Abstract:
A method for transversely tautening a print-carrier sheet includes applying a twisting movement to a belt and transversely tautening the print-carrier sheet with the belt having the twisting movement. A device for performing the method and a print-carrier sheet processing machine, such as a sheet-fed printing press, including the device, are also provided.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and a device for transversely tautening a print-carrier sheet and a to machine having the device.  
         [0002]     Devices of this general type are used in deliveries of printing presses for the purpose of improving the stackability of sheets by reducing sagging in the direction of the width of the sheet due to the transverse tautening. Moreover, devices of this general type can additionally act as a sheet brake. For example, a sheet brake having a transverse tautening effect is described in German Published, Non-Prosecuted Patent Application DE 39 39 212 A1. That sheet brake includes suction rings for contacting the sheet in so-called print-free corridors thereof. Some of the suction rings are inclined relatively to the sheet running or travel direction in order to achieve the transverse tautening effect.  
         [0003]     The more pronounced the inclination of the suction rings, the wider the print-free corridors must be. In general, however, it is desirable to keep the print-free corridors as narrow as possible, in order to optimize the use of the sheet format during printing and to minimize the trimming of wastage. A reduction in the inclination of the suction rings, which would serve those aims would, however, necessarily be associated with a reduction in the transverse tautening effect and consequently a deterioration in the stackability of the sheets.  
       SUMMARY OF THE INVENTION  
       [0004]     It is accordingly an object of the invention to provide a method and a device for transversely tautening a print-carrier or printing-material sheet which has only a very narrow print-free corridor, as well as a machine having the device, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type.  
         [0005]     With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for transversely tautening a print-carrier sheet. The method comprises applying a twisting movement to a belt and transversely tautening the print-carrier sheet with the belt having the twisting movement.  
         [0006]     With the objects of the invention in view, there is also provided a device for transversely tautening a print-carrier sheet. The device comprises a belt with a twisting movement. The belt with the twisting movement transversely tautens the print-carrier sheet.  
         [0007]     In accordance with a further feature of the invention, the belt has revolving axes. A twisting run is oriented obliquely with respect to the revolving axes.  
         [0008]     In accordance with an added feature of the invention, the belt has wrap-around sections. The sections are offset from one another along the revolving axes.  
         [0009]     In accordance with an additional feature of the invention, the belt is formed with kinks. The twisting run merges into the wrap-around sections at the kinks.  
         [0010]     In accordance with yet another feature of the invention, the belt is a round belt.  
         [0011]     In accordance with yet a further feature of the invention, the belt is a brake belt.  
         [0012]     In accordance with yet an added feature of the invention, the device further includes another belt to which a twisting movement is applicable, like the first-mentioned belt.  
         [0013]     In accordance with yet an additional feature of the invention, the twisting movements of the two belts are in opposite directions to one another.  
         [0014]     With the objects of the invention in view, there is additionally provided a print-carrier sheet processing machine. The machine comprises a device for transversely tautening a print-carrier sheet. The device has a belt to which a twisting movement is applicable.  
         [0015]     In accordance with a concomitant feature of the invention, the print-carrier sheet processing machine is constructed as a sheet-fed printing press.  
         [0016]     The method according to the invention which serves for transversely tautening a print-carrier or printing-material sheet is distinguished by providing a belt with a twisting movement for this purpose. The device according to the invention which serves for transversely tautening a print-carrier or printing-material sheet has such a belt to be provided with a twisting movement.  
         [0017]     The twisting movement is a rotational movement which guides the profile of the belt around an imaginary pivot point lying within this profile. The belt is shaped, disposed and driven in such a way as to perform the twisting movement. The twisting movement forms a first movement component of the belt which is superimposed upon a second movement component resulting from an inclination of the belt. The resultant of the superimposition of the two movement components is greater than the second movement component. The transverse tautening is effected transversely, i.e. perpendicularly or obliquely, to the so-called travel or running direction of the print-carrier or printing-material sheet.  
         [0018]     In the invention of the instant application, a reduction in the inclination of the belt, which reduction is performed for the purpose of narrowing the print-free corridors, is also necessarily associated with a decrease in the second movement component. However, the first movement component/twisting movement is capable of compensating for the decrease. Therefore, sufficiently great transverse tautening is allowed with the invention despite the narrowness of the print-free corridors. The narrowness of the print-free corridors which is made possible by the invention is, in turn, advantageous with regard to optimizing the use of the sheet format during printing and with regard to minimizing the trim wastage produced when the print-free corridors are cut off.  
         [0019]     The invention further relates to a print-carrier or printing-material sheet processing machine. More particularly, the invention relates to a sheet-fed printing press, which is equipped with the device according to the invention.  
         [0020]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0021]     Although the invention is illustrated and described herein as embodied in a method and a device for transversely tautening a print-carrier or printing-material sheet and a machine having the device, 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.  
         [0022]     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 DRAWINGS  
       [0023]      FIG. 1  is a fragmentary, diagrammatic, side-elevational view of a sheet-fed printing press having a multi-functioning sheet brake functioning also as a device for transversely tautening;  
         [0024]      FIG. 2  is an enlarged, fragmentary, top-plan view of  FIG. 1 , showing the sheet brake in a viewing direction II indicated in  FIG. 1 ;  
         [0025]      FIG. 3  is a side-elevational view of a brake module of the sheet brake;  
         [0026]      FIG. 4  is a cross-sectional view of the brake module, which is taken along a line IV-IV of  FIG. 3 , in the direction of the arrows; and  
         [0027]      FIG. 5  is a plan view of  FIG. 3 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a sheet-fed printing press  1  having a sheet delivery  2 . The sheet delivery  2  includes a chain conveyor  3 , a delivery stack or pile  4  and a sheet brake  5 . The chain conveyor  3  drags print-carrier or printing-material sheets  7  along a sheet travel direction  8  to the delivery pile  4 , through the use of gripper systems  6 . The sheet brake  5  is disposed below the chain conveyor  3  and, as viewed in the sheet travel direction  8 , in front of the delivery pile or stack  4 .  
         [0029]     In  FIG. 2 , the sheet brake  5  is shown as including only three brake modules  9   a  to  9   c , namely a brake module  9   a  on the drive side of the sheet-fed printing press  1 , a brake module  9   b  on the operator side, and a central brake module  9   c  which is disposed exactly in the center between the brake modules  9   a  and  9   b . The brake modules  9   a  to  9   c  are at least approximately aligned with print-free corridors  10  on the underside of the print-carrier or printing-material sheet  7 . Those print-free corridors  10  with which the two outer brake modules  9   a  and  9   b  are aligned are print-free sheet edges. Due to the small amount (three in number) of brake modules  9   a  to  9   c , only a likewise small amount of print-free corridors  10  are required and, accordingly, a particularly large proportion of the surface of the print-carrier or printing-material sheet  7  is available for the printed image thereof.  
         [0030]     Each brake module  9   a  to  9   c  includes a belt set formed of a first belt  11  and a second belt  12  running parallel to the first belt  11 . When the print-carrier or printing-material sheet  7  is being braked in the sheet travel or running direction  8  and simultaneously tautened transversely (specifically obliquely or inclined in this case) with respect to the sheet travel or running direction  8 , the belts  11  and  12  make contact with the print-free corridors  10  of the print-carrier or printing-material sheet  7 . With respect to the sheet travel or running direction  8 , the belts  11  and  12  of the two outer brake modules  9   a  and  9   b  are set to be oblique or inclined in sections of the belt length, and the belts  11  and  12  of the central brake module  9   c  are set to be parallel over the entire belt length thereof. The local belt inclination is selected in such a way that, as viewed in the sheet travel or running direction  8 , the belts  11  and  12  of the drive-side brake module  9   a  deviate from the belts  11  and  12  of the operator-side brake module  9   b . Furthermore, it is believed to be apparent from  FIG. 2  that the two outer print-free corridors  10 , despite the belt inclination of the brake modules  9   a  and  9   b  assigned thereto, are only insignificantly wider than the central corridor  10  to which the central brake module  9   c  without belt inclination is assigned. This advantage results from the small size of an angle of inclination a (note  FIG. 5 ) of the belts  11  and  12  of the outer brake modules  9   a  and  9   b.    
         [0031]     According to one modification which is not shown in greater detail in the drawing, it would also be possible, in order to reduce the corridor width further, to equip the brake modules  9   a  to  9   c  with only a single belt each instead of the belt set. For example, the first belt  11  would remain and the second belt  12  would be omitted.  
         [0032]     Referring to FIGS.  3  to  5 , the hereinafter following text explains the structural conditions of the operator-side brake module  9   b  in detail. Those structural conditions are valid in an equivalent sense for the drive-side brake module  9   a  which is configured as a mirror image of the operator-side brake module  9   b . The brake module  9   b  has a basic body  13  wherein a front roller  14  and a rear roller  15 , as viewed relative to the sheet travel or running direction  8  (note  FIG. 2 ), are rotatably mounted for guiding the endless belts  11  and  12 . The rear roller  15  serves as a drive roller for effecting a revolving movement (represented by the curved arrow  16 ) of the belts  11  and  12 , and the front roller  14  serves as a deflection roller for deflecting the belts  11  and  12 . The rollers  14  and  15  define revolving axes  17  and  18  about which the belts revolve in synchronism with one another.  
         [0033]     The belts  11  and  12  are driven in such a manner that, at least at the beginning of the braking process, a difference in velocity exists between the velocity of the revolving movement represented by the curved arrow  16  and the velocity determined by the chain conveyor  3  of the print-carrier or printing-material sheet  7  to be braked and, in the process, tautened transversely. Each belt  11 ,  12  is, therefore, a brake belt. It is believed to be apparent from  FIG. 4  that each belt  11 ,  12  is a round belt and, therefore, has a belt profile with a circular contour. The belt profile of the respective belts  11  and  12  performs a twisting movement represented by the respective arrows  19   a  and  19   b  in  FIGS. 2 and 4 .  
         [0034]     It is believed to be readily apparent from  FIG. 3 , wherein the first belt  11  is shown, by way of example, that each belt  11 ,  12  has an upper, first run or strand  20  and a lower, second run or strand  21 . The first run  20  is a return run or strand and the second run  21  is a load run or strand. It is believed to be readily apparent from  FIG. 4  that the first run  20  is not self-supportingly subject to tension but rather is guided in a belt bed  22 . The belts  11  and  12  are respectively guided in a circumferential annular groove  23  formed in the front roller  14  and an annular groove  24  of identical type formed in the rear roller  15 , with the formation of wrap-around sections  32  and  33  of the respective belts  11  and  12 . The wrap-around sections  32  and  33  of the respective belt  11  and  12 , for example of the belt  11 , are offset with respect to one another along the revolving axes  17  and  18 . The belts  11  and  12  each have two kinks  25  at which the respective wrap-around sections  32  and  33  merge into the first run  20 . With regard to minimizing the necessary complexity in terms of mechanism technology for driving the belts  11  and  12  (omission of clutches for angular compensation), it is advantageous for the revolving axes  17  and  18  to be aligned precisely perpendicularly relative to the sheet running or travel direction  8  (note  FIG. 2 ).  
         [0035]     The first run  20  of the respective belt  11 ,  12  performs the twisting movement  19   b  about an imaginary central strand  26  which determines the pivot point thereof and is, therefore, also referred to herein as the twisting run. This respective twisting run of the belts  11  and  12  is not aligned perpendicularly but rather, in accordance with the angle of inclination a, obliquely with respect to the revolving axes  17  and  18  of the respective belts  11  and  12 . The annular grooves  23  and  24  are concentric with the revolving axes  17  and  18 . The two kinks  25  of each respective belt  11  and  12  have different kink or turn directions relative to one another, so that the respective belt  11  and  12  extends or runs in a cranked manner, i.e. alternately angled away. These belt angle deviations are very small, with the angle of inclination α being indeed greater than 0° but smaller than 5°.  
         [0036]     Consequently, the twisting movement represented by the curved arrow  19   a  does not take place absolutely perpendicularly with respect to the sheet travel or running direction  8 , but rather approximately perpendicularly with respect to the latter.  
         [0037]     A vacuum line  27  is introduced into the basic body  13  and opens into a groove-shaped vacuum duct  28  of the belt bed  22 . The duct  28  is open at the top or towards the print-carrier or printing-material sheet  7  to be tautened. The vacuum line  27  is configured as a drilled or bored hole and is connected to a non-illustrated vacuum source. The vacuum duct  28  is situated-between the two belts  11  and  12  and, even in the modification which has been mentioned above wherein the second belt  12  was omitted, would be situated directly adjacent the first belt  11 . The vacuum duct  28  serves for drawing the print-carrier or printing-material sheet  7  pneumatically to the belts  11  and  12  and for holding the sheet  7  on the latter. Therefore, a frictional connection which brakes and laterally tautens the print-carrier or printing-material sheet  7  comes into effect between the belts  11  and  12 , on one hand, and the print-carrier or printing-material sheet  7 , on the other hand.  
         [0038]     The belts  11  and  12  run equidistantly to one another in sections, at a belt spacing s corresponding approximately to twice the diameter of the respective belts  11  and  12 . An angle of inclination a between the sheet guiding direction represented by the arrow  8  and the first run (twisting run)  20  of each belt  11  and  12  results from a groove offset a between the front annular groove  23  and the rear annular groove  24 . The groove offset a is measured axially parallel to the revolving axes  17  and  18 . The two annular grooves  23  and  24  are disposed out of alignment with one another and are respectively disposed offset axially parallel to one another. The front annular groove  23  is situated closer than the rear annular groove  24  to a lateral edge  29  (note  FIG. 2 ) of the print-carrier or printing-material sheet  7  lying closest to the brake module  9   b . The rear annular groove  24  is disposed closer to the center of the sheet  7  than the front annular groove  23 . A corridor width c shown in  FIG. 2  must be at least as wide as a contact width b (shown in  FIG. 5 ) of the sheet brake  5  and can advantageously be kept small due to the method of operation of the invention as explained below.  
         [0039]     Due to the revolving movement represented by the arrow  16 , the print-carrier or printing-material sheet  7  which is in contact with the belts  11  and  12  is respectively conveyed in the transverse direction and transversely tautened an amount corresponding to the groove offset a on the path of the sheet  7  along the sheet brake  5 . At the same time, the groove offset a produces the twisting movement  19   b  of the belts  11  and  12  which is likewise respectively oriented outwardly and in the transverse direction. The twisting movement  19   b  of each belt  11 ,  12  of the operator-side brake module  9   b  is oriented towards the lateral edge  29  in the region of the belt surface which is in contact with the print-carrier or printing-material sheet  7 .  
         [0040]     The twisting movement represented by the curved arrows  19   b  is produced by the different behavior of the respective belts  11  and  12  at a contact point  30  and at a separation point  31  of the corresponding belt. The contact point  30  and the separation point  31  are situated opposite one another on flanks or edges of the rear annular groove  24  and, with regard to the rear roller  15 , approximately at that circumferential point at which the wrap-around section  33  of the belt merges into the first run (twisting run)  20 . The contact point  30  lies on that side of the respective belt  11  or  12  towards which the belt is turned or kinked at the kink or turning point  25  defined by the rear roller  15 , and the separation point  31  lies on the opposite belt side. At the separation point  31 , the belt has already been respectively detached from and lifted off the respective flank or edge of the rear annular groove  24 , while it is still in contact with the respective annular groove  24  and edge thereof at the contact point  30 . At the contact point  30 , the transition from static friction between the annular groove  24  and the respective belt  11  and  12  to sliding friction occurs, and the rear roller  24  has a tangential velocity v 24  and the first run  20  has a belt velocity v 20 . With respect to  FIG. 3 , a vector for the belt velocity v 20  is directed horizontally to the left-hand side and a vector for the tangential velocity v 24  is directed downwardly and to the left-hand side, with the result that the two velocities v 20 , v 24  enclose an angle β between one another in the vertical projection. By studying  FIGS. 2 and 5  together, it can be seen that the vector for the belt velocity v 20  is directed in the running or travel direction of the first run  20  and that the vector for the tangential velocity v 24  is directed in the sheet running or travel direction  8 , with the result that the vectors for the two velocities v 20 , v 24  enclose an angle having a magnitude corresponding to the angle of inclination α in the horizontal projection (note  FIG. 5 ). The resultant of the two velocities v 20 , v 24  is a relative velocity v rel , in the acting direction of which the sliding friction force acting on the respective belt  11  or  12  also acts. This sliding friction force ultimately produces the respective twisting of the respective belt  11  or  12  about the central strand  26  thereof and the twisting movement  19   b  which is perpendicular to the central strand  26 . A respective flank or edge of the rear annular groove  24  should be exactly as high as the other respective flank or edge opposite thereto, in order for the respective belt  11  or  12  to be twisted uniformly.  
         [0041]     It is believed to be readily apparent from  FIG. 2  that the belts  11 ,  12  of the drive-side brake module  9   a  likewise perform a respective twisting movement  19   a  which is in the opposite direction to the twisting movement  19   b  of the belts  11 ,  12  of the operator-side brake module  9   b . As viewed in the sheet running or travel direction  8 , the twisting movement  19   a  is performed in clockwise direction and the twisting movement  19   b  is performed in counterclockwise direction, with the result that the print-carrier or printing-material sheet  7  is tautened uniformly towards both sheet sides by the twisting movements represented by the arrows  19   a  and  19   b.    
         [0042]     This application claims the priority, under 35 U.S.C. § 119, of German Patent Application 103 50 537.7, filed Oct. 29, 2003; the entire disclosure of the prior application is herewith incorporated by reference.