Abstract:
A system for producing reinforcing cages for wind turbine tower segments, wherein a reinforcing cage has in each case substantially horizontally oriented ring segments and substantially vertically oriented stiffening elements. 
     It is proposed that the system has a receiving area which is adapted so as to receive the preferably inner, substantially horizontally oriented ring segments of the reinforcing cage, a first handling robot for supplying and positioning the stiffening elements, and a second handling robot for connecting the ring elements to the stiffening elements.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a system for producing reinforcing cages for wind turbine tower segments, wherein a reinforcing cage has in each case substantially horizontally oriented ring segments and substantially vertically oriented stiffening elements. 
         [0003]    2. Description of the Related Art 
         [0004]    Towers such as those which are used, inter alia, for wind turbines often have a wall made from concrete or reinforced concrete. In particular in the case of dynamically loaded towers, which applies to the majority of towers owing to the effect of the wind, stiffening structures, so-called reinforcing cages, are additionally provided inside the tower wall in order to improve stability. A tower hereby has a segmental structure, i.e., a tower is composed of multiple superposed ring-shaped tower segments. 
         [0005]    In the production of such tower segments, the reinforcing cage is first produced and concrete is then poured into formwork provided for this purpose and left to set. 
         [0006]    In known devices for producing reinforcing cages for tower segments, a support structure is provided which holds a plurality of bars, so-called rakes. These bars each have holders for holding reinforcing steel wire, wherein the reinforcing steel is passed around the support structure or the support structure is set in rotation in order to form ring elements. These ring elements are connected to bracket-like (steel) stiffening elements which extend substantially perpendicularly to the rings or substantially vertically, as a result of which a grid-like reinforcing cage is formed. 
         [0007]    The reinforcing steel wire is either passed around a stationary support structure in a circular motion or, which is preferable, is situated in a stationary feed unit and is pulled out of the holder by the support structure which can be driven in rotation and is applied around the support structure owing to the rotational motion of the latter. During the whole time, the shape of the ring-shaped steel strands is stabilized by the support structure and the bars by means of multiple spokes which extend between the support structure and the bars. In order to remove the reinforcing cages from the device, in known systems the spokes must each be removed or the stabilizing bars are unhooked individually and manually from the finished cage. 
         [0008]    Depending on the size of the tower segments to be produced, the reinforcing cages already have a considerable weight and, depending on the tower segment, sizable dimensions. A reinforcing cage has, for example, for the lowest, i.e., largest tower segment of a type E126 wind turbine from the ENERCON company, a diameter of approximately 14 m, a height of approximately 3.7 m and a weight of approximately 8.5 t. Because of its grid-like structure and the enormous dimensions, during manufacture reinforcing cages can only be handled with difficulty using conventional crane systems. 
         [0009]    A gripping device for handling such reinforcing cages is known from DE 10 2012 221 453. 
         [0010]    As well as handling the reinforcing cages, in the known manufacturing environments there is, however, a need to design the connection of the substantially vertical elements to the substantially horizontal ring elements of the reinforcing cages more efficiently and at the same time to be able to handle them using the known gripping device referred to above. 
       BRIEF SUMMARY 
       [0011]    One or more embodiments provide a system of the type described at the beginning which ensures efficient production of the reinforcing cages. In particular, the invention is also to be able to use said system in combination with, for example, the above-described known gripping device. 
         [0012]    Provided is a system having: 
         [0013]    a receiving area which is adapted so as to receive the preferably inner, substantially horizontally oriented ring segments of the reinforcing cage, 
         [0014]    a first handling robot for supplying the stiffening elements, and 
         [0015]    a second handling robot for connecting the ring elements to the stiffening elements. 
         [0016]    By using a first and a second handling robot, the number of manual work steps can be reduced, overall working safety is increased, and improved work planning is enabled. It has surprisingly proven to be the case that, despite the complex structure of the system and the many degrees of freedom during operation, it is possible to produce reinforcing cages in an efficient manner in terms of time. 
         [0017]    The invention is preferably further developed by the system having an electronic control unit which is configured so as to control the first and second handling robots for supplying the stiffening elements in a coordinated manner and for connecting the stiffening elements to the ring elements. To do this, the electronic control unit preferably has one or more computer-assisted workstations which are configured so as to import and process a virtual representation of the reinforcing cage to be produced and of the system producing the reinforcing cage, including the handling robots. The virtual representation can be supplied in the form of CAD data and/or CAD/CAM data. Data sets which link a specific movement pattern of the handling robots to a respective type of reinforcing cage to be produced are preferably stored in the electronic control unit. Reinforcing cages have different sizes depending on which tower segment they are to be used for. The sizes can, for example, be stored in data memories and the electronic control unit is preferably configured so as to access them, read the corresponding data sets and convert them into operating instructions for the first and second handling robots. 
         [0018]    In a preferred embodiment of the invention, the receiving area is arranged on a rotatable platform. The first and second handling robots are preferably arranged in a fixed location adjacent to the platform and/or can preferably be adjusted radially with respect to the center point of the platform. Because the handling robots are arranged adjacent to the preferably rotatable platform, an improved gain in space is obtained for the production site. Reinforcing cages for tower segments have a substantially cylindrical or frustoconical design so that rotation of the reinforcing cages on the receiving platform does not require any additional space in any direction. 
         [0019]    According to a further preferred embodiment, the receiving area is configured in order to interact with a gripping device for handling a reinforcing cage. The gripping device is preferably designed according to DE 10 2012 221 453. 
         [0020]    The first handling robot is furthermore preferably configured so as to bring the stiffening elements to bear against the ring elements in a substantially vertical orientation. It is hereby irrelevant if individual ring elements are not brought to bear against the stiffening elements. The crucial thing is that the stiffening elements and ring elements which are brought to bear with one another are those where a connection is subsequently to be effected by the second handling robot at the points where they meet. According to the invention, the phrase “substantially vertical” is also understood to mean at such an angle of inclination to the vertical as can arise from an oblique helical path, for example in the region of ±1 to 10°. 
         [0021]    Different types of stiffening elements can be formed in order to become part of the reinforcing cage. According to a first aspect, the stiffening elements are formed from a helically bent endless material. The stiffening elements are particularly preferably formed from a single helically bent steel wire that runs around the complete circumference of the ring elements. This structure is also called an upright helix. Such a design of the stiffening elements has the advantage that a bending and welding device for supplying the stiffening elements that is separate and hence has associated transport costs can be dispensed with. 
         [0022]    The first handling robot is preferably configured so as to form and arrange this structure along the substantially horizontal ring elements. 
         [0023]    According to a preferred embodiment, the first handling robot has bending means and interacts with a feed unit which feeds the endless material to the bending means, wherein the bending means are configured so as to bend the fed endless material in such a way that the stiffening means are formed helically. 
         [0024]    The bending means preferably have deflecting rollers between which the endless material is passed, wherein the positions of the deflecting rollers relative to one another can be modified. The positions of the deflecting rollers relative to one another can be modified in such a way that different bending radii and bending directions can be introduced into the endless material. 
         [0025]    The arrangement of the deflecting rollers can, for example, take the form of tube bending tools. 
         [0026]    In another preferred embodiment, the bending means are arranged so as to be stationary on the cage production system, wherein a handling robot preferably does not undertake the bending itself but only the handling of the bent reinforcing steel. 
         [0027]    According to a second aspect of the invention, the stiffening elements are designed as separate, preferably closed brackets. This design has the advantage that the arrangement of the individual stiffening elements around the ring elements can be handled in a more flexible manner and the handling process can be managed more simply. In the design according to this aspect of the invention, the stiffening elements are prefabricated in a separate production process and then held in stock in large quantities. 
         [0028]    In a preferred embodiment, the first handling robot has gripping means for non-slip grasping and removal of the stiffening elements from a stocking unit. Non-slip is hereby understood to mean that the gripping means grip the stiffening elements either in an interlocking fashion or force-locking fashion in such a way that, taking into account the acceleration to be expected when the handling robots move, static friction occurs between the gripping means and the stiffening elements but dynamic friction does not, and of course the gripping means also do not release the stiffening elements. 
         [0029]    The gripping means are preferably configured so as to grip the stiffening element at opposite ends of the stiffening element in each case on the inside of at least one corner. 
         [0030]    According to a further preferred embodiment, the gripping means have a first and second pivotable coupling link which is configured so as to grip the stiffening element in each case at at least one corner by means of pivoting. 
         [0031]    The coupling links preferably each have a guide roller for gripping the stiffening elements, preferably on the inside, at a corner, and preferably a supporting section or a further roller at an opposite end of the coupling link. The supporting section or the further roller are preferably each arranged in such a way that, when the coupling link is pivoted, a sufficient spreading force is exerted on the stiffening element to allow the first handling robot to lift, lower and displace the stiffening element in a non-slip manner. 
         [0032]    According to a further preferred embodiment of the invention, the second handling robot has a pivotable working head on which a connecting means is arranged which is selected from a list consisting of: 
         [0033]    adhesive dispensing device, 
         [0034]    welding device, 
         [0035]    soldering device, 
         [0036]    device for automatically twisting metal wires. 
         [0037]    The device for automatically twisting metal wires is preferably designed as known from DE 10 2012 216 831. 
         [0038]    The above embodiments have each referred to ring elements generally. They can be understood as a first set of ring elements when, in a preferred embodiment, the system has a third handling robot for supplying a second set of substantially horizontally oriented, preferably outer ring elements, wherein the ring elements are designed as separate, preferably closed rings or are designed as helically bent endless material. The electronic control unit is preferably likewise configured so as to also control the third handling robot in a coordinated fashion with the first and second handling robots, in particular based on a corresponding virtual representation. 
         [0039]    The third handling robot preferably has a guide device, preferably with one or more guide rollers, and interacts with a feed unit which feeds the endless material to the guide device, wherein the guide device is configured so as to guide the fed endless material in such a way that the second set of ring elements has a helical design. 
         [0040]    The second handling robot is preferably moreover configured so as also to connect the second set of ring elements to the stiffening elements. 
         [0041]    The electronic control unit is preferably configured so as to control the second and third handling robots, preferably all the handling robots of the system, in order to supply in a coordinated fashion the second set of ring elements and to connect the stiffening elements to the second set of ring elements. Reference is hereby preferably made to the same means and resources as with respect to the first and second handling robots. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0042]    The invention is explained in detail below with the aid of preferred exemplary embodiments and with reference to the attached drawings, in which: 
           [0043]      FIGS. 1 a  and 1 b    show a schematic partial view of a system according to a first exemplary embodiment, 
           [0044]      FIGS. 2 a -2 g    show different working positions of the first handling robot according to the first exemplary embodiment, 
           [0045]      FIGS. 3 a -3 c    show different schematic partial views of a system according to a second exemplary embodiment, 
           [0046]      FIGS. 4 a -4 c    show different schematic partial views of a system according to a third exemplary embodiment, 
           [0047]      FIGS. 5 a  and 5 b    show different working positions and schematic partial views of a third handling robot as examples for the second exemplary embodiment, and 
           [0048]      FIGS. 6 a -6 c    show different working positions of a further handling robot for a system according to one of the exemplary embodiments, illustrated as examples of the first exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    A system  1  according to a first exemplary embodiment of the invention is shown in  FIG. 1 a   . The system  1  has a first handling robot  3  which is designed to form helically arranged stiffening elements  27  by means of corresponding bending means. The first handling robot  3  has a working head with a bending device  19 . The first handling robot  3  is arranged in  FIGS. 1 a  and 1 b    on a support structure  5 . This can be a pedestal as in  FIGS. 1 a  and 1 b    or another support structure, as shown for example in one of the other exemplary embodiments. 
         [0050]    The system  1  has a receiving area  7 . The receiving area  7  is configured so as to receive a gripping device  11 . The gripping device  11  has coupling means, for example in the form of hook-shaped rake arms on which substantially horizontally oriented ring elements  13  are arranged in each case. The receiving area  7  is arranged on a preferably rotatable platform  9 . The platform  9  is preferably connected to an electronic control unit by a data line so that the rotation can be effected in a coordinated fashion by means of the electronic control unit, depending on the progress of the work of the handling robots  3  and  21 . 
         [0051]    The first handling robot  3  is connected, inter alia, to a feed unit  15  by means of an electronic control device and interacts with the feed unit  15  so that the latter can feed to the handling robot  3  an endless material  17  to produce the helical stiffening elements  27 . 
         [0052]    The system  1  moreover has a second handling robot  21  which has a working head  25  with a connecting means, for example in the form of a welding wheel. The second handling robot  21  is preferably likewise connected to the electronic control unit and interacts in a coordinated fashion with the first handling robot  3  and the platform  9  in order to connect the generated stiffening elements  27  to the substantially horizontally oriented ring elements  13  which are held by the gripping device  11 . The second handling robot  21  can be arranged, for example, on a support structure  23 , adjacent to the receiving area  7 , or on an alternative support structure together with the first handling robot, as shown for example in the following exemplary embodiments. 
         [0053]    The first handling robot  3  can move along multiple axes in order to enable the working head  19  to generate bends in the endless material  17  in such a way that the substantially vertically oriented stiffening elements  27  are formed. For this purpose, the working head  19  can also be reconfigured and repositioned, as is shown in  FIG. 1 b   , and in particular as is illustrated in detail in  FIGS. 2 a    to  2   g.    
         [0054]    The system moreover has an electronic control device  10  for controlling the handling robots  3 ,  21  on the platform  9  in a coordinated fashion. 
         [0055]    A portion of the system  1  according to the first exemplary embodiment is shown in  FIGS. 2 a  to 2 g   , in which the working head  19  of the first handling robot  3  is shown in operation. In the Figures, a first substantially vertically oriented stiffening element  27  has already been created, adjoining the ring elements  13  in the receiving area  7 . The working head  19  has a base body  29  on which multiple deflecting rollers  31   a,    31   b,    31   c  ( FIGS. 2 c  to 2 g   ) are arranged. A first bend for a stiffening element  27  has been generated in  FIG. 2 a   . Starting from the situation in  FIG. 2 a   , in  FIG. 2 b    the endless material  17  is deformed further by adding a further bend. To do this, the first handling robot  3  has performed a corresponding pivoting motion about a working axis b. In order to complete the bending of the endless material  17 , the first handling robot  3  briefly withdraws from the situation in  FIG. 2 b    and pivots the body of the handling robot  3  outwards so that the first handling robot  3  does not collide when the endless material  17  is then guided upwards to the point at which the next bend which needs to be made. 
         [0056]    The working head  19  of the first handling robot  3 , formed by bending means in the form of a bending device, has adjustable deflecting rollers  31   a,    31   b,    31   c  which are arranged on the base body  29 . An example of altering the position of the rollers, in conjunction with a repositioning motion of the working head  19 , is illustrated in  FIGS. 2 c    to  2   g.    
         [0057]    In Figure c, the working head  19  on the first handling robot  3  is initially still situated in engagement with the endless material  17 . In order to prevent twisting of the endless material  17  using the handling robot  3 , in  FIG. 2 d    the working head  19  is pivoted about an axis c on the first handling robot  3  in the direction of the arrow  33  so that the rollers  31   a,    31   b,    31   c  are brought out of engagement with the endless material  17 . Then, as can be seen in  FIG. 2 e   , the positions of the rollers  31   a  and  31   c  are altered in a first direction, whilst the deflecting roller  31   b  arranged between the deflecting rollers  31   a,    31   c  is shifted in the opposite direction. The deflecting rollers  31   a,    31   b ,  31   c  can be repositioned either steplessly or according to a pattern, for example by moving them into dedicated openings. Once the repositioning is complete, as shown in  FIG. 2 f   , the working head  19  is pivoted again about the axis c in the direction of the arrow  35  so that the deflecting rollers  31   a,    31   b ,  31   c  are again in engagement with the endless material  17 . This situation is depicted in  FIG. 2 g   . In  FIGS. 2 c  to 2 g   , the rotated position of the base body  29  relative to the first handling robot  3  is constant. It is, however, optionally also possible to pivot the base body  29  of the working head  19  about an axis a, as can be seen, for example, by comparing  FIG. 2 b    with  FIG. 2   c.    
         [0058]      FIGS. 3 a  and 3 b    show schematically a portion of a system  100  according to a second exemplary embodiment of the invention. The essential features are the same as in the first exemplary embodiment. In particular, the type of arrangement of a first handling robot  103  of the system  100  and a second handling robot  121  of the system  100  can in principle be swapped or combined with the type of arrangement for the system  1 . On its working head  119 , the first handling robot  103  of the system  100  has a gripping device by means of which the handling robot  103  can grip stiffening elements  127  on the inside and hold them in a non-slip fashion. The stiffening elements  127  according to the second exemplary embodiment are separate, preferably closed brackets. The first handling robot  103  is designed to remove the bracket-like stiffening elements  127  from a stocking unit using the working head  119  designed as a gripping device, bring them to bear against the ring elements  13  on the gripping device  11  of the system  100 , and hold them there until the second handling robot  121  has connected the stiffening elements  127  to the ring elements  13  using its working head  125  designed as a welding device, for example as a welding wheel. In  FIGS. 3 a  and 3 b   , the first handling robot  103  and the second handling robot  121  are arranged on an annular platform  105  surrounding the gripping device  11  and the (not shown) rotatable platform  9  ( FIG. 1 a   ). However, support structures like those for example in  FIGS. 1 a  and 1 b    could also be chosen, in exactly the same way as a support structure like the platform  105  depicted here could be chosen in the first exemplary embodiment of the system  1  in  FIGS. 1 a    and  1   b.    
         [0059]    The precise design of the stocking unit is not shown in this exemplary embodiment for reasons of clarity. It can, for example, be a stocking unit like the stocking unit  204  from the exemplary embodiment of  FIGS. 4 a  to 4 c    explained below. 
         [0060]    In the situation in  FIG. 3 a   , the second handling robot  121  is positioned in such a way that a stiffening element  127  is connected to one of the ring elements  13  in the upper area of the reinforcing cage to be created. On the other hand, in  FIG. 3 b    the second handling robot  121  is positioned such that the working head  125  can connect the stiffening element  127 , in a lower area of the reinforcing cage to be produced, to a ring element in the gripping device  11 , or alternatively effects a weld on the stiffening element  127  itself. During these processes, the first handling robot  103  holds the stiffening element  127  in position in a non-slip manner. This happens by means of pivotable coupling links which are arranged at opposite ends of the working head  119 .  FIG. 3 c    shows the coupling link  141 , although it is covered by the working head  125  of the second handling robot  121 . The coupling link with its component parts is likewise also explained in greater detail in an exemplary embodiment which is still to be discussed below. 
         [0061]    The coupling link  141 , which can be seen in  FIG. 3 c   , has at its first end a guide roller  145  which is configured so as to be inserted into the bend, and therefore the corner, of a stiffening element  127  and to grasp the stiffening element there. At the opposite end of the coupling link  141  from the guide roller  145 , a support section  147  is arranged which is configured so as to exert, when the coupling link  141  is pivoted together with the guide roller  145 , a spreading force on the stiffening element  127  which is great enough to be able to hold the stiffening element  127  in a non-slip manner. 
         [0062]    The coupling link  141  can preferably be displaced by means of an actuator  143 . 
         [0063]    A system  200  for producing reinforcing cages according to a third exemplary embodiment is shown in  FIGS. 4 a  to 4 c   . The third exemplary embodiment is very similar in structure to the second exemplary embodiment so reference is only made to structural differences. In contrast to the system  100 , the system  200  has a height-adjustable portal  206  on which a second handling robot  221  is arranged so that its height can be altered. A first handling robot  203  is mounted on a support structure  205  separately from the second handling robot  221 . The system  200  has a stocking unit  204  for stiffening elements  127 . The first handling robot  203  is configured so as to remove these stiffening elements  127  from the stocking unit  204  and place them against the ring elements  13  which are held on the gripping device  11  and are arranged in the receiving area  7  on a rotatable platform  9 . This removal process is shown by way of example in  FIG. 4 a   . In  FIG. 4 b   , which shows the same system  200  from  FIG. 4 a    from a different point of view, the first handling robot  203  has brought a previously removed stiffening element  127  to bear against the ring elements  13  on the gripping device  11 . Starting from the operating situation in  FIG. 4 b   , the second handling robot  221  is configured so as to shift heightwise along the portal  206  to the appropriate point and then bring a working head  225  into position, which creates a connection of the stiffening element  127  in each case to a section of a ring element  13  at different heights along the reinforcing cage which is to be produced. 
         [0064]    In the exemplary embodiments shown hereabove, the substantially horizontally oriented ring elements  13  were the ring elements for a so-called internal helix of the reinforcing cage to be produced. It is likewise within the scope of the invention that these ring elements represent a so-called external helix, wherein the stiffening elements could then be arranged on the inside with respect to these ring elements. Not all combinations of corresponding shifts of the positions of the handling robots are shown here in order to make the view clear. 
         [0065]    In order to remain within the above-described exemplary embodiment of an internal helix for the substantially horizontally oriented ring elements  13 , it is provided within the scope of a further exemplary embodiment, which is to be understood as a supplement to all the exemplary embodiments shown above, but by way of example is only illustrated with the aid of the exemplary embodiment from  FIGS. 3 a  to 3 c   , that the substantially horizontally oriented ring elements  13  represent a first set of ring elements. In  FIGS. 5 a  and 5 b   , an automatic winding unit  150  is additionally provided in the system  100 , which is configured so as to supply a second set of substantially horizontally oriented ring elements  14  on an opposite side of the stiffening elements  127  (or also of the helically formed stiffening elements  27  in the first exemplary embodiment) with respect to the first set of ring elements. In the exemplary embodiment shown in  FIGS. 5 a  and 5 b   , the winding unit  150  has a guide device  153  which is configured so as to apply endless material, which can be the same endless material for the helically formed stiffening elements  27  of  FIGS. 1 a    to  2   g,  annularly or spirally around the stiffening elements  127 . To do this, the winding unit  150  is shifted heightwise on a portal  151  whilst the platform  9  is rotated about a vertically oriented axis e together with the gripping device  11 , the ring elements  13  and the stiffening elements  127 . As can be seen from  FIG. 5 b   , the endless material is preferably supplied by a feed device in the form of a stocking unit  155  which can hold ready a cylindrical spool of the endless material. The guide device can have multiple guide rollers which allow the endless material to be dispensed in a specific fashion in order to form the rings  14 . The winding unit  150  is preferably connected via a data line to a central electronic control unit, for example the one mentioned above, which coordinates the work of the different system components such as the handling robots, winding unit and rotatable platform. This control unit is indicated in  FIG. 1   a.    
         [0066]    The winding unit which is shown in  FIGS. 5 a  and 5 b    can, for example, also be the feed device  15  which is used in the exemplary embodiment of  FIGS. 1 a  to 2 g    in order to supply the endless material  17 . 
         [0067]    An additional option for a combination of features, given by way of example, of the above-described different exemplary embodiments in  FIGS. 6 a  to 6 c    is described below with reference to a further exemplary embodiment. The system  1  according to the exemplary embodiment from  FIGS. 1 a  to 2 g    preferably has a further handling robot  61 . The handling robot  61  in particular has an identical design to the first handling robot  103  from the exemplary embodiment of  FIGS. 3 a  to 3 c   . Although there is no need to supply prefabricated stiffening elements from a stocking unit in the system  1 , this handling robot  61  can also advantageously be used in the system  1  by it engaging in the already formed helical stiffening elements  27  in order to stabilize them and hold them in a non-slip manner until the second handling robot  21  has carried out the necessary work of connecting the stiffening elements  27  to the ring elements  13 . 
         [0068]    In  FIGS. 6 b  to 6 c   , further details are shown with respect to the working head  63  of the handling robot  61 , visible in  FIG. 6 a    and designed as a gripping device, which, to simplify the drawing, were omitted in the case of the working head  119  from the exemplary embodiment of  FIGS. 3 a  to 3 c    and similarly in the exemplary embodiment of  FIGS. 4 a  to 4 c   . The coupling device, which has the reference numeral  67  instead of  141 , is arranged on the working head  63  so that it can be shifted by means of an actuator  65 . The supporting section now has the reference numeral  71  and the guide roller the reference numeral  69 . The operating mode of the coupling link is shown by way of example in  FIGS. 6 b  and 6 c   . The gripping device  63  is first brought into the situation shown in  FIG. 6 a   . In this situation, the coupling link  67  shown in  FIG. 6 b    is situated in the “internal area” of a corner of a spiral of the stiffening elements  27 . From this position, a piston rod  75  is extended in the direction of the arrow  73  by means of the actuator  65 . 
         [0069]    According to  FIG. 6 c   , this has the consequence that the guide roller  69  of the coupling link comes to bear against an end area  27   a  of the stiffening element  27  and, when the piston rod  75  continues to move, rolls in the direction of one of the corners caused by the bending. In  FIG. 6 c   , the guide roller  69  has reached the corner  27   b  caused by the bending. The piston rod  75  is displaced so far by means of the actuator  65  that the supporting section  71  arranged at the opposite end of the coupling link  67 , with respect to the guide roller  69 , bears against an substantially vertical section  27   c  of the stiffening element  27 . In this position, the actuator  65  is, by virtue of the piston rod  75  being pushed out further, capable of exerting a spreading force on the stiffening element  27  by means of which the latter is fixed and stabilized. In this position, it is possible for the stiffening elements directly adjacent to the held stiffening element  27 , and including the stiffening element  27  itself, to be connected by the second handling robot  21 . 
         [0070]    For the sake of clarity, a spring return for the coupling link and different sensor means which are part of the system equipment and assist error-free and collision-free operation of the system have not been shown. 
         [0071]    As is apparent from the above embodiments, features which are shown in the respective exemplary embodiments can be combined with one another so that different system components from the different exemplary embodiments can be used to form a common system in a common exemplary embodiment.