Abstract:
A device for fixing the position of a sheet includes a feeding table for transporting the sheet; at least one front lay disposed in vicinity of the feeding table and, in a working position, protruding upwardly beyond the plane of the feeding table; a swivellable holder to which the front lay and an adjusting device for the front lay are secured; and a adjusting device secured to the holder, the front lay and the adjusting device being disposed separated from one another on the holder, the front lay being in continuous biasing engagement, under tension, with the adjusting device, so that, by changing the position of the holder, the front lay and the adjusting device are movable from the working position into a neutral position and, conversely, from the neutral position into the working position.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a device for fixing the position of a sheet on a feeding table of a sheet-fed printing press. 
     A printing press comprises a feeding table whereon a sheet is transported to a printing unit. During the transportation of the sheet, an edge of the sheet comes into contact with front lays which limit the movement of the sheet and define a line for aligning the sheet. After the alignment of the sheet, the front lay is moved away from the table, so that the edge of the sheet, which is disposed on the alignment or adjustment line, can be picked up by a gripper, and the sheet can consequently be transported to the printing unit. 
     From the published German Patent Document DE 40 04 447 C2, a feed lay or lay mark for aligning sheets which are guided on a feeding table have become known heretofore. The feeding table has an adjustable stop which is permanently connected to the feeding table. The feed lay is biased in the direction of the stop by a spring element. The front lay is articulatedly connected to a base body and can be pivoted together with the spring element from a working position into a neutral position. The working position is the position wherein the front lay defines the line for aligning the sheet. In the neutral position, the front lay is disposed beneath the feeding table, so that the front edge of the sheet can be picked up by a gripper. 
     A disadvantage of the arrangement described in the aforementioned German patent document is that the time at which the front lay leaves the stop is dependent upon the setting of the stop and is thus not precisely specified. This time uncertainty must be accounted for, and shortens the time available for aligning and stabilizing the sheet. The time at which the front lay leaves the working position must therefore be moved ahead or advanced accordingly. Wear is also to be expected due to the contact of the front lay with the adjustable stationary stop, which can result in the front lay being disadjusted or moved out of alignment. 
     The published German Patent Document DE 43 06 238 A1 discloses a device for fixing the position of a sheet, and a feed table for transporting the sheet, including a front lay that is disposed in the region of the feed table and that, in a working position, protrudes upwardly from the plane of the feed table, the front lay being fixed at a pivotable holding device and serving simultaneously as the adjusting device. Devices of this type are difficult to handle. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to make available an improved device for fixing the position of a sheet on a feeding table by aligning at front lays a sheet that is transported on a feeding table. 
     With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for fixing the position of a sheet, comprising a feeding table for transporting the sheet; at least one front lay disposed in vicinity of the feeding table and, in a working position, protruding upwardly beyond the plane of the feeding table; a swivellable holder to which the front lay and an adjusting mechanism for the front lay are secured; and an adjusting device secured to the holder, the front lay and the adjusting device being disposed separated from one another on the holder, the front lay being in continuous biasing engagement, under tension, with the adjusting device, so that, by changing the position of the holder, the front lay and the adjusting device are movable from the working position into a neutral position and, conversely, from the neutral position into the working position. 
     In accordance with another feature of the invention, the adjusting device is rotatably mounted, and is rotatable for adjusting the position of the front lay. 
     In accordance with a further feature of the invention, the adjusting device is formed with lock recesses and includes a lock element, the lock recesses cooperating with the lock element for enabling rotation of the adjusting device at prescribed angles. 
     In accordance with an added feature of the invention, the lock element is constructed as a leaf spring, which is prestressed with the aid of a lock nose in a direction towards the adjusting device and, when the adjusting device is rotated, the lock element catches in the lock recesses, so that the adjusting device is rotatable further only with increased torque. 
     In accordance with an additional feature of the invention, the position-fixing device includes a servomotor connected to the adjusting device for adjusting the rotational position of the adjusting device. 
     In accordance with yet another feature of the invention, the adjusting device is formed with a contact surface to which a tool for adjusting the position of the adjusting device is applicable. 
     In accordance with yet a further feature of the invention, the adjusting device is disposed beneath the feeding table; and the feeding table is formed with an opening in vicinity of the adjusting device, via which the contact surface is accessible with the aid of a tool. 
     In accordance with yet an added feature of the invention, the adjusting device includes a rotary element mounted so as to be rotatable about an axis of rotation; the front lay having a contact part in contact with a side margin of the rotary element; at least one of the rotary element and the position of the axis of rotation being constructed so that, when the rotary element is rotated about the axis of rotation, a spacing between the contact part and the axis of rotation is modified. 
     In accordance with yet an additional feature of the invention, the contact part and the rotary element are operatively connected to one another via at least one of an anti-friction bearing and a slide ring. 
     In accordance with still another feature of the invention, the adjusting mechanism serves for adjusting the spacing between the front lay and the adjusting device. 
     In accordance with still a further feature of the invention, the position-fixing device includes at least one tensioning device for prestressing the front lay in a direction towards the stop element. 
     In accordance with still an added feature of the invention, the front lay is formed at least partly of an elastic material; and is secured to the holding device in a manner that the front lay is prestressed in a direction towards the adjusting device. 
     In accordance with still an additional feature of the invention, the rotary element is formed as an Archimedes&#39; spiral. 
     In accordance with another feature of the invention, the rotary element is formed as a disk which is rotatable about an eccentrically disposed axis of rotation. 
     In accordance with a concomitant feature of the invention, the adjusting device is connected to a disk formed with lock recesses in a side margin thereof; the disk having a first and a second stop surface; and a stop bolt is disposed between the first and the second stop surfaces, the stop bolt, by coming into contact with the first and the second surfaces, serving to limit the range of rotation of the adjusting device. 
     The invention offers the advantage that the front lay is preferably prestressed against an adjusting device without play and connected to the adjusting device in one structural unit, the front lay being movable together with the adjusting device from a working position into a neutral position. In this way, the front lay is always in contact with the adjusting device, so that, subsequent to the transition from the neutral position into the working position, the front lay is aligned at the predetermined adjustment line. 
     Because at least two, and in most instances more than two, front lays are advantageously distributed over the width of the feeding table, it is expedient for the front lays to be individually adjustable. For straight sheet edges, all front lays can be used as stops for the sheet. The sheet edge is thus given optimal support in the stopping process. 
     For convex sheet edges, the middle front lays are preferably removed. Consequently, only two front lays at the outer region are used to prevent the sheet from rocking. For thin sheets with edges that are not straight, it may be necessary to adapt several front lays to the curvature of the sheet in order to prevent displacement or stressing of the sheet. This ensures an optimal adjustment of various printing materials. 
     A simple embodiment of the adjustable adjusting device calls for it to be rotatably mounted and provided with lock recesses. The rotatable mounting of the adjusting device ensures a simple adjustment of the position of the front lay. The use of lock recesses in conjunction with a lock element is advantageous in that the adjusting device is enabled to be rotated at prescribed angles in a precise manner. It is possible, thereby, to achieve very precise settings of the front lay. 
     In a preferred embodiment, the lock element is formed as a leaf spring having a lock nose which is allocated or assigned to the lock recesses. This embodiment ensures a cost-effective realization of the lock element. 
     The adjusting device is advantageously connected to a servomotor with which the position of the adjusting device can be set. The use of a servomotor permits a very precise adjustment of the adjusting device, which is additionally independent of the local position of the adjusting device. The adjusting device is thereby easy to adjust even when access thereto is difficult. 
     The adjusting device is also easy to adjust because it has a surface upon which a tool for adjusting the position of the adjusting device is able to be placed. Thus, the position of the adjusting device can be adjusted without using complex technical equipment. 
     The adjusting device is advantageously disposed beneath the feeding table, thereby providing a compact construction. In addition, an opening is formed in the feeding table in the vicinity of the adjusting device, via which the contact surface of the adjusting device can be accessed with a tool. In this way, the adjusting device can be adjusted easily from above. 
     The adjusting device is advantageously constructed in the form of a rotating element adjoined by the front lay via a contact part at a side margin of the rotating element. The rotating element and/or the axis of rotation of the rotating element are constructed so that, when the rotating element is rotated about the axis of rotation, the distance between the contact part and the axis of rotation is changed. This embodiment represents a simple construction of the adjusting device. 
     To prevent friction and to increase the accuracy of the position of the front lay, the contact part is braced against the adjusting device via a slide ring or anti-friction bearing. 
     In a further development of the invention, the front lay includes an adjusting mechanism with which the distance between the contact part and the front lay can be set. An initial setting of the front lay can be performed by using the adjusting mechanism. With this initial setting, a number of front lays can be aligned on a prescribed adjusting line. 
     In a preferred embodiment, the front lay is biased in a direction towards the stop element and the adjusting mechanism, respectively, by a tensioning mechanism. By using a prestressed front lay, freedom of play is afforded to the front lay in any situation. 
     A particularly advantageous embodiment of the invention provides for the front lay be produced at least partly from an elastic material. Additional stressing mechanisms for biasing the front lay in the direction towards the stop element are thus dispensed with or spared. A compact and economical construction is thereby possible. 
     A preferred embodiment of the rotating element is formed as an Archimedes&#39; spiral or a disk which is rotatable about an eccentrically arranged axis. In both embodiments, the distance between the side margin of the rotating element and the axis of rotation can be varied in dependence upon the rotational position of the rotating element. 
     Another advantageous embodiment of the invention is realized by an adjusting device comprising a disk at the outer margin of which lock recesses are provided, the disk being formed with first and second stop surfaces which are bringable into contact with a stop bolt. By using the stop bolt and the stop surfaces, a defined angular range is prescribed for the rotation of the adjusting device. A setting in which all the front lays stand on a common straight line is thereby easy to find. 
     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 device for fixing the position of a sheet on a feeding table, 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, wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side elevational view, partly in cross section, of a front lay with a holding device; 
     FIG. 2 is a top plan view of FIG. 1 showing the front lay with a feeding table; 
     FIG. 3 is a front elevational view of FIG. 1 showing a shaft with two front lays; 
     FIG. 4 is a view similar to that of FIG. 1 of a front lay in a neutral or inactive position, shown with a slide bearing; 
     FIG. 5 is a view similar to that of FIG. 1 showing a front lay with an anti-friction bearing; 
     FIG. 6 is a view similar to that of FIG. 5 showing a front lay in a second embodiment; 
     FIG. 7 is a top plan view similar to that of FIG. 2 showing a front lay in another embodiment with an adjusting device in the form of an Archimedes spiral; 
     FIG. 8 is a view like that of FIG. 1 of a front lay in a third embodiment; and 
     FIG. 9 is a view similar to that of FIG. 9 of the front lay of FIG. 8 from the perspective of the feeding table; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is described hereinbelow by way of example in a sheet-fed printing press, the device according to the invention being introducible into any type of printing press wherein a part must be aligned at a predetermined adjustment line and then picked up from the side of the adjustment line and moved forward. 
     Referring now to the drawings and, first, particularly to FIG. 1 thereof, there is shown therein a feeding table  3  with a front lay  1  in working position. In the working position, a contact plate  20  of the front lay  1  is disposed at a front edge  47  of the feeding table  3  so that the contact plate  20  protrudes upwardly beyond a supporting surface  49  of the feeding table  3  and is disposed parallel to the front edge  47  on a predetermined alignment or adjustment line  46  (note FIG.  2 ). 
     The contact plate  20  has an intercepting surface  48 , which, in the working position, is oriented approximately perpendicularly to the supporting surface  49  of the feeding table  3 . 
     The contact plate  20  extends beneath the feeding table  3  into a first region  51  following a bend  50 . As shown in FIG. 1, in the working position of the contact plate  20 , also shown in phantom at  25  in FIG. 4, the first region  51  is realized approximately parallel to the supporting surface  49  and extends in a direction towards an adjusting device  4 . The first region  51  merges into a second region  52 , which is disposed approximately perpendicularly to the first region  51 . The second region  52  merges via a third region  53  into a fourth region  54 . The third region  53  has an asymmetrical U shape, and the fourth region  54  extends approximately parallel to the second region  52 . The fourth region  54  is in contact with a contact surface  55  of a shaft  6 . The fourth region  54  is fixedly screwed to the shaft  6  by a first screw  14 . The contact surface  55  is advantageously oriented perpendicularly to the feeding table  3 . 
     The shaft  6  is formed with a centrally oriented borehole  56  which is oriented parallel to the contact surface  55 . Thus, in the working position, the borehole  56  is oriented perpendicularly to the feeding table  3 . In the borehole  56 , a rod  19  having a lock disk  7  at the top end thereof, as viewed in FIG. 1, for example, is rotatably mounted. The lock disk  7  lies on the shaft  6 . Above the lock disk  7 , a stop element  8  in the form of an eccentric disk is provided. A side margin  57  of the stop element  8  is disposed parallel to the longitudinal axis of the rod  19 . The stop element  8  has a substantially cylindrical construction, with an axis of rotation situated outside the midpoint of the cross-section of the cylinder formed by the stop element  8 . The axis of rotation of the stop element  8  is coaxial with the axis of rotation  59  of the rod  19 . 
     The stop element  8  has an upper side, as viewed in FIG. 1, for example, which is oriented parallel to the underside of the feeding table  3 , and is formed with an opening  58 , which is bounded by an interior wall  9  of the stop element  8 . The interior wall  9  is advantageously constructed as a contact surface in the shape of an interior hexagon. The feeding table  3  is formed with a second recess  5  above the opening  58 . The second recess  5  is constructed so that a tool can be guided into the opening  58  through the feed table  3  from above, in order to vary the rotational position of the stop element  8 . A hex or hexagon key is preferably used as the tool. In its simplest form, the second recess  5  is a cylindrical recess. 
     The lock disk  7  is disposed centrosymmetrically to the axis of rotation  59  of the rod  19 . Lock recesses  13  are provided at the outer perimeter of the lock disk  7 . A lock element  12  is provided in the shape of a leaf spring, which is screwed to the shaft  6  by the first screw  14 , the lock element  12  having a lock nose  23  in the shape of an outward bend at the top end thereof, as viewed in FIG.  1 . The lock nose  23  is disposed in a region of the outer perimeter of the lock disk  7  and engages in a respective lock recess  13 . Interaction of the lock recesses  13  and the lock element  12  ensures a precise rotation of the stop element  8  into predetermined angular positions. 
     The second region  52  of the front lay  1  is braced, via a contact part  15 , against a side edge of the stop element  8 , which represents the outer perimeter  57  thereof. The contact part  15  is advantageously constructed in the shape of a nut  16  through which a threaded adjusting screw  17  is guided. The nut  16  is secured at the second region  52  of the front lay  1  via a second weld or joint  44 . The front end of the adjusting screw  17  is in contact with the side edge  57  of the stop element  8 . The front lay  1  is shaped by the third region  53  thereof so that the second region  52  of the front lay  1  has a tensioning bias acting in a direction towards the stop element  8 . In the second region  52 , a borehole is formed, through which the other end of the adjusting screw  17  extends. The contact part  15  is thus clamped between the second region  52  and the outer perimeter  57 . The contact part  15  serves for setting or establishing a defined spacing between the outer perimeter  57  and the second region  52  and thus a defined position of the intercepting surface  48 . By turning the adjusting screw  17 , the position of the intercepting surface  48  relative to the feeding table  3  can be adjusted. The adjusting screw  17  and the nut  16  represent an adjusting mechanism. By the adjusting mechanism  16 ,  17 , a basic setting of the front lay  1  can be executed. With the basic setting, several front lays can be aligned on a predetermined adjustment line. 
     In addition, due to the eccentric shape of the stop element  8 , the position of the intercepting surface  48  can be set by turning the stop element  8 . The shaft  6  with the rod  19  and the stop element  8  represent an adjusting device  4  by which the position of the intercepting surface  48  can be adjusted from the basic setting that was previously set using the contact part  15  and the adjusting screw  17 . 
     The rod  19  has a connecting element  60  at the bottom end thereof, as viewed in FIG. 1, to which an elastic shaft  11  is attached. The elastic shaft  11  is connected to a controllable servomotor  10 . The rod  19  and thus the stop element  8  are turned, via the elastic shaft  11 , by actuating the servomotor  10  accordingly. In this manner, the intercepting surface  48  can be displaced, regardless of the accessibility of the front lay  1 , by actuating the servomotor  10  accordingly. Because a servomotor  10  is used, the front lay  1  can be adjusted by remote control. The remote control can be accomplished via programs of a control computer of the sheet-fed printing machine. Of course, this is also possible during the printing-machine cycle. 
     In a relatively simple embodiment, the front lay  1  comprising the contact plate  20 , and the first, second, third, and fourth regions  51 ,  52 ,  53  and  54 , is constructed in the shape of a suitably bent thin plate. Advantageously, the front lay  1  is produced from spring steel. Because the front lay  1  is biased in the direction towards the stop element  8  in the second region  52 , due to the shape and the connection thereof to the shaft  6 , additional devices for biasing the contact plate  20  can be dispensed with. This ensures a cost-effective and compact construction. 
     The lower end of the rod  19  has an axial guard  61  which limits the axial mobility of the rod  19  in the shaft  6 . The shaft  6 , the screw  14  and the rod  19 , together, represent a holding device  2  for the front lay  1  and the adjusting device  4 . 
     FIG. 2 shows the arrangement of FIG. 1, as viewed from above and from the perspective of the feeding table  3 , which is represented only diagrammatically, in phantom. The feeding table  3  is formed with notches  45  in the region of a front lay  47 , through which respective contact plates  20  are guided from below. The intercepting surfaces  48  of the contact plates  20  are aligned at the adjusting line  46 . The notches  45  permit the arrangement of the adjustment line  46  in the region of the support surface  49 . Thus, a sheet that is situated on the feeding table  3 , with the leading edge of the sheet abutting the intercepting surface  48 , is located in the region of the support surface  49 , so that the whole surface of the sheet is held by the feeding table  3 . 
     The first region  51  and the third region  53  of the front lay  1  are clearly visible in FIG.  2 . The adjusting screw  17  contacts the outer perimeter  57  of the stop element  8 . The shape of the lock nose  23  of the lock element  12  is also clearly visible. In this exemplifying embodiment, the lock nose  23  is locked in the first lock recess  13 . The lock disk  7  is formed with a recess which is bounded by first and second stop surfaces  21  and  22 . Installed in the shaft  6  is a stop bolt  18 , which is disposed in the region of the recess of the lock disk  7 , so that rotation of the stop element  8  is limited by the fact that the first or second stop surface  21 ,  22  strikes the stop bolt  18 . The lock disk  7  can be rotated only within a predetermined angular range due to the stop bolt  18  and the first and second stop surfaces  21  and  22 . A maximum permissible angular range for rotating the adjusting device  4  is thereby prescribed. FIG. 2 clearly shows the shape of the lock disk  7 , which has a central opening through which the stop element  8  extends. The lock disk  7  is firmly connected to the stop element  8 . 
     FIG. 3 shows a device with two front lays  1 , which are affixed onto a common shaft  6 . The front lays  1  are aligned so that the stop plates  20  of the two front lays  1  are arranged on a common adjustment line  46 . In the same way, additional front lays  1  on the shaft  6  can also be distributed along the front or leading edge  47  of the feeding table  3 . A drive is also provided for rotating the shaft  6 , by the aid of which the shaft  6  shown in FIG. 4, for example, is rotatable. The shaft  6  is mounted in a bearing support  76  and connected to the sheet-fed printing machine. 
     FIG. 4 shows a device similar to that of FIG. 1, but with a slide ring  28  disposed between the adjusting screw  17  and the stop element  8  for reducing sliding friction. The slide ring  28  prevents wear of the stop element or the adjusting screw  17  and additionally accomplishes a precise adjustment of the position of the intercepting surface  48  due to low-frictional movement of the stop element  8  relative to the adjusting screw  17 . The slide ring  28  is rotatably mounted on the stop element  8  and secured against axial movement. The adjusting screw  17  is braced against the outer circumference of the slide ring  28 , and is resiliently prestressed against the slide ring  28 . 
     FIG. 4 shows the front lay  1  in the neutral or inactive position thereof at  26 , wherein the contact plate  20  is tilted about a central axis  63  over a pivot angle  27  relative to the working position  25  of the contact plate  20 , which is represented in phantom. The pivot angle  27  is so dimensioned that, in the neutral or inactive position  26  of the contact plates  20 , the latter are tilted far enough away from the front or leading edge  47  in the forward and downward directions so that the feeding table  3  and, thus, the sheet  64  lying thereon can be accessed freely in the region of the front or leading edge  47 . This is necessary because the sheet  64  is seized by a gripper in the region of the front or leading edge  47  and moved off the feeding table  3 . The gripper seizes the sheet  64  between the individual front lays. 
     How the device according to the invention operates or functions is described hereinafter in detail with reference to FIGS. 1 and 4. A sheet  64  coming from the righthand side, as represented in FIGS. 1 and 2, is transported in a direction towards the intercepting surface  48 . The leading edge  65  of the sheet  64  strikes the intercepting surface  48 . The sheet  64  is stopped and aligned, with the leading edge  65  thereof on the adjustment line  46 . 
     After the sheet  64  is aligned and settled on the feeding table  3 , it is seized by a gripper. The front lays  1  are then tilted away forwardly over the pivot angle  27  by rotating the shaft  6  about the central axis  63 , as is represented in FIG. 4, and the sheet is drawn off and away from the feeding table  3 . The shaft  6  is then tipped back into the working position thereof, so that the front lay  1  again assumes the working position thereof, as represented in FIG.  1 . Because the front lay  1  is always in contact with the stop element  8  during the movement of the front lay  1  from the working position thereof into the neutral or inactive position thereof and back into the working position thereof again, the front lay  1 , with respect to the stop element  8 , is always at a defined spacing and always returns to the working position thereof at the same instant of time. Because it is unnecessary to take into account any time reserve for undefined swinging-away and returning, more time is available for aligning and stabilizing the sheet. 
     FIG. 5 illustrates an additional embodiment of the invention wherein the adjusting screw  17  engages the stop element  8  via an anti-friction bearing  66 . In this regard, the adjusting screw  17  engages an exterior ring  67  of the anti-friction bearing under prestressing. 
     FIG. 6 shows an additional embodiment of the invention wherein the front lay  1  has a different shape than that of FIG.  1 . In FIG. 6, the first region  51  is longer and, shortly before the stop element  8 , the first region  51  buckles downwardly in a direction towards the shaft  6  and merges into a fifth region  68 . The fifth region  68  extends to a location beneath the shaft  6 , and merges into a sixth region  69 , which is disposed approximately parallel to the feeding table  3  and abuts a lower contact surface  70  of the shaft  6 . The sixth region  69  is formed with an opening out of which the rod  19  extends in a downward direction. A hexagon screw  35  that has been bored through is provided for bolting the sixth region  69  to the lower contact surface  70  and thus fixes the front lay  1  in position. The rod  19  extends through the hollow hexagon screw  35  and is secured against axial movement. The hexagon screw  35  additionally has an exterior thread mating with an interior thread of the second borehole  56 . 
     Also provided is a clamping or retaining nut  29  which is connected to the underside of the first region  51  of the front lay  1  via a weld  30 . The clamping nut  29  has an inner thread through which a bolt  71 , which extends through a corresponding opening in the fifth region  68  of the front lay  1  to the exterior perimeter  57  of the stop element  8 , is screwed. The bolt  71  is screwed so far into the clamping nut  29  in the direction towards the stop element  8  that the basic adjustment of the intercepting surface  48  of the contact plate  20  is correctly performed. The shapes of the first, fifth and sixth regions  51 ,  68  and  69  of the front lay  1  are selected so that the fifth region  68  is biased in the direction towards the stop element  8  in the region of the bolt  71 . 
     In this embodiment, the lock element  12  is fixed to the shaft  6  laterally opposite the fifth region  68  by a second screw  34 . Accordingly, the lock disk  7  also is formed with the lock recesses  13  on the side of the lock element  12 . In this embodiment also, the rod  19  extends downwardly through the hexagon screw  35  and has a connecting element  60  for connecting the servomotor  10  thereto. 
     FIG. 7 is a top plan view of an embodiment like that of FIG. 6, but with the stop element  8  constructed in the shape of an Archimedes&#39; spiral  31 . The Archimedes&#39; spiral  31  is constructed approximately in the shape of a plate, with the distance from the spiral wall  74  to the axis of rotation varying in dependence upon the rotational position of the disk. In this way, the spacing between the bolt  71  and the axis of rotation of the Archimedes&#39; spiral  31  can be varied in dependence upon the rotational position of the spiral  31 . The illustrated embodiment of the Archimedes, spiral  31  is formed with a bolt opening  32  and has a graduated or index ring shape extending over a predetermined angular range at a defined distance from the axis of rotation. The two side edges of the bolt opening  32  are formed by first and second stop surfaces  21  and  22 . The stop bolt  18  extends through the bolt opening  32  and serves to limit the permissible rotational angular range of the Archimedes&#39; spiral  31 . 
     FIG. 8 shows an additional embodiment of the front lay  1 , which includes a connecting part  37  and a plate  36 . The connecting part  37  is mounted in a holding arm  42  parallel to the feeding table  3  and is movable parallel to the feeding table  3 . The holding arm  42  is formed with a guide borehole  72  which is disposed parallel to the feeding table  3 . The connecting part  37  is disposed so as to be axially movable in the guide borehole  72 . An end of the connecting part  37  protrudes from the guide borehole  72  at an exterior side of the holding arm  42 , and the connecting part  37  is connected at this end to the plate  36 , which is disposed perpendicularly to the connecting part  37 . The plate  36 , at the top thereof, as viewed in FIG. 8, extends beyond the plane of the supporting surface  49  of the feeding table  3 , and the interior side surface of the plate  36  serves as the intercepting surface  48 . 
     The connecting part  37  protrudes from the borehole  72  in the direction towards the stop element  8 , in like manner. At this end of the connecting part  37 , a second adjusting screw  39  is screwed into the connecting part  37  via an inner thread formed therein. The second adjusting screw  39  includes a stop  40  in the form of a nut engaged by a tension spring. The tension spring  41  is placed in contact with the holding arm  42 , as well, so that the second adjusting screw  39  is prestressed in the direction towards the stop element  8 . The intercepting surface  48  of the plate  36  is also prestressed in the direction towards the stop element  8 . 
     The holding arm  42  is fixed to the shaft  7  through the intermediary of a bushing  73  through which the rod  19  extends. In this regard, a second contact surface  43  of the bushing  73  comes into contact with a correspondingly assigned supporting surface of the shaft  6 . The second contact surface  43  is expediently disposed parallel to the feeding table  3 . The bushing  73  is fixed to the shaft  6  by a hollow-bored hexagonal screw  35 . The hexagonal screw  35  has an exterior thread, which is suitably mated with an interior thread of the bushing  73 . The rod  19 , which is connected to the stop element  8 , extends downwardly through the hollow-bored hexagonal screw  35  and out of the shaft  6  and the hexagonal screw  35 . The bottom end of the rod  19  has a connecting element  60  for connecting a flexible shaft  11  and a servomotor  10  thereto. 
     The device in FIG. 8 has a leaf spring  12  located opposite to the second adjusting screw  39 , which is fixed to the bushing  73  of the holding arm  42  by a third screw  75 . A lock nose  23  of the lock element  12  is assigned to lock recesses  13  of a lock disk  7 . 
     FIG. 9 is a top plan view of the device of FIG. 8, as viewed from the perspective of the feeding table  3 . The shape of the Archimedes&#39; spiral, which is formed with lock recesses  13  opposite the second adjusting screw  39 , can be clearly recognized therein. In this embodiment, the function of the lock disk and the function of the stop element  8  are integrated in a single component. This permits the construction of a low building structure. The shape of the recess  58 , which is bounded by an interior hexagonal form  24 , can also be readily recognized. 
     The embodiment of FIG. 8 differs from the embodiment of FIG. 6 with respect to the development of the front lay  1 . 
     An essential core of the invention is in constructing the front lay  1  and the stop element  8  as one internally stressed entity which is moved from a working or operating position in order to release the leading edge  65  of a sheet  64 , into a neutral or inactive position wherein the contact plate  20  releases the leading edge  47 . To accomplish this, the component can be moved, swung or rotated in any manner whatsoever. The shaft  6  used in the foregoing description, to which the stop element  8  and the front lay  1  are fastened, merely represents a preferred embodiment. The invention is not limited to using a shaft  6 . 
     For example, the front lay  1  and the stop element  8  can also be fastened onto a component which is swung away from the leading edge  47  of the sheet by using lever arms in order to release the leading edge  47 . 
     Furthermore, the invention is exemplarily described as having a rotary element as the adjusting device  4 . But other shapes can be used to adjust the position of the front lay relative to the edge of the sheet. 
     The holder  2 , e.g., formed of the shaft  6  and the screw  14 , can be displaceably mounted. By this measure, all front lays can be displaced jointly in or opposite to the direction of sheet transport, i.e., at an angle.