Abstract:
A clamping device for releasably holding a tool holder shank is formed with an engagement bore in a rear end. The clamping device includes a housing having a mounting bore for receiving the tool holder shank; a drawbar being mounted reciprocally movable inside the housing and which in a forward end is provided with an engagement segment which is arranged to engage with an engagement formation inside the engagement bore of the tool holder shank, wherein the drawbar is in a rear portion formed with a drawbar aperture extending through the drawbar, and a cam shaft extending through the drawbar aperture and comprising a cam formation. The cam shaft is rotatably journalled in the housing and arranged to impart an axial displacement to the drawbar in relation to the housing by the cam formation when rotating the cam shaft. The cam shaft includes two identical cam formations, which are spaced apart by a recess, and the drawbar is on the inside of the aperture formed with a ridge on each side of the aperture which each fits in the recess of the cam shaft when rotating the same.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority under 35 U.S.C. §119 to EP Patent Application No. 14181386.5, filed on Aug. 19, 2014, which the entirety thereof is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a clamping device for releasably holding a tool holder shank formed with an engagement bore in a rear end, including a housing having a forwardly facing surface and a mounting bore intersecting the forwardly facing surface and extending rearward therefrom for receiving the tool holder shank; a drawbar being mounted reciprocally movable inside the housing and which in a forward end is provided with an engagement device which is adapted to go into engagement with an engagement formation inside the engagement bore of the tool holder shank, the drawbar being in a rear portion formed with a drawbar aperture extending through the drawbar in a transverse direction in relation to a longitudinal axis of the same; and a cam shaft extending through the drawbar aperture and comprising a cam formation, wherein the cam shaft is rotatably journalled in the housing and adapted to impart an axial displacement to the drawbar in relation to the housing by the cam formation when rotating the cam shaft 
       BACKGROUND 
       [0003]    Clamping devices are well known and widely used within the manufacturing industry for holding different kinds of tools for machining of work pieces of various materials. The clamping device may optionally be carried on a rotatable spindle, for holding e.g. a drill or a milling tool, or be unrotatable for holding e.g. a lathe tool. 
         [0004]    One advantage with a clamping device of this kind is that it allows for a quick clamping of the tool, simply by rotating the cam shaft by about 100° to 200°, which has to effect that the tool will be drawn by a large force into the mounting bore of the housing and thereby be securely held by the clamping device. Also the releasing of the tool can be easily and rapidly performed by rotating the cam shaft in the reverse direction. Normally, the bore of the housing as well as the tool holder shank are also made slightly conical such that they are tapering in an axial direction rearward from the tool. In this way the connection between the tool and the clamping device also can be made totally free from any play which has to effect that the tool will be held in an exact position which allows for high precision machining by means of the tool. 
         [0005]    However, one disadvantage with prior art clamping devices of this kind is that the drawbar is made with a comparatively large cross-sectional dimension such that it cannot, with the desirable cross-sectional measures of the tool holder shanks frequently being used, be inserted through the bore of the housing from its forward end. The reason why the drawbar has to be made with such a large cross-sectional dimension is that the drawbar aperture has to accommodate a cam shaft having a cam formation of a sufficient size in order to provide the desired displacement of the cam shaft and the desired force reduction for the operator performing the rotation of the cam shaft during clamping and releasing. However, in order to ensure sufficient tensile strength of the drawbar to withstand the desirable forces by which the tool holder shank is drawn into the shank bore, the remaining leg portions of the drawbar surrounding the drawbar aperture must be made with a sufficient cross-sectional dimension. An example of a prior art design of a clamping device will be described more in detail in connection with the hereinafter detailed description. 
         [0006]    Accordingly, in order to position the drawbar in place when assembling the clamping device, the drawbar has up to the present been inserted from the rear end of the clamping device or a shank bore sleeve has been mounted in the forward end of the clamping device after that the drawbar has been inserted into the housing from the forward end. One consequence of this is that the overall dimensions of the clamping device cannot be made as small and slim as desired. Another consequence is that the clamping device will comprise extra mounting details which will render the clamping device more expensive to manufacture, both in respect of material costs and costs for performing the assembling. 
       SUMMARY 
       [0007]    It is an aspect of the disclosure to provide a clamping device by which the drawbar is insertable into the housing through the bore of the housing from its forward end. 
         [0008]    Accordingly, the drawbar can be made with an overall cross-sectional dimension, which is so small such that it can be inserted through the housing bore from the forward end of the housing. This is accomplished in that instead of a single continuous cam formation, as in prior art clamping devices, the cam shaft is provided with a recess which divides the cam formation into two separate cam formations. In this way, it is possible to provide the inside surfaces of the two leg portions, which interconnect the forward and rear portions of the drawbar with each other, with reinforcing ridges in the longitudinal direction of the drawbar, which ridges fit within the recess between the cam formations when rotating the cam shaft. 
         [0009]    Due to the contribution from these ridges to the structural strength of the drawbar, the overall cross-sectional dimension of drawbar can be made so small such that the drawbar can be inserted through the housing bore from the forward end of the housing. The aperture for the cam shaft through the drawbar can be made with a larger free space in the axial direction than in the direction perpendicular to the axial direction, such that the largest dimension of the cam shaft can be oriented in the axial direction during insertion of the cam shaft through the aperture. 
         [0010]    It is apparent that the device can be varied and modified in many different ways within the scope of the claim. For example, in the hereinafter described and illustrated exemplary embodiment, the mounting bore of the clamping device is conically formed and has a somewhat “triangular” or polygonal shape in cross section for clamping a tool holder having a similarly shaped mounting shank. However, the mounting bore could also have a different shape for clamping other types of mounting shanks. Moreover, in the exemplary embodiment the drawbar of the clamping device is provided with a separate detachable bolt in the forward end. This is advantageous inter alia because it makes it easier to arrange the fluid channels for cooling medium through the drawbar. However, the drawbar could of course also be formed with a forward directed stud of a suitable shape which is integrated with the rest of the drawbar. 
         [0011]    In the description and claims throughout this application the term “forward” is used to indicate a direction or position towards the outer opening of the mounting bore through which the tool holder shank is inserted during clamping. In analogy, the terms “rear” or “rearward” are used to indicate a direction or position away from the outer opening of the mounting bore. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    An embodiment of a prior art clamping device as well as an exemplary embodiment of a clamping device according to the present disclosure, will hereinafter be described with reference to the accompanying drawings, in which: 
           [0013]      FIGS. 1-3  illustrate an embodiment of a prior art clamping device. 
           [0014]      FIG. 4  is a perspective view of a clamping device according to the disclosure coupled to a tool holder. 
           [0015]      FIG. 5  is an exploded perspective view according to  FIG. 4 . 
           [0016]      FIG. 6  is a perspective view of a cam shaft of the clamping device. 
           [0017]      FIG. 7  is a view from below of the cam shaft in  FIG. 6 . 
           [0018]      FIG. 8  is a perspective view of a drawbar of the clamping device. 
           [0019]      FIG. 9  is a cut-off perspective view of the drawbar in  FIG. 8 . 
           [0020]      FIG. 10  is a partly cut-through perspective view of the housing, the drawbar and the cam shaft of the clamping device. 
           [0021]      FIG. 11  is a longitudinal section through the clamping device and the tool holder, along the line XI-XI in  FIG. 12 , in an initial, unlocked stage. 
           [0022]      FIG. 12  is a side view according to  FIG. 11 . 
           [0023]      FIG. 13  is a partly cut-through perspective view according to  FIGS. 11 and 12 . 
           [0024]      FIG. 14  is a longitudinal section through the clamping device and the tool holder, along the line XI-XI in  FIG. 12 , in an activated, locked stage. 
           [0025]      FIG. 15  is a longitudinal section along the line XV in  FIG. 14 . 
           [0026]      FIG. 16  is a longitudinal section along the line XVI in  FIG. 14 . 
           [0027]      FIG. 17  is a cross-section along the line XVII-XVII in  FIG. 14 . 
           [0028]      FIG. 18  is a longitudinal section through the clamping device and the tool holder, along the line XI-XI in  FIG. 12 , in a released, unlocked stage. 
           [0029]      FIG. 19  is a longitudinal section along the line XIX in  FIG. 18 . 
           [0030]      FIG. 20  is a longitudinal section along the line XX in  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    A prior art clamping device will now briefly be described by reference to  FIGS. 1-3 . This prior art clamping device is of an unrotatable kind, which is adapted to hold e.g. a lathe tool. As evident from  FIG. 1  an outer housing of the clamping device  1  is generally box-shaped and is shown connected to a schematically illustrated tool holder  2 .  FIG. 2  is an exploded perspective view of the clamping device and the tool holder showing all the separate components comprised in the clamping device. One of the components is a drawbar  3  being inserted into the housing in a bore  4 . The drawbar  3  regulates the clamping mechanism, the function of which is not described here, between a locked stage, in which the tool holder is firmly coupled to the clamping mechanism, and a released stage in which the tool holder is released from the clamping device. The regulating of the clamping mechanism is performed by displacement of the drawbar  3  in the axial direction of the bore  4  in the housing. The displacement of the drawbar is in its turn performed by rotating a cam shaft  5 , which extend through the housing and through an aperture in the drawbar, and which is provided with a cam formation which as desired can act on a rear surface of the aperture through the drawbar, which will displace the drawbar rearward, or on a forward surface of the aperture, which accordingly will displace the drawbar forward. 
         [0032]    However, due to the cam formation comprising a locking cam surface as well as a releasing cam surface, the cam shaft will have a rather large cross-sectional dimension and, accordingly, the aperture of the drawbar has to be formed with a correspondingly large cross sectional dimension in order to accommodate the cam shaft with its cam formation. As a result, the drawbar will be formed with rather large cross sectional dimensions since also the leg portions, which connect the forward and rear portions of the drawbar and are situated on a respective side of the drawbar aperture, must have a certain cross-sectional dimension in order to withstand the forces that will occur. This has the effect that with the commonly used dimensions of the mounting shanks for tools and tool holders, the drawbar cannot be inserted from the forward end of the clamping device since the passage will be too small. In the herein disclosed prior art clamping device this problem has been solved by mounting a separate sleeve  6  within the bore  4  of the housing which will define the shank bore for the mounting shank of the tool holder. Accordingly, the drawbar is mounted into the housing prior to mounting the shank bore sleeve  6 . 
         [0033]    One problem with such a solution is that the costs for manufacturing the clamping device will increase. Another problem is that using a separate shank bore sleeve will introduce one further component having its own manufacturing tolerances, which will deteriorate the precision of the machining work performed by means of the tool. 
         [0034]    Reference is first made to  FIG. 4  in which a clamping device  10  according to the disclosure and a schematic and cut-off tool holder  11  coupled to a forward end of the clamping device are illustrated in a perspective view. The tool holder is here schematically illustrated such that only its cut-off, rear end is shown but in practice some form of machining tool is connected to the tool holder, either integrated with the tool holder or as a separate connected part. In a rear end the clamping device is provided with a mounting shank  12 , which is arranged to be connected to e.g. a rotating spindle (not shown) of a working machine or the like. The clamping device includes a somewhat elongated, cylindrical shaped housing  13  having an inner bore  14  ( FIG. 5 ). On its envelope surface the housing is provided with a through-hole  15  for mounting of a cam shaft  16  through the housing, and which gives access to an engagement formation in form of a hex socket drive  17  at an end of the cam shaft. 
         [0035]      FIG. 5  is an exploded perspective view of the clamping device and tool holder  11  according to  FIG. 4  showing the various components forming part of the clamping device. Like the clamping device, also the tool holder is provided with a mounting shank  18 , which in the illustrated embodiment both are of a kind disclosed in U.S. Pat. No. 5,340,248, comprising a conical shank having an axial bore and a somewhat “triangular” or polygonal, non-circular cross section, which is adapted to be drawn into a correspondingly shaped mounting bore  14 . The conical shape ensures a connection free from play in the radial as well as the axial direction, whereas the “triangular” shape ensures an unrotatably fixation of the mounting shank in relation to the mounting bore. In order to draw the mounting shank  18  of the tool holder into the mounting bore of the clamping device, the latter is provided with a coupling mechanism including a drawbar  19 , a compression spring  20 , a retainer ring  21 , an elastic o-ring  22 , a plurality of engagement segments  23  and an end bolt  24  arranged within the bore  14  of the cylindrically formed housing  13 . Two sealing rings  25  are also arranged between the drawbar and the inner bore of the housing. The through hole  15  is formed through the housing perpendicular to its center axis  26  and in an assembled state the cam shaft  16  is inserted into the through hole and through an aperture  27  in the drawbar. 
         [0036]    The cam shaft  16  is illustrated more in detail in a perspective view according to  FIG. 6  and an end view in  FIG. 7 , which is seen from below in  FIG. 6 . In one end the cam shaft includes a head being formed with an engagement formation in form of a hex socket drive  17  arranged to be engaged by a hex socket wrench for setting of the cam shaft. Around the hex socket drive the head is provided with a large, circular surface which functions as a bearing surface  28  to be rotatably journalled at one side of the housing. 
         [0037]    The middle portion of the cam shaft is formed with two identical cam formations  29  spaced apart by a recess  30 , which extends in the circumferential direction of the cam shaft. In the other end the cam shaft is provided with a small, circular surface which functions as a bearing surface  31  to be rotatably journalled at the other side of the housing, as well as a stop lug  32  to limit the extent of rotation in relation to the housing. As can be seen from  FIG. 7  the cam formations each have two cam surfaces. More particularly, one first, locking cam surface  33  is operative for displacing the drawbar rearwardly in the axial direction away from the mounting bore and locking the tool to the clamping device, and one second, releasing cam surface  34  being operative for displacing the drawbar forward in the axial direction towards the mounting bore and releasing the tool from the clamping device. 
         [0038]    Referring to  FIGS. 8 and 9 , the drawbar  19  is illustrated in a complete perspective view and a cut-off perspective view, respectively. As with prior art clamping devices of this kind, an aperture  27  is formed through the drawbar in a direction perpendicular to its longitudinal axis, through which the cam shaft extends in the assembled state of the clamping device. However, according to the invention, the inside surfaces of two leg portions  35 , which interconnect the forward and rear portions of the drawbar with each other, are provided with reinforcing ridges  36  in the longitudinal direction of the drawbar, which ridges fit within the recess  30  between the cam formations  29  when rotating the cam shaft. Due to the contribution from these ridges to the structural strength of the drawbar, the overall cross sectional dimension of drawbar can be made so small such that the drawbar can be inserted through the housing bore from the forward end of the housing. The aperture for the cam shaft through the drawbar is made with a larger free space in the axial direction  26  than in the direction perpendicular to the axial direction, such that the largest dimension of the cam shaft can be oriented in the axial direction during insertion of the cam shaft  16  through the aperture  27 , as is illustrated in  FIG. 10 . 
         [0039]      FIG. 11  is a section along the longitudinal or center axis of the tool holder  11  and the clamping device  10  in an assembled state with all its components mounted in place. The clamping device is here in an initial stage when the tool shank  18  just has been inserted into the mounting bore but before the cam shaft  16  has been activated such that the tool shank has been coupled to the clamping device and drawn with a large force into the mounting bore of the housing  13 . As can be seen, the end bolt  24  is screwed into a hole in the forward end of the drawbar  19  and concentric with its centre axis  26 . Moreover, the engagement segments  23  are mounted around the drawbar and the end bolt in a space formed between an inner surface of an engagement bore in the rear end of the tool holder as well as the end bolt and the forward end of the drawbar. The engagement segments are held in place by means of an outward extending flange portion  37  of each engagement segments being in engagement with an inner groove inside the retainer ring  21 , and the elastic o-ring  22  being positioned in an outward facing groove formation in the rear end of the engagement segments. The forward ends of the engagement segments are formed with outward directed engagement flanges  38 , which are adapted to go into engagement with an inner engagement groove  48  inside the engagement bore of the tool holder but are in this initial stage out of engagement with the engagement groove. Moreover, the compression spring  20  is mounted between the drawbar  19  and the retainer ring  21  and act to displace the retainer ring and the engagement segments forwards. In this initial stage the cam shaft is rotated such that the releasing cam surfaces  34  act on the forward surface of the drawbar aperture and forces the drawbar forward. 
         [0040]    From the initial stage according to  FIG. 11 , the cam shaft can be rotated about 105° from a release position to a lock position, as is illustrated in  FIG. 12 , in which the locking cam surfaces  33  of the cam formations act on the rear surface of the drawbar aperture and forces the drawbar  19  rearward. This lock position is illustrated in a partly cut through perspective view along the center axis  26  of the clamping device and the tool holder according to  FIG. 13  and a longitudinal section along the center axis according to  FIG. 14 . As can be seen from these figures the retainer ring  21  and the engagement segments  23  are still pushed forward toward the end surface of the tool holder shank  18  by means of the compression spring  20 , while the drawbar  19  and the end bolt  24  are drawn rearward by means of the locking cam surfaces  33  of the cam shaft  16  acting on the rear surface of the drawbar aperture. This has to effect that the forward ends of the engagement segments will be displaced outwards by sliding on a rearward facing bevelled surface  39  on the end bolt  24 . In this way the engagement flanges  38  of the engagement segments will be displaced outwards and go into engagement with the engagement groove inside the engagement bore of the tool holder such that the tool holder shank  18  will be drawn by means of the drawbar  19  into firm bearing against the surfaces of the mounting bore of the housing. 
         [0041]      FIG. 15  is a longitudinal section along the line XV in  FIG. 14 , showing the locking cam surface  33  acting on the rear surface of the drawbar aperture  27  and consequently forcing the drawbar  19  rearwards into the locked stage. 
         [0042]      FIG. 16  is a longitudinal section along the line XVI in  FIG. 14 , showing the stop lug  32  of the cam shaft being in the locked position. However, the stop position is not an exactly predefined position since it can vary somewhat depending on the exact measures of e.g. the tool holder shank and the components being part of the locking mechanism of the clamping device. 
         [0043]      FIG. 17  is a cross section along the line XVII-XVII in  FIG. 14  showing the reinforcing ridge  36  on the inside surface of one of the leg portions  35  of the drawbar being positioned within the recess between the cam portions  29  of the drawbar in the locked stage. 
         [0044]    In  FIG. 18  is illustrated a longitudinal section along the center axis  26  of the tool holder  11  and the clamping device  10  in a releasing stage of the same. As evident, the cam shaft  16  is rotated to the release position such that the releasing cam surface  34  of each cam portion is acting on the forward surface of drawbar aperture and the drawbar  19  is thus forced forward. Accordingly, the engagement segments  23  will be displaced inward such that their engagement will be disengaged from the engagement groove on the inside of the engagement bore of the tool holder shank , which now therefore can be drawn out from the mounting bore of the housing  10 . 
         [0045]      FIG. 19  is a longitudinal section along the line XIX in  FIG. 18 , showing a releasing cam surface  34  of the cam shaft acting on the forward surface of the drawbar aperture  27  and forcing the drawbar in the forward direction. 
         [0046]      FIG. 20  is a longitudinal section along the line XX in  FIG. 18 , showing the stop lug  32  of the cam shaft being in a releasing position. Unlike the locking position the releasing position is a distinct position defined by a recess formed in the housing, since it is not desirable that the cam shaft should be able to rotate further than to that position. 
         [0047]    The illustrated embodiment of the invention is also provided with a system of fluid channels for cooling medium, which optionally can be liquid or gas, for allowing distribution of cooling medium from the mounting shank to the not disclosed machining tool in the outer end of the tool holder. The fluid channels, which commonly are indicated by reference number  40 , extend from the rear end of the mounting shank  12  of the housing to the bore of the housing, as can be seen from  FIGS. 11 ,  14  and  18 , through the drawbar  19  and its leg portions  35 , as can be seen from  FIGS. 8 ,  9 ,  10  and  17 , and debouch in the forward end of the drawbar as can be seen from  FIG. 5 . The cooling medium can then flow through the engagement mechanism of the clamping device and thereafter reach the engagement bore of the tool holder through channels formed in the end bolt as can be seen from  FIGS. 5 ,  10 ,  11  and  18 . One advantage with a system of fluid channels arranged like this is that the cooling medium will never pass the drawbar aperture and the cam shaft positioned therein, such that the cam shaft does not have to be sealed for avoiding leakage of cooling fluid between the cam shaft and the housing. Instead, it is sufficient to arrange sealing rings  25  between the drawbar and the inner bore of the housing on each side of the drawbar aperture. 
         [0048]    Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.