Abstract:
A sheet punching and embossing machine includes a device for punching blanks from sheets. The device has a frame and a bearing plate is mountable in the frame. The bearing plate is equipped with punching and grooving knives. Hydraulically activated clamping elements are provided for clamping the bearing plate in the frame. A hydraulic system includes a piston braced by a mechanical spring for building up hydraulic pressure for activating the clamping elements.

Description:
BACKGROUND OF THE INVENTION 
   FIELD OF THE INVENTION 
   The invention relates to a sheet punching or cutting and embossing machine including a device for stamping or punching blanks from sheets, and a frame for accommodating a bearing plate equipped with cutting and creasing knives. The bearing plate is held in the frame by hydraulic clamping elements. 
   Such a device for a sheet punching or cutting and embossing machine has become known heretofore from German Published, Non-prosecuted Patent Application DE 195 16 073 A1. In the frame of the device described therein, the bearing plate is clamped in and roughly aligned by justifying and retaining screws. Fine adjustment is then accomplished by setting or adjusting stops in the frame of the bearing plate. In order to perform clamping, aligning and subsequent fine adjusting, an operator must manually tighten the justifying and retaining screws and likewise manually adjust the take-up frame until the bearing plate is precisely aligned in the device. 
   The integration of hydraulic clamping elements into the frame of the bearing plate, which is described in the 2001 annual corporate report of the firm Jagenberg in Neuss, Germany is a conventional procedure for reducing set-up times. That report describes a take-up frame, also known as a chase, wherein the stamping or punching die is fixed in the frame by hydraulic cylinders as opposed to conventional clamping by screws. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a sheet punching and embossing machine with a device for punching blanks from sheets for a sheet punching and embossing station, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which, with minimal structural devices, makes possible a reduction of set-up times for maximum repeatable accuracy, while being simultaneously capable of compensating for pressure fluctuations in the hydraulic system. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet punching and embossing machine, comprising a device for punching blanks from sheets. The device has a frame and a bearing plate is mountable in the frame. The bearing plate is equipped with punching and grooving knives. Hydraulically activated clamping elements are provided for clamping the bearing plate in the frame. A hydraulic system including a piston braced by a mechanical spring is provided for building up hydraulic pressure for activating the clamping elements. 
   In accordance with another feature of the invention, the sheet punching and embossing machine further includes at least another hydraulic system. At least two of the hydraulic systems are independently operable for clamping-in the bearing plate. 
   In accordance with a further feature of the invention, a first one of the hydraulic systems serves for positioning the bearing plate in the frame in a direction of travel. A second one of the hydraulic systems serves for positioning the bearing plate in the frame transversely to the direction of travel. 
   In accordance with an added feature of the invention, at least two of the clamping elements respectively serve for positioning and fixing the bearing plate on both sides transversely to a direction of travel. At least one of the clamping elements serves for positioning and fixing the bearing plate on one side in the direction of travel. 
   In accordance with a concomitant feature of the invention, the hydraulic systems are integrated into the frame. 
   Thus, the object of the invention is attained by providing a piston braced or supported by a mechanical spring for building up the pressure in the hydraulic system. The hydraulic clamping of the bearing plate, in accordance with the invention, eliminates a need for a mechanical clamping by justifying and retaining screws. The bearing plate merely has to be inserted by the operator in order to be positioned and fixed in the frame. During the insertion of the bearing plate into the frame, the positioning occurs by a cylinder pin that is fastened to the frame. Thereafter, the bearing plate is fixed by a successive pressure build-up in the hydraulic system. Since only the application of pressure to the hydraulic system must be performed by the operator, manual aligning in the frame is completely eliminated, and consequently the set-up time is appreciably reduced. 
   Integrating a spring or spring package, for example, in the form of successively disposed disk springs, into the cylinder of the hydraulic system, with the spring being connected with the piston, creates the possibility of counteracting a pressure drop, for example, in the event of a leak. A bias tension or prestressing is applied to the spring during the build-up of pressure in the hydraulic system, so that the spring is able to compensate for a pressure drop. 
   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 diagrammatic, side-elevational view of a main structure of a sheet punching and embossing machine; 
       FIG. 2  is a plan view of a frame for accommodating a bearing plate; 
       FIG. 3  is an enlarged, fragmentary, sectional view of  FIG. 2 , showing a hydraulic cylinder of a hydraulic system in greater detail; and 
       FIG. 4  is another enlarged, fragmentary, sectional view of  FIG. 2 , showing a clamping element in greater detail. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a main structure of a sheet punching and embossing machine  1  for punching or cutting, stripping, and distributing sheets of paper, board such as cardboard or pasteboard, and the like. 
   The punching and embossing machine  1  is made up of stations, namely a punching or cutting device  2 , a stripping device  3  and a distributing device  4 , which are carried by and encased in a common machine housing  5 . 
   Sheets  6  are grasped at respective front or leading edges thereof by gripper bars  8  which are fastened on revolving chains  7  and are intermittently pulled through the various stations  2 ,  3  and  4  of the punching and embossing machine  1 . 
   The punching or cutting device or station  2  contains a device made up of a lower table  9  and an upper table  10 . The lower table  9  is fixed in the frame of the machine  1  and provided with a counterplate for a punching or cutting knife. The upper table  10  is mounted so as to be vertically movable and is drivable by a drive for the device. In this regard, as is seen in  FIG. 2 , the upper table  10  contains a frame  15  for receiving a bearing plate  16  that is provided with punching and grooving knives. 
   The gripper bar  8  transports the sheet  6  from the punching and embossing device or station  2  into the following stripping device or station  3 , which can be equipped with stripping tools. In the stripping station  3 , waste pieces  11  which are not needed are forced down off of the sheet by the stripping tools. These pieces  11  drop into a receptacle-type carriage  12  that is inserted beneath the station. 
   From the stripping device or station  3 , the sheet  6  reaches the distributing device or station  4 , wherein the sheet is either simply deposited, or the individual blanks are advantageously simultaneously separated. The distributing station  4  can also contain a pallet  13  whereon the individual sheets are accumulated in a stack or pile  14 . The pallet  13  with the sheets stacked or piled thereon is removable from the vicinity of the punching and embossing machine  1  after the stack or pile  14  has reached a given height. 
   As is apparent from the figures, the chains  7  carry a number of gripper bars  8 , namely eight in the example of  FIG. 1 , so that several sheets  6  can be processed simultaneously in the various stations  2 ,  3  and  4 . 
     FIG. 2  is a plan view of the frame  15  for accepting the bearing plate  16  as part of a device which is movable out of the punching or cutting station  2 . Revolving clamping elements  17  and  18  for fixing the bearing plate  16  are integrated in the frame  15 . The exemplary embodiment of  FIG. 2  has a frame  15  which is equipped with four clamping elements  18  on one side in a direction of travel  19  and two clamping elements  17  on either side transverse to the direction of travel  19 . The clamping elements  17  and  18  are connected to respective hydraulic cylinders  22  and  21  via pressure lines  20  for supplying pressure. As shown, the clamping elements  18  are pressure-charged by the hydraulic cylinder  21 , and the clamping elements  17  are pressure-charged by the hydraulic cylinder  22 . Two mutually independently operating hydraulic systems  23  and  24  are thus integrated into the frame  15 . 
   The frame  15  is provided on a long side  25  thereof, which is shown at the bottom of  FIG. 2 , with a cylinder pin  26  by which the bearing plate  16  is positioned during insertion. Alignment of the bearing plate  16  then occurs first by the fixing thereof by the hydraulic system  21  and then by the fixing thereof by the hydraulic system  24 , as is described in greater detail below. 
   The bearing plate  16  is inserted into the frame  15  by the operator and roughly positioned by the cylinder pin  26  that is fastened on the long side  25  of the frame  15 , which is shown at the bottom of  FIG. 2 . There are no hydraulic clamping elements  17  and  18  integrated into the frame  15  on this long side  25 . First, the clamping elements  18  are charged with pressure by the operator. This occurs when the operator manually actuates the clamping screw  27  at the hydraulic cylinder  21 , which results in a successive pressure build-up in the hydraulic system  23 , causing the clamping elements  18  to fix the bearing plate  16  against the cylinder pin  26  and the long side  25  of the frame  15  at the bottom of  FIG. 2 . Next, the hydraulic system  24  is charged with pressure by rotation of a clamping screw  28  at the hydraulic cylinder  22 . Due to the successive pressure build-up in the clamping elements  17 , all of the pistons of the clamping elements  17  initially contact the bearing plate  16 . As the pressure rises in the clamping elements  17 , the bearing plate  16  also becomes fixed transversely to the direction of travel  19 . In order to align the bearing plate  16 , the operator must simply actuate the two respective clamping screws  27  and  28  of the hydraulic systems  23  and  24 , so that the bearing plate  16  is clamped in the frame  15  and aligned with minimal set-up time periods. 
   The hydraulic systems  23  and  24  are formed primarily of the hydraulic cylinders  21  and  22 , the pressure lines  20  and the clamping elements  17  and  18 .  FIG. 3  is a sectional view of a hydraulic cylinder  21 . The hydraulic cylinder  21  is made up for the most part of a cylinder  29 , a clamping screw  27 , a guided piston  30 , and a spring package  31 . The pressure line  20  is connected to the hydraulic cylinder  29 . 
   In order to pressurize the hydraulic fluid, which is particularly in the form of hydraulic oil, the piston  30  is pushed into a cylinder chamber  32  by the clamping screw  27 . 
   Upon the attainment of a defined pressure, the piston  30  compresses the spring package  31  in the direction of the clamping screw  27 , building up a bias tension or pretensioning in the hydraulic fluid. Should a pressure drop occur, for example in the event of a leak, the spring package  31  then counteracts the pressure drop. The hydraulic system  23  is thus in a position to compensate for a pressure drop. Leakage wherein very small amounts of hydraulic fluid escaped would cause a large pressure drop, because only small amounts of hydraulic fluid are present in the hydraulic system  23 . 
     FIG. 4  illustrates the main construction of a clamping element  17 . The pressure line  20  is screwed directly into the clamping element  17  and supplies a piston-cylinder unit  33 ,  34  with hydraulic fluid, the piston  33  being provided with a pressure part  35  which acts directly upon the bearing plate  16 . When the clamping element  17  is charged with pressure, the piston  33  moves in the direction of the bearing plate  16  and fixes it in the frame  15 , a normal operating pressure being several hundred bars in this case. The clamping elements  17  generate a force clearly over 500 N per clamping element. In the pressure-free state, the piston  33  returns to the initial setting thereof. Resetting can also occur by a non-illustrated piston reset spring. 
   It is also imaginable, in accordance with the invention, to provide guided wedges which can be pushed against one another as clamping elements  17  and  18 . In that case, the piston-cylinder unit acts upon one wedge and pushes the other wedge in the direction of the bearing plate  16 , so that the bearing plate  16  is positioned and fixed by the wedges or a piston which is disposed on the wedge. The wedges are then reset either by the depressurizing of the piston-cylinder unit or by a resetting spring.