Abstract:
A device ( 1 ) for the stepped displacement of workpieces inside a press ( 2 ) or similar processing equipment is provided. The device includes at least one or two gripper rails ( 4 ) that can be displaced back and forth in the direction of a longitudinal extent thereof and in the feed direction, the rails being displaced transversely in relation to one another in order to engage workpieces. To execute a gripping movement, the gripper rail ( 4 ) includes levers ( 5 ) that run at an angle and in opposite directions to one another, whereby the ends of the levers that face away from the gripper rail can be displaced towards or away from one another. Pivoting arms ( 11 ), which together with the levers ( 5 ) form scissors or half scissors type drives, are hinged on the levers ( 5 ) to guide the resultant transverse movement. A scissors drive of this type permits a parallel displacement of the gripper rail ( 4 ), even where space is limited, without the use of a drive that protrudes beyond the longitudinal extension of the gripper rails ( 4 ).

Description:
BACKGROUND 
     The invention relates to a device for the stepped displacement of work pieces, especially within a press, comprising at least one or two gripper rail(s), which can be displaced back and forth in the feed direction for the feed and return motion, which have gripper parts or gripper zones for engaging the work pieces, and which then can be moved back into the original position for engaging the work pieces and for moving in the feed direction, wherein at least two levers that can pivot parallel or mirror-symmetric to each other in the plane of motion, in a plane parallel to this plane of motion, or in a plane at an angle to this plane of motion are attached to the gripper rail(s), and for a device with two parallel gripper rails, these levers of one of the gripper rails can pivot in the opposite sense to those of the other gripper rail. 
     Such a device with two parallel gripper rails is known from DE 102 06 773 C1, with additional state of the art concerning such gripper rails being cited in this publication. This device has proven advantageous, primarily in presses, in which the gripper rails are arranged between the press stands overlapping in their longitudinal direction and in the feed direction of the work pieces. Here, it is favorable that only the gripper rails and the work pieces grasped by these rails, as well as possible grippers or gripper parts on the gripper rails, that is, relatively small masses, must be moved. 
     Presses are also known, however, in which the spacings of the press stands are too small to allow the gripper rails to project through these stands. In such presses, the gripper rails must be arranged within the intermediate spaces of the press stands and also must be moved back and forth, so that only a limited space is also available for the drive for these movements of the gripper rails. 
     Indeed, presses with such gripper rails are already known, in which the movements of the gripper rails run transverse to their longitudinal extent within the spacing of the press stands, but these presses require drives, which are arranged outside of the press outline and therefore special protective measures for the operator and also safety spacings are necessary due to the movements running outside of the press outline. Here, linear drives are known, which are arranged transverse to the feed motion and to the longitudinal extent of the rails, which project out of the press outline perpendicular to the gripper rails, and which require not only the mentioned safety spacings, but also make the accessibility and the ability to monitor the running of the gripping and feed motions more difficult, because a user must be positioned at a correspondingly large distance to the gripper rails. 
     SUMMARY 
     Therefore, the objective arises of creating a device of the type named above, in which the drive or drives of the gripper rails, in particular, the drives for the gripping motions, do not have to move outwards transverse to the outline of the press, in order to set the gripper rail or rails in the gripping motion and in the opposite direction. This objective also applies for a device with only one gripper rail, on which grippers for work pieces are arranged. 
     To meet this objective, the device defined above is characterized in that the two levers pivotably hinged to the gripper rail are attached so that their ends or zones facing away from the gripper rail are pivotally attached to sliding parts that can move towards or away from each other parallel to the direction of the gripper rail extent, and the spacing of these sliding parts can be changed for the back and forth movements of the gripper rail perpendicular to their longitudinal extent, and the gripper rail is positively driven perpendicular to its direction of longitudinal extent. 
     Thus, the drive for the transverse motion of the gripper rail initially causes a motion parallel to the gripper rail, namely on the sliding parts. Therefore, the levers are pivoted, whereby this parallel motion of the sliding parts is converted via the levers into a transverse motion of the gripper rail. By moving the ends of the levers facing away from the gripper rail towards or away from each other with the help of the sliding parts, the gripper rail can be adjusted parallel to itself as desired, with a positive drive providing the corresponding precise parallel adjustment. Thus, movements perpendicular to the longitudinal extent of the gripper rail can be avoided for an adjustment drive, so that the drive and the levers can be arranged within or to a large degree within the outline of the press stands, for example, between two such press stands, so that not only are there no movements past the outline of the press stands perpendicular to this outline, but the drive can also be housed to a large degree within the outline of the press or at least within the typical outline of protective doors on such presses. 
     The levers and the drive of the sliding parts can thus be arranged at least partially within the outline of stands of the press, in particular, between two press stands that are adjacent to each other in the feed direction. Thus, a space-saving arrangement within the press is possible not only for the gripper rails, but also for its drive, which also simplifies monitoring and control for the operator. 
     In addition, it is preferable when the drive for the feed movements of the gripper rail or rails is also arranged in its direction of longitudinal extent at least partially within the outline of the press stands. Thus, the gripper rails can be moved in their direction of longitudinal extent after engaging work pieces, without the drive necessary for these movements having to project a great deal past the outline or the horizontal projection of the press. According to the selection of the drive, it can also be located completely within the outline or horizontal projection of the press. 
     An effective and space-saving positive drive for the transverse motion of the respective gripper rail can be achieved, such that pivot arms are hinged to the levers between their attachment points to the gripper rail and the respective sliding part. These pivot arms are mounted so that they can pivot with their end facing away from the hinge point and the gripper rail on displacement elements or stationary bearings, and so that the spacing of the sliding part, on one side, and the sliding element or bearing, on the other side, can be changed or enlarged for the transverse adjustment or during the transverse adjustment of the gripper rail. Thus, the respective lever is stabilized with a pivot arm, so that the adjustment of the sliding parts leads to a safe and precise parallel adjustment of the gripper rail for changing their respective spacing. 
     An improvement can be provided, in that the pivot arm crosses the lever at the common hinge point and also attaches to the gripper rail via a joint, wherein the hinge points of the lever and the pivot arm pivotably mounted on this lever to the gripper rail can be changed in terms of their spacing when the gripper rail is adjusted perpendicular to itself analogous to the spacing of the displacement part and the displacement element. In this case, the gripper rail is practically engaged by one or two scissors and adjusted perpendicular to itself, while in the case, in which the pivot arm does not reach up to the gripper rail, it can be called “single-arm scissors.” In comparison with a scissors-like arrangement of the lever and pivot arm, the “single-arm scissors” have the advantage that a joint close to the gripper rail can be eliminated. 
     For simplifying the motion profile, it is useful when the hinge point of the pivot arm facing away from the lever and the gripper rail is stationary and the adjacent hinge point of the lever located on the sliding part can move relative to the other hinge point—parallel to the longitudinal extent of the gripper rail. In this way, an adjustment element can be eliminated or at best constructed as a stationary part or bearing, on which the corresponding pivot arm has to perform only a pivoting motion. The entire kinematics are correspondingly simple for the transverse adjustment of the gripper rail by changing the spacing of the sliding part for the corresponding pivoting of the lever. 
     The two sliding parts of the two levers attached to one gripper rail can be moved towards each other for moving the gripper rail closer to these sliding parts and can be moved away from each other for the opposite engaging motion, and the hinge points of the pivot lever are here, in particular, stationary. 
     For such an arrangement of the lever and the pivot arms, as well as their respective joints, the displacement of the sliding parts is almost sufficient for changing their mutual spacing, in order to adjust the gripper rail perpendicular to this displacement motion. Thus, the entire kinematics and drive arrangement can be housed in a space-saving way within a tight space and here at least to a large extent within the outline of the press stands. 
     The gripper rail or rails can be moved after engaging work pieces in the direction of their longitudinal extent—thus, in the feed direction—such that the hinge points of the levers and the pivot arms facing away from the gripper rail can be moved by means of slides on a guide arranged parallel to the gripper rail and that a spindle motor or work cylinders or a linear drive, for example, is provided for this displacement motion. Slides are understood to be a part, which attaches to a guide with a counter-stay and here engages in this guide and/or wraps around the guide. With a drive that acts parallel to the extent of the gripper rail, for example, a spindle motor, the entire arrangement composed of the gripper rail, the lever, the pivot arm, and their hinge points, including sliding parts, can be moved, in order to be able to execute the desired feed motion of the gripper rail and also its return motion. 
     For the motion of the sliding parts in opposite directions—for the transverse movement of the gripper rail—a spindle with two opposite-direction threaded zones and spindle nuts having opposite-direction threads on the slide parts can be provided. The respective threaded zones of the spindle can engage in these spindle nuts and the spindle can have a single drive motor. For the transverse adjustment of a gripper rail, despite the two levers and the sliding parts acting on these levers, a single drive motor is sufficient for a use of an opposite-direction spindle, so that this drive can have a space-saving and economical arrangement. 
     The slides, which have the hinge points of the levers and the pivot arms facing away from the gripper rail and which belong to a gripper rail, can be coupled to each other or connected, in particular, via a connecting rod, so that for each gripper rail, a single feed drive can be sufficient, which can adjust these coupled slides together. 
     An especially useful improvement of the invention, which is favorable primarily for holding larger masses or weights, can be provided in that the pivot arm attaching to the respective lever can be moved in a plane that runs at an angle to the plane, in which the levers can move. This arrangement produces a tensile or compression load on the pivot arms, which can increase the flexural strength of the entire lever and pivot arm arrangement, so that heavier rails and/or heavier work pieces and/or light levers and/or pivot arms are allowed. 
     In this way, the pivot arm or arms can run at an angle upwards or downwards relative to the plane of motion of the levers independent of whether the plane of motion of the levers is arranged horizontally or also at an angle upwards or downwards relative to a horizontal plane. For reinforcing the scissors or single-arm scissors drive, it is important that the ends of the pivot arms facing away from the levers and the ends of the levers adjacent to these arms are arranged at different heights and the pivot arms move closer to the levers in the direction towards the common joint. This leads to good reinforcement of the levers and pivot arms, wherein an arrangement of the end of the pivot arm past the end of the lever makes the pivot arm into a tension rod and an arrangement underneath the end of the lever makes it into a compression rod. 
     It is still to be mentioned that the drive devices for the gripper rails can be mounted and moved up and down on vertical guides or threaded spindles, so that objects grasped by the gripper rails can also be raised and/or lowered. Here, a lifting unit can be provided for each press stand, which allows over-travel upwards or downwards relative to the transport plane, wherein a pneumatic mass equalization can be performed. The lifting units at the front and back in the feed direction can be connected to a base cross arm, on which the feed drive for the gripper rails can be mounted. 
     Primarily by combining individual or several of the prescribed features and measures, a device is produced with gripper rails, which can be housed together with their drive in a narrow space, wherein the drive for the transverse movements of the gripper rails acts parallel to these rails and is converted into corresponding transverse movements of the gripper rails via pivot levers and positive drives. Therefore, drives arranged and moving perpendicular to the gripper rails can be eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, embodiments of the invention are described in more detail with reference to the drawings. Shown in partially schematic representation are: 
         FIG. 1  a front view of a press shown only partially and in outline, and a device according to the invention is arranged between the stands of this press for stepped feeding of work pieces, which also is adjustable in height, 
         FIG. 2  a top view of the arrangement according to  FIG. 1 , wherein stands of the press or similar processing equipment can be seen in outline in terms of its cross section and pivotable levers, as well as pivot arms used for their guide for the movements of the gripper rails perpendicular to their longitudinal extent are mounted on cross arms located between the stands, wherein two gripper rails that can move towards and away from each other are provided, 
         FIG. 3  at an enlarged scale, a view of a gripper rail corresponding to  FIG. 2  with its drive that is located, similar to the gripper rail itself, between two stands of the press or the like adjacent in the longitudinal direction of the gripper rail, 
         FIG. 4  a representation according to  FIG. 3  after a displacement of the gripper rail and its displacement drive in the direction of its longitudinal extent, 
         FIG. 5  a representation according to  FIG. 4  after a displacement of the gripper rail outwards away from the middle of the press, 
         FIG. 6  a representation according to  FIG. 5  after a displacement of the gripper rail adjusted outwards into the position according to  FIG. 3 , 
         FIG. 7  a representation according to  FIG. 3  of a modified embodiment, in which the adjustment and guide of the adjustment motion of the gripper rail can be executed perpendicular to its longitudinal extent or parallel to itself with the help of two crossing levers, 
         FIG. 8  a representation according to  FIG. 7  after a displacement of the gripper rail away from the middle of the press (and thus away from another not-shown gripper rail in a mirror-symmetric arrangement), 
         FIGS. 9 to 14  end views of the device on a press with different spatial arrangement of the levers and the pivot arms, wherein the levers and pivot arms have different angles relative to the planes of motion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the embodiments described below, matching parts or parts that match in terms of function are provided with matching reference symbols, even for different configurations or different structural shapes. 
     A device designated as a whole with  1  is used, in particular, for the stepped displacement of work pieces, not shown in more detail, within an only partially shown or indicated press  2 , in which the work pieces are subjected to an additional processing step after each feed motion or after each feed step. 
     Primarily for better understanding, in  FIGS. 3 to 8  the centers of the press  2  are indicated by center lines between its press plungers  3 , with the longitudinal center being designated with LM and the transverse center being designated with QM. 
     Analogous to DE 102 06 773 C1, the device  1  has two parallel gripper rails  4 , which are also parallel to the longitudinal center LM, which can be moved and pulled back again in the direction of a longitudinal extent thereof and thus in the feed direction, and on which gripper parts or gripper zones for engaging the work pieces are provided in a way that is not described in more detail but is generally known. Here,  FIGS. 3 to 8  simultaneously indicate that a device  1  could also be provided with only one gripper rail  4 , if this rail has corresponding grippers or gripper parts for the work pieces. 
     For engaging such work pieces, the respective gripper rail  4  can move parallel to itself, in the case of two gripper rails  4 , these can move towards each other and back away from each other for the release, while the already mentioned movements in the direction of the longitudinal extent of the gripper rails  4  are provided for the feed. 
     By comparing  FIGS. 2 ,  3 , and  4 , one sees the gripper rail  4  first in a left position and then in a right position. 
     By comparing  FIGS. 5 and 6 , one sees an opposite feed motion of the gripper rail  4 , which is moved away from the longitudinal center LM also parallel to itself in comparison with  FIGS. 3 and 4  and thus has released one or more work pieces. 
     In all of the embodiments, two levers  5 , which can pivot in parallel or in a mirror-symmetric arrangement relative to each other in the respective plane of motion, in a plane parallel to this plane of motion, or in a plane at an angle to this plane of motion, are attached to the gripper rails  4 , wherein, for a device  1  with two parallel gripper rails  4 , accordingly  2  of these levers  5  of one gripper rail  4  can pivot in the opposite direction relative to those of the other gripper rail  4 , as is visible in  FIG. 2 . 
     In  FIGS. 2 to 8  it is shown that the two levers  5  pivotably hinged to the gripper rail  4  are attached in an articulating way so that they can pivot with their ends or zones facing away from the gripper rail  4  on sliding parts  6  that can move towards or away from each other in parallel to the direction of the extent of the gripper rail  4 , wherein the comparison of  FIGS. 4 and 5  or  3  and  6  makes it clear that the spacing of these sliding parts  6  can be changed for the back and forth movements of the gripper rails  4  transverse to their longitudinal extent or parallel to themselves. The respective gripper rails  4  are also positively driven in a way still to be described transverse to the direction of their longitudinal extent. 
     If the two sliding parts  6  of the two levers  5  of one gripper rail  4  are arranged with the greatest possible spacing relative to each other, then the gripper rail  4  is at the closest position to the longitudinal center LM of the press, thus it assumes its engaging and conveying position. 
     In contrast, if the sliding parts  5  according to  FIGS. 5 and 6  or  8  approach each other, which pivots the levers  5  accordingly, the gripper rail  4  is located in its position farthest from the longitudinal center LM, in which position any work pieces are released. By moving the displacement parts  6  towards each other from the greatest possible distance, that is, the two levers  5  already at a somewhat inclined arrangement in the original position are retracted and therefore the gripper rail  4  moves away from the center LM parallel to itself, because the two levers  5  and their sliding parts  6  are arranged symmetric to each other and have matching dimensions. 
     Here, the levers  5  and the drive  7 , which is still to be described for the sliding parts  6 , are located practically completely within the outline of the stands  3  of the press  2  and, here, between two press stands  3 , which are adjacent in the longitudinal direction and in the feed direction. Thus, the drive  7  and the levers  5  interacting with the drive requires no space outside of the horizontal projection of the press  2 . 
     Also, the drive  8  for the feed movements of the gripper rail  4  or rails  4  is arranged in the direction of its longitudinal extent according to  FIGS. 2 to 8  at least partially within the outline of the stands  3  of the press  2 , wherein the minimal excess seen in  FIG. 2  can be housed in all cases within the typical outline of protective doors found in such presses  2 . 
     For the already mentioned positive drive of the motion of the gripper rails  4  parallel to themselves, pivot arms  11 , which are mounted pivotably with their end facing away from the hinge point  12  and the gripper rail  4  on displacement elements or stationary bearings  13 , are hinged, in turn, in an articulating way on the levers  5  between the hinged contact points  9  on the gripper rail  4  and the hinged contact points  10  on the respective sliding part  6 . The spacing of the sliding part  6 , on one side, and the displacement element or bearing  13 , on the other side, can be changed and/or increased for the transverse movement or during the transverse movement of the gripper rail  4 , as becomes clear from the comparison of  FIGS. 4 and 5  or  7  and  8 . 
     In the embodiments according to  FIGS. 2 to 6 , the pivot arm  11  runs only between its hinge point  12  and the bearing  13 , which produces relatively simple kinematics with the help of the lever drive comprising the levers  5  and pivot arm  11 . This arrangement practically corresponds to “single-arm scissors,” which allow an effective transverse adjustment of the gripper rail  4 . 
     In the embodiment according to  FIGS. 7 and 8 , it is shown that the pivot arm  11  crosses the lever  5  at the common hinge point  12  and also attaches to the gripper rail by means of a joint  14 , wherein the hinge points  9  and  14  of the lever  5  and the pivot arm  11  that can pivot on this lever on the gripper rail  4  can be changed in terms of its spacing when the gripper rail  4  is moved perpendicular to itself analogous to the spacing of the sliding part  6  and the displacement element or bearing  13 , as made clear by the comparison of  FIGS. 7 and 8 . In the position according to  FIG. 8  moved outwards away from the center LM, the joints  14  of the pivot arms  11  approach each other just like the sliding parts  6  of the lever  5 . In this case, the arrangement comprising the levers  5  and pivot arm  11  involves “true” scissors, that is, in the embodiment according to  FIGS. 7 and 8 , the gripper rails  4  can be adjusted and driven positively perpendicular and parallel to themselves by scissor drives. 
     Here, it is advantageous that the hinge point of the pivot arm  11  located on the bearing  13  and facing away from the lever and the gripper rail  4  is stationary just like the hinge points  9  of the lever  5  on the gripper rail, that is, only the hinge point  10  of the lever  5  located on the respective sliding part  6  must be adjusted in the embodiment according to  FIGS. 2 to 6 . 
     The two sliding parts  6  of the two levers  5  attached to a gripper rail  4  can be moved towards each other for moving the gripper rail  4  closer to the sliding parts  6  or away or apart from each other for the engaging motion of two gripper rails  4 . The hinge points on the bearings  13  of the pivot lever  11  advantageously remain stationary. 
     It was already mentioned that the gripper rails  4  can be moved into the position according to  FIG. 4  after engaging work pieces, that is, in the position, for example, according to  FIGS. 2 and 3  in the direction of their longitudinal extent. In the embodiments, this can be realized in that the hinge points  10  of the levers  5  and the hinge points or the bearing  13  of the pivot arms  11  each facing away from the gripper rail  4  can be moved by means of slides  15   a  on a guide  15  arranged parallel to the gripper rail  4  and that for this adjustment motion, for example, a spindle motor  8  with the threaded spindle  8   a  and the spindle nut  8   b , which can be adjusted in the axial direction by the direction of the threaded spindle  8   a  and which is connected directly or indirectly to the slide or slides  15   a  or instead, a work cylinder or some other linear drive is provided. By comparing  FIGS. 3 and 4  or  7  and  8 , one can clearly see how the spindle nut  8   b  is moved in the axial direction relative to the spindle  8   a  by the motor  8  according to the position of the gripper rail  4  together with the slide  15   a  engaged by it. 
     For the motion of the sliding parts  6  in opposite directions for generating the transverse motion of the gripper rail  4  parallel to itself, in the exemplary embodiments there is a spindle  16  having two opposite-direction threaded zones and spindle nuts  17  having opposite-direction threads on the sliding parts  6 . The respective threaded zones of the spindle  16  attach to these nuts so that they can rotate, wherein for the spindle  16  a single drive motor  7  is sufficient, in order to move both sliding parts  6  towards each other or away from each other. 
     The guide  18  of the sliding parts  6  that can move with the help of the spindle nuts  17  can be clearly seen in  FIGS. 2 to 8 . Here, it also becomes clear that this guide  18  and thus the displacement path  6  are arranged parallel to the longitudinal extent of the gripper rails  4 . 
     The slides  15   a , which have the hinge points  10  of the lever and the bearing  13  with the hinge points for the pivot arms  11  each facing away from the gripper rail  4 , maintain their mutual spacing when they move, as becomes clear from the comparison of the individual figures, and thus can be coupled with each other or connected via a connecting rod, which can be arranged on the cross arm  19  having the guides  15 . Thus, one feed drive  8 , in the embodiment with the spindle  8   a , is sufficient for each gripper rail  4  and its slides  14 . 
     In  FIGS. 9 to 14  it is shown in different arrangements that the pivot arm  11  attached to the respective lever  5  lies and is movable in a plane that extends at an angle to the plane in which the levers  5  are located and can pivot. 
       FIG. 9  shows an example, in which the relatively compact levers  5  are arranged horizontally and can pivot in a horizontal plane, in order to act on the gripper rails  4  accordingly, while, in contrast, the pivot arms  11  extend at an angle upwards. 
       FIG. 10  shows an analogous arrangement, wherein, however, the pivot arms  11  extend at an angle downwards from their hinge point on the lever  5 . 
     In the case of  FIG. 9 , the pivot arms  11  form tension rods, while in the embodiment according to  FIG. 10  they form compression rods, wherein, however, in both cases they improve the carrying capacity or the flexural strength of the holder of the gripper rails  4 . 
     In all of the embodiments according to  FIGS. 9 to 14 , the angle between the lever  5  and pivot arm  11  is an acute angle, whose vertex is arranged in or at the hinge point  12  of the pivot arm  11  on the lever  5 . 
       FIGS. 11 and 12  show examples, in which the levers  5 , on their sides, are arranged at an angle to a horizontal plane and can move, wherein according to  FIG. 11  the levers  5  are arranged at an angle upwards starting from the sliding parts  6  towards the gripper rail and in the opposite direction in  FIG. 5 . Nevertheless, in both cases, the pivot arms  11  are also arranged, in turn, at an angle to these levers  5  and their planes of motion. According to  FIG. 11 , the pivot arms  11  extend downwards at an angle from their hinge points  12  and are compression rods, while according to  FIG. 12  they extend upwards at an angle opposite the lever  5  starting from the hinge points  12  and form tension rods. 
       FIGS. 13 and 14  are also examples for angled levers  5 , wherein  FIG. 13  represents an example, in which the associated pivot arms arranged at an angle relative to the levers  5  are tension rods for levers  5  extending upwards at an angle, while the reverse arrangement according to  FIG. 14  shows levers  5 , which extend downwards at an angle to the gripper rails and on which angled pivot arms  11  located underneath act as compression rods. 
     In all of the embodiments, the pivot arms  11  extend opposite to the plane of motion of the lever  5  at an angle upwards or downwards independent of whether the plane of motion and the course of the lever  5  is arranged horizontally or also at an angle upwards or downwards relative to a horizontal plane. This angled position relative to the levers  5  give a double function to the pivot arms  11 , in that they create a precise guide for the movement of the gripper rails  4  parallel to themselves and also reinforce the support system for the gripper rail  4  formed by the rails themselves and by the levers  5 . 
     One can also see, primarily in  FIG. 1 , as well as in  FIGS. 10 to 14 , that the drive devices  7  and  8  with the slides  14  and their guides, as well as the cross arm  19 , are mounted on vertical supports  21  fixed to the stands  3  and can move up and down by means of threaded spindles  20  and threaded nuts. Thus, the gripper rails  4  can also be adjusted in their height, that is, can execute lifting and lowering motions. 
     The device  1  for stepped displacement of work pieces within a press  2  or similar processing equipment has at least one or two gripper rails  4 , which can move back and forth in a direction of their longitudinal extent and in the feed direction and which can be adjusted perpendicular to themselves for engaging work pieces. For this engaging motion, the gripper rail  4  has levers  5 , which extend at an angle to the rail, which can move in opposite directions, and whose ends facing away from the gripper rail can move towards or away from each other, wherein for guiding the resulting transverse motion, pivot arms  11  are hinged to the levers  5 , wherein these arms form scissors or single-arm scissors together with the levers  5 . By means of such a scissors drive, the adjustment motion of the gripper rail  4  parallel to itself can also be executed in a very narrow space and without a drive projecting past the longitudinal extent of the gripper rails  4 .