Abstract:
The invention relates to an exchange device ( 30 ) for grip heads ( 20 ) comprising a plurality of clamping jaws ( 21 ), consisting of a carrier plate ( 31 ) having a borehole ( 32 ). Pivoting arms ( 33 ) are axially staggered in relation to the carrier plate ( 31 ) and are concentrically arranged in relation to the borehole ( 32 ). Said pivoting arms are articulated by means of a joint ( 34 ) in such a way that they can be pivoted in a plane containing the axis ( 37 ) of the borehole. The pivoting movement is thus carried out radially in relation to the axis of the borehole. Coupling elements ( 35 ) are arranged on the pivoting arms ( 33 ), by which means the exchange device ( 30 ) can be coupled to the clamping jaws ( 21 ) of the grip head ( 20 ) and detached from the same.

Description:
FIELD OF APPLICATION AND PRIOR ART  
         [0001]    The present invention relates to a changing device for closers having several gripping jaws. In connection with lathes it is known to make use of two-part collet chucks. Such collet chucks comprise a draw-in or push-out tube part and a closer. By means of a coupling device the draw-in tube can be coupled axially to the closer and, if necessary, they can be separated from one another.  
           [0002]    Changing devices are known for coupling and uncoupling the closer with respect to the collet chuck.  
           [0003]    A changing device for such closers is e.g. known from DE 28 31 140 C2. A closer changing device described therein comprises a carrier plate with a bore or hole. Swivel arms are articulated by means of a joint to the carrier plate in axially displaced manner with respect thereto and concentric to the bore. The joint is aligned in such a way that the swivel arms can be swivelled in a plane radial to the bore axis. The swivel arms have coupling members for coupling the changing device to the gripping jaws of the closer. Action takes place on the swivel arms by means of an axially movable tension bolt, which traverses the carrier plate.  
           [0004]    The changing device is used for the application thereof to the closer and by means of coupling members a connection is formed between the changing device and the gripping jaws. Actuation then takes place and as a result the connection between the closer and the draw-in tube is released or can be restored again.  
           [0005]    The actuation of the changing device in the embodiment involved e.g. takes place by means of a handwheel. The handwheel is provided on its inside with a thread, whose corresponding element appears on the tension bolt. By turning the handwheel the tension bolt can be drawn further into the carrier plate and removed from the closer. There is a swivelling movement of the swivel arms and therefore an operation of the gripping jaws permitting a release of the closer from the draw-in tube. On turning the handwheel in the opposite direction there is an opposing actuation of the tension rod, which is moved back into its original position. Thus, a release of the changing device from the closer is again possible. The closer is either to be secured again in the draw-in tube or is in a position remote from said tube, so that it can be manually manipulated.  
           [0006]    Besides this form of manual operation of the changing device, there are also various external force actuations, e.g. using pneumatic or hydraulic operating cylinders. Such a pneumatic or hydraulic actuation of the operating cylinder always presupposes that there is a corresponding fluidic external force source with connection possibilities on the particular machine where the changing device is to be used.  
           [0007]    Thus, a manual operation is a simplified variant which can be universally used as compared with such an external force-controlled actuation. Manual actuation is possible independently of the circumstances of the particular machine and no separate power supply connection is required. In the case of manual actuation it is necessary to introduce high actuating forces into the closer in order to permit a release of said closer from the draw-in tube. In the hitherto known manual changing devices such forces have been introduced via a screw thread using a handwheel. This is disadvantageous if for the operation of the device it is necessary to use both hands, e.g. one hand for preparing and holding the device and the other for operating the handwheel. It is also often unfavourable to perform rotary movements in the interior of the machine area. This more particularly applies with multi-spindle machines, where numerous tools project into the machine area and where the spatial arrangement of the closers for the chucking of workpieces is restricted.  
           [0008]    Problem and Solution  
           [0009]    The problem of the invention is to provide a changing device of the aforementioned type, which permits simplified operation and greater operating safety.  
           [0010]    This problem is solved by a changing device having the features of claim  1 . Advantageous and preferred developments of the invention form the subject matter of the further claims and are explained in detail hereinafter. By express reference the wording of the claims is made into part of the content of the description.  
           [0011]    A changing device for closers with several gripping jaws according to the invention comprises a carrier plate with a bore. Swivel arms are arranged concentrically to the bore in axially displaced manner relative to the carrier plate. They are articulated by means of a joint in such a way that they are swivellable in a plane comprising the bore axis, the swivelling movement taking place radially to said bore axis. On the swivel arms are provided coupling members by means of which the changing device can be coupled to and then detached from the gripping jaws of the closer. In addition, the changing device has an axially movable tension bolt located in the carrier plate bore and which engages on the swivel arms. Thus, the radial swivelling position of the swivel arms is influenced by means of the tension bolt position.  
           [0012]    Operating levers are provided for manually operating the changing device. A first operating lever is fixed with respect to the carrier plate. The second operating lever is arranged in rotary manner with respect to the first lever and engages at least indirectly on the tension bolt.  
           [0013]    According to a preferred development the operating levers can be transferred from a starting position into an operating end position. In the starting position the operating levers are spaced far apart. They are in particular so far apart that they can just be grasped with one or both hands. The operating levers can be transferred into an operating end position, where they are adjacent to one another.  
           [0014]    The transfer of the operating levers from the starting position into the operating end position can take place through a relative movement of the second operating lever with respect to the first operating lever. In the starting position of the manually operable operating levers, the changing device can be engaged with the closer by means of coupling members and said engagement can be removed again. Thus, in the starting position of the operating levers the changing device can be applied to or released from the closer. In the operating end position of the operating levers an engagement on the closer is possible in such a way that it can be coupled to or uncoupled from a machine-side holder and generally the closer is held on the draw-in tube.  
           [0015]    The connection between the closer and the machine-side holder can be in the form of a groove made in the latter and behind which engage the corresponding retaining tongues on the individual gripping jaws of the closer. This engaging-behind connection is preferably cancelled out through the gripping jaws being moved relative to one another. There is an elastic deformation of the elastomeric material connecting the gripping jaws in the vicinity of the slots between the latter.  
           [0016]    According to an advantageous development of the invention the second operating lever can be rotated about a rotation axis parallel to the bore with respect to the first operating lever. The second operating lever can in particular be rotated coaxially to the bore. According to a preferred development the second operating lever is constructed in projecting manner on a swivel, which is supported by means of at least two levers at least indirectly on the carrier plate. The levers are used for guiding the rotary movement and for producing an axial displacement path of the tension bolt relative to the carrier plate when an operation of the operating lever takes place.  
           [0017]    There are in particular three levers. They are preferably positioned equidistantly and uniformly relative to the bore centre axis. In particular, the levers can have on each of their two ends a ball end, which is held in a corresponding cup in the carrier plate or the swivel.  
           [0018]    According to a further development the two ends of the levers are held in such a way that on operating the operating levers out of the starting position in the direction of the operating end position they tilt up and increase the spacing between the carrier plate and the swivel. The tension bolt, which is in particular fixed to the swivel, effects a translatory movement relative to the bore in the carrier plate. A swivelling of the swivel arms is produced by this movement of the tension bolt.  
           [0019]    According to another development the second operating lever is rotatable about a rotation axis perpendicular to the bore axis with respect to the first operating lever. Between the first and second operating levers there can in particular be a toggle lever arrangement. The toggle lever arrangement more particularly guides the operating movement of the second operating lever relative to the first operating lever, which is fixed with respect to the carrier plate. Preferably the first operating lever projects radially from a pipe section arranged on the carrier plate in the axial extension of the bore.  
           [0020]    A toggle lever arrangement preferably has two toggle lever arms. The second operating lever is connected by means of the longer of the two lever arms to the tension bolt. According to a development of the invention a sleeve is inserted in the bore. The tension bolt projects into the pipe section and has two parallel, diametrically facing elongated holes, together with a recess in the intermediate area. The tension bolt is longitudinally displaced arranged in the pipe section with respect to the king pin. The king pin traverses the second operating lever at a certain distance from the bearing opening of the longer lever arm. This spacing forms the shorter lever arm of the toggle lever arrangement. In such an arrangement the second operating lever is on the one hand guided by the construction of the elongated holes in the sleeve and on the other by means of the longer lever arm with respect to the pipe section is secured in an area fixed relative to the carrier plate. This fixes the swivelling movement of the second operating lever relative to the first operating lever.  
           [0021]    A sleeve insertable in the pipe section is secured in the latter in order to guide a safety bolt relative to its own longitudinal axis and the tension bolt within the pipe section. According to a preferred development said safety bolt simultaneously constitutes the pivot bearing of the longer operating lever on the tension bolt.  
           [0022]    It is also possible for the second operating lever to be supported on the inner face of the sleeve by means of a rounded rolling edge.  
           [0023]    With toggle lever arrangements it is advantageous if the three swivel axes of the arrangement are at least approximately in one plane in the operating end position. This plane is preferably in the median plane of the elongated holes of the toggle lever arrangement.  
           [0024]    It is possible in all the arrangements to provide a return spring between the first and second operating levers and which acts on the second lever in such a way that it automatically moves back into the starting position. It is also possible for the swivel lever to be supported only in the pull direction, i.e. the force introduction direction, by forces from the operating levers on the tension bolt, i.e. the tension bolt is supported there both in the pull and push directions. Supporting in both directions makes it possible on retracting the operating levers into the starting position to move the swivel levers back into the starting position in which they can be coupled to corresponding closers. For fixing the starting position of the swivel levers a support on the tension bolt in the push and pull directions is unnecessary if corresponding restoring means are provided between the swivel levers and carrier plate. These restoring means can simultaneously serve as restoring means for the operating levers, because they act back indirectly on the operating means by means of the operating bolts. They are also suitable to restore the original starting position.  
           [0025]    These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    The invention is illustrated further hereinafter by embodiments and the attached drawings, wherein show:  
         [0027]    FIGS.  1  to  4  In each case side and plan views of a first embodiment of an inventive changing device, which is coupled to a closer.  
         [0028]    [0028]FIGS. 5 and 6 Part sectional representations of a second embodiment of an inventive changing device in the unoperated and operated positions of said device without showing the closer. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0029]    [0029]FIGS. 1 and 2 show in an unoperated starting position a first embodiment of a changing device  30 . FIGS. 3 and 4 show the same changing device  30  in the operating end position. The upper half of the drawing in each case shows a part sectional, diagrammatic side view in the case of FIGS. 1 and 3, whereas in the lower drawing half in FIGS. 2 and 4 is shown the plan view also in the form of a diagrammatic, part sectional representation.  
         [0030]    The changing device  30  is coupled to a closer  20 . The closer  20  comprises several gripping jaws  21  separated from one another by slots  22 . Connecting bodies  23  are placed in the slots  22 . The connecting bodies  23  are made from elastically deformable material, particularly rubber-like, deformable material, such as e.g. natural and artificial rubbers with different additives influencing the material characteristics or colour. The connecting bodies can be positively and/or non-positively fixed to the two adjacent gripping jaws  21  by bonding and/or vulcanizing, but also by means of other fastening procedures. The connecting bodies  23  can fill all the slots  22 , so that to the outside a body with a closed contour line is formed.  
         [0031]    To be able to couple a changing device  30  to the closer  20 , the latter has several receptacles  24  for coupling members. At least one receptacle  24  for a coupling member is provided for each clamping or gripping jaw  21 . The receptacles  24  are here provided on the workpiece-receiving side of the closer. The free end face of the closer  20  is particularly suitable.  
         [0032]    For the machine-side fastening of the closer, e.g. in a draw-in tube, the closer  20  has an all-round groove  25 , which in particular serves for the positive, axial and radial holding of the closer on the draw-in tube. The collet chuck is formed by the closer and the draw-in tube.  
         [0033]    In the starting position shown in FIGS. 1 and 2 the closer  20  is in its assembly or storage state. The connecting bodies  23  are in a starting state in which the opposing forces compensate one another. On mounting the closer  20  on a draw-in tube there is a positive engagement behind of the groove  25  of closer  20 . As a result the closer is at least axially held in the draw-in tube. FIGS. 3 and 4 show the position where the changing device  30  is in the operating end position. Through elastic deformation of the connecting bodies  23 , which in particular reduces the outer circumference of the closer  20  in the vicinity of the groove  25 , the positive connection between the closer  20  and draw-in tube is released. Thus, the closer  20  can be removed from or inserted in the draw-in tube.  
         [0034]    In order to carry out the operation of the closer, the changing device  30  is provided. The changing device serves to release the positive connection between the closer  20  and the draw-in tube, as well as for handling the closer  20  when it has been released from the draw-in tube.  
         [0035]    The changing device  30  can be coupled to the closer  20  by coupling members  35 . In the embodiment shown here the coupling members  35  are constructed as lugs, which can be introduced into receptacles in the form of bores  24 .  
         [0036]    In the starting position shown in FIGS. 1 and 2, the coupling members  35  project axially from the swivel arms  33  in the direction of the closer  20 . The swivel arms  33  are held by means of joints  34  on the carrier plate  31 . The rotation axis  34  of each swivel arm  33  is positioned on the radial outside relative to a bore  32  in the carrier plate  31 . The rotation axis of a joint  34  is tangential to the bore. This makes it possible to swivel the swivel arms in a plane containing the bore centre axis  37 . They can therefore be swivelled radially to the bore axis.  
         [0037]    The carrier plate  31  is traversed by the bore  32  in which is held in guided manner the tension bolt  36 . In the manner shown in FIGS.  1  to  4 , the tension bolt  36  can be a built-up part comprising a cylindrical shaft and a cover projecting radially outwards from said shaft. The tension bolt  36  traverses the carrier plate and with the cover engages behind the swivel arms  33 . Through the back-engagement of the swivel arms, it is possible by means of the tension bolt  36  to exert tensile forces on the swivel arms  33 , so that the coupling members  35  are swivelled about the joints  34  and are inclined inwards towards the bore centre axis  37 . The swivelling movement leads to the leaving of the starting position shown in FIGS. 1 and 2 until the operating end position shown in FIGS. 3 and 4 is reached. Counter to the action of the rubber-like deformation of the connecting members  23 , there is a deformation of the closer  20 , which permits the release of the closer from the draw-in tube. The deforming forces introduced into the connecting bodies act as restoring forces, so that by means thereof a return from the operating end position of FIGS. 3 and 4 to the starting position of FIG. 1 takes place. In the case of such a swivelling back, the swivel arms  33  introduce the forces from the closer  20  into the changing device  30  and the tension bolt is moved back into the starting position of FIG. 1 by its back engagement of the swivel arms  33 .  
         [0038]    So that this return movement also takes place when no closer  20  is coupled to the changing device  30 , it is possible to provide corresponding return springs. This makes it possible to construct the return springs between the two operating means, namely the two operating levers  38 ,  39 . It is also possible to place corresponding return springs between the swivel arms  33  and the carrier plate  31 . In order to bring about a good leverage for the restoring force, it is advantageous to position the corresponding return springs as close as possible to the bore  32 .  
         [0039]    An abutment  41  is formed on the back of the carrier plate  31  remote from the receptacle for the closer  20 . The abutment is constructed as a fixed disk located on the carrier plate  31  and which also has a bore  32 . The abutment  41  comprises a cylindrical body in which are shaped joint cups  46 . Ball ends  45  of levers  44  are mounted in said joint cups  46 . According to the invention there are three regularly spaced levers. In addition, the abutment  41  and swivel  43  have grooves, in which can come to rest the levers  44  when the swivel  43  and abutment  41  are mutually engaged, as is the case in the starting position shown in FIGS. 1 and 3/ 4 . The grooves run substantially tangentially to the bore centre axis.  
         [0040]    The facing ends of the levers  44  also have ball ends  45  held in joint cups  46 , which are constructed on the swivel  43 . The swivel  43  is held indirectly on the carrier plate  31  by the levers  44 . The number and arrangement of the levers are determined in such a way that the swivel  43  can be swivelled about the bore centre axis  37  relative to the carrier plate  31 . However, with said swivelling movement is forcibly coupled an axial movement with respect to this axis. In order to permit such a guiding holding of the swivel with respect to the carrier plate  31  by means of levers  44  alone, it is advantageous if there are at least three levers. The number of levers can also be reduced, but then possibly further guidance means are needed. It must be borne in mind that the tension bolt  36  also traverses the swivel  43 , because the swivel  43  also has a corresponding bore and to this extent said tension bolt can also fulfil certain guidance functions. However, it is still advantageous to provide three or an even larger number of levers  44 . In this case the degrees of freedom of the swivel  43  relative to the carrier plate  31  are adequately determined by the levers  44  alone.  
         [0041]    The first operating lever  38  is at least indirectly held in fixed manner on the carrier plate  31  of the changing device  30  and projects substantially radially outwardly from the carrier plate  31  and can be ergonomically shaped to obtain good gripping characteristics. The second operating lever  39  is firmly connected to the swivel  43  and in the starting position of FIGS. 1 and 2 projects under a certain angle in the radial direction from the swivel  43  with respect to the first operating lever  38 . The angle between the two operating levers  38 ,  39  is upwardly limited in that the two levers  38 ,  39  must be graspable by one hand in order to allow a one-handed operation and a one-handed manipulation of the changing device  30 . The second operating lever  39  can also be ergonomically shaped with regards to its gripping characteristics. It is in particular possible to adopt shapes such as are used for gripping pliers.  
         [0042]    With regards to the useability of the changing device  30  with both the left and right hands, it can be advantageous for the shape of the two levers to be the same. The choice of hand is not only dependent on the user and his habits, but also on the accessibility within the machine area.  
         [0043]    On carrying out an operation of the changing device  30 , there is a relative movement between the first and second operating levers due to the operating forces manually introduced by the user. The relative movement between the two operating levers  38 ,  39  initiated by the operating forces leads to an identical relative movement of the swivel  43  with respect to the carrier plate  31  with the abutment  41 . It is a rotary movement about the bore centre axis  37 , which consequently also defines the rotation axis  40  between the swivel and the carrier plate  31 . In this case the rotation axis  40  and bore centre axis  37  are not only oriented coaxially to one another, but in fact correspond with one another.  
         [0044]    As a result of the rotary movement and the supporting of the levers  44  in bilaterally positioned joint cups, there is a tilting up of the levers  44  between abutment  41  and swivel  43 . This increases the axial spacing between these two parts with respect to the rotation axis  40 . As, at least in the axial direction, the tension bolt  36  is held in fixed manner on the swivel  43 , there is also an axial displacement of the tension bolt in the bore  32 . The tension bolt is drawn away from the closer  30 , e.g. through the axial tension bolt head  42  engaging over the swivel  43 . Through the coupling of the tension bolt  36  with the swivel arms  33 , a swivelling movement of said arms is brought about. There is a transition from the starting position shown in FIGS. 1 and 2 into the operating end position shown in FIGS. 3 and 4. The operating end position of FIGS. 3 and 4 reveal the first operating lever  38  and the second operating lever  39  in a position where they are immediately adjacent to and engage with one another, provided that this is permitted by their shaping.  
         [0045]    Such a construction with a pivot bearing and levers  44  tilting over the same can be gathered from FIGS. 3 and 4, where the levers  44  are aligned as coaxially as possible with the rotation axis  40  in the operating end position. Thus, if the forces opposing operation, namely the deformation forces for the rubber-like connecting bodies  23 , are at a maximum, there is a maximum leverage between the swivel  43  and abutment  41  via levers  44 . Thus, the necessary operating forces for operating the two operating levers  38 ,  39  remain within appropriate limits. The power ratio and power path are significantly co-determined by means of the length of the levers  44 . Thus, in accordance with circumstances and the necessary forces, adaptation takes place to the conditions for each individual changing device.  
         [0046]    [0046]FIGS. 5 and 6 show a second embodiment of the changing device  30  according to the invention. In the embodiment according to FIGS. 5 and 6 the rotation axis  40  of the second operating lever  39  is not coaxial to the bore centre axis  37 , but instead perpendicular thereto, relative to the first operating lever  38 .  
         [0047]    In the embodiments according to FIGS. 5 and 6 the design of the carrier plate  31  and swivel arms  33 , together with the use of the latter by means of joints  34  on carrier plate  31  essentially correspond to the embodiment according to FIGS.  1  to  4 , so that a further description will not be given. The coupling members  35  constructed as lugs also correspond to the coupling pieces of FIGS.  1  to  4 . To illustrate the swivelling movement and for simplifying study, the closer  20  is not shown in FIGS. 5 and 6. However, the changing device  30  according to FIGS. 5 and 6 is suitable for use in connection with closers, which correspond to the closers  20  shown in FIGS.  1  to  4 . FIG. 5 again shows the unoperated starting position and FIG. 6 the corresponding operating end position of the changing device  30 . Both drawings are part sectional, diagrammatic representations of a corresponding changing device.  
         [0048]    A cylindrically constructed, high section  51  projects from the back of the carrier plate  31  remote from the swivel arms  33 . A sleeve  54  is located in the interior of the pipe section, which is positioned concentrically to the bore  32  in carrier plate  31 . It is closed at its rear end remote from the carrier plate  31 . The sleeve  54  is located in the interior of the pipe section  51 . The wall thickness of the sleeve  54  and the internal diameter of the pipe section  51  are such that the internal diameter of sleeve  54  corresponds to the diameter of bore  32 . In the vicinity of the carrier plate can be provided a widening  61  of the bore  32 , so that the internal diameter in the vicinity of the widening  61  corresponds to the internal diameter of the pipe section  51 . Thus, the sleeve  54  can project into the vicinity of the widening  61 .  
         [0049]    On one side of the pipe section  51  and in a substantially radially projecting manner is provided a first operating lever  38 . The latter is in particular shaped in such a way that a particularly good engagement is provided in the hand in the area between thumb and hand surface. In the area between the carrier plate  31  and the first operating lever  38 , the pipe section  51  has an opening  63 , which is in particular in slot form. The second operating lever  39  passes through said opening  63  into the interior of the sleeve  54 , which for this purpose has a slot  62  in this area. The second operating lever  39  is held by the toggle lever arrangement  50  and can be swivelled about a rotation axis perpendicular to the drawing plane with respect to the first operating lever. The second lever is in particular constructed in such a way that it can be grasped in an ergonomically favourable manner by the fingers of one hand, whose thumb engages behind the first operating lever  38 .  
         [0050]    The toggle lever arrangement  50  comprises three fulcrum or rotation points. There is firstly the rotation axis fixed by the safety bolt  58 , which also forms the rotation centre of the longer of the two lever arms  52  on the safety bolt  58 . At the other end of the longer lever arm  52  the bearing opening  57  produces a rotary connection between the longer lever arm  52  and the second operating lever  39 . The shorter lever arm  53  is defined by the spacing b between the bearing opening  57  and the king pin  56  and is part of the second operating lever  39 . The king pin  56  traverses the diametrically facing elongated holes  55  of the tension bolt  36 . The king pin  56  defines a rotation point fixed with respect to the pipe section  51 , because it is constructed in such a way that it traverses both the sleeve  54  and pipe section  51  in corresponding bores and therefore fixes the position relative to the pipe section  51 . The king pin projecting through the elongated holes  55  limits the maximum path of the tension bolt  36  in the pipe section  51  and consequently defines the starting position and operating end position. The second operating lever projects into the recess  65  which is constructed for this purpose in the tension bolt  36  and with respect to which the elongated holes  55  are laterally positioned.  
         [0051]    In order to obtain a clearly defined operating starting position for the second operating lever  39 , between the latter and the carrier plate  31  or a component fixed with respect thereto the return spring  60  is provided. The latter draws the second operating lever  39  into a position in which it is far removed from the first operating lever  38 , but should still be grippable with one hand. As a result of the coupling between the second operating lever  39  and the tension bolt  36  by means of the king pin  56  guided in the elongated hole  55 , there is a clearly defined position of the swivel arms  33 . The swivel arms  33  are so held in the diameter-reduced area of the tension bolt that to the same can be transferred both tension and tensile forces. The tension bolt  36  has in the vicinity of the swivel arms  33  a section whose external diameter is smaller than the external diameter in the vicinity of the bore  32  in carrier plate  31  in which tension bolt  36  is held in guided manner. Following the area over and beyond which the swivel arms  33  can be bilaterally embraced by the king pin, a cover  64  is provided, which again increases to the original amount the external diameter of the tension bolt. The swivel arms  33  are so held between the parts of the tension bolt  36  that it is able to transfer to the latter both push and pull forces. The cover  64  can in particular be the head of a screw or a head part detachably fixed on the tension bolt by means of a screw.  
         [0052]    If there is a transfer of the second operating lever  39  in the direction of the operating end position shown in FIG. 6, the second operating lever is swivelled about its rotation centre defined by the king pin  56 . As a result of the spacing b formed by the shorter lever arm  53  of the toggle lever arrangement  50  and the guidance of the tension bolt  36  in pipe section  51  or in sleeve  54 , the safety bolt  58 , by means of which the free end of the longer lever arm  52  is fixed to the tension bolt  36 , is rearwardly pressed away from the closer  20 . The toggle lever arrangement extends into a position in which the three swivel axes of said arrangement are approximately in one plane. This is in particular the median plane of the elongated hole  55 . In this operating end position as shown in FIG. 6, the second operating lever almost completely engages on the first operating lever. Thus, during operation the tension bolt  36  is shoved rearwards. The most favourable lever transmission which most increases the leverage between the first and second operating levers is obtained when the operating end position is at least approximately reached. It is here that the greatest restoring forces from the closer act on the changing device and the swivel arms  33 . To ensure the return of the second operating lever into the starting position shown in FIG. 5, the return spring  62 , which can be constructed as a tension spring, is connected between the second operating lever  39  and carrier plate  31  or a component fixed with respect thereto. During the return movement the tension bolt  36  again slides forward in the pipe section  56 . Due to the fact that the swivel arms  33  are in engagement with the tension bolt  36  in both the push and pull directions, the swivel arms  33  are returned to their starting position in which they can be coupled to and uncoupled from the closer  20 . In the operating end position shown in FIG. 6, the swivel arms  33  are so swivelled about the joint  34  with a radial component that the tips of the coupling members  35 , constructed as stay bolts, move towards one another. Thus, they perform a corresponding movement moving the gripping jaws of a closer towards one another, such as is also produced with the changing device according to FIGS.  1  to  4 .