Patent Publication Number: US-2021187586-A1

Title: Device and Method for De-Stacking Planar Parts

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/EP2018/073089 filed Aug. 28, 2018, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The invention relates to an apparatus for unstacking plate-like parts, in particular sheet metal blanks, with at least one supply station, in which at least one part stack of plate-like parts is located and with an unstacking device which is assigned to the supply station, for the singularised unstacking of the part stack and for bringing an unstacked part along a run-through direction onto a function station which is arranged downstream, wherein the unstacking device comprises a carrier device with at least one runner rail which is aligned along a run-through direction and on which an unstacking slide is movably guided in the run-through direction between the supply station and the function station, wherein the unstacking slide comprises a carrier structure, on which several gripping units are arranged, wherein the gripping units each comprise at least one gripping head which can be moved in the height direction for lifting the parts out of the part stack. 
     Related Art 
     An apparatus of the initially mentioned type is known for example from DE 101 17 607 B4. The unstacking apparatus which is described there comprises several gripping units in the form of suction grippers, to which a linear drive is assigned. The linear drives are arranged in a stationary manner above the part stack, so that the lifted parts can be moved exclusively in the height direction by the linear drives. An endlessly circulating transport belt, on which adhesion devices with suction heads are arranged and circulate together with the transport belt, is located on the beam, on which the linear drives are also fastened in a stationary manner. On lifting up the uppermost part of the part stack by way of the linear drives and the suction heads which are connected to these, the lifted part with its region which is located next to the suction heads gets below the adhesion device of the transport belt and is so to speak taken over by these. 
     Another system for unstacking plate-like parts is disclosed in EP 2 195 267 A1, concerning which robots which act alternately access the part stack and ensure the unstacking, wherein the robots are cycled such that one of the robots removes the uppermost stack from the part stack whilst the other robot deposits an already lifted part onto a conveying belt for the further transport, for example to a function station which is arranged downstream and with regard to which it can be a centring station. 
     Furthermore, apparatus for unstacking plate-like parts, for example sheet metal blanks are known, concerning which an unstacking slide, a so-called feeder, is movably guided on a carrier unit and for lifting the uppermost part can be traversed over the part stack and whose gripping unit then subsequently ensure a lifting of the uppermost part. After the lifting, the slide moves in the run-though direction to a depositing location for the unstacked part. 
     SUMMARY 
     It is the object of the invention to provide an apparatus and a method for unstacking plate-like parts, concerning which apparatus or method the bringing-out is yet increased further compared to the state of the art and the quality and the reliability of the unstacking procedure is improved. 
     This object is achieved by an apparatus with the features described herein as well as by a method with the features described herein. 
     The apparatus according to the invention for unstacking plate-like parts, according to one non-limiting embodiment is characterised in that the gripping units can be displaced relative to one another and relative to the carrier structure in the run-through direction and can be positioned into different working positions by way of a motoric gripping unit drive device of the unstacking slide. 
     By way of this, it is possible to position the gripping units to one another such that an optimal distance of the gripping units to one another for the gripping and lifting of the parts is adjusted in dependence on the dimensions of the parts which are to be unstacked. The adjusting of the gripping units to one another and relative to the carrier unit can be carried out before the lifting of each individual part, wherein as a rule the parts which are located in the part stack, in particular sheet metal blanks, essentially have the same dimensions. The invention particularly excels given the change to another part stack with differently dimensioned parts, since the gripping units can be newly orientated to one another, so that an optimal gripping and lifting of the parts of the new part stack is also possible. 
     Concerning a further development of the invention, the motoric gripping unit drive device comprises several gripping unit drives which are each assigned to one of the gripping units. Particularly preferably, at least components of the gripping unit drive are located on board the assigned gripping unit. 
     Although in principle it would also be possible to provide a central gripping unit drive device which then via a gear drives the respective gripping units individually and independently of one another, it is however advantageous if the motoric gripping unit drive device comprises several gripper drives which are expediently located at least partly on board the assigned gripping units. 
     In a particularly preferred manner, a control device for the control of the gripping unit drives is present. Expediently, the control device is designed in a manner such that the gripping unit drives can be controlled independently of one another. The control device can be for example a superordinate control device, for example an SPS control which for example is arranged externally of the unstacking apparatus and transmits the control signals to the different gripping device drives, in particular in a wireless manner. 
     Concerning a further development of the invention, the carrier structure of the unstacking slide is designed as a guide rail which is aligned in the run-though direction and on which the gripping units are movably guided given their displacement. 
     In a particularly advantageous manner, the gripping unit drives are designed in particular as electrical linear drives. However, other types of linear drives are also conceivable, for example fluidic, in particular pneumatic linear drives. 
     Expediently, the linear drive is a linear direct drive with the guide rail as a stator and the gripping units as the rotor. 
     In a particularly preferred manner, the carrier device comprises several runner rails which are orientated parallel to one another in the run-through direction and at a distance to one another in the transverse direction to the run-through direction and on which at least one unstacking slide is movably guided between the supply station and the function station. Expediently, unstacking slides operate on different runner rails and herewith interact together with the gripping units which are arranged thereon, on unstacking and with the subsequent deposition of the parts. 
     It is particularly preferable for unstacking slides which are guided on runner rails which are adjacent one another in the transverse direction to the run-through direction to be controlled into movements which are in opposite directions to one another, in a manner such that if the one unstacking slide is located over the supply station, the adjacent other unstacking slide is located at the function station and vice versa. 
     Concerning the function station, this for example can be a conveying belt which transports the deposited parts further for the further processing. However, a centring station for centring the deposited parts or a part washing machine or a part oiling facility or a forming press can also serve as a function station. 
     Concerning a further development of the invention, the unstacking device comprises a runner rail drive device for adjusting the distance of the runner rails to one another in the transverse direction. 
     In a particularly preferred manner, the runner rail drive device comprises several runner rail drives which are each assigned to one of the runner rails. 
     The runner rail drive device in combination with the gripping unit drive device permits the adjusting of an individual gripping head pattern which is matched to the dimension of the part to be unstacked, in a plane which is spanned by the run-through direction and the transverse direction to the run-through direction. The gripping heads can be arbitrarily positioned to one another within this plane in dependence on the range of the travel path of the gripping units and of the runner rails. Such a gripping head displacing unit could also be denoted as a universal tooling. 
     In a particularly preferred manner, the runner rail drives can be controlled independently of one another by way of the control device, for the transverse adjusting of the runner rails independently of one another. 
     Concerning a further development of the invention, the unstacking device comprises a slide transverse drive device for the transverse displacing of the carrier structure with the gripping units with respect to the assigned runner rail. By way of this, it is possible for oppositely driven unstacking slides to evade one another. 
     Expediently, the slide transverse drive device comprises several slide transverse drives which are each assigned to one of the unstacking slides. Particularly preferably, the slide transverse drives are controllable independently of one another by way of a control device into transverse movements of the unstacking slides which are independent of one another. 
     The apparatus according to the invention for unstacking plate-like parts according to one non-limiting embodiment is characterised in that the unstacking device comprises a runner rail drive device for adjusting the distance of the runner rails to one another in the transverse direction. 
     By way of this, the distance of the gripping heads to one another in the transverse direction can be adjusted, by which means a gripping head pattern which is matched in dependence on the dimensions of the part to be unstacked can be adjusted in the transverse direction, so that the uppermost part can be securely gripped and lifted. 
     It is to be noted that the displacement of the gripping units to one another in combination with the displacement of the runner rails in the transverse direction is not absolutely necessary. Already, the displacement of the gripping units relative to one another or the displacement of the runner rails to one another in the transverse direction permits an unstacking of the parts from the part stack which is improved compared to the state of the art. The combined movement of the displacement of the gripping units to one another and the transverse displacement of the runner rails however achieves an even better result on unstacking. 
     Concerning a further development of the invention, the gripping units are designed as suction grippers with a gripping head which is designed as a suction head. Alternatively, it would be conceivable to design the gripping units as magnet grippers with a gripping head which is designed as a magnet head. 
     Concerning the parts which are to be unstacked, these are preferably plate-like parts, in particular sheet metal blanks. Gripping heads which are designed as suction grippers provide the advantage of also being able to unstack non-magnetic parts, for example aluminium sheet metal blanks. 
     In a particularly preferred manner, the carrier device comprises several beams which are orientated parallel to one another along a run-through direction and at a distance to one another in the transverse direction to the run-through direction, on which beams an assigned runner rail is fastened. The beams can be designed for example in a T-like or I-like manner. 
     In a particularly preferable manner, two runner rails are each fastened to the beams. Such an arrangement with two runner rails on the beams and unstacking slides assigned to the runner rails can also be denoted as a double feeder unit. Expediently, the runner rails are aligned to one another with an offset in the run-through direction. 
     In a particularly preferred manner, the runner rail drive device is coupled to the beams in a manner such that the beams can be displaced in the transverse direction for adjusting the distance of the runner rails in the transverse direction. 
     In a particularly preferred manner, the unstacking device comprises a slide longitudinal drive device for driving the unstacking slides in the run-through direction along the assigned runner rail between the supply station and the function station. Expediently, the slide longitudinal drive device comprises several slide longitudinal drives which are each assigned to an unstacking slide. 
     Particularly preferably, the unstacking slides can be controlled independently of one another by way of the control device, into longitudinal movements in the run-though direction which are independent of one another. 
     In a particularly preferred manner, the unstacking device comprises a gripping head drive device for moving the gripping heads in the height direction. Expediently, the gripping head drive device comprises several gripping head drives. 
     Particularly preferably, the gripping head drives are each assigned to one of the gripping units and in particular are located on board the respective gripping unit. 
     The method according to the invention for unstacking plate-like parts amid the use of an apparatus according to the embodiments described herein comprises the following steps:
         determining the dimensions of the uppermost part of the part stack which is to be unstacked and transferring the determined dimensional data to the control device,   positioning the at least one unstacking slide over the part to be unstacked,   controlling the gripping unit drive device in dependence on the determined dimensions of the uppermost part for adjusting a suitable gripping distance of the gripping heads to one another for the lifting of the uppermost part and adjusting the gripping distance by way of moving the gripping units relative to one another in the run-through direction,   applying the gripping heads onto the uppermost part and lifting the part out of the part stack.       

     Concerning a further development of the method, several unstacking slides are positioned together over the part to be unstacked and the gripping unit drive device and the runner rail drive device are controlled in dependence on the determined dimensions of the uppermost part in a manner such that the gripping heads of the unstacking slides are moved together relative to one another in a plane which is spanned by the run-through direction and a transverse direction to the run-through direction, into a two-dimensional gripping head pattern which is suitable for the lifting of the uppermost part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment example of the invention is represented in the drawing and is explained hereinafter in more detail. In the drawing are shown in: 
         FIG. 1  a preferred embodiment example of the apparatus according to the invention for unstacking plate-like parts, integrated into a press line, 
         FIG. 2  a plan view of the unstacking apparatus according to the invention, 
         FIG. 3  a front elevation of the unstacking apparatus of  FIG. 2 , 
         FIG. 4  a lateral view upon a beam of the unstacking apparatus of  FIG. 2 , wherein the runner rails and the unstacking slides which are arranged thereon are shown, 
         FIG. 5  a plan view of the beam of  FIG. 4 , 
         FIG. 6  an enlarged representation of the detail X from  FIG. 4 , 
         FIG. 7  a section through the unstacking slides of  FIG. 6  along the line VII-VII in  FIG. 6 , 
         FIG. 8  a perspective representation of a runner rail with an unstacking slides which is arranged thereon, according to the arrangement of  FIG. 4  and 
         FIG. 9  a front elevation of the beam with the runner rails and of the unstacking slides of  FIG. 4  which are arranged thereon. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 9  show a preferred embodiment example of the apparatus  11  according to the invention for unstacking plate-like parts  12 . The apparatus  11  is hereinafter described by way of example as a constituent of a press line  13  which serves for de-stacking the stacked-in parts  12  in the form of sheet metal blanks, in particular car body sheets and reshaping them in a forming press  14 . 
     The press line  13  by way of example comprises a supply station  15  in which the parts  12 , thus sheet metal blanks, are stacked. The supply stations  15  are in process, which means that parts  12  which are stacked in this are de-stacked by the apparatus  11 . If e.g. two sheet metal blanks cannot be singularised, then these are ejected into a container  90 . 
     The transport of parts in the press line  13  is effected along a run-through direction  17  with the end station of the forming press  14 . 
     In the shown example case, a part  12  after the unstacking or lifting out of the part stack  16  is moved in the run-through direction  17  to a conveying belt  18  and is deposited thereon. 
     A washing machine  19  and an oiler  20  connect onto the conveying belt  18  in the run-through direction. The parts are cleaned in the washing machine  19  and are oiled in the oiler  20 . 
     After the oiler  20 , the purified and oiled parts  12  get onto a further conveying belt  21  where they are then gripped by an inserting unit  22  in the form of a robot, in particular articulated arm robot and are inserted into the forming press  14 . The invention which is described hereinafter in a detailed manner, relates to the apparatus  11  for unstacking the parts  12 . 
     As is particularly shown in  FIGS. 1 and 2 , apart from the already mentioned supply station  15 , the apparatus  11  comprises an unstacking device  23  for the singularised unstacking of the part stack  16  and for bringing an unstacked part  12  along the run-through direction  17  onto a function station which is arranged downstream and in the example case is therefore the conveying belt  18 . 
     The unstacking device  23  according to the embodiment example is designed in a portal construction manner and comprises a carrier device  24  with at least one runner rail  25  which is aligned along the run-through direction and on which an unstacking slide  26  is movably guided in the run-through direction  17  between the supply station  15  and the function station, in particular the conveying belt  18 . 
     As is particularly shown in  FIGS. 1 and 2 , the carrier device  24  comprises a mount  27  which comprises two mount bridges  28   a ,  28   b  which are arranged distanced to one another in the run-through direction  17  and bridge the conveying belt  18  or the supply station  15  in a portal-like manner. The mount bridges  28   a ,  28   b  each consist of two vertical pillars  30  which in a transverse direction  29  to the run-through direction  17  are arranged to the left and right of the supply station  15  or of the conveying belt  21  and which are connected to one another in the transverse direction  29  by way of a transverse beam  31 . 
     As is particularly shown in  FIGS. 2 and 3 , several beams  32  which are arranged parallel to one another in the run-through direction  17  and are aligned at a distance to one another in the transverse direction  29  and which can also be denoted as longitudinal beams are arranged on the two transverse beams  31  of the mount bridges  28  in a manner which is described in more detail hereinafter. 
     As in particular  FIG. 3  shows, two runner rails  25  which are arranged parallel to one another in the run-through detection and on which an unstacking slide  26  is movably guided are arranged on each beam  32 . The runner rails  25  are fastened to the assigned beam  32  with an offset in the run-through direction  17 . 
     The unstacking slides  26  each comprise a carrier structure  33 , on which several gripping units  34  are arranged, wherein the gripping units  34  each comprise at least one gripping head  35  which can be displaced in the height direction for lifting the parts  12  out of the part stack  16 . The gripping units  34  in the example are designed as suction grippers and comprise a gripping head  35  which is designed as a suction head. The lifting of the uppermost part  12  of the part stack  16  is therefore effected by way of suction heads being brought to bear onto the upper side of the part  12  to be unstacked and a vacuum within the suction head being subsequently generated, which leads to a fixed sucking of the suction head on the upper side of the part  12  to be lifted, so that the part  12  can be lifted from the part stack  16 . 
     The vacuum generation of the suction grippers can be effected for example by way of a venturi nozzle or by a vacuum pump. 
     In particular,  FIGS. 4 and 6  together show that several gripping units  34  which are arranged on the carrier structure  33  one after other in the run-through direction  17  are arranged on the unstacking slide  26 . The unit of the beam  32 , the two runner rails  25  which are fastened thereto and the unstacking slides  26  which are movably guided thereon with the gripping units  34  and the gripping heads  35  can also be denoted as a “double feeder”. 
     Important components of the apparatus  11  for unstacking the parts  12  are several drives with which the different components of the device  11  can be movably guided and positioned in different directions, which is described in more detail hereinafter: 
     Whereas with conventional unstacking slides the gripping units  34  and the gripping heads which are arranged thereon are fastened to the assigned carrier structure in a positionally fixed manner, the gripping units  34  now according to the invention are displaceable relative to one another and relative to the carrier structure  13  in the run-through direction  17  and can be positioned into different working positions by way of a motoric gripping unit drive device  36  of the unstacking slide  26 . 
     As is particularly shown in  FIG. 6 , the motoric gripping unit drive device comprises several gripping unit drives  37  which are each assigned to one of the gripping units  34 . At least components of the gripping unit drives  37  are located on board the assigned gripping units  34 . 
     As is particularly shown in  FIG. 6 , the carrier structure  33  of the unstacking slide  26  is designed as a guide rail  38 , on which the gripping units  34  are movably guided in the run-through direction. The gripping unit drives  37  can be designed as electrical linear drives. By way of example, what is shown in an electrical linear direct drive, concerning which the guide rail  38  is designed as a stator and the gripping units  34  as a rotor. 
     As is further shown in  FIG. 6 , the guide rail  38  of the unstacking slide  26  comprises two guide tracks  39  which are aligned above one another in the height direction and extend parallel to one another in the run-through direction  17 . The gripping units  34  each comprise a base housing  40 , on whose rear side two sliding pieces which project into the guide tracks  39  engage. Furthermore, a coil (not shown) which can be subjected to current is located in the base housing  49 . 
     Furthermore, a control device  80  ( FIG. 2 ) for controlling the gripping unit drives  37  is provided, concerning which it is expediently an external control device  80  which is located outside the apparatus  11  and which outputs control signals to the individual gripping unit drives  37 . In the specific case, the control signals initiate current subjection of the coils in the gripping units  34 , by way of which a movement of the gripping units along the guide rail in the guide tracks  39  can take place on account of the permanent magnets which are arranged in the guide rail  38 . Each gripping unit further comprises a trailing cable device  42  which on the one hand is arranged on the guide rail  38  and on the other hand on the base housing  40 . 
     As is further shown in  FIG. 6 , apart from the gripping unit drive device  36 , a gripping head drive device  43  for moving the gripping heads  35 , in the shown exemplary case suction heads, is present in the height direction. The gripping head drive device  43  comprises several gripping head drives  44  which are located on board the gripping units  34 . 
     The gripping head drives by way of example are shown in the form of electrical linear drives. 
     The linear drive which is shown by way of example as a gripping head drive  44  comprises a drive housing  45 , in which a rotor  45  is movably guided in the height direction  47 . The rotor  46  at its free end is connected to a coupling piece  48 , on whose lower side the gripping head  35  which is designed as a suction head is fastened. The drive further comprises two guide rods  49   a ,  49   b  which are arranged to the left and right of the rotor  46  and extend parallel to this. The guide rods  49   a ,  49   b  serve for the rotation locking of the coupled-on suction head. The guide rods are likewise movably guided in the drive housing  45  and are fastened with their free ends to the coupling piece  48 . 
     The gripping head drives  44 , thus in particular the shown linear drives are controllable likewise independently of one another via the control device  80 , so that the lowing and lifting movement of the suction heads can take place independently of one another. Above all, this is advantageous for the lifting procedure of the parts from the part stack  16 , said procedure being yet described in more detail hereinafter. 
     The unstacking device  23  further comprises a slide longitudinal drive device  50  for driving the unstacking slide  26  along the assigned runner rail  25  in the run-through direction  17  between the supply station  15  and the function station, thus in particular the conveying belt  18 . The slide longitudinal drive device  50  comprises several slide longitudinal drives  51  which are each assigned to one of the unstacking slides. As is particularly shown in  FIGS. 8 and 9 , two runner rails  25  are fastened parallel to one another, to the carrier  32 . As is particularly shown in  FIG. 4 , the runner rails are arranged offset to one another in the run-through direction  17 . The slide longitudinal drives  51  are seated on one end of the runner rail  25 . Herein, the slide longitudinal drive  51  of the one runner rail  25  is seated at the one end and the slide longitudinal drive of the other unstacking slide  26  opposite this at the other end of the other runner rail  25 . The lateral offset of the runner rails  25  which are arranged on an assigned carrier  32 , in the run-through direction permits the arrangement of the slide longitudinal drives  51  laterally next to the assigned longitudinal rail. 
     The slide longitudinal drives  51  by way of example are shown as linear drives in the form of servo-motors. 
     As is particularly shown in  FIG. 8 , the unstacking slides  26  each comprise a runner vehicle  52  which engages into the guide tracks (not shown) of the assigned runner rail  25  and is guided thereon along the runner rail  25 . Two vertical struts  53  which are orientated distanced to one another in the run-through direction and which extend in the height direction are fastened to the runner vehicle via coupling means  54 . The already mentioned carrier structure  33  in the form of the guide rail  38  for the gripping units  34  is located on the free ends of the vertical struts  53 . As is particularly shown in  FIG. 4 , a trailing cable device  54  which is guided along a cable trailing rail  55  ( FIG. 8 ) is arranged on the runner vehicle  52 . The trailing cable device  75  permits the electrical supply of the components of the unstacking slide  26  despite the movement of the unstacking slide  26  in the run-through direction  17 . 
     The unstacking device  23  further comprises a slide transverse drive device  54  for the transverse displacement of the carrier structure with the gripping units  34  with respect to the assigned runner rail  25 . The slide transverse drive device  54  comprises several slide transverse drives which are each assigned to one of the unstacking slides  26 . 
     The aforementioned slide longitudinal drives  51  as well as the slide transverse drives  55  can be individually controlled by the control device, so that the unstacking slides  26  can be displaced independently of one another in the run-through direction along the assigned runner rail and additionally independently of one another in the transverse direction  29  transverse to the run-through direction  17 . By way of the transverse movement of the unstacking slide which can be produced by the slide transverse drives  55 , it is possible for the unstacking slides  26  which are driven in opposite directions to evade one another on an assigned carrier  32 . In particular, the unstacking slide which is not loaded evades the unstacking slide which is loaded with a part, by way of a transverse movement. The unstacking slide  26  which is not loaded, after passing the loaded unstacking slide, can then change back into the same track as the loaded unstacking slide, so that the positions of the gripping heads  35  above the part to be lifted can be set in an exactly equal manner as the position of the other unstacking slide. The gripping heads  35  of the unstacking sides  26  of a unit (carrier with two unstacking slides) can therefore always grip at the same position. However, it would also be conceivable for the runner rails  25  of a unit to be distanced to one another in the transverse direction  29  in a manner such that the unstacking slides  29  pass one another. In this case, no slide transverse drive device  54  would be necessary. The position of the gripping heads  35  on gripping the one unstacking slide  26  would be different from the position of the gripping heads  35  on gripping the other unstacking slide  26 . 
     The slide transverse drives  55  each comprise a drive unit which is arranged on the lower side of the runner vehicle  52 . 
     The drive unit  56  by way of example is shown in the form of a fluid, in particular pneumatic linear drive. The pneumatic linear drive comprises a pneumatic cylinder which comprises a cylinder housing  57  in which a piston is guided in a movable manner by way of subjection to pressurised air. The piston is connected to a position rod  58  which is led out of the cylinder housing  57  and is connected to the coupling means which have already been mentioned above. The coupling means comprise lever gears  59  which on the one hand are connected to the piston rod  58  and one the other hand are connected to an assigned vertical strut  53 . The lever gears  59  each comprise a first lever  60  which on the one hand is connected to the piston rod  58  of the pneumatic cylinder and is pivotably mounted on the runner vehicle  532  about a pivot axis  61 . The first lever at its free end which is opposite to the end which is connected to the piston rod comprises a joint  62 , on which a connection lever is articulated. The connection lever is connected via a further joint  64  to a second lever  65  which at the end side is mounted on the runner vehicle via a further pivot axis  66 . An identically constructed lever gear  59  is assigned to the other vertical strut  53 , so that given a pressure impingement of the piston and for example an extension of the piston rod as a whole a type of parallelogram gear arises, and this ensures that the coupled vertical struts  53  and herewith the carrier structure  33  with the gripping units  34  is displaced transversely to the runner rail  25  and herewith in the transverse direction  29 . 
     The unstacking device  23  further comprises a runner rail drive device  67  for adjusting the distance of the runner rails  25  to one another in the transverse direction  29 . The runner rail drive device  67  comprises several runner rail drives  68  which are each assigned to one of the runner rails  25 . The runner rail drives  68  can also be individually activated by the control device  80  so that the distance of the runner rails  25  to one another in the transverse direction  29  can be changed. 
     As is particularly shown in  FIGS. 1 and 2 , it is not the runner rails  25  per se which are displaced in the transverse direction  29  by way of the runner rail drive device  67 , but the beams  32 , on which in the exemplary case two runner rails  25  are arranged. As is particularly shown in FIG.  3 , guide rails  68  on which the carriers are movably guided in the transverse direction  29  are arranged on the lower sides of the transverse beams  31  of the mount bridges  28 . 
     As shown by way of example in  FIG. 3 , a runner rail drive  68  in the form of a linear motor is assigned to each carrier  32 . 
     On unstacking plate-like parts  12 , in particular sheet metal blanks from a part stack  16 , one proceeds as follows: 
     The parts  12  are firstly located in the supply station  15  in a manner stacked above one another into a part stack  16 . The parts are sheet metal blanks, for example car body parts which can indeed have dimensions of several square metres. For this reason, several unstacking slides  26  which interact are necessary for unstacking the parts  12 . 
     Firstly, the dimension of the uppermost part  12  of the part stack  16  is determined. The determined dimensional data, concerning which it can not only be a surface, but also an arching, is then transferred to the control device  80 . The control device  80  then controls the different drive devices. 
     Firstly, the slide longitudinal drives  51  are activated, so that one of the slides of the double slide system or of the “double feeder” is placed above the part to be unstacked. As a whole therefore, several unstacking slides  26  are positioned together above the part  12  to be unstacked. The other unstacking slides  26  which each run on the other runner rail  25  of the same carrier  32  are simultaneously located in the region of the further function station, thus of the conveying belt  18  and are ready to deposit a commonly unstacked and gripped part  12  onto the conveying belt  18 . 
     The unstacking slides  26  which are positioned above the part  12  to be unstacked, with their gripping units  34  and the gripping heads  35  which are arranged thereon form a two-dimensional gripping head pattern in a plane which is spanned by the run-through direction  17  and the transverse direction  29 . 
     Before the lifting procedure of the uppermost part  12  out of the part stack  16  begins, the gripping heads  35  are positioned to one another in a manner such that a gripping head pattern which is optimal for the lifting is adjusted in dependence on the dimensions of the part  12  which is to be unstacked. 
     The gripping unit drives  37  are therefore activated by the control device  80 , so that the gripping units  34  and thus the coupled-on gripping heads  35  are positioned and distanced relative to one another in the run-through direction  17  so that the positions of the gripping heads  35  in the run-through direction  17  are optimal for the lifting of the part. Furthermore, the runner rail drives  68  are activated, by which means the carriers  32  which are movably guided on the guide rails  69  which are formed on the transverse beams  31  can be positioned relative to one another so that the distance of the gripping heads  35  can also be changed in the transverse direction. Since in any case only one of the unstacking slides  26  of the double slide arrangement is in operation on unstacking and the other unstacking slide is located in the region of the conveying belt  18 , it is insignificant that on displacing the beams  32 , the other unstacking slides which are located above the conveying belt are also co-displaced together. The transverse displacement of the gripping heads  35  as a rule is effected only a single time per part stack  16 . 
     After adjusting this gripping head pattern which is optimal for the lifting, the gripping head drives  44  are subsequently activated, so that the gripping heads  35  in the form of suction heads come to bear on the upper side of the part  12  to be lifted. 
     In the exemplary case, the suction heads are then evacuated, which is to say a vacuum is produced, so that the suction heads are fixedly sucked to the uppermost part  12 . The lifting of the part can herein be effected by way of simultaneously moving up the gripping heads  35  or in a preferred manner by way of the staggered lifting-up of different gripping heads, as is described for example in DE 101 17 607 B4. Herein, the gripping heads  35  during the lifting procedure can each execute a movement with movement phases which become fastener and slower, wherein the movements of the different gripping heads  35  are asynchronous to one another, so that a continuously changing, wave-like deformation of the part which is held by the gripping heads  35  results during the lifting procedure, by which means the uppermost part can be released more easily from the rest of the part stack  16 . 
     After lifting the uppermost part  12 , the gripping heads  35  of the unstacking slides  26  move together into a transport position. The slide longitudinal drives  51  are subsequently activated, so that the unstacking slides move together to the conveyor belt  18 . At the same time, the unstacking slides which had previously been located above the conveying belt  18  are moved in the direction of the supply station  18 . In order to avoid a collision of the unstacking slides which are driven in opposite directions, in particular in the region of a double-slide arrangement, the slide transverse drives  55  are activated, so that one of the unstacking slides  26 , in particular the one which is not loaded can evade in the transverse direction  29 . As soon as the unstacking slides  26  which are loaded with the singularised part  12  are arranged above the conveying belt  18 , the gripping heads  35  together are moved downwards to an ejection height and the part is deposited by way of introducing a pressure impulse onto the gripping heads  35 . At the same time, a renewed stacking of the uppermost part  12  is effected at the supply station by way of the unstacking slide  26  which is located there. By way of the displaceability of the gripping heads  35  to one another in the run-through direction and in the transverse direction  29 , the griping head pattern can be individually changed and adapted to different dimensions of the parts which are to be unstacked.