Abstract:
A sheet punching and embossing machine includes a device for stripping waste from a punched and embossed sheet at a stripping station, the device having a stripping plate for supporting the sheet. Also included are gripper carriages fixed to revolving chains, for gripping the sheet at a leading edge thereof and for then pulling the sheet intermittently through the stripping station and further stations in the machine. The stripping plate has, in an inlet region for the sheet and before stripping openings, at least one suction opening to which vacuum is applicable from below.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a sheet punching and embossing machine having a device for stripping waste from a punched and embossed sheet, the device having a stripping plate for supporting the sheets, and having gripper carriages fixed to revolving chains, for gripping the sheets at a leading edge thereof and then pulling the sheets intermittently through a stripping station and further stations in the machine. 
   The German Published Non-prosecuted Patent Application DE 41 19 511 A1, corresponding to U.S. Pat. No. 5,221,079, discloses a device for braking sheets, in particular, paper or board sheets, which are transportable on a conveyor belt in one plane and at a spaced distance from one another. Upstream from a pile-forming or stacking location, at the end of the machine, a braking device is provided wherein an overlapping or imbricated sheet stream is produced. The braking device is made up of a plurality of revolving belts and a guide table. The guide table is constructed as a suction table, and the belts are formed with suction holes spaced apart in the circumferential direction of the belts. In this manner, air between the belt and the sheet may be extracted or sucked away, so that the ends of the sheet from the inlet plane can be laid without any difficulty onto the belts, thereby affording fault-free overlapping of the sheets. 
   A device of the general type for stripping waste from sheets is described in the published German Non-prosecuted Patent Application (DE-OS) 24 54 056, corresponding to U.S. Pat. No. 4,015,495. The sheets are held on a gripper carriage and moved intermittently by a chain between stations. The stripping station, in this regard, has an upper part and a lower part, which perform upward and downward movements, and have stripping tools arranged thereon. The fixed intermediate center part is formed as a plate. In order to achieve the greatest possible utilization of the machine, the sheets are fed into the individual stations at high speed. The sheets coming from the punching station are sharply accelerated and braked and correctly positioned in the stripping station. The positioning of the gripper carriage is effected against a mechanical stop. Due to the great retardations and the movement against the mechanical stop, the sheet can be backed up or buckled behind the gripper carriage, and inadequate positioning of the sheet in the stripping station can occur. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide an improved stripping station of a sheet punching and embossing machine for holding the sheet as it is fed into the stripping station, so as to avoid backing up or buckling of the sheet behind the gripper carriage. 
   With the foregoing and other objects in view, there is provided, in accordance with the invention, a sheet punching and embossing machine. The machine contains a stripping station for stripping waste from a punched and embossed sheet. The stripping station has a stripping plate for supporting the sheet. The stripping plate has stripping openings and an inlet region for receiving the sheet. The inlet region has at least one suction opening disposed upstream of the stripping openings, and the suction opening is provided for receiving a vacuum applied from below. Further processing stations are disposed in the machine. Revolving chains are provided and gripper carriages are fixed to the revolving chains for gripping the sheet at a leading edge thereof and for then pulling the sheet intermittently through the stripping station and the further stations. 
   In accordance with an added feature of the invention, the suction opening is one of a plurality of suction openings disposed in the stripping plate in at least one row extending transversely with respect to a sheet running direction. Alternatively, the suction opening is one of a plurality of suction openings disposed in the stripping plate in two successive rows extending transversely with respect to a sheet running direction. The rows are disposed one after another in the sheet running direction. 
   In accordance with an additional feature of the invention, the stripping station has a pressure line and a suction bar with a plurality of suction openings. The suction bar is disposed in the stripping plate and extends transversely to a sheet running direction. The suction bar is connected to the pressure line. Alternatively, the stripping station has four suction bars each with a plurality of suction openings. The suction bars are disposed in the stripping plate and extend transversely to a sheet running direction. The suction bars are each connected to the pressure line. Preferably, at least two rows of the suction bars are disposed in the stripping plate in the sheet running direction. 
   In accordance with a further feature of the invention, the stripping station contains a controllable unit for producing vacuum, respectively, for depressurizing and for providing positive pressure. The controllable unit for producing vacuum is fixed to an underside of the stripping plate, in vicinity of each of the suction openings, respectively, and is connected through the pressure line to each of the suction openings. 
   In accordance with a concomitant feature of the invention, a controllable unit for producing vacuum is provided for depressurizing and for providing positive pressure. The controllable unit for producing vacuum is fixed to an underside of the stripping plate, in vicinity of the suction bar, and connected through the pressure line to the suction bar. 
   Thus, the object of the invention is achieved by providing the stripping plate, in the inlet region of the sheets and before the stripping openings, with at least one suction opening to which vacuum can be applied from below. As a result of the arrangement of a suction opening in the inlet region of the sheets, the sheet can be drawn or sucked directly to the stripping station during feeding. The vacuum at the suction opening draws the sheet onto the stripping plate and thus prevents the sheet from backing up or buckling during the retardation of the gripper carriage and upon striking the mechanical stop. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a sheet punching and embossing 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. 
   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 
       FIG. 1  is a schematic and diagrammatic side elevational view of the main structure of a sheet punching and embossing machine; 
       FIG. 2  is an enlarged fragmentary side elevational view of  FIG. 1 , showing a stripping station of the sheet punching and embossing machine; 
       FIG. 3  is a plan view of an inlet region of a stripping plate formed with stripping openings; and 
       FIG. 4  is a sectional view of  FIG. 3  taken along the line IV—IV in the direction of the arrows, showing the stripping plate in the vicinity of a suction bar. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings and, first, particularly to  FIG. 1  thereof, there is shown therein a basic structure of a sheet punching and embossing machine  1  for punching, stripping and depositing sheets  6  of paper, paperboard and the like. The punching and embossing machine  1  includes a punching device  2 , a stripping device  3  and a depositing device  4 , which are carried and enclosed by a common machine housing  5 . 
   The sheets  6  are gripped at respective leading edges thereof by gripper bars  8  fixed to revolving chains  7 , and are intermittently pulled through the various stations  2 ,  3  and  4  of the punching and embossing machine  1 . 
   The punching station  2  has a lower table  9  and an upper table  10 . The lower table  9  is fixedly mounted in a frame of the machine  1  and is provided with a plate opposing a punching knife provided in the upper table  10  which is mounted so as to be reciprocatingly movable vertically. 
   The gripper bar  8  transports the sheet from the punching and embossing machine  2  into a next following stripping station  3 , which is equipped with stripping tools. In the stripping station  3 , with the aid of these stripping tools, the nonrequired pieces of waste are expelled downwardly away from the sheet  6 , as a result of which the pieces of waste  11  fall into a container-like cart  12  that has been pushed in under the station  3 . 
   From the stripping station  3 , the sheet passes into a depositing station  4 , wherein the sheet is either only simply deposited or, however, simultaneous separation of the individual blanks is performed. The depositing station  4  can also contain a pallet  13 , whereon the individual sheets are stacked up in the form of a stack or pile  14 , so that after a specific stack or pile height has been attained, the pallets  13  with the sheets  14  piled or stacked up thereon can be moved away out of the region of the punching and embossing machine  1 . 
   As is believed to be apparent, the chains  7  carry a plurality of gripper bars  8 , for example, eight gripper bars shown here, so that a plurality of sheets  6  can be processed simultaneously in the various stations  2 ,  3  and  4 . 
   In  FIG. 2 , a preferred embodiment of the stripping device  3  of the punching and embossing machine  1 , which is constructed in accordance with the invention, is illustrated in greater detail. The stripping device  3  includes a stripping plate  15  and two holding frames  18  and  16  which are provided with stripping tools  17  and can be moved vertically reciprocatingly. The sheet  6  is held in the stripping station  3  by a gripper carriage  8 ′ and the latter is, in turn, held by a register stop  19 . In order to strip the waste, stripping openings  20  are machined into the stripping plate  15 . 
   The sheet  6  oncoming from the punching station  2  is fed to the stripping station  3 . Suction openings  22  are provided in the stripping plate  15  in an inlet region  21  thereof. Controllable pneumatic units  23  are fixed to the underside of the stripping plate  15 . 
   The sheets  6  are fed to the stripping station  3  at high cycle frequencies and, accordingly, high speeds. Braking the gripper carriage  8 ′ is likewise performed with high retardation, so that the sheet  6  backs up behind the gripper carriage  8 ′ and comes to lie buckled or warped under the stripping tool  17  if no suitable countermeasures are taken. By introducing the suction openings  22  in accordance with the invention, the sheet  6  is then drawn or sucked against the stripping plate  15  as the sheet  6  is fed into the stripping station  3 , and is braked at the trailing side or edge thereof. The sheet  6  is thus under continuous tension as it is fed in, and cannot back up or buckle. In order to avoid holding the sheets  6  unnecessarily firmly as they move out of the stripping station  3 , controllable pneumatic units  23  are arranged underneath the suction openings  22 . The controllable pneumatic units  23  are capable of producing a vacuum, depressurizing the suction openings  22  and leading a positive pressure to the suction openings  22 . 
   In order to move the sheets  6  out, the vacuum can then be switched off and the suction openings  22  can be provided with a positive pressure. The positive pressure causes the sheets  6  to be loosened or separated from the stripping plate  15 . In particular, the use of antistatic compressed air has proven to be advantageous. 
   The suction openings  22  are preferably arranged in the inlet region  21  of the stripping station. This offers the advantage that the sheets  6  can be gripped by the vacuum of the suction openings  22  immediately at the start of the insertion thereof into the stripping station  3 , so that the sheets  6  are held under tension during the entire feeding time. In a preferred embodiment of the invention, two rows of suction openings  22  are arranged after one another in the stripping plate  15  in the sheet running or travel direction, as represented by the accompanying directional arrow in  FIG. 1 . 
     FIG. 3  is a plan view of the inlet region  21  of a stripping plate  15 . The stripping plate  15  is provided with suction bars  24  having a plurality of suction openings  22 , in this case, three suction openings  22 , however, two or more than three suction openings  22  can also be provided in the suction bars  24 . In order to produce greater retention and greater tension on the sheets  6 , in this preferred exemplary embodiment, two rows of suction bars  24  are arranged after one another in the sheet running direction. The suction bars  24  are connected to the pneumatic units  23  via pressure lines  25 , as illustrated in  FIG. 4 . 
     FIG. 4  is a sectional view of  FIG. 3  taken along the line IV—IV. A section through the stripping plate  15  in the inlet region  21  is shown therein. The suction bars  24  are introduced into the stripping plate  15  as inserted parts. On the underside of the stripping plate  15 , the suction openings  22  of the suction bars  24  are connected to the controllable pneumatic units  23  via a pressure line  25 . The pneumatic unit  23 , in turn, has a positive pressure applied thereto via a pressure line  25 . Through the intermediary of the pneumatic unit  23 , the suction opening  22  can be provided with a vacuum or a positive pressure. It is likewise possible to depressurize the pressure line  25  but, should the stripping unit not be used, the suction openings  22  can be depressurized.