Abstract:
A method for destroying stacked sheets according to which the sheets are mechanically individualized, grasped and cut. To this end, the down-most individual sheet in the stack is grasped in its center section from below, is folded and removed from the stack as a part preceding the stack in the direction of conveyance and is then supplied to a cutting tool with the fold of its center section first.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation, under 35 U.S.C. § 120, of copending international application No. PCT/EP03/00658, filed Jan. 23, 2003, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application No. 102 03 126.6, filed Jan. 25, 2002; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]     The invention relates to a document destroyer, namely an apparatus for destroying stacked sheet material substantially sheet by sheet using a cutting unit. Such a unit is disclosed in International Patent Disclosure No. PCT WO 01/54820 A1.  
         [0003]     In the case of the known document destroyer, the sheet material is fed from a sheet stack to its cutting unit—if appropriate also for cross cutting—not by hand, in more or less separated sheet form, but automatically in a motor-driven manner. The known document destroyer uses preferably a continuously circulating friction-wheel drive to execute the drawing-off action automatically sheet by sheet from the underside of the sheet stack, to fold the sheet centrally and to feed it, with the fold in front, to the cutting unit located beneath the support for the sheet-material stack.  
         [0004]     The separated feeding of sheets to the cutting unit makes it possible, even for a high sheet-destroying capacity, to use a straightforward cutting unit of known conventional document destroyers. The operations of drawing off the sheet and folding it and feeding it to the cutting unit can be realized mechanically in a straightforward manner by a continuously circulating friction-type drive. Although the operation of destroying the sheet-material stack sheet by sheet takes up a certain amount of time, once the sheet stack has been fed, it takes place completely automatically, without manual intervention, with comparatively low outlay in structural terms.  
         [0005]     A significant part of the transporting configuration, which grips the individual sheets from the underside of the sheet-material stack and draws them off, is formed by two carry-along rollers that are driven in opposite directions at a constant speed of circulation. They grip the bearing surface of the sheet at the bottom of the sheet-material stack by way of their circumference, which is provided as a friction coating or with gripping teeth, and push this sheet, from both sides, in the direction of the sheet center. The sheet center is thus deflected in the direction of the through-passage between the two carry-along rollers. The crease or fold vertex which is produced by the deflection is fed between the two carry-along rollers, in the downward direction away from the stack, to the cutting unit of a conventional configuration, which is located beneath, by way of the pushing action exerted by the friction rollers. At the cutting unit, the leading fold vertex is gripped by the cutting disks of the cutting unit. The folded sheet here is drawn through the cutting unit, by the cutting disks, with its doubled sheet sides located one upon the other.  
         [0006]     In order to ensure, during the operation of gripping the sheet which is located at the bottom of the stack in each case, that the crease or fold vertex, which forms in the sheet center when the sheet halves are guided together, is deflected downward away from the stack in the direction of the cutting unit, the known document destroyer contains a pressure-exerting apparatus which acts on the sheet-material stack centrally from above. The pressure-exerting apparatus is positioned above the interspace above the two carry-along rollers and forces the sheet-material stack downward there. Its main task is to bring about, in the individual sheet, drawn off on the underside of the sheet-material stack, the formation of a crease or fold vertex which is produced in the downward direction, toward the cutting unit, and away from the sheet-material stack.  
       SUMMARY OF THE INVENTION  
       [0007]     It is accordingly an object of the invention to provide a document destroyer with individual sheet feeding for stacked sheet material which overcomes the above-mentioned disadvantages of the prior art devices of this general type. The pressure-exerting apparatus which, during the operation of drawing off the sheet located at the bottom of the stack, causes a crease or fold vertex which is oriented downward in the direction of the cutting unit to be generated even more reliably and efficiently, which screens the drawing-off configuration in the outward direction, in order to avoid any risk of injury, and which allows straightforward operation with good operational reliability.  
         [0008]     With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for destroying stacked sheet material substantially sheet by sheet. The apparatus includes a support surface for receiving a sheet stack. The support surface has a slot-shaped through-opening formed therein positioned approximately centrally in the support surface and intended for removing a sheet drawn off from an underside of the sheet stack. A conveying configuration is provided for drawing off the sheet material from the support surface and for feeding the sheet material to a cutting unit. A support chamber houses the sheet stack. Bearing bases flank the support chamber on both sides of the slot-shaped through-opening. Closure elements having pivot pins pivotably mount the closure elements on the bearing bases. The pivot pins are disposed substantially parallel to a slot direction of the slot shaped through-opening and flank the support chamber on both sides. The closure elements cover the support chamber from above during a sheet-destroying operation and, for this purpose, the closure elements can each be pivoted, in a manner of covering halves, above the pivot pins, from an open position, in which the support chamber is open, into a closed position, in which the support chamber is substantially covered, and vice versa. Pressure-exerting elements are positioned between the support surface and the closure elements and press the sheet stack against the support surface. Each of the pressure-exerting elements is articulated on one of the bearing bases, in a manner of a connecting rod of a crank-rocker linkage. Displacement links are provided and each is connected between a respective one of the pressure-exerting elements and a respective one of the bearing bases. Control links are provided and each is connected between a respective one of the pressure-exerting elements and a respective one of the bearing bases. Articulation elements are provided and each functions as a connecting link acting on a respective one of the displacement links and connected to a respective one of the closure elements, such that, by virtue of the respective closure element being pivoted open or closed, the respective pressure-exerting element being pivoted along into a pressure-exerting position or open position corresponding to the open position of the respective closure element.  
         [0009]     The solution makes it possible for the fed sheet-material stack to be covered in the outer direction, during the sheet-destroying operation, by closure elements that can be operated by manual pivoting. The closure elements screen the sheet-material stack in the direction of the charging side, that is to say the upward direction, in the manner of cover halves that can be pivoted in the direction of one another. Furthermore, both in their closed position and in their open or loading position and when they are transferred manually into their open position and into their closed position, they control the positioning of the pressure-exerting elements. During their opening movement, it is not just the case that the closure elements themselves free the unobstructed access to the sheet-stack support of the document destroyer. Rather, during their opening movement, they also remove the pressure-exerting elements from the access path to the sheet-stack support. This is made possible by the particular mechanism-based articulation of the pressure-exerting elements. When the closure elements are pivoted open, the pressure-exerting elements are automatically removed from the support chamber and thus cannot form an obstruction during the loading operation.  
         [0010]     When the closure elements are transferred into their closed position, the closure elements move the pressure-exerting elements in dependence on the height of the sheet stack that is to be destroyed, into a suitable pressure-exerting position. Moreover, once the closed position has been reached, they control the contact pressure of the pressure-exerting elements on the top side of the sheet-material stack. This control is brought about in a manner that ensures optimum contact pressure and pressure-exerting positioning of the pressure-exerting elements automatically in each case without separate drives acting from the outside.  
         [0011]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0012]     Although the invention is illustrated and described herein as embodied in a document destroyer with individual sheet feeding for stacked sheet material, 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.  
         [0013]     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  
       [0014]      FIG. 1  is a diagrammatic, longitudinal section view through an apparatus according to the invention at the beginning of an operating cycle for destroying a sheet stack;  
         [0015]      FIG. 2  is a diagrammatic, enlarged, left-hand sectional view of the apparatus according to  FIG. 1 , the right-hand part of which can be imagined analogously in mirror-inverted form (see  FIG. 1 );  
         [0016]      FIG. 3  is a sectional view analogous to  FIG. 2  with the height of the sheet stack already markedly reduced, e.g. once more than half the stack illustrated in  FIGS. 1 and 2  has been destroyed;  
         [0017]      FIG. 4  is a sectional view of an illustration analogous to  FIG. 3  with the stack height processed further to just a few sheets;  
         [0018]      FIG. 5  is a sectional view analogous to FIGS.  2  to  4  once the final sheet of the original sheet stack ( FIGS. 1 and 2 ) has been drawn off and destroyed;  
         [0019]      FIG. 6  is a sectional view analogous to FIGS.  2  to  5  in which the left-hand closure element—for the sake of simplicity also referred to herein below as “closure cover”—has been pivoted up by a few angular degrees from its closed position, which is illustrated in FIGS.  1  to  5 , in the direction of its open position and raises the pressure-exerting element along with it;  
         [0020]      FIG. 7  is a sectional view analogous to  FIG. 6  once the closure cover has been opened beyond a larger pivoting angle than  FIG. 6 , in which case it raises the pressure-exerting element further;  
         [0021]      FIG. 8  is a sectional view showing a guide protrusion being positioned on a control arm, in particular on a control curve;  
         [0022]     FIGS.  9  to  13  are sectional views of yet further-open positions of the closure cover analogous to  FIG. 6  up to the maximum open position in  FIG. 13 , in the case of which the support for a new sheet-material stack and the feed shaft for the sheet-material stack are completely empty;  
         [0023]      FIG. 14  is an exploded illustration showing, in separated form, the essential framework and operating parts of the apparatus according to the invention;  
         [0024]      FIGS. 15 and 16  are illustrations showing the elements of the mechanism for securing the two pressure-exerting elements on their bearing bases; and  
         [0025]      FIG. 17  is an illustration showing the connecting element that is intended for transmitting the pivoting drive power and is located between a closure element and the coupling mechanism for the pivoting control of a pressure-exerting element. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a destroyer  1  which contains a support surface  4  with a through-opening  5  positioned centrally in the support surface  4 . The through-opening serves for the removal of individual sheets which are drawn off from an underside  6  of the sheet-material stack  7  by the two carry-along rollers  2 ,  3 . The carry-along rollers  2 ,  3  are located partly within the through-opening  5  and have their outer circumference projecting at the top beyond the support surface  4  in the direction of the sheet stack  7 . They are driven continuously in circulation in the directions of rotation  48 ,  49 , which run counter to one another.  
         [0027]     By means of their circumference, which provides for the action of friction or is covered by carry-along elements, the rollers  2 ,  3  grip the respectively lowermost sheet in the stack  7  on its underside  6  and guide its gripped sheet halves together in an inward direction. This produces a fold vertex that is inclined downward in a feeding direction  8  to the cutting unit. The doubled sheet is removed in the feeding direction  8  with the fold vertex in front, as is described in more detail in the generically determinative prior art. The carry-along rollers  2 ,  3  thus do not just draw off the bottom sheet of the sheet stack  7  from the support surface  4 ; rather, they also feed it in the described manner, as the conveying configuration, to a non-illustrated cutting unit located beneath the support surface  4 .  
         [0028]     A support chamber  9  for the sheet stack  7 , extends into a region above the support surface  4 , and is flanked on both sides of the through-opening  5  by in each case one bearing base  10  for pivotably mounting in each case one closure element  11 . For the sake of simplicity, a closure element  11  is also referred to herein below as a “closure cover”. The closure elements  11  are mounted on the respective bearing base  10  such that they can be pivoted about the pivot pin  12 . In their closed position (FIGS.  1  to  5 ), the closure elements  11  close the support chamber  9  in the upward direction. The support chamber  9  is not accessible during the sheet-destroying operation.  
         [0029]     In the case of the document destroyer according to the invention, the two bearing bases  10  flanking the support chamber  9  are each assigned a closure element  11  in a pivotable manner about the respective pivot pin  12 . The closure elements  11  thus have their covering extension arms  13 , which function as covers, and project toward one another from their pivot-bearing ends  14  ( FIG. 1 ). The pivot pins  12  flank the support chamber  9  for the sheet stack  7  on both sides. They run parallel to the slot direction of the through-opening  5  in the support surface  4 , the slot direction not being illustrated but extending perpendicularly to the plane of  FIG. 1 .  
         [0030]     The document destroyer contains pressure-exerting elements  15  positioned between its support surface  4  and the closure elements  11 . The pressure-exerting elements  15  are in the form of pressure-exerting plates that extend, perpendicularly to the direction of the figures of the drawing, over more or less most of the widthwise extent of the closure elements  11 . The pressure-exerting elements  15  force the sheet stack  7  in the direction of the support surface  4 . Those sides of the two pressure-exerting elements  15  which are directed toward the respective bearing base  10  are configured as base-like articulation-carrier holders  16 . Each articulation-carrier holder  16  contains pivot pins  17 ,  18  ( FIG. 2 ) which run perpendicularly to the planes of the drawing and are intended for bearing a control link  19  and a displacement link  20  both in a pivotable manner in the plane of the figures.  
         [0031]     The two pivot pins  17 ,  18  of each articulation-carrier holder  16  only bear those ends of the control link  19  and of the displacement link  20  that project into the support chamber  9 . The base (bearing base  10 ) ends of the control link  19  and of the displacement link  20  (FIGS.  2  to  9 ) in each case are mounted on the bearing base  10  such that they can be pivoted about the respective pivot pins  21  and  22  running perpendicularly to the plane of the figures. While the housing-mounted bearing base  10  of the document destroyer is positioned in a stationary manner, the control link  19  and the displacement link  20  form the two elements of the articulation-carrier holder  16 , which function as a connecting rod of a crank-rocker linkage, and of the pressure-exerting element  15  assigned thereto. The pressure-exerting element  15  is thus secured on the articulation-carrier holder  16  by an articulation mechanism or coupling mechanism in the manner of a crank-rocker linkage.  
         [0032]     A connecting link  23  between the closure element  11  and the associated displacement link  20  contains a rotary/pushing-action articulation  24  at its bearing-base-like end. The top end of the connecting link  23 , this end being directed away from the rotary/pushing-action articulation  24 , is connected to the closure element  11  such that it can be pivoted about the pivot pin  25  ( FIG. 3 ). The pivot pin  25 , like all the other pivot pins, extends perpendicularly to the planes of the drawing.  
         [0033]     The pivoting connection between the connecting link  23  and the displacement link  20  acts on an extension spur  26  of the displacement link  20 , the spur  26  functions as a lever. The extension spur  26  projects in the manner of a stublike-lever arm beyond the base-side (bearing base  10 ) articulation pin  22  of the displacement link  20  and thus forms a two-armed lever with the displacement link  20 .  
         [0034]     The rotary/pushing-action articulation  24  of the connecting link  23  with an articulation  45  as a rotary-articulation part, engaging at the free end of the extension spur  26 , acts on the displacement link  20  as a lever that is active about the articulation  45 . The pushing-action direction of the rotary/pushing-action articulation  24  runs in the longitudinal direction of the connecting link  23 .  
         [0035]     The bearing bases  10  are integrated or fixed in side walls of a feed shaft  27  to the support surface  4 .  
         [0036]     Each pressure-exerting element  15  has its projecting end  29 , which is directed away from its articulation-carrier holder  16  and projects into the support chamber  9 , extending as far as the through-opening  5  for the drawn-off sheet material.  
         [0037]     A tension spring  28  is active between the control link  19  and pressure-exerting element  15 . The tension spring  28  forces the pressure-exerting element  15  in the direction away from where it bears on the sheet stack  7 . It thus tries, to a certain extent, to raise the pressure-exerting element  15  upwards by way of its free, projecting end  29 . In conjunction with the four-bar mechanism  10 ,  19 ,  16 ,  20 , the tension spring  28  provides additional pressure in the downward direction on the paper stack  7  for the overall movement of the pressure-exerting element  15 .  
         [0038]     The tension spring  28  has its end that is directed toward the control link  19  fixed on the control link  19  approximately centrally between the articulation ends  17 ,  21  thereof. The fixing takes place on a fixing protrusion  30  which projects in the direction of the closure element  11 .  
         [0039]     In the case of a large stack thickness  31  ( FIGS. 1 and 2 ) with a corresponding vertical spacing from the support surface  4 , the pressure-exerting element  15  has its projecting end  29  inclined in the direction of the through-opening  5  of the support surface  4  (angle of inclination  32 ). The magnitude of the angle of inclination  32  decreases along with the stack thickness until, in the case of an average stack thickness  33 , a more or less parallel position is reached. In the case of a small spacing  34  close to or equal to a stack height of zero, the pressure-exerting element  15  has its articulation carrier holder  16  resting on the sheet stack  7 . In this position, the respective pressure-exerting element  15  is inclined in a state in which it slopes up in the direction of the through-opening  5  (angle of inclination  35 ;  FIG. 4 ), with the result that its projecting end  29  no longer exerts any pressure in the direction of the support surface  4 . In the end position ( FIG. 5 ), however, the pressure-exerting element  15  acts on that end edge of the support surface  4  that is directed toward it and serves as a stripping edge  36  for staples, possibly with the rest of the sheet material of the processed stack being clamped in between.  
         [0040]     That end of the control link  19  which is directed toward the pressure-exerting element  15  projects beyond its pivot pin  17 , which is positioned there, in order to form a carry-along stop  37 , which projects at an angle in the direction of the abutment surface  4 . In the case of the pressure-exerting-element-side pivot pin  18  of the displacement link  20  being located above the framework-side pivot bearing  21  of the control link  19  and in the case of the closure element  11  being pivoted open in part ( FIGS. 9 and 10 ), with the pressure-exerting-element-side pivot bearing  17  of the control link  19  being positioned at a correspondingly high level, in order to be pivoted along, the carry-along stop  37  strikes against a mating stop  38  which is mounted on the pressure-exerting element  15  in the region of the articulation carrier  16 . As the closure element  11  pivots open  47  further, the carry-along stop  37  transmits the resulting torque in order to raise the pressure-exerting element  15  further in the direction away from the support surface  4  ( FIG. 9 ). This applies as far as the raised rotary position of the closure element  11  according to  FIG. 10 . The rest of the upward pivoting movement of the pressure-exerting element ( FIGS. 11 and 12 ) as far as the extreme open position according to  FIG. 13  takes place via a control curve  39  of a control arm  46 , which extends the control link  19 , by way of the guide protrusion  50 , beyond its pivot pin  21  on the bearing base and is configured as a two-armed lever which is active on both sides of the pivot pin  21 .  
         [0041]     At its end that is directed away from the pressure-exerting element  15 , the control link  19  thus has its control arm  46  extending beyond its pivot bearing  21  on the bearing base  10 . Furthermore, at its end that is directed away from the pivot pin  21 , the control arm  46  contains a shoulder surface  40  and an end stop surface  41 , and these are located at an obtuse angle in relation to one another. In the case of the closure element  11  being pivoted open beyond the top of its pivoting path ( FIG. 12 ), the end stop  43 , which is disposed at the outer end of the closure element  11 , comes into contact with the shoulder surface  41  of the control arm  46 .  
         [0042]     By virtue of this contact, the driving torque which is applied to the closure element  11  by the operator in the continued-opening direction  44 , and is active in the counterclockwise direction about the pivot pin  12 , is fully transmitted to the control arm  46  via the end stop  43  and is active on the control link  19  as a pivoting moment which is active in the counterclockwise direction about the pivot pin  21 . The control link  19  thus forces the pressure-exerting element  15  in the counterclockwise direction, beyond its vertical top dead-center position ( FIG. 12 ), into a position in which it is more or less parallel to the closure element  11 , which has pivoted further outward in relation to the support chamber  9 . This renders the support chamber  9  easily accessible from above for the introduction of a sheet stack  7 .  
         [0043]     A description is given herein below of an operating cycle of the document destroyer in its individual steps, starting from the introduction position for the sheet stack  7  ( FIG. 13 ), via the closure of the support chamber  9  by virtue of the closure elements  11  being pivoted closed (going back from  FIG. 12  to  FIG. 8  and then  FIGS. 1 and 2 ) and via the subsequent processing of the sheet stack  7  in order to destroy it (FIGS.  1  to  5 ), until, finally, the closure element  11  is (or, even better, the two closure elements  11  are) pivoted open into the fully open position ( FIG. 13 ).  
         [0044]     The two closure elements  11  of the document destroyer interact correspondingly with one another in each case. Therefore, the pivoting-open movement of one of the closure elements  11  synchronously brings about an analogous pivoting-open movement of the other closure element  11  as well, by way of a non-illustrated synchronizing drive. A pulling connection between the two closure elements  11  ensures that the closure elements  11  are each positioned at an identical angle in relation to their pivot pins  12 , even if the operator only pivots one of the two closure elements  11 . This gives rise to the synchronized pivoting.  
         [0045]     With the closure elements  11  and pressure-exerting elements  15  located in the extreme open position ( FIG. 13 ), the sheet stack  7  is positioned in the support chamber  9  from above. The closure elements  11  then pivot from their upright open position into the essentially horizontal closed position ( FIG. 1 ). The pivoting movement is executed synchronously, at the same pivoting angle in each case, by the two closure elements  11 . The pressure-exerting elements  15  assigned to the two closure elements  11  are carried along here in the manner described. The closed position, which follows on from the loading operation, is illustrated in  FIG. 1 . In this case, the two pressure-exerting elements  15  have their projecting ends  29 , which are inclined downward in the direction of the region of the through-opening  5 , acting on the center of the sheet stack  7 .  
         [0046]     The drawing-off configuration, in the form of the two carry-along rollers  2 ,  3  rotating permanently in opposite directions, is then switched on. The sheet stack  7  is processed sheet by sheet from its underside  6 , as is described in detail in International Patent Disclosure WO 01/54820 A1, which was mentioned in the introduction.  
         [0047]     During the processing of the sheet stack  7 , the rotary position of the two pressure-exerting elements  15  in relation to the sheet stack  7  changes in the manner illustrated in FIGS.  2  to  5 . These figures merely illustrate the left-hand pressure-exerting element  15  and, as the sheet stack  7  is processed to an increasing extent, i.e. as its stack height  31 ,  33  decreases to zero, the pressure-exerting element is pivoted in the counterclockwise direction, with the result that, in the case of the stack height being zero ( FIG. 5 ), the pressure-exerting element  15  acts to a pronounced extent on the stripping edge  36  of the support surface  4 . At the beginning of the sheet-destroying operation with the stack height at a maximum, the pressure-exerting elements  15  have their projecting ends  29  acting in the center of the sheet stack  7  in the drawing-in region of the carry-along rollers  2 ,  3 . This enhances the friction of the carry-along rollers  2 ,  3  with the facing surface of the bottom layer of the sheet stack  7  and, ultimately, gives rise to the desired center fold. In this initial state, the dead weight of the residual stack which bears on the bottom layer of the sheet in the region of the stripping edges  36  is sufficient to ensure that any adhering staples are stripped off.  
         [0048]     However, the dead-weight action decreases along with the stack thickness  33 , the reduction in the stack thickness increasing during the sheet-destroying operation. The resulting reduction between the bearing pressure to which the stripping edge  36  is subjected by the sheet-stack weight is substituted, as the residual-stack height  33  approaches a zero height, by the stripping edge  36  being subjected to external pressure from above by the pressure-exerting element  15 . The pressure exertion is intensified and, in order to generate the desired stripping action, assisted by the pressure-exerting element  15  being pivoted in the counterclockwise direction (FIGS.  2  to  5 ). The pivoting takes place along with the pressure-exerting element  15  being lowered downward in the direction of the support surface  4 . The lowering of the pressure-exerting element  15  is brought about by the dead weight of the latter, and the counterclockwise pivoting of the pressure-exerting element  15  that is illustrated in FIGS.  2  to  5  follows as a consequence of the four-bar mechanism. This results from a specifically different magnitude for the pivot point/articulation spacings of the four-bar chain. The tension spring eliminates any possible play in the articulations and braces the four-bar chain in such a manner that an additional force of the pressure-exerting element in the downward direction is produced.  
         [0049]     Once the sheet stack  7  has been fully processed or destroyed ( FIG. 5 ), the covering extension arm  13  of the closure element  11  is pivoted open in the opening direction  47  ( FIG. 5 ). The synchronous connection of the pivot mountings on both sides results in an analogous pivoting-open movement on the right-hand side with the closure element  11  there. The connecting link  23  is drawn upward by the pivoting-open movement in the opening direction  47 . The connecting link  23  pivots the extension spur  26  in the counterclockwise direction, in the region of its end articulation  45 , about the pivot pin  22  on the bearing base  10 . This pivoting drive causes the displacement link  20  to be pivoted up in a counterclockwise direction about the pivot pin  22 . As a result, the pressure-exerting element  15  is raised upward from the support surface  4 . The operation of the closure elements  11  being pivoted open in the opening direction  47  is transmitted to the pressure-exerting element  15 , by the displacement link  20 , as far as the displacement position that is illustrated in  FIG. 9 .  
         [0050]     Beginning from the half-open rotary position reached by the closure elements  11  ( FIG. 9 ), the guide protrusion  50 , which is positioned at the rear end of the closure element  11 , runs onto the control curve  39  of the control arm  46  ( FIG. 10 ). Furthermore, the final pivoting of the two pressure-exerting elements  15  into their definitive open position ( FIG. 13 ), which completely frees the access to the support surface formed from above and in which the elements are swung apart from one another in the upward direction in a cup-like manner, this final pivoting movement going beyond  FIG. 9  and being illustrated in FIGS.  10  to  13 , is brought about by the closure elements  11  being pivoted apart from one another in the opening direction  44 . Starting from the partially open position of the closure elements  11 , this position being illustrated for example in  FIGS. 9 and 10 , the rotary drive power which is produced by the closure elements  11  being pivoted apart from one another is transmitted from the control arm  46  to the control link  19 , as the torque which is active in the counterclockwise direction about the pivot pin  21 , by virtue of the guide protrusion  50 , which is connected to the rear pivoting arm  51  of the closure element  11 , sliding onto the control curve  39 . By way of its end that is directed toward the support chamber  9  for the sheet stack  7 , the control arm  19  thus raises the pressure-exerting element  15  in the opening direction  47  via the pivot pin  17 . The rotary pivoting of the control link  19  about the pivot pin  21  is associated with the raising-action pivoting of the pressure-exerting-element end of the control link  19 . The pivoting movement causes the pressure-exerting element  15  to pivot in the counterclockwise direction in the region of the articulation-carrier-side pivot pin  17  of the control link  19 . The pivots open the projecting end  29  of the pressure-exerting element  15  counterclockwise in the opening direction  47 . Starting from the closed position of the closure element  11  according to  FIG. 5 , the pivoting-open movement of the pressure-exerting element  15  lags behind the pivoting-open movement of the closure element  11  in the first instance, as far as a half-open position of the closure element  11  (FIGS.  9  and  10 ). The guide protrusion  50  then runs onto the control curve  39  of the control arm  46 . As the closure element  11  pivots open further, the pressure-exerting element  15  then pivots at a higher speed of rotation than the closure element  11 . The pressure-exerting element  15  regains, to a certain extent, the lost angled position in relation to the closure element  11  as far as the half-open position ( FIGS. 9 and 10 ), until the extreme, swung-apart open position according to  FIG. 13  is reached, the pressure-exerting element  15  being more or less parallel to the closure element  11  in this position.  
         [0051]     During closure of the closure elements counter to the direction  47 , the guide protrusion  50  moves in the opposite direction along the control curve  39  and thus allows the pressure-exerting element  15  to lead during the closing movement.  
         [0052]     By virtue of two individual covers, this overall configuration also allows individual sheet feeding.