing from the idea of the invention. For example, in the described configuration of the clamping device  02 , the first clamping element  04  or the L-profile bar  04  is a bar that extends over the entire length of the groove  11 , the second clamping element  06  also being configured as a continuous bar. As an alternative to this, the second clamping element  06  can be composed of a plurality of clamping levers which are attached to a plurality of bearing blocks  17 . Likewise, the first clamping element  04  can be composed of a plurality of L-profile pieces  04 , on which the bearing blocks  17  rest, instead of being formed as a continuous L-profile bar  04 . Quite generally, the first clamping element  04  and the second clamping element  06  can be formed in any desired combination in one piece as bars or can be composed of a plurality of pieces.  
       LIST OF DESIGNATIONS  
       [0000]    
       
           01  Cylinder  
           02  Clamping device  
           03  Plate, printing plate  
           04  First clamping element, L-profile bar  
           05  -  
           06  Second clamping element, clamping bar  
           07  Spring part  
           08  Tensioning element, spindle  
           09  Spring, disk springs  
           10  -  
           11  Groove  
           12  First flat  
           13  Second flat  
           14  Third flat  
           15  -  
           16  Pin  
           17  Bearing block  
           18  Vertical limb  
           19  Horizontal limb  
           20  -  
           21  Recess  
           22  Aperture  
           23  Rotary bearing  
           24  Groove, bearing  
           25  -  
           26  Aperture  
           27  Holes  
           28  Plate  
           29  Protrusion  
           30  -  
           31  Tensioning screw