Abstract:
A clamping system for detachably assembling two pieces. The clamping system includes a clamping device concentrically mounted in a receiving section which extends in a hollow shaft of one of the two pieces, when the two pieces are engaged. The clamping system further includes at least two clamping bodies which can move in opposite directions and an actuating device which actuates the clamping bodies. The clamping bodies can be engaged with an undercut clamping shoulder of the hollow shaft and disengaged therefrom, whereby a pressure force is applied between the flat surfaces of the two pieces to be assembled.

Description:
FIELD OF THE INVENTION 
     1. Background of the Invention 
     The present invention relates to a clamping system for detachably connecting two parts, such as is used for coupling a workpiece or tool carrier, for example in the form of a tool base holder, to a manipulator unit such as a spindle of a machine tool, or for coupling tool system modules to one another. 
     2. Discussion of the Background 
     In such clamping systems the objective is to clamp the parts to be connected reliably and firmly against one another, thus ensuring exact positional fixation of the parts to be connected relative to each other via close-fitting engagement between the faces of a hollow shank of the one part and of a holding portion of the other part. The tightening or clamping of the two parts to be connected against one another is achieved by the fact that the hollow shank is pulled into the holding portion against an undercut clamping shoulder formed in the hollow shank during application of clamping members of a clamping device. In the process a pressing force is developed between plane faces of the parts to be connected, so that the two parts clamped against one another are provided with exact axial and also radial positional fixation by the firm connection between the close-fitting faces. 
     In more recent times there has been increasing acceptance of the hollow-shank clamping system, in which the hollow shank has either cylindrical or tapered structure. In the joined-together condition of the two parts to be connected to each other, the clamping members used for clamping the parts against one another ensure not only that an adequate axial pressing force is developed but also that the hollow shank experiences a certain radial flaring, whereby the accuracy of fit between hollow shank and holding portion is additionally improved. 
     In conventional clamping systems according to the principle described hereinabove, the assembly and disassembly of the clamping device in the holding portion provided therefor represents a special problem,. however, since the clamping system must also absorb the reactions to the clamping force in addition to ensuring exact axial and radial positional fixation of the two parts to be connected. 
     From German Patent Application DE A 4220873, there is known a clamping system for detachably connecting two parts, which preferably are rotationally symmetric, of which one part has a preferably cylindrical or tapered hollow shank and the other part has a corresponding holding portion for holding the hollow shank in accurately fitting relationship. There is provided a clamping device which is disposed concentrically in the holding portion and which, in the joined-together condition of the two parts, extends into the hollow shank of the one part and is provided with at least two clamping members which can move in opposite directions as well as with an actuating device for driving the clamping members, by means of which device the clamping members can be synchronously moved into and out of engagement with an undercut clamping shoulder of the hollow shank, whereby a pressing force is generated between plane faces of the two parts to be connected. 
     This clamping system is based on the principle described hereinabove of clamping two parts to be connected by a clamping device having clamping members. In this clamping system the problem cited hereinabove is solved by exact positional fixation of the parts to be connected, in that a support member decoupled from the clamping members as regards assembly is fixed interlockingly in the holding portion. The positionally fixed support member brings about bracing of the clamping members and thus indirectly absorbs the reactions to the clamping force. The indirect absorption of the reaction via the support member as well as the fastening and positional fixation thereof can be achieved, however, only by additional fixing and fastening elements. Furthermore, special assembly attachments are generally necessary. 
     In another known clamping system, as is described, for example, in German Patent DE C2 3807140, a plurality of loosely disposed or at least not distinctly fixed clamping elements must be nested interlockingly in the holding portion. In this case an additional support member is indeed unnecessary, but the direct nesting of the clamping elements is associated with considerable assembly complexity, since the individually disposed clamping elements are not distinctly fixed in assembly position. Accordingly, the clamping elements must be moved into a special assembly/disassembly position during assembly/disassembly. Additional components and assembly attachments are necessary for this purpose also. 
     From German Utility Model DE U1 29518660 there is known a clamping system according to the preamble of the new claim  1 . 
     A threaded sleeve, a clamping ring and a plurality of segmented bracing elements are necessary for fixation of the clamping-element halves in the tool spindle. The head parts of the clamping-element halves are therefore braced against the undercut clamping shoulder of the tool mandrel via a “mechanism” formed by the clamping ring and the bracing elements. 
     The object of the present invention is therefore to provide a clamping system for two parts to be connected, for example a tool system module and a machine tool spindle, which clamping system on the one hand performs adequately with a minimum of components and on the other hand permits simple, reliable and dimensionally stable coupling of the two parts to be connected without the need for additional assembly or fastening attachments. 
     This object is achieved by a clamping system with the features of claim  1 . 
     According to the invention, the clamping elements are each provided in a region between head and foot portions with a retaining portion, which can be brought into engagement with an undercut recess of the holding portion. 
     Just as heretofore, therefore, the clamping members are still designed as head portions of elongated clamping elements disposed substantially parallel to the longitudinal or rotational axis of the holding portion. The clamping elements are constituents of the clamping device. The foot portions of the clamping elements are inventively connected to one another such that the clamping device has substantially the form of a V-shaped or U-shaped split chuck or clamping fork. 
     These clamping elements can be connected to one another movably, interlockingly and frictionally or in one piece. By means of an actuating device the clamping members can be made to move in opposite directions, or in other words to move toward or apart from one another. The inventive clamping system with such a predetermined arrangement of clamping elements relative to one another therefore obviates the support members which in conventional clamping systems are necessary for the clamping elements or clamping members. 
     This arrangement of the clamping elements also permits, without additional fixing components, distinct axial as well as radial fixation of the clamping members relative to one another in both the clamped position and detached position of the clamping system. The inventive clamping system is therefore characterized by simple and compact structure, which also permits reliable and dimensionally stable clamping of the parts to be connected without a plurality of loose components. In addition, the connection of the clamping elements in the manner described hereinabove creates a clamping device which, since it does not comprise any loose parts, can be fixed in the holding portion without great mechanical complexity. 
     Since, moreover, a minimum of movable parts is present in the inventive clamping system, only little friction is developed during movement thereof. In this way a relatively large clamping force is achieved between the two parts to be connected. 
     Further advantageous embodiments of the inventive clamping system are subject matter of the dependent claims. 
     The clamping elements are preferably designed as the arms of a U-shaped clamping fork of one-piece construction. In such a configuration the clamping device therefor e comprises only the clamping fork and the actuating device, and so the number of necessary components is reduced to two components. The one-piece configuration of the clamping elements in the form of a clamping fork further creates the possibility of increasing the clamping force between the two parts to be connected by bending stresses of the clamping fork. The clamping force is generated by the spring tension of the clamping fork when the actuating device is released. This spring tension can be adjusted by appropriate forming in the stress-free condition. The one-piece design of the clamping elements in the form of an elastically deformable clamping fork also permits simple assembly of the clamping device in the holding portion, since there is no need to dispose and fix a plurality of loose components. 
     It is also possible, however, to connect the clamping elements of the clamping device by an articulated joint which includes the foot portions of the clamping elements, the axis of rotation of which joint is disposed perpendicular to the longitudinal or rotational axis of the parts to be connected. This design provides substantially the same advantages as the one-piece design of the clamping elements. 
     The clamping device of the inventive clamping system is preferably provided in a region between head and foot portions with a radially outwardly projecting retaining portion in the form. of a clamping shoulder, and by means of this retaining portion can be nested in an undercut recess of the holding portion. By virtue of this technically simple expedient the clamping device can be engaged with or disengaged from the recess of the holding portion synchronously with the movement of the clamping members or with the pivoting movement of the clamping elements, depending on whether the clamping members are engaged with or disengaged from the undercut clamping shoulder of the hollow shank. Accordingly, therefore, axial fixation of the clamping device in the holding portion can be achieved without additional fixing elements. 
     In particular, the configuration of the recess in the form of a closed annular cross section does not represent any weakening of the nesting shoulder of the recess of the holding portion, as can occur in conventional clamping systems, for example due to countersunk portions in the case of a bayonet fastener. Compared with the production of a plurality of recesses, which extend in the direction of rotation of the tool holder only over portions of the inside circumferential wall of the holding portion, the production of a single recess in the form of a closed annular cross section additionally proves to be particularly simple. Such a configuration has also proved to be advantageous with regard to assembly of the clamping device, since the clamping device can be introduced: into the holding portion without any concern over its angular orientation relative to the holding portion. 
     In order to achieve the highest possible pressing force between the two parts to be connected, it has proved particularly advantageous to provide each of the clamping members with one wedge face, which cooperates with a mating wedge face provided on an undercut clamping shoulder of the hollow shank, this clamping shoulder preferably being formed by a recess in the form of a closed annular cross section. By means of this type of configuration, therefore, there can be created a wedge-type mechanism, which is characterized by relatively high efficiency. 
     According to a further development of the inventive clamping system, there is provided a push-off attachment which is automatically actuated or moved axially upon detachment of the engagement of the clamping members with the undercut clamping shoulder of the hollow shank. Axial actuation of the push-off attachment leads to separation of the two connected parts. In this case the forced movement of the clamping members upon detachment of the clamped engagement of the clamping members with the undercut shoulder can be utilized to generate a push-off force acting axially on the components to be separated. 
     According to the invention this is accomplished in simple manner by a push-off piston as part of the push-off attachment, which piston is disposed in a central recess of the part supporting the hollow shank and which, when the engagement of the clamping members with the undercut clamping shoulder of the hollow shank: is detached, can press synchronously with increasing force against a bracing face of the part supporting the hollow shank. By virtue of the central disposition of the push-off piston, therefore, a centrally acting, positive force is applied on the part supporting the hollow shank, ultimately leading to separation of the two connected parts. Because of the centrally acting force on the part supporting the hollow shank, the jamming and faulty gripping of the two parts that occur under some circumstances can also be prevented. 
     For this purpose it has proved advantageous to provide on the push-off piston a tapered face over which the clamping members can travel upon detachment of the clamping system. A sufficiently large push-off force between the parts can be generated with this simple “wedge-type mechanism”, and so even a firm connection produced by the fact that two parts with tapered close-fitting faces have been clamped together . . . with the detachment of the engagement of the clamping members with the undercut . . . . 
     When the push-off piston and the clamping device are held in sealed relationship in the corresponding recesses, preferably by sealing rings disposed in appropriate recesses, a coolant and lubricant can additionally be supplied via the parts clamped against one another to, for example, a cutting tool clamped in the one part. The seal of the push-off piston and of the clamping device can also be used to stabilize these components, and so vibration-induced chattering noise can be prevented. 
     Accordingly, the inventive clamping system can be combined with a coolant and lubricant supply system. This coolant and lubricant supply system comprises in particular a channel portion which is formed in the part supporting the holding portion, a channel portion which is formed in the part supporting the hollow shank, plus at least one line portion which bridges the clamping device and ensures fixation of its angular orientation. The line portion of the coolant and lubricant supply system can then ensure fixation of the angular orientation of the clamping device in the holding portion, and so further structural expedients or other fixation elements are not needed in this regard. 
     The line portion is preferably designed as a tube which is disposed between the parts to be connected, the end of this tube on the hollow-shaft side being held interlockingly and/or frictionally, preferably by sealed brazed joint, in a corresponding recess of the push-off piston, the shank portion of this tube being guided movably, preferably in a manner sealed by a sealing ring, through a corresponding recess in the connecting portion of the foot portions of the clamping elements, and the end of this tube on the holding-portion side being held in close-fitting relationship in a corresponding recess in the part supporting the holding portion. 
     As already described hereinabove, the line portion or the tube can be used for fixation of the angular orientation of the clamping device in the holding portion. The line portion or the tube is then disposed between the clamping members in such a way that the clamping members pinch the line portion or the tube between them when the clamping system is in detached position. This means that the coolant and lubricant supply system is securely retained in the holding portion without the need for additional fixation elements when the clamping system is in detached position. 
     Preferably the parts to be connected are designed as rotationally symmetric parts and the pressing faces of the parts to be connected are designed as radial annular faces. This contributes decisively to a simple and thus low-cost clamping system. 
     In order to achieve the most intimate possible connection between the two parts to be connected and thus to keep the torque-transfer losses as small as possible, the close-fitting faces between hollow shank and holding portion preferably have the form of tapered faces. 
     The drive of the actuation device is provided preferably via a radial opening oriented perpendicular to the longitudinal or rotational axis of the two parts to be connected, preferably via a radial bore, into which a tool, in the form, for example, of an Allen key, . . . from outside. 
     Furthermore, in a preferred embodiment of the clamping system, the actuating device for actuating the clamping members is constructed as a tightening screw with a head portion and a threaded portion, the head portion being disposed in a correspondingly configured recess of the one clamping member and the threaded portion in a corresponding threaded bore of the other clamping member. 
     An advantageous embodiment of the tightening screw has been found to be one in which the threaded portion of the tightening screw has a left-hand threaded portion and a right-hand threaded portion, of which one is disposed in the threaded bore of the other clamping member and the other is disposed in a nut functioning as the head portion, the nut being disposed in the correspondingly configured recess of the one clamping member. The advantage of this embodiment is that, by virtue of the left-hand/right-hand thread of the tightening screw, relatively small turning movements are necessary in order to bring about a relatively large “stroke” of the clamping elements; furthermore, the nut functioning as the head portion is subjected only to tension and thus does not undergo any frictional wear. 
     In addition to a rotationally symmetric configuration of the two parts to be connected, it has proved advantageous to make the clamping device also from a cylindrical part, so that the clamping elements and the clamping members have an arcuate outside face and the foot portion of the clamping elements has a cylindrical outside face. 
     As regards a simple possibility for limiting the clamping stroke of the clamping members, it has proved to be particularly advantageous when the clamping elements can bear against the inside circumferential wall of the recess of the holding portion while the two parts to be connected are in the tightened or clamped-together condition. In this way a maximum permissible clamping stroke of the clamping elements and thus of the clamping members can be safely maintained without additional limiting elements or stops. 
     In order to shorten the axial overall length of the clamping device and thus of the clamping system as a whole by a structurally simple means, it is further advantageous to provide each clamping element on the side of its foot portion with at least one notch which reduces the cross section. Thereby the force necessary to pinch the clamping elements together can be reduced and, as a positive consequence thereof, the necessary “lever-arm length” of the clamping elements can be considerably shortened. 
     Further advantageous features of the present invention will become apparent from the description hereinafter, wherein a preferred practical example of this invention will be explained in more detail with reference to a schematic drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 a schematic axial section—in partly cutaway view—of the inventive clamping system according to the preferred practical example with the two parts to be connected in clamped-together condition; 
     FIG. 2 is a schematic axial section—in partly cutaway view—of the inventive clamping system according to the preferred practical example with the two parts to be connected in clamped-together condition; 
     FIG. 3 is a cross section through the inventive clamping system in FIG. 1 along line “III—III”; 
     FIG. 4 is a cross section through the inventive clamping system in FIG. 2 along line “IV—IV”; 
     FIG. 5 is a schematic view—partly cutaway—of a clamping device of the inventive clamping system; 
     FIG. 6 is a cross section through the clamping device along line “VI—VI” in FIG. 5; 
     FIG. 7 is a schematic top view of the clamping device in FIG. 5; 
     FIG. 8 is a schematic view—partly cutaway—of a coolant and lubricant push-off attachment; 
     FIG. 9 is a schematic view of a push-off piston viewed in a direction corresponding to arrow “IX” in FIG. 8; 
     FIG. 10 is a cross section of the holding portion of the tool holder according to a second practical example; 
     FIG.  11  and FIG. 12 are cross sections through the clamping device along line XI—XI in the detached condition of the clamping system according to the second practical example; 
     FIG. 13 is a cross section through the clamping device along line XIII—XIII in the clamped condition of the clamping system according to the second practical example; 
     FIG. 14 is a schematic axial section—in partly cutaway view—of the inventive clamping system according to a third practical example with the two parts to be connected in clamped-together condition; 
     FIG. 15 is a schematic axial section—in partly cutaway view—of the inventive clamping system according to the preferred practical example with the two parts to be connected in clamped-together condition; 
     FIG. 16 is a cross section through the inventive clamping system in FIG. 14 along line “XV—XV”; 
     FIG. 17 is a cross section through the inventive clamping system in FIG. 16 along line “XVII—XVII”; 
     FIG. 18 is a side view—partly cutaway—of the clamping device of the inventive clamping system according to the third practical example; 
     FIG. 19 is a top view—partly cutaway—of the clamping device of the inventive clamping system according to the third practical example; and 
     FIG. 20 is a front view of the clamping device of the inventive clamping system according to the third practical example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 there is illustrated a part denoted by reference numeral  20  and referred to hereinafter as the tool, for example a tool system module in the form of a tool base holder, and a part denoted by reference numeral  22  and referred to hereinafter as the tool holder, for example a spindle of a machine tool. It must be emphasized here and now, however, that the clamping system to be described in more detail hereinafter relates to the interface of two parts to be connected and is therefore qualified for all practical applications in which it is necessary to connect two parts to one another in centered and detachable relationship. 
     In FIG.  1  and FIG. 3, tool  20  and tool holder  22  are shown in the clamped-together condition or tightened condition, in which a radial annular face  24  of tool  20  is pressed against a radial annular face  26  of tool holder  22 , while at the same time a hollow shank  28  of tool  20  is held in centered relationship in a corresponding recess  30  of a holding portion  32  of tool holder.  22 . 
     FIG.  2  and FIG. 4 show tool  20  and tool holder  22  in the joined-together but not clamped-together condition. Even in this condition, hollow shank  28  of tool  20  is already held in recess  30  of tool holder  22 . Between the two radial annular faces  24 ,  26 , however, there is formed a plane gap, since tool  20  becomes stopped against a push-off piston  82  of a push-off attachment  80  to be described in more detail hereinafter. 
     In the practical example shown in FIG.  1  and FIG. 2, the close-fitting faces between hollow shank  28  and recess  30  are formed by tapered faces. It is equally possible, however, to provide for centering of hollow shank  28  in recess  30  via cylindrical faces. 
     Although the intimate connection between the tapered close-fitting faces already ensures that tool  20  and tool holder  22  are secured against relative turning when tool  20  and tool holder  22  are in clamped-together condition, additional security against relative turning between tool  20  and tool holder  22  can also be achieved by, for example, at least one tang block, which engages in a corresponding end recess either of the hollow shank or of the holding portion. 
     In the practical example shown in FIG.  1  and FIG. 2, parts  20 ,  22  to be connected as well as hollow shank  28  and the recesses formed in these parts, such as recess  30 , have rotationally symmetric geometry. It must be emphasized, however, that the invention is not limited merely to such geometry. 
     The inventive clamping system must be capable of clamping parts  20 ,  22  to be connected firmly against one another in predesignated radial and also axial position. A further feature essential to the invention, besides a minimal number of components and simple assembly capability, is easy detachability of the connected parts in combination with short stroke distances. For this purpose the inventive clamping system has the following structure: 
     Hollow shank  28  is provided on the inside with a radially oriented undercut clamping shoulder  34 . Clamping shoulder  34  is formed by a wedge face of an annular recess of hollow shank  28 , this face being directed toward the tool holder. During actuation of the clamping system, wedge faces  36  of two clamping members  38  can bear against clamping shoulder  34 , in order to bring about, preferably with force conversion, firm clamping of tool  20  against tool holder  22 . 
     In an axial guide recess  31  of holding portion  32  of tool holder  22  there is disposed a clamping device  39 , which at the bottom of the guide recess bears via a sealing ring against the inside circumferential wall of guide recess  31 . As can be seen in FIG.  5  and FIG. 6 in particular, clamping device  39  comprises a U-shaped clamping fork of one-piece structure and an actuating device in the form of a tightening screw  42 . The clamping fork is preferably made from a cylindrical member, as can also be recognized from the diagram according to FIG.  6 . FIG. 7 shows a top view of the clamping fork. It comprises two clamping elements  40 , which are oriented substantially parallel to longitudinal or rotational axis  43  of tool holder  22 , and which are formed by the arms of the U-shaped clamping fork. Clamping elements  40  preferably have an arcuate outside face corresponding to the circumferential face of axial guide recess  31  of holding portion  32 . The head portions of the two clamping elements  40  form clamping members  38 , which are equipped with wedge faces  36 . As can be seen in FIGS. 5 and 6 and will be described in more detail hereinafter, tightening screw  42  is connected interlockingly and frictionally with the two clamping members  38 . Clamping elements  40  are connected to one another in one piece at their foot portions  41 , preferably in the form of a “material articulated joint”. According to the present invention, however, it would also be possible to design the foot portions of clamping elements  40  as constituents of an articulated joint connecting clamping elements  40 . 
     Between clamping members  38  and articulated joint  41  there are provided on clamping elements  40  retaining portions  44 , with which clamping device  39  can be nested in an undercut recess  46  of axial guide recess  31  of holding portion  32  and thus can be fixed axially in tool holder  22 . Undercut recess  46  has a closed annular cross section. Since the clamping fork, as mentioned hereinabove, has a cylindrical outside contour, retaining portions  44  are accordingly disposed in diametrically opposite relationship on clamping elements  40  and have the form of radially projecting bracing noses or shoulder portions. 
     According to the diagram in FIG.  5  and FIG. 6, tightening screw  42  has a spherical head portion  52 , a neck portion  53  adjoining head portion  52  and having diameter smaller than that of the head portion, an annular portion  54  following neck portion  53  and having diameter larger than that of neck portion  53 , a shank portion  55  adjoining annular portion  54  and having diameter smaller than that of a threaded bore  62  of upper clamping member  38  in FIG. 5, as well as a threaded portion  56  which adjoins shank portion  55  and is held in threaded bore  62  of upper clamping member  38  in FIG.  5 . Threaded portion  56  of tightening screw  42  has a recess  60  indicated by broken lines, preferably a hexagon socket. 
     Lower clamping member  38  in FIG. 5 has a concave recess  57  corresponding substantially to the contour of spherical head portion  52 , this recess being limited in the direction of the upper clamping member by a bottom portion  58 , which has a height H (FIG. 6) corresponding approximately to the axial length of neck portion  53 . Bottom portion  58  is provided with a slot  59 , which starts from its end side, or in other words from the left side in FIG. 5, and which has a width B (FIG. 6) somewhat larger than the diameter of neck portion  53 . Tightening screw  42  can therefore be inserted with its neck portion  53  into slot  59 , as is shown, for example, in FIG.  5  and FIG. 6, in which case bottom portion  58  of recess  57  is held with clearance between head portion  52  and annular portion  54 . 
     Upper clamping member  38  in FIG. 5 has a threaded bore  62 , in which there is held threaded portion  56  of tightening screw  42 . Threaded portion  56  is therefore functionally engaged with clamping member  38 . 
     As already mentioned hereinabove, tightening screw  42  is connected to the two clamping members  38  of clamping device  39 . Thus, when tightening screw  42  is turned, it brings about pivoting movement of clamping elements  40  around an imaginary axis of rotation (not illustrated) oriented perpendicular to axis  43  of tool holder  22 . As illustrated in FIGS. 1 and 2, turning of tightening screw  42  is achieved by a tool  63  introduced radially from outside in a direction substantially perpendicular to longitudinal or rotational axis  43  of tool holder  22 , the said tool preferably having the form of an Allen key, which is introduced through a radial opening  64  in holding portion  32  of tool holder  22  on the one hand and through a radial opening  66  in hollow shank  28  of tool  20  on the other hand into the aforesaid recess  60  of tightening screw  42 . 
     From FIG.  1  and FIG. 2 it is further apparent that a rotational axis  70  of tightening screw  42  is substantially aligned with the axes of radial openings  64 ,  66 . Radial openings  64 ,  66  are preferably designed as bores. 
     When tightening screw  42  is turned to the right, it leads to synchronous movement of clamping members  38  apart from one another and thus to clamping of tool  20  against tool holder  22 . When tightening screw  42  is turned to the left, it leads to synchronous movement of clamping members  38  toward one another and thus to detachment of the wedge-type surface connection between wedge faces  34 ,  36  and thus of the connection of tool  20  and tool holder  22 . By virtue of the detachment of the clamping system, or in other words the movement of the two clamping members  38  together as a result of the turning of tightening screw  42  to the left, there are generated in clamping elements  40  and in foot or connecting portion  41  bending stresses, which of course are relaxed once again when the clamping system is tightened, or in other words when clamping members  38  are moved apart from one another as a result of the turning of tightening screw  42  to the right, and which therefore support the stroke of clamping members  38  in radially outward direction as well as the clamping of tool  20  against tool holder  22 . The spring tension of the clamping fork can therefore be transformed to a clamping force for clamping the two parts  20 ,  22  against one another. By appropriate forming of the clamping fork in the stress-free condition, therefore, it is possible to increase the spring tension of the clamping fork and thus the bending stresses generated when tightening screw  42  is turned to the left. 
     The diagram in FIG. 5 makes it evident that the maximum extent to which clamping members  38  can be pinched together as tightening screw  42  is being turned to the left is when the two clamping members  38  become stopped against annular portion  54  of tightening screw  42 . By appropriate dimensioning of the axial length of shank portion  55 , therefore, it is ensured that threaded portion  56  cannot become disengaged from threaded bore  62 . In this fully pinched-together condition of clamping members  38 , the engagement of wedge faces  36  of tightening screw  38  with undercut clamping shoulder  34  of hollow shank  28  is released, and so tool  20  can be removed from the tool holder. 
     From the diagram according to FIG. 1 it is evident that clamping members  38  can be moved apart from one another when tightening screw  42  is turned to the right only to the extent that they bear against the inside circumferential wall of holding portion  32  of the tool holder. In this way, even without a tool-dependent stop for limiting the clamping stroke of the clamping members, it is ensured that a maximum permissible clamping stroke, beyond which threaded portion  56  of tightening screw  42  would become disengaged from threaded bore  62  of clamping member  38 , cannot be exceeded. Further turning of tightening screw  42  after the maximum permissible clamping stroke of clamping members  38  has been reached is therefore prevented automatically by the fact that the clamping elements bear against the circumferential wall of the recess in the holding portion. 
     According to the clamped position shown in FIG. 1, clamping members  38  are pushed back via wedge faces  36  against the wedge face of clamping shoulder  34 , thus becoming mutually braced against tightening screw  42 . 
     In the clamped position of the inventive clamping system shown in FIG. 1, the contact between wedge faces  34 ,  36  ensures that hollow shank  28  of tool  20  tends to be flared, whereby the close-fitting contact between hollow shank  28  and recess  31  becomes even more intimate. In this clamped condition, therefore, a frictional and nonpositive connection exists between the close-fitting faces of hollow shank  28  and recess  30  on the one hand and between wedge faces  34 ,  36  on the other hand, whereby clamping device  39  becomes fixed in its angular orientation relative to tool holder  22 . 
     Further constituents of the inventive clamping system constitute a push-off attachment as well as a coolant and lubricant supply system, which in this practical example are designed as one component and will therefore be referred to hereinafter as C&amp;L push-off attachment  80 . 
     The structure of this C&amp;L push-off attachment is illustrated in particular in FIG.  8  and FIG.  9 . C&amp;L push-off attachment  80  comprises substantially a push-off piston  82  as well as two tubes  84 ,  86 . Push-off piston  82  is designed as a rotationally symmetric component with a centrally disposed projection  88  as well as two axial recesses, preferably bores  90 ,  92 , as is evident from FIG.  9 . Tubes  84 ,  86  are brazed in sealed relationship into axial recesses  90 ,  92  of the part supporting the hollow shank, and in the installed condition according to FIG. 1 or FIG. 2 they extend from push-off piston  82  into guide recess  31  of holding portion  32  of tool holder  22 . 
     As shown in FIG.  1  and FIG. 2, push-off piston  82  is disposed in sealed relationship in a central recess  94  of tool  20 , by means of a sealing ring held in a corresponding annular groove on the outside circumference of push-off piston  82 . As follows in particular from FIG.  3  and FIG. 4, a plane El connecting the central axes of tubes  84 ,  86  and including longitudinal or rotational axis  43  is turned by 90° relative to a plane E 2  connecting clamping elements  40  and also including longitudinal or rotational axis  43 . According to FIG.  1  and FIG. 2, tubes  84 ,  86  extend into guide recess  31  of holding portion  32  of tool holder  22  via correspondingly disposed axial recesses  94 ,  96  of foot or connecting portion  41  of the clamping fork to correspondingly provided recesses  98 ,  100  of tool holder  22 . Whereas the shank portions of tubes  84 ,  86  are held in easily movable relationship in axial recesses  94 ,  96  of articulated joint portion  41 , they are held in close-fitting relationship in axial recesses  98 ,  100  of tool holder  22 , there being provided for sealing recesses  94   a  ,  96   a , in each of which there is held a sealing ring, as shown in FIG.  6 . 
     Axial recesses  94 ,  96  of the tool as well as axial recesses  98 ,  100  of the tool holder constitute channel portions of the coolant and lubricant supply system. Tubes  84 ,  86  on the one hand have the function of line portions communicating between the channel portions in tool  20  and tool holder  22  and bridging clamping device  39 , and on the other hand provide further fixation of the angular orientation of the clamping device in the tool holder in addition to that created by the bracing of the tool and tool holder, by the fact that they are held in axial recesses of articulated joint portion  41  of clamping device  39 . In this way relative turning of the clamping device in the tool holder is prevented, especially in detached position of the clamping system. 
     As follows in particular from FIG. 4, the two clamping members  38  in detached position of the clamping system pinch the two tubes  84  and  86  in such a way that C&amp;L push-off attachment  80  is prevented by simple means from falling out when the clamping system is in detached position. 
     Push-off piston  82  of C&amp;L push-off attachment  80  has a central projection  88  with a tapered face  102  on the side directed toward the tool holder and especially clamping members  38 . When the engagement of wedge faces  36  of clamping members  38  with the wedge face provided on undercut clamping shoulder  34  is detached by turning tightening screw  42  in appropriate direction, clamping members  38  move radially inward toward one another. The functional contact between wedge faces  36  and clamping shoulder  34  is gradually released. At the same time, clamping members  38  travel synchronously over tapered face  102  of push-off piston  82 . When tightening screw  42  is turned further, the radially acting force applied by tightening screw  42  on clamping members  38  is transformed to an axially directed force acting on push-off piston  82 , whereby this is pushed with increasing force against a bracing face  104  of central recess  94  of tool  22 , so that a centrally acting, positive force is applied on the tool. In this way clamping members  38  become synchronous with the constituent of a wedge-type mechanism, with which hollow shank  28  can be forced out of holding portion  32 , while push-off piston  82  is braced against bracing face  104 . This leads accordingly to automatic separation of the connection created between tool and tool holder by the engagement of wedge faces  36  of clamping members  38  with undercut clamping shoulder  34 . Since the push-off piston is centrally disposed, symmetric force relationships can be achieved very easily for the push-off process, and so reliable separation of the two parts  20 ,  22  can be achieved even in the case of the most intimate adhesion between tapered centering faces on the outside face of the hollow shank on the one hand and on the sides of recess  30  of holding portion  32  on the other hand. 
     Assembly/disassembly of the tool on/from the tool holder as well as the mode of operation of the inventive clamping system will be described in more detail hereinafter, assuming an initial condition in which all components, meaning the tool, the tool holder and the clamping device constitute individual parts, or in other words are separated from each other. 
     The first step of assembly of the tool on the tool holder is to pinch clamping members  38  together. To do so, a suitable tool  63 , which in the explained practical example is an Allen key, is first introduced into recess  60 , which in the case of this practical example is a hexagon socket, of tightening screw  42  and then turned to the left. Of course, the tightening screw must already have been inserted beforehand into the corresponding recesses  62 ,  57  of clamping members  38 , as illustrated in FIG.  5  and FIG.  6 . The leftward turning of tightening screw  42  causes the two clamping members  38  to move toward one another, until upper clamping member  38  in FIG. 5 bears against annular portion  54  of tightening screw  42 , which is securely retained in lower clamping member  38 . In this condition, retaining portions  44  of clamping elements  40  can be fitted into a circle having a diameter corresponding approximately to that of recess  31  of holding portion  32  of tool holder  22 ; in any case, retaining portions  44  are not permitted to hinder the insertion of the clamping device into tool holder  22  as described hereinafter. With the pinching together of clamping members  38  in the manner described hereinabove, bending stresses are generated in the clamping fork, or in other words in clamping elements  40  and in connecting portion  41  in particular, which stresses are relieved once again when the tightening screw is subsequently turned to the right and which can therefore be used positively on the one hand for the radial stroke of the clamping members and on the other hand for bracing the tool with the tool holder. 
     Even in the case of a clamping device in which the clamping elements are connected to one another by an articulated joint, bending stresses can be generated by appropriate configuration of the foot portions forming the articulated joint. 
     Since the clamping elements are connected to one another at their foot portions and thus are moved radially outward in opposite directions in any case when the tightening screw is turned to the right, it is not absolutely necessary, however, that the radial stroke of the clamping members be assisted by bending stresses generated beforehand when the clamping elements were pinched together. It is self-evident that the bracing or mutual clamping of the tool against the tool holder can also be achieved merely by the force applied radially to clamping members  38  by virtue of actuation of tightening screw  42 . 
     In the pinched-together condition of the clamping fork, clamping device  39  can be introduced into guide recess  31  of holding portion  32  of tool holder  22 , as can be seen from FIG.  2  and FIG.  4 . 
     Clamping members  38  are then moved radially outward by turning tightening screw  42  to the right by means of tool  63  inserted via radial openings  64  and  66  of tool  20  and tool holder  22  into recess  60  of tightening screw  42 , whereby the bending stresses generated when clamping members  38  were pinched together are relieved. As clamping members  38  or clamping elements  40  move apart from one another, retaining portions  44  simultaneously engage in recess  46  of holding portion  32 , thus achieving axial fixation of clamping device  39  in guide recess  31  of holding portion  32  of tool holder  22 . This condition is evident from the diagram in FIG.  1  and FIG.  3 . 
     C&amp;L push-off attachment  80  can now be introduced into tool holder  22  and its angular orientation adjusted in the manner evident from the diagram in FIG.  1  and FIG.  3 . Once C&amp;L push-off attachment  80  has been correctly positioned, tubes  84 ,  86 , which extend through the axial recesses of foot or connecting portion  41 , bring about fixation of the angular orientation of clamping device  39  in guide recess  31  of holding portion  32  of tool holder  22 . 
     By turning tightening screw  42  to the left, clamping members  38  are then pinched together once again until they bear against tubes  84 ,  86 , as illustrated in FIG.  2  and FIG.  4 . From the diagram in FIG. 4 it follows in particular that upper clamping member  38  is prevented from becoming stopped against annular portion  54  of tightening screw  42  in this condition by the fact that it bears against tubes  84 ,  86 . Consequently retaining portions  44  are still engaged, albeit only partly, with recess  46  of guide recess  31  of holding portion  32  of tool holder  22 . This is sufficient to prevent clamping device  39  from falling out of recess  31 , especially when tool holder  22  is in vertical position. As is further evident from FIG. 2, the portions of clamping elements  40  adjoining clamping members  38  no longer bear over the full support length against the inside circumferential wall of recess  31 . This condition corresponds to the detached condition of the clamping system, in which tool  20  can be exchanged. 
     In the detached position of the clamping system, clamping members  38  additionally bear against tapered face  102  of push-off piston  82  of C&amp;L push-off attachment  80 , as can be seen in FIG.  2 . 
     In the detached position, tool  20  with its hollow shank  28  can be inserted into the corresponding recess  30  in holding portion  32  of the tool holder, as is evident in FIG.  2 . When in detached position, tool  20  becomes stopped against push-off piston  82 , which itself bears in turn against clamping members  38 . In the detached position, a plane gap in the range of 1/10 mm remains between radial annular faces  24 ,  26  of tool  20  and tool holder  22 , because push-off piston  82  projects axially from tool holder  22  when the clamping system is in detached position. 
     After insertion of tool  20  into corresponding recess  30  of tool holder  22 , actuating screw  42  is turned to the right, thus causing clamping members  38  to move radially apart from one another. As tightening screw  42  is turned further, wedge faces  36  provided on clamping members  38  become engaged with undercut clamping shoulder  34  of hollow shank  28  on the one hand, while the end faces of clamping members  38  synchronously become disengaged from tapered face  102  of push-off piston  82 . Accordingly, further turning of tightening screw  42  leads to clamping of tool  20  against tool holder  22 , whereupon the force directed radially toward the clamping members and applied on clamping members  38  by the action of turning of the tightening screw and relaxation of the bending stress caused during pinching together of clamping members  38  is transformed via the wedge-type mechanism between wedge faces  34 ,  36  into an axial force directed toward tool holder  22 , thus pulling tool  20  into the recess of tool holder  22 . Similarly, because tool  20  is pulled into tool holder  22 , push-off piston  82  is pushed into holding portion  32  of tool holder  22 . Because of the tapered close-fitting faces on hollow shank  28  and in the corresponding recess of tool holder  22 , there is produced slight flaring of holding portion  32 , whereby firm bracing between tool  20  and tool holder  22  is obtained. Simultaneously, retaining portions  44  become completely engaged with corresponding recess  46 , leading to a tensile stress with increasing clamping force in the regions of the clamping elements between clamping members  38  and the retaining portions. The clamped position of the inventive clamping system is shown in FIG.  1  and FIG.  3 . 
     During clamping of tool  20  against tool holder  22 , tool  20  pushed C&amp;L attachment  80  into tool holder  22 , as mentioned hereinabove. Coolant and lubricant supply lines for the supply of coolant and lubricant to the tool are created via channels formed in tool  20 , which supports hollow shank  28 , and in the tool holder, as well as via tubes  84 ,  86 . 
     Tool  20  is changed substantially in the reverse sequence. The initial condition in this case is the clamped position shown in FIG.  1 . By turning tightening screw  42  to the left, clamping members  38  move toward one another, whereupon the engagement of wedge faces  36  of clamping members  38  with undercut clamping shoulder  34  of recess  30  of holding portion  32  is relaxed on the one hand and clamping members  38  travel over tapered face  102  of push-off piston  82  on the other hand. By means of these processes the bracing between tool  20  and tool holder  22  is relaxed as tightening screw  42  is further turned, and at the same time tool  20  is pushed out of tool holder  22 . 
     Naturally it is not necessary to remove the clamping device from tool holder  22  in order to change the tool; instead, it is sufficient to bring the clamping system into the detached position shown in FIG.  2 . 
     As regards the permissible stresses in the components disposed in the flow of force from clamping system to tool to tool holder, the favorable circumstance arises that clamping elements  40  of the clamping fork, which have limited cross section for structural reasons, are subjected in clamped position of the clamping system to pure tensile stresses, whereas bending stresses prevail in the detached position of the clamping system. Since the loadability of the clamping elements represents a limit for the achievable clamping force of coupling of the tool and tool holder, a maximum level of clamping force for given cross section of the clamping elements can be achieved with pure tensile loading. 
     The necessary radial stroke of the clamping members for changing the tools, as well as the mechanical conversion of the radially applied tightening-screw force into an axially acting clamping force can be achieved by taking advantage of the elastic deformation of the clamping fork, without additional movable interlocking parts in the clamping system. The friction in the clamping system is thereby reduced to a minimum, whereby a distinct increase of clamping force is achieved compared with conventional clamping systems. 
     Compared with conventional clamping systems, the clamping system according to the invention substantially comprises only three components, namely the clamping fork, the tightening screw and the C&amp;L push-off attachment. The detached position of the inventive clamping system is also its assembly position. Additional components and assembly attachments are therefore unnecessary. 
     In the practical example described hereinabove, the clamping fork has two clamping elements, each with one clamping member. The present invention is not limited merely to such a configuration, however, but can also be provided with more than two clamping members. 
     In the practical example described hereinabove, the clamping fork is of one-piece design. Within the meaning of the present invention, however, it would also be conceivable to construct the clamping fork from two “hemispherical” clamping elements, which can be connected movably to one another at their foot portions via an articulated joint, the axis of rotation of which is disposed perpendicular to the longitudinal or rotational axis of the holding portion. Similarly, the clamping elements could also be connected to one another in rotationally fixed relationship via an appropriate configuration of their foot portions that permits an interlocking and/or frictional connection. For example, the foot portions of the clamping elements could be designed as portions which are “hemispherical” relative to the axis of rotation of the holding portion, each being provided at the joint face directed toward the other with a wedge-type toothing, which permits reliable clamping together of the two clamping elements. 
     FIG. 10, FIG. 11, FIG.  12  and FIG. 13 show a second practical example of the present invention. This second practical example differs from the first practical example substantially only in the axial fixation of clamping device  39  in the holding portion. Thus only the differences compared with the first practical example will be explained hereinafter. 
     Holding portion  32  of tool holder  22  is illustrated in longitudinal section in FIG.  10 . As follows from FIG. 10, holding portion  32  is provided with an axial, central recess  120 , which substantially comprises recess  30  for hollow shank  28 , a recess  121  in the form of an elliptical cross section and cylindrical guide recess  31 . In recess  121  of elliptical cross section there is formed recess  46  in the form of a closed annular cross section for nesting of retaining portions  44  of clamping elements  40 . 
     Recess  121  in the form of an elliptical cross section can be seen in particular in FIG. 11, FIG.  12  and FIG.  13 . FIG.  11  and FIG. 12 correspond substantially to a cross section through the inventive clamping system shown in FIG. 2 in joined-together condition, clamping device  39  together with clamping elements  40  being shown in different angular orientations. FIG. 13 corresponds to a cross section through the inventive clamping system in clamped condition, as shown in FIG.  1 . 
     On the basis of the diagrams in FIG. 11, FIG.  12  and FIG. 13, installation/removal of clamping device  39  in/from recess  120  of holding portion  32  of tool holder  22  will be explained hereinafter. Assembly/disassembly of the tool on/from the tool holder takes place substantially in the same manner as in the first practical example, and so further explanations in this regard are unnecessary. 
     Installation of clamping device  39  begins firstly with pinching together of the clamping fork, or in other words clamping members  38  of clamping elements  40 . This takes place in the same manner as was explained in relation to the first practical example. 
     In the pinched-together condition of the clamping fork, clamping device  39  can then be introduced axially into recess  120  of holding portion  32  of tool holder  22 , the angular orientation of the clamping device relative to tool holder  22  during introduction into recess  120  being illustrated in FIG.  11 . In this angular orientation, plane El is oriented perpendicular to a plane EB, which connects the foci of the elliptical cross section of recess  121  and includes longitudinal or rotational axis  43 . Accordingly, clamping elements  40  of clamping device  39  only have to be pinched together radially to the extent that substantially cylindrical clamping device  39  can be introduced into elliptical recess  121 . 
     Whereas in the first practical example clamping members  38  are moved radially outward only by turning tightening screw  42  to the right in order to be able to fix clamping device  39  axially in recess  120 , in the second practical example clamping device  39  is merely turned around axis of rotation  43  by 90° relative to tool holder  22  after it has been inserted completely into recess  121 , or in other words is bearing against the bottom of guide recess.  31 , so that plane El and plane EB are disposed in a common plane. In the process, the direction in which the clamping device is turned is immaterial. As shown in FIG. 12, such turning of the clamping device has the consequence that retaining portions  44  are brought into engagement with undercut recess  46 , and so clamping device  39  becomes axially fixed in holding portion  32  of tool holder  22 . 
     After insertion of the tool into the tool holder, the clamping system is ultimately brought into the clamped condition by turning tightening screw  42  to the right, as is known from the first practical example illustrated in FIG.  1 . 
     Removal of clamping device  39  from recess  121  of tool holder  22  naturally takes place in reverse sequence. 
     Accordingly, this second practical example differs from the first practical example only in the features of the axial fixation of the clamping device in the tool holder, which in this case takes place substantially in the manner of a bayonet fastener. 
     FIGS. 14 to  20  show a third practical example of the inventive clamping system. The third practical example of the inventive clamping system differs from the first and second practical examples substantially only in the configuration of clamping elements  40  of the clamping fork as well as tightening screw  42 . Thus only the differences compared with the first practical example will be explained hereinafter. 
     FIGS. 14 and 15 show the inventive clamping system in the clamped condition. FIGS. 16 and 17 show the inventive clamping system in detached condition. In FIGS. 18 to  20 , the clamping fork of the inventive clamping system is illustrated in various views. 
     As is evident in particular from FIGS. 18 and 19, clamping elements  40  are each provided on the sides of their foot portions  41  connected as one piece with two notches  130  and  132  normal to longitudinal or rotational axis  43  of tool holder  22 , the said notches being produced, for example, by milling. Notches  130  and  132  reduce the cross section of clamping elements  40  compared with the cross sections of clamping elements  40  in the first and second practical example. In the third practical example of the inventive clamping system, portion  131  in the region of notches  130  functions in particular as a “material articulated joint”, which is elastically deformed when the clamping system is detached, or in other words when the two clamping elements  40  are pinched together as tightening screw  42  is turned. By virtue of this feature, which is simple to achieve structurally, the force necessary to pinch the two clamping elements  40  together, or in other words to bring the clamping system into the detached position illustrated in FIGS. 16 and 17, is smaller by comparison with the first and second practical examples, in which clamping elements  40  are not provided with notches. In order to be able to apply the force necessary to pinch clamping elements  40  together in the clamping system according to the first and second practical examples, clamping elements  40  must have a certain “lever length”, considered in axial direction. In the third practical example, by virtue of the reduction of the cross section of clamping elements  40  by notches  130  and  132 , a smaller force is necessary to pinch clamping elements  40  together, or in other words to bring the clamping system into the detached position illustrated in FIGS. 16 and 17. If it is required that the same pinching force can be applied on the two clamping elements  40  in the clamping system according to the first, second and third practical example by turning tightening screw  42 , notches  130 ,  132  provided on clamping elements  40  of the clamping system according to the third practical example therefore permit considerable shortening of clamping elements  40  and thus of the clamping system on the whole. Besides the material and weight savings achieved in this way and the resulting lower manufacturing costs, simpler assembly is additionally possible by this feature, which is simple to achieve structurally. 
     Bracing segments  140 , which can be seen in FIGS. 14 and 16, are disposed in notches  132 . The purpose of bracing segments  140  is to prevent “kinking” of clamping elements  40  in response to a torque, oriented in clockwise direction relative to FIGS. 14 and 16, while the clamping system is being clamped, or in other words when clamping elements  40  are moving apart from one another. In the detached position of the clamping system shown in FIG. 16, these bracing elements, which preferably are made from aluminum or another metal, are freely movable in notches  132 . In the clamped position of the clamping system shown in FIG. 16, these bracing segments  140  are pinched between the flank faces defining notches  132 , thus imparting stiffness to clamping elements  40 , so that neither one can kink “backward” around an imaginary fulcrum represented by the inside circumferential wall portion of guide recess  31  of holding portion  32  between undercut recess  46  and recess  30  of holding portion  32 . 
     A further difference of the clamping system according to the third practical example compared with the clamping system according to the first and second practical examples can be recognized in the configuration of tightening screw  42 . Whereas tightening screw  42  in the first and second practical examples is made in one piece with head portion  52  and threaded portion  56 , tightening screw  42  according to the third practical example has two-piece configuration. From FIGS. 14 to  17  it follows that tightening screw  42  has a threaded portion  56  with a left-hand threaded portion  56   b  and a right-handed threaded portion  56   a , one of which is disposed in threaded bore  62  of upper clamping member  38  in FIGS. 14 to  17  and the other is disposed in a nut functioning as head portion  52  and disposed in recess  57  of lower clamping member  38 . The advantage of this configuration is that, by virtue of the left-hand/right-hand thread of tightening screw  42 , relatively small turning movements are necessary to bring about a relatively large “stroke” of clamping members  38 ; furthermore, the nut functioning as head portion  52  is loaded substantially only in tension, and so neither the nut nor the corresponding clamping members  38  are subjected to severe frictional wear. Further refinements of this tightening screw  42  according to the third practical example are evident in FIGS. 14 to  17 . 
     Assembly/disassembly of the tool on/from the tool holder as well as the mode of operation of the clamping system according to the third practical example take place in principle in the same manner as in the clamping systems according to the first and second practical examples, and so more detailed explanation is not necessary at this place. 
     Naturally the specific features of the first, second and third practical examples can be combined with one another or substituted for one another as desired, to the extent that this is technically possible and seems to be expedient. 
     The present invention therefore provides a clamping system for detachably connecting two parts, which preferably are rotationally symmetric, of which one part has a preferably cylindrical or tapered hollow shank and the other part has a corresponding holding portion for holding the hollow shank in accurately fitting relationship. The clamping system is provided with a clamping device, which is disposed concentrically in the holding portion and which, in the joined-together condition of the two parts, extends into the hollow shank of the one part and is provided with at least two clamping members which can move in opposite directions as well as with an actuating device for driving the clamping members. The clamping members can be engaged with and disengaged from an undercut clamping shoulder of the hollow shank, whereby a pressing force is generated between plane faces of the two parts to be connected. The clamping members are constructed as head portions of elongated clamping elements, which are disposed substantially parallel to the longitudinal or rotational axis of the holding portion and the foot portions of which are connected to one another.