Abstract:
A clamping device for a tool or a workpiece, comprising at least one chuck and at least one holder for the workpiece or the tool. The holder is provided with a tubular extension.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a clamping device for a tool or a workpiece, comprising at least one chuck and at least one holder for the workpiece or the tool. 
         [0002]    Clamping devices of this generic type are used to clamp workpieces or tools, very high precision being demanded in the machining of the workpiece. In addition, an exactly reproducible clamping of the workpiece or the tool in the x, y and z directions must be ensured. 
         [0003]    From EP-A-255 042, a clamping device is described wherein, for the accurate positioning of the two coupling members (chuck and holder) relative to one another in the z direction, which usually coincides with the clamping direction, a plurality of uprights are present on one of the clamping members and the z reference surfaces are configured on the free end faces of said uprights. On the other coupling member there are, in an arrangement corresponding to the uprights, a plurality of z counter reference surfaces, which lie in a common plane and, when the coupling members are clamped together, cooperate with the z reference surfaces. A similar arrangement for the z positioning of two coupling members is known from German registered utility model DE-U-295 21 030. 
         [0004]    Another clamping device comprising two coupling members and a clamping mechanism is disclosed in EP 1 013 375 A2. A coupling device is described, consisting of a first coupling member and a second coupling member, as well as a clamping mechanism for the axial clamping together of the two coupling members, wherein projecting from the first coupling member are at least three prism pins, each of which is provided on at least one side with a prismatic surface, and wherein on the first coupling member there are configured at least three mutually spaced z reference surfaces, which lie in an x-y plane extending transversely to the clamping direction, and wherein, furthermore, the second coupling member has at least three grooves, which are aligned to the prism pins and on which axial-elastic elements for the accurate positioning of the coupling members relative to one another in the x-y plane are provided. In order to simplify the structural design of the z positioning of two coupling members, it is provided that the z reference surfaces are configured on the free end faces of the prism pins and a z counter reference surface is configured on the groove floor of each groove. 
         [0005]    The problems and drawbacks associated with the current state of the art are described below. 
         [0006]    The previous clamping devices can generally be used only for specific applications, so that a multiplicity of clamping devices are necessary to cover as wide a range of applications as possible. For the powder pressing process, for instance, high requirements are placed upon the tools and their clamping devices, in particular a high exposure to forces. It would further be advantageous if a clamping device could be used for different machining processes, for example in milling, in grinding, in EDM, or with other machine tools. Similarly, the clamping device should be usable for different tool forms (for instance, electrode forms in EDM), without time-consuming conversion times. One problem is to find a solution to clamping both the small-sized holders and the larger-sized holders to tools or workpieces on workpiece plates by means of a universally designed clamping device. 
         [0007]    In addition, there is a requirement to provide in the coupling part designed for the clamping of a tool (drill, electrode, etc.) room to allow the tool to be firmly seated such that it can adequately withstand load. In high-speed milling cutters, specifically, this problem of the present state of the art is yet to be solved. 
         [0008]    In addition, the drawback of undesirable lateral forces in the clamping phase often arises, caused by clamping balls or other clamping elements. 
         [0009]    The object of the invention is thus to propose a clamping device which remedies these abovementioned drawbacks. 
       SUMMARY OF THE INVENTION 
       [0010]    According to the invention, this object is achieved by the fact that the holder has an upper part and a tubular extension, the upper part being detachably connected to the tubular extension. 
         [0011]    The feature according to which the holder is constructed in two parts from an upper part and a tubular extension lessens or eliminates the abovementioned drawbacks of the prior art. 
         [0012]    The two-part holder according to the invention can be used in a chuck which is known per se and in a clamping device composed of two chucks. 
         [0013]    Further drawbacks as occur in the prior art are remedied by the further inventive embodiment of two concentric chucks. Firstly, by virtue of this “double chuck”, both small holders with tools and large holders with tool plates are able to be used. The inner and the outer chuck have similar or identical x-y references. The z references are disposed in the same plane or virtually in the same plane. The x-y-z coordinates of the two chucks are fully coordinated. The z coordinate of one chuck is disposed close to the z coordinate of the other chuck. The two chucks are connected coaxially to one another to form a unit. In the connected state, the two chucks are perfectly centrically adjusted. No separate adjustment is necessary. Due to this inventive device, it is possible to produce chucks of substantially smaller diameter than chucks according to the prior art, generally up to 25% smaller. 
         [0014]    The inner chuck has in the center a continuous opening. This allows the reception of tools with long clamping pins. The previous central openings in the clamping devices served exclusively as a passage for liquids and not for the clamping of tools or workpieces. 
         [0015]    In order to reduce or eliminate the adverse lateral forces, the middle fastening part is of tubular configuration and is advantageously provided on the outer periphery as a bayonet fastening. 
         [0016]    The clamping device according to the invention, comprising an inner and an outer chuck and comprising a tubular extension for clamping the holder to the chuck(s) offers a high and precise accuracy under extreme load, in particular in high-speed milling cutters, in EDM or in other machine tools. 
         [0017]    The holder can be clamped to the inner and/or outer chuck or to a single chuck. 
         [0018]    According to a preferred embodiment, the inner chuck has in the center a continuous opening running in the axial direction. 
         [0019]    This inner pass-through opening provides sufficient room for clamping elements of tools or workpieces. 
         [0020]    In addition, the holder can have in the center a pass-through opening for the evacuation of chips generated in the machining. 
         [0021]    The inner chuck as well as the outer chuck has x-y references and z references, which, in the clamping operation, cooperate with corresponding means of the holder. In addition, the means of the holder for the x-y references can advantageously be configured as elastic inner and/or outer tongue pairs. 
         [0022]    A further advantageous embodiment of the chuck consists in the holder having as z references inner and outer contact surfaces. 
         [0023]    According to a preferred embodiment of the chuck according to the invention, the holder has a tubular extension for clamping to the inner and/or outer chuck, the external diameter D of the tubular extension lying in the order of magnitude of the internal diameter of the continuous opening up to the external diameter of the inner chuck. 
         [0024]    In addition, the diameter of the central opening of the tubular extension can lie in the region of or can be at least half as large as the diameter which is given by the inner margin of the inner x-y surfaces. 
         [0025]    Similarly, the diameter of the central opening in the upper part of the holder can lie in the order of magnitude of the diameter of the tubular extension. 
         [0026]    The x-y references of the inner chuck can be disposed at the same height—viewed in the z direction—as the surfaces of the x-y planes of the outer chuck. 
         [0027]    The x-y references and the z references of the outer chuck lie within two imaginary circles. 
         [0028]    The holder can be clamped in a manner which is known per se to the inner and/or outer chuck or individual chucks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The invention is represented below with reference to illustrative embodiments in the drawings, in which: 
           [0030]      FIG. 1  shows a sectional view of a clamping device, 
           [0031]      FIG. 2  shows a top view of the clamping device of  FIG. 1 , 
           [0032]      FIG. 3  shows a holder of a chuck with the clamping device  1 , 
           [0033]      FIG. 4  shows a sectional view of the clamping device of  FIG. 1 , with holder clamped in place, 
           [0034]      FIG. 5  shows a top view of the clamping device, with holder, of  FIG. 4 , 
           [0035]      FIG. 6  shows two different applications for holders, 
           [0036]      FIG. 7  shows a first embodiment according to  FIG. 6  in the clamped-together state, 
           [0037]      FIG. 8  shows a top view according to  FIG. 7 , 
           [0038]      FIG. 9  shows a second embodiment according to  FIG. 6  in the clamped-together state, 
           [0039]      FIG. 10  shows a top view according to  FIG. 9 , 
           [0040]      FIG. 11  shows another embodiment of a holder, 
           [0041]      FIG. 12  shows the embodiment of  FIG. 11  in the clamped-together state 
           [0042]      FIG. 13  shows a further embodiment of the holder  19  with chuck in the machining of a workpiece. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    In  FIG. 1  is shown a possible embodiment of a clamping device  1  according to the invention. The inner chuck  2  is fixedly connected by means of the screws  18  to the outer chuck  3 , the inner chuck  2  being disposed concentrically to the outer chuck  3 . The basic element of the inner chuck  2  consists of the parts  15 , which are held together by means of the screws  17 . The inner chuck  2  has clamping balls  4 , which cooperate with an inner clamping plunger  12  and a clamping spring  5  in a manner which is known per se. The outer chuck  3  is correspondingly constructed. The basic element consists of the parts  14 , which are held together by means of the screws  16 . It likewise has clamping balls  6 , an outer clamping plunger  13  and a clamping spring  7 . The two clamping plungers  12 ,  13  can be acted upon in a known manner by means of compressed air. Both the inner and the outer chuck  2 ,  3  possess both inner  8  and outer  9  x-y references and inner  10  and outer  11  z references. 
         [0044]    The arrangement of the x-y and z references  8 ,  9 ,  10 ,  11  can be seen in the top view in  FIG. 2 . The inner x-y references  8  of the inner chuck  2  and the outer x-y references  9  are configured, for instance, as bars with conical edges, and the center lines of the inner and outer x-y references coincide with extreme accuracy. Between the inner x-y references  8 , inner z references  10  are provided. Correspondingly, the outer chuck  3  has on the peripheral side between the outer x-y references  9  the z references  11 , the surface of the z references  10  and  11  having the same height or being slightly offset. 
         [0045]    In  FIG. 3 , the clamping device  1  (as shown in  FIGS. 1 and 2 ) is shown with the holder  19 , which serves as an element for a plate. The holder  19  has an upper part  36  and a tubular extension  24 , the upper part  36  being detachably connected to the tubular extension  24  by means of a bayonet connection  26 . The holder  19  can be clamped to the clamping device  1 , as is shown in  FIGS. 4 and 5 . In addition, in the holder  19 , the outer tongue pairs  21  can be seen, which, in the clamped-together state, cooperate with the outer x-y references  9 . In addition, the continuous opening  25  of the inner chuck  2  is shown. The diameter D of the tubular extension  24  lies, according to application, in the region of the diameter D′ of the continuous opening  25  up to the diameter D″ of the inner chuck  2 , as is represented in  FIG. 4 . 
         [0046]    The top view in  FIG. 5  shows the bayonet device  26  of the upper part  36  with the tubular extension  19  of the holder  19 . The other reference symbols correspond to the reference symbols of  FIGS. 1 to 4 . 
         [0047]      FIG. 6  shows two embodiments of holders  27  and  28 . Both holders  27  and  28  respectively have a detachable hollow, tubular extension  24  of a diameter D, which lies in the order of magnitude of the diameter D′ of the continuous opening  25  of the inner chuck  2 . The holder  27  possesses a soldered or glued receiving fixture  29 . The holder  28  has a special chuck  30 .  FIG. 7  shows the holder  27  in the clamped-together state. The top view can be seen in  FIG. 8  with the x-y and z references. The x-y references  9  and the z references  11  lie between two imaginary circles  37  and  38 . The other holder  28 , in the clamped-together state, illustrates  FIG. 9 , together with the top view in  FIG. 10 . 
         [0048]    In  FIG. 11 , the side view of a holder  31  for a plate element can be seen. In particular, the holder  31  has inner and outer tongue pairs  20 ,  21  and inner and outer contact surfaces  22  and  23 .  FIG. 12  shows the holder  31  in the clamped-in state. 
         [0049]      FIG. 13  shows an embodiment of a holder  19  clamped into a chuck  39 . The workpiece  34  is machined by means of the tool  33 . The holder  19  has a pass-through opening  32 , the diameter of which lies in the order of magnitude of the pass-through opening of the tubular extension  24  of the holder  19 . In the illustrative embodiment, the continuous opening serves for the evacuation of chips  35  generated in the machining.