BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention refers to a coupling device having two coupling parts and clamping means for releasably axial clamping of both coupling parts. A number of non parallel grooves spaced circumferentially are provided within one of both coupling parts as a reference system in a plane perpendicular to the clamping direction. Pins projecting from the surface of the other coupling part and having two opposing lateral surfaces are provided. At least one of the lateral surfaces of each pin includes an angle with the clamping direction.  
           [0003]    2. Description of Related Art  
           [0004]    In case one of the coupling parts is connected to the head of a machine tool, e.g. an EDM machine, and the other coupling part supports a work piece to be worked upon by the machine, the work piece may be positioned relative to the machine with very high precision within a plane (x-y-plane) perpendicular to the clamping direction (z-direction). The positional deviation amounts to only a few μm even after a very great number of clamping procedures and releasing procedures for the work piece and its coupling part. Such high position is achieved with a coupling device according to EP-A-722 809 (=U.S. Pat. No. 5,791,803) by creating a force acting circumferentially upon the coupling part during clamping.  
           [0005]    A counterforce created when machining the workpiece, e.g. when producing a deep recess within the work piece by a lathe, may counteract to such force which may impair maintaining the close positional tolerance.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention therefore is based on the object to improve the repeatability precision of the positioning of one coupling part relative to the other coupling part under high load of one of the coupling parts in circumferential direction.  
           [0007]    To this end the invention provides for a coupling device according to the above-mentioned type within which at least one clamping plate is disposed at one of the coupling parts such that during clamping it is clamped between one of the lateral surfaces of one of the pins and a flank of a groove cooperating with the pin for obtaining the desired adjustment of both coupling parts. The coupling device according to the invention allows therefore not only for an excellent repeatability of the precise positioning of the coupling parts with respect to each other but exhibits substantial stiffness of the alignment under heavy load which is limited only by the compressibility of the material of the clamping plate.  
           [0008]    In a preferred embodiment of the invention the clamping plate is fixedly connected to the coupling part and preferably is integral therewith. Advantageously the clamping plate has a first section extending parallel to the clamping direction, and a second axially elastic section mounted to the associated coupling part.  
           [0009]    In an aspect of the invention two clamping plates are provided the second sections of which are combined by a connecting base to form an overall U form configuration. According to one embodiment the base is mounted to a pin of a coupling part from which said pin projects. In an alternative the base is mounted to the bottom of a groove in a coupling part into which the grooves are cut. To this end the bottom may have a projection to which the base is mounted centrally.  
           [0010]    According to another aspect of the invention the groove may be extended inwardly and laterally by an undercut. In such case the clamping plate may be made by driving a cut into the body of the coupling part such that the first section of the clamping plate extends in clamping direction and the elastic second section therof extends transversely into the undercut.  
           [0011]    Releasing the clamped coupling parts is simplified if according to another aspect of the invention the flanks of the grooves and/or the pins and/or the clamping plates are provided with hardened surfaces. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention is hereinafter described in detail with reference to the attached drawings with show some embodiments of the invention.  
         [0013]    [0013]FIG. 1 shows a schematic representation of a first embodiment of a coupling device, the coupling parts being separate from each other;  
         [0014]    [0014]FIG. 2 a schematic representation of the first embodiment wherein the coupling parts are clamped;  
         [0015]    [0015]FIG. 3 a schematic representation of a second embodiment of the coupling device;  
         [0016]    [0016]FIG. 4 a schematic representation of a third embodiment of the invention;  
         [0017]    [0017]FIG. 5 a schematic representation of a fourth embodiment of the invention, and  
         [0018]    [0018]FIG. 6 a schematic representation of a detail according to a fifth embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The first coupling part  1  from which only the front section is represented may be mounted centrally to a not shown spindle head of a lathe. Normally, three posts of same length and equally spaced in circumferential direction project from the free end surface  2  of the coupling part  1 . In the drawings only two posts  4 ,  6  are shown. The end surface  5 ,  7  of each post  4 ,  6  is made plane. All end surfaces  5 ,  7  extend within one common x-y-plane which is perpendicularly to the rotational axis  10  usually designated as z-axis. All posts are arranged around the z-axis along an imaginary circle The flat surface  22  of the removable coupling part  20  has areas  25 ,  27  which are arranged in correspondence with the arrangement of the posts  4 ,  6  of coupling part  1  and are made such that all areas extend within a common x-y-plane. Thus, clamping of coupling parts  1 ,  20  is performed when under the influence of the not shown clamping means all surfaces  5 ,  7  abut all the corresponding areas  25 ,  27 .  
         [0020]    A not shown axial and central throughbore is provided in the center of the coupling part  1  for allowing passage of a drawbar which is a portion of usual clamping means for both coupling parts.  
         [0021]    Approximately in the middle in circumferential direction between adjacent posts a pin  3  projects from the end surface  2  in z-direction and has a length which is a little bit greater than the length of each of the posts  4 ,  6 . The pin  3  is provided with a prismatic and hardened reference surface  8  which extends parallel to a radius of the imaginary circle. Similar reference surfaces are provided on everyone of the not shown further pins at the positionally same side thereof. Thus, reference surface  8  includes a small angle with the z-axis  10 .  
         [0022]    The second removable coupling part  20  is adapted to support a not shown work piece to be machined by the lathe or a similar machine tool to which the first coupling part is mounted, the work piece being fixed to the underside  21  of the second coupling part  20 .  
         [0023]    In circumferential direction equally spaced grooves each extending parallel to a radius of the imaginary circle, are cut into the upper side  22  of the second coupling part  20 . The number of grooves equals the number of pins  3 . In the drawing only the groove  24  is shown which faces the pin  3  upon clamping. It may be noted that all grooves are formed similarly to the groove  24  so that only the latter is described in detail. The groove  24  has two opposing flanks  28 ,  32  extending parallel to the radius. Flank  28  is associated to a lateral surface  9  of pin  3  which is opposite to the reference surface  8  with respect to pin  3 . Flank  32  is associated to reference surface  8 . Opposite to the flank  28  the groove  24  is extended laterally and inwardly by an undercut  23  the bottom of which is flush with the bottom  29  of the groove. An incision  11  made e.g. by an electric erosion wire is cut into the coupling part  20  in proximity to the flank  32  of the groove  24 . The depth of the incision  11  is made over a substantial portion of the depth of the groove and is turned by a rectangular angle in form of a cut  12  which extends substantially parallel to the upper side  22 . As shown the cut  12  terminates in proximity to the lateral end of undercut  23 . Thereby, the flank  32  facing flank  28  of the groove  24  is formed to a clamping plate  35  integral with coupling part  20  which has a somewhat angular cross-section. Thus, the clamping plate has an upper first section  34  extending substantially parallel to the z-direction, and an adjoining second section  36  extending substantially transverse to the z-direction along the undercut  23 . So the second section  36  is axially elastic because of its connection to the coupling part  20  at one end thereof. Thus, first section  34  is movable axially elastically and substantially parallel to flank  28 , i.e. in z-direction.  
         [0024]    In the course of clamping both coupling parts  1 ,  20  by the not shown clamping means the pin  3  penetrates the groove  24  until the reference surface  8  engages the upper free edge of the clamping plate  35 . Simultaneously an adjustment of the second coupling part  20  relative to the first coupling part  1  is obtained within the x-y-plane. Upon further tightening the clamping means pin  3  continues to penetrate the groove  24  and pushes downwardly the clamping  35  according to the enlarged detailed representation of FIG. 2 thereby bending inwardly the second section  36  of the clamping plate  35  into the space of the undercut  23 . In the course of such downward pushing the pin  3  will clamp the clamping plate  35  substantially at that instant when the end surfaces  5 ,  7  abut areas  25 ,  27 .  
         [0025]    The adjustment of the coupling part  20  relative to coupling part  1  within the x-y-plane after clamping will be kept also in the event a very high force is applied to the coupling part  20  in both circumferential directions. The abutment of lateral surface  9  to flank  28  after adjustment takes place without elasticity because no elastic member is coupled inbetween. Moreover, the clamping of the reference surface  8  to the clamping plate  35  does not exhibit any lateral yield because the clamping plate  35  is elastic only in z-direction and incompressible in circumferential direction.  
         [0026]    Both flanks  26  and  32  have hardened surfaces in order to ease release of the clamped coupling parts and to improve the axial yield of the clamping plate  35 .  
         [0027]    The second embodiment of the invention shown in FIG. 3 does not deviate from the above explained embodiment with respect to the reference elements for adjusting the movable coupling part relative to the machine coupling part in z-direction. On the other hand, the coupling part  50  connected to the machine is provided with a number of pins  52  similar to the coupling part  1  which are provided on either sides with prismatic reference surfaces  54 ,  56  which are parallel to the radius. Grooves  64  are cut into the movable coupling part  60  in correspondence to the positions of the pins  52 . The bottom  63  of groove  64  has a central projection  62 . An insert  70  having a U-formed cross section is held within the groove  64  by fixing the base  72  of the insert  70  to the projection  62 . The opposing legs  76 ,  78  of the insert  70  abut the opposing flanks  66 ,  68  of groove  64 . According to FIG. 3 the base  72  of the groove  64  has end portions  71 ,  73  which are suspended over the bottom  63  of groove  64 . Base  72  consists of an elastic material so that the upright legs  76 ,  78  may yield axially under influence of a force directed in clamping direction.  
         [0028]    Thus, legs  76  and end section  71  as well as leg  78  with end section  73  each function as a clamping plate similar to the first embodiment of the invention. Both clamping plates are connected to the coupling part  60  through their common base  72 . Therefore, the functional behaviour of both clamping plates upon clamping is the same as explained above.  
         [0029]    The third embodiment of the invention according to FIG. 4 deviates from the above substantially therein that the clamping plate  45  is mounted to the first coupling part  40  which supports pins  42  having opposite lateral surfaces  44 ,  46  parallel to the axis. The clamping plate  45  may be cut by electric wire erosion out of the body of the coupling part  40  or may be exchangeably mounted to the coupling part  40  by not shown screws. The clamping plate  45  consists of a block  41  connected to the coupling part  40  and of a second section  43  extending towards the lateral surface  44  and being axially elastic. The second section  43  continues into a first vertical section  47  abutting the lateral surfaces  44  and being vertically movable.  
         [0030]    The flank  31  of the groove  38  within the second coupling part  30  which is associated to the lateral surface  44  is sloped downwardly and inwardly so that it forms a small angle with the lateral surface  44  upon clamping. The opposite flank  33  of groove  38  is parallel to the axis and forms a reference for abutment to the lateral surface  46  for positioning the coupling parts  30 ,  40  with respect to each other within an x-y-plane.  
         [0031]    Upon clamping both coupling parts  30 ,  40 , the pin  42  penetrates the associated groove  38  until the lower outer edge of the first section  47  engages flank  31 . The first section  47  clamps between flank  31  and lateral surface  44  when the pin  42  continues to penetrate to the effect that the lateral surface  46  is urged against flank  33 . If the pin  42  continues to penetrate a movement of section  47  along the pin  42  will take place which is possible by the axial elasticity of the second section  43 . The penetration terminates when both coupling parts  30 ,  40  reach the exact z-position (abutment of posts  48 ,  49  of coupling part  40  upon the surface  39  of coupling part  30 ).  
         [0032]    In a third embodiment of the invention shown in FIG. 5 the pin  82  of the first coupling part  80  is surrounded by an annex  85  which may be mounted to a surface  84  of pin  82  at a position marked by a cross. The first section  81  of a first clamping plate  86  extends from such annex  85  along the lateral surface  92  of pin  82  and a first section  87  of a further clamping plate  88  extends from annex  85  along the lateral surface  96  of pin  82  parallel and opposite to surface  92 . Both sections  81  and  87  are vertically movable. First section  87  of clamping plate  88  is connected to the first section  81  of clamping plate  86  through second sections  89  and  83  which extend laterally and axially elastically from both ends of a thickened base mounted to surface  84 . The groove  94  associated to the pin  82  has two opposing flanks  91 ,  93  of which the flank  91  is associated to the lateral surface  92  and the flank  93  is associated to the lateral surface  96 . Everyone of both flanks  91 ,  93  is slightly sloped downwardly and inwardly to form a small angle with the z-axis.  
         [0033]    Upon clamping both coupling parts  80 ,  90 , the pin  82  penetrates the groove  94  so that the outer lower edge of first section  81  engages flank  91  and the outer lower edge of first section  87  engages the flank  93 . The groove  94  is thereby centrally adjusted with respect to pin  82 . As shown the first sections  81 ,  87  are clamped and upon further penetration of pin  82  may shift upwardly relative to the pin  82  because of the axial elasticity of the second sections  83 ,  89  of the clamping plates  86 ,  88  as shown in the enlarged detailed representation of FIG. 5. The penetration of pin  82  is terminated when the posts  98 ,  99  projecting from the coupling part  80  abut the upper surface  95  of the coupling part  90  and thus the z-positioning is reached.  
         [0034]    The fifth embodiment of the invention according to FIG. 6 deviates from the second embodiment according to FIG. 3 mainly by modifying the insert  70  thereof which now has a different form and operational behaviour. Only the groove  64   a  of coupling part  60   a  with insert  70   a  is specifically described because the further grooves are structured in the same manner. A projection  62   a  is formed from the bottom  63   a  of the groove  64   a  and the center thereof upon which the base of the insert  70   a  is mounted. The opposing flanks  66   a  and  68   a  of the groove  64   a  extend parallel to the z-axis.  
         [0035]    The insert  70   a  has two opposing legs  76   a  and  78   a.  Only the upper section  77   a,    79   a,  respectively of the legs  76   a,    78   a  which terminate in proximity to the surface of the movable coupling part  60   a  abut or almost abut the adjacent flanks  66   a  and  68   a.  The inner section  73   a  and  75   a  of the legs  76   a  and  78   a,  respectively connecting the upper section  77   a  and  79   a  to the base  72   a  of the insert  70   a  is buckled at  69   a,    71   a,  respectively towards the opposing leg  78   a  and  76   a.  At least the inner section  73   a  and  75   a  is made from spring steel, in any case is axially yieldable.  
         [0036]    Each pin projecting from the underside of the other coupling part  50   a  (only pin  52   a  associated to the groove  64   a  is represented in FIG. 6) comprises two opposite prismatic surfaces  54   a  and  56   a  which are parallel to the radius of the imaginary circle, and include an angle with the z-axis.  
         [0037]    When pin  52   a  penetrates in the groove  64   a  upon clamping of the coupling parts  50   a  and  60   a  the prismatic lateral surfaces  54   a,    56   a  engage the upper inner edge of each upper section  77   a,    79   a  and adjust the groove  64   a  (and thereby the coupling part  60   a ) to the coupling part  50   a.  When continuing clamping the pin  52   a  shifts the upper section  76   a,    78   a  which now abut flanks  66   a,    68   a  into the groove  64   a  until the mentioned posts of the coupling part  50   a  abut the upper surface of coupling part  60   a.  Simultaneously the inner sections  73   a  and  75   a  buckle at  69   a  and  71   a  elastically. The legs  76   a  and  78   a  remain clamped between pin  52   a  and flanks  66   a  and  68   a.  Thus, each leg  76   a  and  78   a  forms a clamping plate which is axially elastical by forming inwardly extending buckles  69   a,    71   a  thereon.  
         [0038]    According to FIG. 6 the base  72   a  of insert  70   a  is screwed upon projection  62   a.  Thus, by removing the screw insert  70   a  may be exchanged by another similar insert which again may be screwed upon projection  62   a.
Disclosed is a coupling device having two coupling parts and clamping means for releasably axially clamping both coupling parts. A plurality of circumferentially spaced non parallel grooves are cut into the surface of one of both coupling parts for having a reference in a plane perpendicular to the clamping direction. Pins project from the surface of the other coupling part each pin having two opposing parallel lateral surfaces for obtaining alignment of the grooves with the pins upon clamping. At least one of the lateral surfaces of each pin forms an angle with the associated flank of each groove upon axial alignment of the coupling parts. For improving the repeated precision of the positioning of one of the coupling parts relative to the other coupling part even upon high stress on one of the coupling parts in circumferential direction a clamping plate is provided between the lateral surface and the associated flank which is axially elastic and is mounted to one of the coupling parts.