Abstract:
A method and a device for combining an auxiliary stack and a main stack include a rake carrying the auxiliary stack and being abruptly movable out of a stack area to prevent sheets that contact the rake from being entrained and to preserve the structure of the stack. A sheet-fed printing press or sheet punching machine having the device 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 2014 013 688.4, filed Sep. 17, 2014; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a method and a device for combining an auxiliary stack and a main stack during non-stop operation of a feeder in a machine for processing sheets. The invention also relates to a sheet-fed printing press or sheet punching machine having the device. 
         [0003]    When an auxiliary stack that is temporarily supported by an auxiliary stack carrier such as a rake is to be merged or combined with a main stack, the auxiliary stack carrier needs to be withdrawn from the stack area. Frictional forces between the sheets that are in contact with the stack carrier may cause those sheets to be pulled out together with the stack carrier or to develop creases, which may impede further processing. Those sheets then have to be removed from the stack area by hand. 
         [0004]    German Patent DE 39 22 803 B4, corresponding to U.S. Pat. No. 5,011,126, discloses two auxiliary stack carriers disposed opposite one another and embodied as rakes. The auxiliary stack carriers are laterally movable into the stack area. During a withdrawal the forces acting on the sheets are supposed to cancel one another so that the positions of the sheets remain unchanged. 
         [0005]    German Patent Application DE 10 2010 053 587 A1 discloses an auxiliary stack carrier that includes two endless movable belts guided by deflection rollers. When the auxiliary stack carrier is withdrawn from the stack area, a relative speed between the belts and the sheets in contact therewith is zero, so that the positions of the sheets remain unchanged. 
         [0006]    German Patent Application DE 10 2005 019 511 A1 illustrates an auxiliary stack carrier including a blower device. The blower device is intended to create an air cushion so that a frictional force acting on the sheets due to the auxiliary stack carrier is minimized. 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide an alternative method and device for combining an auxiliary stack and a main stack, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which prevent sheets from entraining sheets when an auxiliary stack carrier is withdrawn from a stack area. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention, a device for supporting an auxiliary stack with an auxiliary stack carrier for combining the auxiliary stack with a main stack by pulling the auxiliary stack carrier out of a stack area with a drive for moving the auxiliary stack carrier. The auxiliary stack carrier has a jolting unit for pulling the auxiliary stack carrier out of the stack area in an abruptly accelerated way. 
         [0009]    With the objects of the invention in view, there is furthermore provided a sheet-fed printing press or sheet-fed die-cutting or stamping machine, comprising a device according to the invention. 
         [0010]    With the objects of the invention in view, there is also provided a method for driving an auxiliary stack carrier as it is pulled out of a stack area to combine an auxiliary stack and a main stack, which comprises imparting a jolt to the auxiliary stack carrier by using a pneumatically drivable jolting unit. The jolt causes the auxiliary stack carrier to experience a rapid acceleration, and the auxiliary stack carrier is subsequently moved out of the stack area at a constant speed by using a drive. 
         [0011]    With the objects of the invention in view, there is concomitantly provided a method for driving an auxiliary stack carrier as it is pulled out of a stack area to combine or merge an auxiliary stack and a main stack, which comprises imparting successive blows to the auxiliary stack carrier at regular intervals by using an electromechanically drivable jolting unit. The blows cause the auxiliary stack carrier to be accelerated in a jerky or sudden or abrupt way as it is being pulled out of the stack area, and the auxiliary stack carrier is moved out of the stack area by using a drive. 
         [0012]    A particularly advantageous feature of the invention is that a non-stop stack change is improved inasmuch as it may reliably be carried out without manual intervention. A particularly advantageous further feature of the invention is that in addition to a drive, a jolting unit is provided to cause a temporary fast acceleration of the auxiliary stack carrier. In this process, the mass inertia of the sheets in the auxiliary stack and in the main stack is greater than the forces created by frictional forces that act on the lowermost sheet in the auxiliary stack and the uppermost sheet in the main stack. Due to this measure, after the abrupt initial movement, the auxiliary stack carrier may be moved continuously out of the stack area at a constant speed. 
         [0013]    In accordance with a first exemplary embodiment, the jolting unit includes a mass that is pneumatically movable against a stop, causing the auxiliary stack carrier, which is preferably embodied as a rake, to experience a temporary acceleration prior to being continuously withdrawn from the stack area. 
         [0014]    In accordance with a second exemplary embodiment, the jolting unit includes a rotary drive for a spring-loaded mass that rolls on a control contour or profile with steep inclines, for instance a toothing. Due to this measure, when the stack carrier is withdrawn from the stack area, acceleration jumps are consistently imparted to the auxiliary stack carrier as it is being withdrawn from the stack area while experiencing recurring bouts of acceleration. 
         [0015]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0016]    Although the invention is illustrated and described herein as embodied in a method and a device for combining an auxiliary stack and a main stack and a sheet-fed printing press or sheet punching machine, 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. 
         [0017]    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 
         [0018]      FIG. 1  is a diagrammatic, longitudinal-sectional view of a printing press; 
           [0019]      FIG. 2  is an enlarged, longitudinal-sectional view of an auxiliary stack carrier including a jolting unit; 
           [0020]      FIG. 3  is an elevational view of the auxiliary stack carrier; 
           [0021]      FIG. 4  is a longitudinal-sectional view of the jolting unit including a pneumatic drive; 
           [0022]      FIG. 5  is a longitudinal-sectional view of a jolting unit including an electromechanical drive; 
           [0023]      FIG. 6  is a motion diagram of the pneumatic jolting unit; and 
           [0024]      FIG. 7  is a motion diagram of the electromechanical jolting unit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a machine, for instance a die-cutting machine or a printing press  1  for processing sheets  7 , which includes a feeder  2  and a delivery  6 . In the case of a printing press  1 , sheets  7  are taken from a sheet stack  8  present in the feeder  2  and are fed either individually or in shingled formation over a feed table  9  to printing units  3  and  4  present in the press  1 . As is known in the art, each one of the printing units  3 ,  4  includes a plate cylinder  11 ,  12 , and each one of the plate cylinders  11 ,  12  has a device  13 ,  14  for mounting flexible printing plates. In addition, a respective device  16 ,  17  for changing plates in a semi-automated or fully automated way is associated with each one of the plate cylinders  11 ,  12 . 
         [0026]    The sheet stack  8  rests on a main stack plate  10 , which may be lifted in a controlled way. A so-called suction head  18  which, among other elements, includes at least one suction gripper for separating the sheets  7 , pulls the sheets  7  off the top of the sheet stack  8 . In addition, blowing devices for loosening the upper layers of sheets and sensing elements for lifting the stack as needed are provided. At least one leading-edge stop  23  is provided to align the sheet stack  8 . 
         [0027]    As is best seen in  FIGS. 2 and 3 , the feeder  2  has a device for non-stop operation, i.e. a device that allows sheets  7  to be continuously conveyed even while a stack change is taking place. For this purpose, an auxiliary stack carrier  19 , for instance in the form of a rake, is provided. The auxiliary stack carrier  19  supports an almost-empty sheet stack (auxiliary stack)  8   a  for as long as it takes to position a new main stack  8  in the feeder  2 . The rake  19  preferably has a number of rake prongs  22  disposed next to one another and at a distance from each other. When the auxiliary stack  8   a  and the new main stack  8  are combined or merged, the auxiliary stack carrier  19  is pulled out of the stack area, preferably in the processing direction of the sheets, by using a drive  24  controllable by a control unit of the machine for processing sheets. A jolting unit  26 ,  34  is provided between the drive  24  and the auxiliary stack carrier  19  which is preferably embodied as a rake. 
         [0028]    In the exemplary embodiment shown in  FIG. 4 , the jolting unit  26  generates an abrupt jolt that causes the rake  19  to experience a brief acceleration and thus to separate from a lowermost sheet  7   a  in the auxiliary stack  8   a  and from a top sheet  7   b  of the main stack  8 . Subsequently, the rake  19  is pulled out of the stack area at a constant speed v. 
         [0029]    The jolting unit  26  has a housing  27  in which a mass  28  is disposed for movement against a stop  29  of the housing  27  at a high speed. The mass  28  is fitted on an end of a piston rod  31  of a pneumatic cylinder  32 , to which compressed air can be supplied from a compressed air source  33 . Due to this measure, the rake  19  experiences a great initial acceleration before it is pulled out of the stack area at a constant speed v as shown in the motion diagram of  FIG. 6 . 
         [0030]    The exemplary embodiment shown in  FIG. 5  includes an electromechanically actuatable jolting unit  34  including a housing  36  with a rotary drive  37  for a mass  38 . The mass  38  is embodied to have a cylindrical shape and includes rollers  39  that are circumferentially distributed on an end face and roll on a profile  41 , preferably a toothing (such as a saw toothing), which is disposed in a circular shape. The mass  38  is driven to rotate by an entrainment element  42  and is pressed against the profile  41  by a pre-loaded spring  43 . Due to this measure, jolts are created that lead to a repeated accelerated movement of the rake  19  as the rake  19  is pulled out of the stack area as shown in the motion diagram of  FIG. 7 .