Abstract:
To provide a device for fixing a covering to a printing-unit cylinder in which, while implementing a narrow gap in the cylinder circumferential surface, the legs of the covering can be tensioned easily and reliably, a spindle bears a trailing channel edge of a tension channel the trailing channel edge can be moved away from the leading channel edge by pivoting the spindle.

Description:
PRIORITY CLAIM 
     This is a U.S. national stage of application No. PCT/EP2003/001816, filed on 22 Feb. 2003. Priority is claimed on that application and on the following application(s): Country: Germany, Application No.: 102 08 262.6, Filed: 26 Feb. 2002. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for fixing a covering to a printing-unit cylinder of a printing machine. 
     2. Description of Prior Art 
     shows a device for fixing a flexible printing plate to a forme cylinder. The device has a spindle arranged in a cylinder channel. The printing plate to be tensioned is hooked in with its angled-over leading leg on a leading channel edge and wound around the forme cylinder. The angled-over trailing leg is then inserted into the tensioning channel and plugged into a slot in the spindle. When the spindle is rotated, it presses the leading leg against a channel wall and pulls the trailing leg into the tensioning channel. 
     The device has a trailing leg of complicated shape, a broad gap in the cylinder circumferential surface being required for its insertion into the tensioning channel. This necessitates a corresponding loss in cylinder circumferential surface, which is not available for a print and manifests itself in unprintable, white margins. Furthermore, a wide gap causes oscillations during printing. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a device for fixing a covering to a printing-unit cylinder in which, while implementing a narrow gap in the cylinder circumferential surface, the legs of the covering can be tensioned easily and reliably. 
     According to the present invention, a device for fixing a covering to the printing-unit cylinder, the covering having a leading angled-over leg and a trailing angled-over leg, comprises a leading channel edge of a tensioning channel defined in the printing-unit cylinder along an axial direction of the printing-unit cylinder for hooking the leading angled-over leg of the covering, and a spindle arranged in the printing-unit cylinder and running along the axial direction of the printing-unit cylinder. The spindle is pivotable to a tensioning position for tensioning the trailing angled-over leg of the covering. Furthermore, the spindle accommodates a trailing channel edge of the tensioning channel, wherein the spindle is pivotable away from the tensioning position for moving the trailing channel edge away from the leading channel edge. By virtue of the ability of the trailing channel edge to be moved back, a narrow channel can be implemented during printing operation and a broad channel when the covering is changed. This permits the use of a simply shaped leading and trailing leg, which can be inserted easily into the tensioning channel. This makes it possible to change a covering automatically. In addition, a very narrow gap in the cylinder circumferential surface can be implemented, as a result of which the loss of area, which is not available for the print, is small. Furthermore, oscillations, channel impacts as they are known, are reduced, which provides preconditions for good printing quality. Further features and advantages emerge from the subclaims in conjunction with the description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below using an exemplary embodiment. In the drawings: 
         FIG. 1  is a side view of a form cylinder according to the invention, 
         FIG. 2  is a sectional view along line II—II from  FIG. 1 , 
         FIG. 3  is a sectional view along line III—III from  FIG. 1 , and 
         FIG. 4  is a sectional view along line IV—IV from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The forme cylinder  1  shown in  FIG. 1  is mounted in side walls by its journals  2 ,  3  (the sidewalls are not illustrated). A spindle  4  is mounted in the forme cylinder  1 , running in the axial direction of the latter. The spindle  4  has a recess which, together with a channel wall  5  of the forme cylinder  1 , forms a tensioning channel  6  (e.g.  FIG. 4 ). The channel wall  5  runs at an acute angle to the circumferential surface of the forme cylinder  1  and, at the point of intersection with the latter, forms a leading channel edge  7 . The spindle  4  accommodates a trailing channel edge  8 , adjacent to which the spindle has a face  9  with which a circumferential area of the forme cylinder  1  may be represented. 
     The spindle  4  is rotatably mounted in the body of the forme cylinder  1  and can be pivoted over a range by a drive. One drive variant is illustrated in  FIG. 3 . In detail, the spindle  4  makes a toothed form fit with a push rod  10 . The spindle  4  bears a lug  11  which engages in a spherical hole  12  in the push rod  10 . As an alternative, the spindle  4  could also bear a toothed segment which engages with a rack on the spindle  10 . Fixed to the push rod  10  is piston  13  which can be displaced in a bore  14  in the forme cylinder  1 . The piston  13  and the bore  14  form an operating cylinder which can be fed with compressed air via lines  15  and  15 . 1 . When fed with compressed air, the piston  13  is acted on accordingly and, together with the push rod  10  and the spindle  4 , assumes the position shown in  FIG. 3 . In the process, a compression spring  17  supported on a plug  16  is stressed. When the compressed air is switched off, the compression spring  17  displaces the piston  13  in the now unpressurized pressure chamber in the bore  14 , the spindle  4  being pivoted in the clockwise direction. In the process, the spindle  4  is pivoted into the end position shown in  FIG. 4 , in which a lug  18 , designed for example as a key, strikes the end of a recess  19  in the cylinder body. The spindle drive described is advantageously arranged many times on the spindle  4 , for example twice in the exemplary embodiment. 
     The stop position of the spindle  4 , shown in  FIG. 4 , is the tensioning position for the printing forme  20  (also referred to as printing plate  20 ), to be tensioned. In this tensioning position, the spindle  4  is blocked by a wedge  21 , as shown in  FIG. 4 . For this purpose, the wedge  21  is moved against a wedge face  22  on the spindle  4 . This is done by the force of a compression spring  23 , which is supported against a plug  24  in the cylinder body and against which there presses a piston  25  which is fixed to the wedge  21 . Together with a bore  26 , the piston  25  forms an operating cylinder. The bore  26  can be filled with compressed air via lines  27  and  27 . 1 . When pressure is applied to the piston  25  in this case, the latter is moved together with the wedge  21  counter to the force of the compression spring  23 , it being possible for the wedge  21  to be brought out of contact with the wedge face  22  and for the blocking of the spindle  4  to be cancelled. A plurality of the above-described blocking devices may be provided on the spindle  4 . In addition, one or more spring hooks  28 , two spring hooks  28  in the exemplary embodiment, can be moved in the tensioning channel  6  ( FIG. 2 ). The spring hook  28  is fixed to a piston rod  29 , which is connected to a piston  31  that can be displaced in a bore  30 . The bore  30  and the piston  31  form an operating cylinder whose pressure chamber is closed by a plug  32  and can be fed with compressed air via lines  33  and  33 . 1 . When the pressure chamber is fed with compressed air, the piston  31  together with piston rod  29  and spring hook  28  assume the position shown in  FIG. 2 , a compression spring  34  supported at the bottom of the bore  30  being stressed. When the compressed air is switched off, that is to say when the pressure chamber on the piston  31  is depressurized, the force of the compression spring  34  effects a movement of the piston  31  towards the plug  32 , the spring hook  28  being pulled into the tensioning channel  6 . 
     The tensioning of the flexible printing forme  20  is carried out by the latter first being hooked in with its leading angled-over leg  35  on the leading channel edge  7  of the forme cylinder  1 . The spindle  4  and the spring hook  28  are in this case in the positions shown in  FIG. 2 . For this purpose, the push rod  10  of the spindle drive inherently has the position shown in  FIG. 3 , and the piston rod  29  bearing the spring hook  28  inherently has the position shown in  FIG. 2 . In this spindle position, the tensioning channel  6  is open wide, and it is easily possible to insert the leading leg  35  (and subsequently the trailing leg  36 ) of the printing forme  20 . The compressed-air supply to the bore  30  is then switched off ( FIG. 2 ) as a result of which the compression spring  34  moves the piston on to the plug  32 , and the spring hook  28  is pulled into the tensioning channel  6 . In the process, it is placed on a notch  37  in the leading leg  35  and pulls the leading leg of the printing forme  20  into the tensioning channel  6  and brings the printing forme  20  with its angled-over edge into contact with the leading channel edge  7 . The printing forme  20  is aligned well with the leading channel edge  7  in the process. Alignment by hand, for example by tapping, is rendered superfluous. Good alignment is important for the following correct-position mounting. In the exemplary embodiment, the notch  37  is designed in the manner of a step. It could also be shaped in a V, for example. 
     The printing forme  20  hooked in at the leading channel edge  7  and firmly clamped on the latter by means of the spring hook  28  is subsequently wound around the forme cylinder  1  ( FIG. 3 ). In the process, one or more pressure rolls  38 ,  39  press the printing forme  20  firmly on to the forme cylinder  1 . Instead of this, an adjacent transfer cylinder can also be brought into rolling contact with the forme cylinder  1 . Towards the end of a rolling revolution, the area of form cylinder  1  in which the spindle  4  is arranged approaches the pressure rolls  38 ,  39 , the trailing leg  36  pivoting into the tensioning channel  6  ( FIG. 3 ). 
     With the tensioning channel  6  opened in the spindle position shown, the pivoting-in action is easily possible. In addition, the point of rotation of the spindle  4  in the body of the forme cylinder  1  is arranged in such a way that the trailing channel edge  8  on the spindle  4  and the face  9  of the spindle do not emerge beyond the circle of the forme cylinder  1 . As a result, it is possible to plug the leading leg completely into the tensioning channel  6 . The trailing edge  36  plugged in comes to rest on a stop  40  on the spindle  4 . In addition, one or more leaf springs  41  arranged beside one another are placed in front of the trailing channel edge  8  ( FIG. 3 ). These leaf springs  41  engage behind the trailing leg  36  hooked in on the trailing channel edge  8  and supported on the stop  40 . The spindle  4  is then rotated into the tensioning position ( FIG. 4 ) by switching off the compressed air in the bore  14 , the leaf springs  41  being moved elastically on to the spindle wall  42  adjacent to them and being prestressed. During printing operation, the prestressed leaf springs  41  hold the trailing plate end under tension and retention the printing plate  20 . The printing plate  20  has now been tensioned and the pressure rolls  38 ,  39  can be set off. 
     The device has the advantage that the tensioned printing plate  20  is not held by compressed air, but that instead the tensioning function is maintained by the compression springs  17 ,  23  and  34 . As a result, the tensioning device is secure against accidents in the event of compressed-air failures. In addition, no compressed air needs to be supplied during printing operation, as a result of which friction losses in rotary inlets are minimized. The pressure fluid used can, for example, also be oil. The fluid is advantageously supplied to the lines  15 ,  27 ,  33  via lines in the journals  2 ,  3 . It is also advantageous that the leading leg  35  and trailing leg  36  can be tensioned independently of each other by separate means. As a result, the leading leg  35  and the plate start can be held during the entire pulling-on operation. Reverse rotations of tensioning means and also of the forme cylinder are not required. The tensioning operation can be carried out with a single revolution of the forme cylinder  1 . This manifests itself in a time saving and permits rapid tensioning of the printing forme  20 . 
     The removal of the printing forme  20  is carried out in the reverse sequence to its mounting. First of all, the forme cylinder  1  is rotated into the position shown in  FIG. 3  with respect to the pressure rolls  38  and  39 , the latter being set on. At the same time or thereafter, the blocking of the spindle  4  is cancelled by compressed air being applied to the piston  25  by supplying compressed air via the line  27  and  27 .  1 , and said piston being pulled back counter to the force of the compression spring  23  ( FIG. 4 ). The spindle  4  is then pivoted into the position shown in  FIG. 3  by compressed air being applied to the piston  13  via the lines  15  and  15 . 1  and said piston being pulled back counter to the force of the compression spring  17 . The trailing end of the printing forme  20 , together with the trailing leg  36 , then springs out of the tensioning channel  6 . During the further rotation of the forme cylinder  1  in the clockwise direction, the printing forme  20  is unwound from the forme cylinder  1  and can be lifted off the leading channel edge  7  in the position shown in  FIG. 2 . Previously, however, the spring hooks  28  still have to be shifted into the position shown in  FIG. 2 . For this purpose, compressed air is applied to the piston  31  via the lines  33  and  33 . 1 , the piston  31  moving upwards counter to the force of the compression spring  34 , the spring hook  28  likewise moving and releasing the notch  37  in the leading leg  35 . 
     Arranged in the cylinder channel  6  is a dirt cover  43 , which protects the deeper areas against contamination. The dirt cover  43  is advantageously screwed to the spindle  4  by a profiled strip  44 , if necessary subdivided into portions. The profiled strip  44  advantageously also bears the stop  40  and a rounded portion  45 , with which the spring hook  28  acting on the notch  37  is prevented from bending out ( FIG. 2 ). The tensioning channel  6  may be cleaned easily as a result of its possible wide opening. In addition, the individual parts of the device are easily accessible. The spindle  4  can be mounted outside the area of Schmitz (bearer) rings  51 ,  52 , which allows the spindle  4  to be removed radially from the forme cylinder  1 , which makes simple maintenance and, if necessary, repair possible. 
     Furthermore, the device does not require any large, complicated mountings for the spindle  4 , since the latter, in the tension state, is mounted in a bore in the forme cylinder  1  reliably and without the risk of bending, and is supported at the points A, B and C and on wedge  21  when in the blocked position ( FIG. 4 ). Only small mountings (not illustrated) are provided at the ends on the cylinder circumference or in the edge regions of the latter, without any qualitative requirements on bearing quality, in order to secure the opened spindle  4 . This, and also the arrangement of the spindle  4  in the circumferential area and its drive in the interior of the forme cylinder  1 , permit the journals  2 ,  3  to be designed with a large diameter and to keep the dimension between the printing-unit walls small, or to design the cylinder bodies to be wide. If appropriate, assisting this, the Schmitz rings can also be dispensed with. The result, overall, is that high rigidity of the printing-unit cylinder can be achieved. 
     The device can be employed for many printing-machine types and at the same time in each case for the smallest to the largest formats. Changing a printing forme can be implemented manually, semiautomatically or fully automatically. By virtue of simple configuration of the leading and trailing legs  35 ,  36 , no special requirements are placed on the preceding systems for printing-plate production, for example edge-angling devices. The angled-over edges can be produced simply and reliably, for example whilst maintaining close tolerances, even relatively small section lengths being feasible. Punched holes can also be introduced. 
     In the operating state, the channel in the cylinder circumferential surface can be closed apart from a very small distance a ( FIG. 4 ), to be specific virtually as far as contact between the printing-forme angled-over edges. The distance between the leading and trailing channel edges  7 ,  8  can thus be dimensioned to be approximately of the size of twice the printing plate thickness. This permits the non-printing area to be minimized in the extreme and the implementation of a large image size. In addition, the excitation of oscillations by channel impacts is reduced, and thus the achievable print quality is improved. 
     Using the device, rubber blanket units  46  can also be tensioned. One such is also shown by thin lines in  FIG. 3 , the item numbers being specified in brackets. The rubber blanket unit  46  includes a carrier plate  47 , on which a rubber blanket  48  is fixed, with the exception of the leading and trailing legs. The legs are tensioned in the device in an analogous way to those of the printing forme  20 . 
     The invention can also be used when a plurality of tensioning channels  6  are arranged on the circumference of the printing-unit cylinder  1 , into which in each case a leading and a trailing leg  35 ,  36  of two adjacent coverings  20 ,  46  to be fixed can be plugged.