Patent Abstract:
A device for fastening printing forms (10) on printing form cylinders (1) of rotary printing presses. The printing forms (10) extend into a clamping channel (3) with their leading edge (12) and their trailing edge (13) and are tensioned therein, via clamping elements, on the lateral surface (2) of the printing form cylinder (1) in a circumferential direction of the printing form cylinder (1) and retained in the clamping channel (3). The clamping elements are accommodated on a tensioning shaft (6) which is rotatably inserted in a bore of the printing form cylinder (1). The clamping elements are designed as spring elements (16, 27) in Y-shape (21), including a first and a second resilient section (17, 19).

Full Description:
Priority to German Patent Application No. 100 60 826.4, which is hereby incorporated by reference herein, is hereby claimed. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a spring element for fixing in place printing forms on printing form cylinders which are contained in printing units of rotary printing presses, the printing forms being printing forms which have a plate-shaped configuration and feature angularly bent leading edges and trailing edges. 
     European Patent No. 0 534 579 B2 relates to a device for changing printing plates in a rotary printing press. In this design approach, provision is made for a plurality of leaf springs which are each formed of a leaf spring member and have a U-shaped cross-section. These leaf springs are accommodated in a spring groove. The leaf springs each include a leg via which the leading end of the printing plate is retained in the clamping channel; the leaf springs, moreover, include a second leg via which an angularly bent trailing printing plate edge is fixed in place in the clamping channel of the printing form cylinder. A tensioning spindle is acted upon by a preloading element so that the tensioning spindle can be moved is such a manner that the leaf springs can act both upon a leading edge and upon a trailing edge of a printing plate. 
     The leaf spring arrangement known from European Patent EP 0 534 579 B2 involves the disadvantageous circumstance that, due to the narrow installation space, the leaf springs cannot be fitted into a preassembled tensioning shaft which is already integrated into the printing form cylinder. 
     SUMMARY OF THE INVENTION 
     In view of the indicated related art, an object of the present invention is to provide a spring element which is easy to mount and dismount, for fixing in place printing forms on cylinders. 
     According to the present invention, this objective may be achieved by a device or fixing printing forms on printing form cylinders of rotary printing presses, the printing forms extending into a clamping channel with their leading edges and trailing edges and, via clamping elements in the clamping channel, being tensioned on the lateral surface of the printing form cylinder in a circumferential direction of the printing form cylinder and retained in the clamping channel. The clamping elements are accommodated on a tensioning shaft which is rotatably accommodated in a bore of the printing form cylinder, and the clamping elements are designed as Y-shaped spring elements including a first and a second resilient section. 
     The advantages which can be attained using this design approach are to be seen above all in that a tension spring element configured in this manner needs an extremely small installation space and that it can be installed after the tensioning spindle has already been introduced into the receiving bore in the printing form cylinder accommodating the printing form. This involves that the installation work is made easier and rationalized; moreover, the spring element configured according to the present invention for fixing in place printing forms can be replaced in the clamping channel of a printing form cylinder easily. During the replacement of the clamping elements configured according to the present invention, it is not required to remove the cylinder from the side walls of the printing unit, which would result in unjustifiably long standstill times (downtime) of the respective printing unit. A further advantageous aspect of the design approach according to the present invention is to be seen in that a spring element having the design proposed according to the present invention allows both the printing form to be tensioned in a circumferential direction on the lateral surface of the respective printing form cylinder and the leading printing form edge to be fixed in place on a side wall of the clamping channel concurrently with the tensioning of the trailing printing form edge. The configuration of a spring element according to the present invention makes it possible for the printing form ends to be fixed in place in the clamping channel, involving a high retention force, while at the same time permitting compensating movements of the printing form on the lateral surface due to the flexural elasticity of the clamping element configured according to the present invention. 
     In an advantageous refinement of the idea of the present invention, a plurality of spring elements can be accommodated side by side in the clamping channel of the respective printing form cylinder. This permits an easy mounting or dismounting of the spring elements on printing units of rotary printing presses which contain extremely slender and therefore relatively wide printing form cylinders. 
     A first variant of an embodiment of the spring elements configured according to the present invention includes a first and a second resilient section made of flexurally elastic material of different material thickness. In this context, in a particularly simple manner in terms of production engineering, the first and the second resilient section can be made of materials of different material thickness which are joined to form a spring element configured according to the present invention, the spring qualities of the spring element being adjustable through the selection of the material thickness. Thus, for instance, the first resilient section which tensions the trailing edge of a printing form in a circumferential direction on the lateral surface of a printing cylinder can be designed with a higher, a greater material thickness in comparison with the second resilient section of the spring element projecting from the first resilient section in a Y-shaped manner. 
     To improve the transfer of the retention force, the first resilient section designed with a greater material thickness is provided with an angularly bent, hook-shaped end region via which the trailing edge of the printing form to be fixed in place on the lateral surface of the printing form cylinder is grasped and tensioned in a circumferential direction. Because of the flexural elasticity inherent in the first resilient section, the tensional force is permanently transferred to the printing form when the spring element is in a tensioning position. 
     At a spreading location, the second resilient section of the spring element branches off from the first resilient section in a Y-shaped fashion in a manner which reduces the required installation space. Because of this, the spring element configured according to the present invention can be inserted into the clamping channel provided on the printing form cylinder with the locating section ahead which can easily be introduced into the receiving slot of the tensioning shaft which accommodates and actuates the spring element. 
     The second resilient section projecting from the first resilient section in a Y-shaped manner includes a curved region at whose side facing the leading edge of the printing form, a linear contact region is formed. Via the linear contact region, the second section abuts against the leading edge of the printing form retained on a side wall of the printing form cylinder and fixes the leading edge permanently in place in the clamping channel while, at the same time, the first resilient section grips under the trailing edge of the printing form with its hook-shaped end, tensioning the printing form in a circumferential direction on the lateral surface of the printing form cylinder. 
     In addition to configuring the second resilient section of the spring element in a manner that a linear contact with the leading printing form edge is provided, this section can also be provided with coatings which increase the coefficient of friction, pin-shaped retaining elements extending through the angularly bent leading printing form edge, thus fixing in place the leading edge on a side wall of the clamping channel in the printing form cylinder. 
     In a further variant of an embodiment of the spring element configured according to the present invention, the spring element can be designed in one piece with a continuous locating section from which first and second resilient sections project in a Y-shaped manner. In this variant of an embodiment of the spring element proposed according to the present invention, the first and second resilient sections can be alternately formed on a workpiece in a segment-like manner. The first and second resilient sections are separated from each other by slot-shaped openings so that the one-piece spring element is easy to manufacture in terms of production engineering, using simple forming processes. In this context, according to the second variant of the design approach of the present invention, the end of the first resilient section of the spring element designed in one piece which end grasps the trailing edge of the printing form can be provided with a rounded region which reduces the risk of injury to the person who manually changes the printing form. Besides, the spring elements configured according to the present invention can, of course, also be used for retaining, tensioning and fixing in place plate-shaped printing forms which can be conveyed to the printing form cylinders of rotary printing presses or removed therefrom via automatic or semi-automatic printing plate changing devices. 
     The design approach proposed according to the present invention, can preferably be used on rotary printing presses, it being particularly preferred for use in web-fed rotary printing presses, for example short-run or newspaper presses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the following, the present invention will be explained in detail with reference to the drawings in which: 
     FIG. 1 provides an enlarged-scale view of a clamping channel for receiving the leading and trailing edges of the printing form; 
     FIG. 2 shows a spring element formed in one piece, featuring a continuous locating section for the fastening on a tensioning shaft; 
     FIG. 3 depicts the spring element configured according to the present invention in an untensioned condition; 
     FIG. 4 is a view of the spring element designed according to the present invention in a first position tensioning the trailing printing form edge in a circumferential direction of the printing form cylinder; and 
     FIG. 5 shows the spring element made according to the present invention in a second tensioning position jointly fixing in place the leading printing form edge and the trailing printing form edge. 
    
    
     DETAILED DESCRIPTION 
     The representation according to FIG. 1 illustrates in greater detail a clamping channel for the leading and trailing printing form edges, the clamping channel being represented at an enlarged scale. 
     A flexible, plate-shaped printing form  10  is accommodated on a lateral surface  2  of printing form cylinder  1 . A leading edge  12  and a trailing edge  13  of printing form  10  extend into a clamping channel  3  in printing form cylinder  1 , the clamping channel being bounded by channel walls  4 . Clamping channel  3  has a cross section having a more or less trapezoidal shaped profile, clamping channel  3  opening in a direction toward tensioning shaft  6 . Clamping channel  3  is bounded at the bottom side by a tensioning shaft  6  in which a receiving slot  7  is formed. Receiving slot  7  is bounded by lateral contact surfaces  8  between which a continuous locating section of a one-piece spring element  27  or the locating sections of a plurality of spring elements  16  arranged side by side in clamping channel  3  are accommodated. 
     The direction of rotation of printing form cylinder  1 , whose lateral surface  2  accommodates printing form  10 , is denoted by the arrow provided with reference numeral  5 . A radius  9  bounding the aperture of clamping channel  3  at lateral surface  2  of printing form cylinder  1  constitutes the location where leading edge  12  of printing form  10  is hung into place at a channel wall  4  of clamping channel  3 . Printing form surface  11  of printing form  10  transfers the print image transferred thereto to the transfer cylinder which, in turn, transfers the print image to the stock, for instance, a continuous material web. 
     The representation according to FIG. 1 illustrates that a spring element  16  designed in Y-shape  21  is inserted in receiving slot  7  of tensioning shaft  6 . This variant of an embodiment of the present invention includes spring element  16  having a first resilient section  17  and a second resilient section  19 . First resilient section  17  and second resilient section  19  are each formed with different material thickness  20 . 1  and  20 . 2 , respectively. First resilient section  17  and second resilient section  19  can be manufactured from different materials, respectively, which are joined via a joining operation to form a spring element  16 . In the process, it is possible to provide both first resilient section  17  and second resilient section  19  with an individual flexural elasticity via the selection of material thickness  20 . 1  and  20 . 2 . Y-shape  21  makes it easier for spring element  16  to be inserted into receiving slot  7  of tensioning shaft  6 . Y-shape  21  is impressed on spring element  16  at a spreading location  26  at which second resilient section  19  branches off from first resilient section  17  at an angle of 10 to 30°. Depending on the selection of the angle of spread at spreading location  26 , it is possible to predetermine the preloading of second resilient section  19  relative to first resilient section  17  of spring element  16 . At its end gripping under a trailing edge angle  15  of trailing edge  13  of printing form  10 , first resilient section  17  is angularly bent and provided with a hook-shaped curvature  18 . Because of this, it is ensured that trailing printing form edge  13  is reliably grasped and tensioned in a circumferential direction on lateral surface  2  of printing form cylinder  1 . 
     Second resilient section  19 , which is formed with a smaller material thickness  20 . 2  compared to material thickness  20 . 1  of first resilient section  17 , is configured to include a curved region  23 . The side of curved region  23  facing leading edge  12  of printing form  10  constitutes a contact line  24  of second resilient section  19  with leading edge  12  at a contact region  22  through openings  25 . Contact line  24  on second resilient section  19  can be provided with a coating which improves the coefficient of friction; besides, pin-shaped projections can be attached in the region of contact line  24  which are capable of extending through openings in leading printing form edge  12  which openings can optionally be formed therein for improving the fixing in place of leading printing form edge  12  on side wall  4  of clamping channel  3 . 
     The narrower the aperture of clamping channel  3  between radii  9  at lateral surface  2  of clamping channel  3  is configured, the smaller is non-printing region  14  which forms between angularly bent leading printing form edge  12  and trailing printing form edge  13 . 
     The representation according to FIG. 2 illustrates in greater detail a spring element formed in one piece, featuring a continuous locating section for the fastening on the tensioning shaft in the printing form cylinder. 
     In place of spring elements  16  depicted in FIG. 1 which are arranged side by side in a clamping channel  3 , it is also possible to insert therein a one-piece spring element  27  which features a continuous locating section  28 . This spring element  27  can have first resilient sections  17  and second resilient sections  19  alternately formed thereon in a segment-like manner. On spring element  27  designed in one piece, first and second sections  17  and  19  are separated from one another preferably by openings extending in a slot-shaped manner which are particularly easy to produce in terms of production engineering. Spring element  27  designed according to the variant of an embodiment in FIG. 2 is also substantially Y-shaped which is why it can be easily mounted in receiving slot  7  of a tensioning shaft  6  with smallest installation space requirements. Spring element  27  designed in one piece can likewise be inserted into a tensioning shaft  6  which is already accommodated in a bore of printing form cylinder  1 . According to the variant of an embodiment of the spring element in FIG. 2, the ends of first resilient sections  17  are provided with rounded regions  29  so that during the handling of the spring element  27  configured in one piece with a continuous locating section, the risk of injury to the person handling it is markedly reduced. Subsequent to producing slot-shaped openings  31  through window or cut-out  30 , spring element  27  configured in one piece can be manufactured by way of cold forming in a simple manner in terms of production engineering, the material thickness of first and second sections  17  and  19  being identical according to this variant of an embodiment of the spring element. 
     FIG. 3 illustrates in greater detail the spring element configured according to the present invention in an untensioned condition. Untensioned position  34  of spring element  16 ,  27  designed in Y-shape  21  is denoted by reference numeral  34 . Spring element  16 ,  27  is inserted into receiving slot  7  of tensioning shaft  6  via its locating section. Trailing printing form edge  13  of printing form  10  to be tensioned in a circumferential direction on lateral surface  2  of printing form cylinder  1  is not yet grasped by curved, hook-shaped end  18  of first resilient section  17 . Likewise, second resilient section  19  does not yet abut, via its linear contact region  24  opposite of curvature region  23 , against leading edge  12  to be fixed in place of printing form  10  while spring element  16 ,  27  is in untensioned condition  34 . In untensioned condition  34  of spring element  16  or  27 , first resilient section  17  and second resilient section  19  are still undeformed relative to each other referred to spreading location  26 , since no forces act upon first or second resilient section  17 ,  19  of spring element  16 ,  27  yet. Only when clamping shaft  3  is rotated counterclockwise in the direction of arrow  33 , spring element  16 ,  27  designed in Y-shape  21  is converted from untensioned condition  34  into a first tensioning position  36  according to FIG.  4 . 
     The representation according to FIG. 4 illustrates in greater detail the spring element designed according to the present invention in a first position tensioning the trailing edge of the printing form in a circumferential direction on the printing form cylinder. 
     In comparison with FIG. 3, in the condition given in FIG. 4, a rotation of clamping shaft  6 , with spring element  16 ,  27  configured according to the present invention being accommodated in receiving slot  7 , has taken place in tensioning direction  33  of clamping shaft  6  so that the shaft is rotated counterclockwise about its axis  32 . The then attained first tensioning position of spring element  16 ,  27  configured according to the present invention is denoted by position  36  and characterized in that hook-shaped end  18  of first resilient section  17  has grasped trailing edge angle  15  of printing form  10 , tensioning it in a circumferential direction on lateral surface  2  of printing form cylinder  1 . Accordingly, trailing edge  13  of printing form  10  is drawn onto clamping channel radius  9  in the direction of clamping channel radius  9  which is covered by leading edge  12  of printing form  10 . In first tensioning position  36 , the side of second resilient section  19  opposite of curved region  23  of this section just touches leading printing form edge  12  at contact region  22  which lies against a side of clamping channel  3 . This contact position is denoted by reference numeral  37 . When rotating clamping shaft  6  further in tensioning direction  33 , second resilient section  19  moves toward first resilient section  17  of spring element  16 ,  27  which grasps the trailing edge with its hook-shaped end  17 , referred to spreading location  26 , compare FIG.  5 . 
     For the sake of completeness, it should be mentioned that clamping shaft  6  is accommodated at its ends at the end face of a printing form cylinder  1  via a clamping  35 , for example, in the form of a clamping screw. 
     The representation according to FIG. 5 illustrates in greater detail the spring element configured according to the present invention in a second tensioning position which jointly fixes in place the leading edge and the trailing edge of the printing form. 
     Compared to first tensioning position  36 , in the second tensioning position denoted by reference numeral  38 , a further rotation of clamping shaft  6  has taken place in tensioning direction  33  about axis  32  of clamping shaft  6 . Trailing edge  13  of printing form  10  is tensioned by hook-shaped end  18  in a circumferential direction relative to lateral surface  2  of printing form cylinder  1 . In second tensioning position  38 , second resilient section  19  makes contact with leading edge  12  of printing form  10  through openings  25  which leading edge lies against channel wall  4 . Via second resilient section  19  of Y-shaped spring element  16 ,  27 , a retention force is imposed on leading edge  12  of printing form  10 , retaining leading edge  12  of printing form  10  on channel wall  4  of clamping channel  3 . In second tensioning position  38 , resilient section  19  has moved toward first resilient section  17  referred to spreading location  26  and, via its inherent flexural elasticity, retains leading edge  12  at tensioning position  39  in its position on channel wall  4  of clamping channel  3 . In this second tensioning position  38 , tensioning shaft  6  is locked so that, via the elasticity inherent in spring element  16 ,  27  configured in Y-shape  21 , both trailing edge  13  of printing form  10  is permanently maintained tensioned in a circumferential direction on lateral surface  2  of printing form cylinder  1  and, at the same time, leading edge  12  of printing form  10  is maintained permanently fixed in place on channel wall  4  below clamping channel radius  9 . During a rotation of printing form cylinder  1  with printing form  10  accommodated on lateral surface  2  being tensioned, ends  12  and  13  of printing form  10 , whose surface  11  transfers the print image, are not able to move out of clamping channel  3  in a radial direction. 
     List of Reference Numerals 
       1  Printing form cylinder 
       2  Lateral surface 
       3  Clamping channel 
       4  Channel wall 
       5  Direction of rotation 
       6  Tensioning shaft 
       7  Receiving slot 
       8  Contact surface 
       9  Clamping channel radius 
       10  Printing form 
       11  Printing form surface 
       12  Leading edge 
       13  Trailing edge 
       14  Non-printing region 
       15  Trailing edge angle 
       16  Spring element 
       17  First resilient section 
       18  Hook-shaped end 
       19  Second resilient section 
       20 . 1  Material thickness of first resilient section 
       20 . 2  Material thickness of second resilient section 
       21  Y-shape 
       22  Contact region of leading edge 
       23  Curvature region 
       24  Contact line 
       25  Openings of leading printing form edge 
       26  Spreading location 
       27  Segmented spring element 
       28  Locating section 
       29  Rounded end 
       30  Window or cut-out 
       31  Slot-shaped openings 
       32  Axis of tensioning shaft 
       33  Tension direction of tensioning shaft 
       34  Untensioned position 
       35  Clamping 
       36  First tensioning position 
       37  Contact position 
       38  Second tensioning position 
       39  Tensioning position

Technology Classification (CPC): 1