Abstract:
A method and an apparatus for laterally aligning a sheet in a processing machine, in particular a printing machine, carries out lateral sheet alignment on a cylinder of the printing machine, e.g. a feed cylinder. In order to achieve large correction distances in relation to a possible lateral movement capability of a gripper bar, the latter is prealigned prior to correction in such a way that, in the event of deviation from predetermined desired values, it is prealigned laterally to defined positions. A sheet-fed rotary printing machine having the apparatus, is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 048 849.6, filed Sep. 25, 2008; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method and an apparatus for laterally aligning a sheet in a processing machine, in particular a printing machine. The invention also relates to a sheet-fed printing machine having the apparatus. 
         [0004]    It is known for the entire cylinder to be displaced for the lateral alignment of a sheet on a cylinder. 
         [0005]    An alternative possibility is disclosed in European Patent EP 1 334 829 B1, in which only one sheet-gripping gripper device of a sheet-guiding cylinder is displaced. That gripper device has an actuating drive, which is disposed in a stationary manner in an extension of the cylinder axis, and a stationary actuating gear mechanism, which acts on the gripper bar through a driver and an axially disposed pulling rail, which rotates synchronously with the cylinder. A device providing for rotary disengagement between the actuating gear mechanism and pulling rail is disposed outside the cylinder. 
         [0006]    European Patent EP 1 354 833 B1 discloses a method of prepositioning a gripper device on a cylinder of a printing machine in which, due to a sheet position being measured through the use of a sensor, the gripper device is displaced in each case by half the position-correction value in the opposite direction, corresponding to the correction, prior to the sheet being gripped. Once the sheet has been gripped, the gripper device is then displaced by the total correction value. 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a method and an apparatus for laterally aligning a sheet in a processing machine and a sheet-fed printing machine having the apparatus, which overcome the hereinafore-mentioned disadvantages of the heretofore-known apparatuses and methods of this general type and which operate with a higher degree of accuracy. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention, a method for laterally aligning sheets on a cylinder of a processing machine. The method comprises sensing an actual position of the sheet with at least one sensor, and prealigning a gripper device to a predetermined position in accordance with the actual position of the sheet relative to its side position, prior to the sheet being gripped by the gripper device. 
         [0009]    With the objects of the invention in view, there is also provided an apparatus for laterally aligning sheets on a cylinder of a processing machine. The apparatus comprises an actuating drive for generating a linear movement, a connecting rod, a rotary disengagement device disposed in a cylinder body of the cylinder, a movably mounted gripper device, and a driver fastened on the gripper device and mounted rotatably and secured against displacement, on the connecting rod. 
         [0010]    With the objects of the invention in view, there is additionally provided an apparatus for laterally aligning sheets on a cylinder of a processing machine. The apparatus comprises an actuating drive, a gripper device, and a gear mechanism, disposed in a cylinder body of the cylinder, for converting a rotary movement of the actuating drive into a linear movement of the gripper device. 
         [0011]    The method and apparatus according to the invention can considerably reduce the distance required by the gripper device for alignment purposes. 
         [0012]    In accordance with another mode of the invention, it is particularly advantageous for sheet-position determination to be divided up into rough determination and precision determination. The rough determination in this case is used for prepositioning the gripper device and the precision determination is used for aligning the sheet in accordance with a determined correction value. 
         [0013]    In accordance with a further mode of the invention, placing a second sensor upstream, as seen in the sheet-transporting direction, results in a larger time window for prepositioning the gripper device. 
         [0014]    In accordance with an added mode of the invention, a second measurement for determining the pulling distance, in particular only with the grippers of the gripper device closed, increases the accuracy of sheet alignment. 
         [0015]    In accordance with an additional feature of the invention, an advantageous configuration of the actuating apparatus is provided by a rotary disengagement device being disposed in the interior of the cylinder. This measure means that the connecting rod, which is disposed in an extension of the actuating drive, is moved only during the aligning operation, or during prepositioning, and need not always be driven along with the cylinder. 
         [0016]    In accordance with a concomitant feature of the invention, a further advantageous measure is constituted by gripper-control rollers being raised up from their control cams during prepositioning of the gripper device. This measure considerably reduces cam/roller wear. 
         [0017]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0018]    Although the invention is illustrated and described herein as embodied in a method and an apparatus for laterally aligning a sheet in a processing machine and a sheet-fed printing machine having the apparatus, 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. 
         [0019]    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 
         [0020]      FIG. 1  is a diagrammatic, longitudinal-sectional view of a rotary printing machine; 
           [0021]      FIG. 2  is an enlarged, fragmentary, cross-sectional view of a cylinder with a laterally movable gripper device; 
           [0022]      FIG. 3  is a view similar to  FIG. 2  of an alternative embodiment with a linear drive; and 
           [0023]      FIG. 4  is an elevational view of a control cam for raising up a gripper-opening control roller during prepositioning of the gripper device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a machine for processing sheets  7 , e.g. a printing machine  1 , which has a feeder  2 , at least one printing unit  3  or  4  and a delivery  6 . The sheets  7  are removed from a sheet stack  8  and fed separately or in imbricated form to the printing units  3  and  4  over a feed table  9 . These printing units each contain, in a known manner, a plate cylinder  11 ,  12  and blanket cylinders  15 ,  20 , each of which interact with a respective one of the plate cylinders. The plate cylinders  11  and  12  each have a clamping device  13 ,  14  for fastening flexible printing plates. Furthermore, each plate cylinder  11 ,  12  is assigned a device  16 ,  17  for semi-automatic or fully automatic printing-plate changeover. 
         [0025]    The sheet stack  8  rests on a stacking panel  10  which can be raised in a controlled manner. The sheets  7  are removed from the top side of the sheet stack  8  through the use of a so-called suction head  18  which has, inter alia, a number of lifting and pulling suckers  19 ,  21  for separating the sheets  7 . Also provided are blowing devices  22  for loosening the top sheet layers and follower elements  23  for stack adjustment. A number of lateral and rear stops  24  are provided in order to align the sheet stack  8 , in particular the top sheet  7  of the sheet stack  8 . 
         [0026]    In order to ensure lateral alignment of the sheets, these sheets are aligned on a cylinder of the printing machine  1 , preferably on a feed cylinder  26 , by virtue of a gripper device  27 , which can be displaced on the cylinder  26  by being moved parallel to the axis of the feed cylinder  26 . A stationary actuating motor  29  or linear drive  45  is provided in order to generate a lateral actuating movement of the gripper device  27 . This motor or drive is driven in order to execute prealignment of the gripper device  27 , e.g. of a gripper bar, or the precision alignment of the sheet. The actuating motor  29  or linear drive  45  is activated by way of a machine-control device  31 , which receives position-related measuring data with respect to the sheet  7  from at least one sensor  32 . 
         [0027]    The sensor  32  (e.g. an LCD sensor) is disposed on the feed table  9  and, upon arrival of the sheet  7  at the end of the feed table  9 , e.g. at front guides  37 , senses the side edge of this sheet. The gripper device  27  is prealigned following a desired-value/actual-value comparison by the machine-control device  31 . The operation in this case is carried out as follows: 
         [0028]    If there is only a small amount of deviation of the actual value from the desired value (e.g. &lt;1.5 millimeters), the gripper device  27  is not prealigned. 
         [0029]    However, if the actual value is too far (e.g. 1.5 to 6 millimeters) to the drive side DS (to the right, as seen in the sheet-transporting direction), then the gripper device  27  is prealigned by a defined value (+3 millimeters) in relation to the drive side DS prior to the sheet being gripped by the gripper device. 
         [0030]    If the actual value sensed is too far (e.g. −1.5 to −6 millimeters) to the operating side OS (to the left, as seen in the sheet-transporting direction), then the gripper device  27  is prealigned by a defined value (e.g. −3 millimeters) in relation to the operating side OS. This measure makes it possible to execute aligning distances of e.g. ±6 millimeters during alignment of the sheet, even though the gripper device  27  covers displacement distances of only ±3 millimeters. 
         [0031]    As soon as the sheet  7  is held with the grippers closed, e.g. by a pregripper  33  or by grippers  44  of the gripper device  27  as seen in  FIG. 2 , the side edge is subjected to a second measurement through the use of the sensor  32  in order to sense the actual position of the sheet  7  with the grippers closed. The machine-control device  31  uses a desired-value/actual-value comparison to determine a correction value, which is fed to the actuating motor  29  or linear drive  45 . The actuating motor  29  or linear drive  45  is assigned to the gripper device  27  and displaces the latter in accordance with the determined correction value. 
         [0032]    In the case of a second exemplary embodiment, provision is made for the prepositioning of the gripper device  27  to be controlled through the use of a second sensor  36 , with the second sensor  36  being required just for correction-movement determination. 
         [0033]    The sensor  36  in this case is, for example, a double switch which is disposed further away from the front guides  37 , in order to sense the side edge of the sheet. This measure allows the prepositioning of the gripper device  27  to take place at a very early stage, that is to say that, even at a high processing speed, there is sufficient time available in order for the gripper device  27  to be prepositioned. The double switch  36  has two sensors, which are disposed transversely to the sheet-transporting direction, for example at a spacing of approximately 3 millimeters apart. This double switch  36  allows the determination of three switching states. If both sensors of the double switch  36  are actuated, the sheet is, for example, too far over to the operating side OS. If neither sensor of the double switch  36  is actuated, the sheet is too far over to the drive side DS. If the sheet is located in the central region, in which there is no need for the gripper device  27  to be prepositioned, only one sensor of the double switch  36  is actuated. 
         [0034]    The actuating drive, e.g. the actuating motor  29  according to  FIG. 2 , is framework-mounted and has an actuating shaft  40  in extension of its drive axle  38 . A gear mechanism  41  for converting a rotary movement into a linear movement (e.g. a nut/thread gear mechanism) couples the actuating shaft  40  to a driver  43 , which is fastened on the gripper device or bar  27 . The gear mechanism  41  is disposed in the body of the cylinder  26 . The gripper device or bar  27  carries the grippers  44 , which are provided for transporting the sheet  7 . The gripper device or bar  27  is mounted in such a way that it can be displaced parallel to the axis  28  of the feed cylinder  26 . 
         [0035]    An alternative exemplary embodiment according to  FIG. 3  uses the linear motor  45  as the actuating drive. This linear motor is disposed in a stationary manner and has a displaceably-mounted connecting rod  39  in extension of its drive axle  38 . The connecting rod  39  has, at its end, a bearing location  42  for a driver  43 , which is fastened on the gripper device  27 , constructed in the form of a gripper bar. The driver  43  is mounted in a rotatable manner on the connecting rod  39 , but is secured against displacement on the connecting rod  39 . 
         [0036]    A stationary control cam  46  is provided in order to control the opening and closing movements of the grippers  44 . This control cam, according to  FIG. 4 , has a contour  47  for a “transporting region” and a contour  48  for an “idling path” of the grippers  44 . Two “control crests”  49 ,  51  enlarge the opening region of the grippers  44  at the locations where the sheet is received and transferred. The contour  48  has a significantly smaller radius r 1  than a radius r 2  of the contour  47 , in which case a control roller  52  of a gripper shaft  53 , which actuates the grippers  44 , is spaced apart from the contour  48 . This region, in which the control roller  52  is spaced apart from a control cam  46  or the contour  48  of the control cam  46 , is used for prealigning the gripper device  27 .