Clamping device

Abstract

A clamping device for releasably holding a tool holder shank formed with a bore includes a housing having a forwardly facing surface and a bore. A drawbar is mounted reciprocally movable inside the bore and in a forward end has engagement device, which is arranged to engage with an engagement formation inside the bore of the tool holder shank. The drawbar is, in a rear portion, formed with a drawbar aperture, and a cam shaft extending through the drawbar aperture and being rotatably journalled in the housing and arranged to impart an axial displacement to the drawbar in relation to the housing. The cam shaft includes first and second spaced apart cam formations and an intermediate circular cylindrical portion located between the cam formations, wherein the first and second cam formations are journalled in a first and second seating apertures, respectively, in the housing on opposite sides of the drawbar.

Claims

1. A clamping device for releasably holding a tool holder shank formed with a bore comprising: a housing having a forwardly facing surface and a bore intersecting the forwardly facing surface and extending rearwardly therefrom for receiving the tool holder shank; a drawbar mounted reciprocally movable inside the bore and which in a forward end includes a plurality of engagement segments arranged to engage with an engagement formation inside the 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 including a cam formation, wherein 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 wherein the cam shaft includes first and second spaced apart cam formations and an intermediate circular cylindrical portion located between the cam formations, the first and second cam formations being rotatably journalled in a first and second seating aperture, respectively, in the housing on opposite sides of the drawbar, whereas the intermediate circular cylindrical portion is extended through the drawbar aperture, wherein each of the cam formations includes a first cam surface, each having a same cam pitch per angular measurement and being operable to urge the drawbar rearward to a locked position, in which it firmly locks the tool holder shank to the clamping device, as well as a second cam surface, each having the same cam pitch per angular measurement and being operable to positively displace the drawbar forward to an unlocked position in which the tool holder shank is releasable from the clamping device, wherein the drawbar is insertable into the bore through the forwardly facing surface, and wherein the second cam formation has a smaller cross-sectional dimension than the first cam formation, such that the second cam formation is insertable through the first seating aperture and the drawbar aperture during mounting of the drawbar into the clamping device.

2. The clamping device according to claim 1, wherein the drawbar aperture has a mainly circular shape being formed with an extended portion in a forward direction.

3. The clamping device according to claim 1, wherein the drawbar is formed with a relatively flat and thin body portion at an area around the aperture.

4. The clamping device according to claim 1, wherein the cam shaft has a length that does not reach through the housing.

5. The clamping device according to claim 1, further comprising a fluid channel extending within the housing from its rear end to its forward end and passes by the cam shaft in an area between the end of the second cam formation and the outer circumference of the housing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1-3 illustrate an embodiment of a prior art clamping device.

(2) FIG. 4 is a perspective view of a clamping device according to the present disclosure.

(3) FIG. 5 is an exploded perspective view according to FIG. 4.

(4) FIG. 6 is a perspective view from above of a cam shaft of the clamping device.

(5) FIG. 7 is a perspective view from below of the cam shaft according to FIG. 6.

(6) FIG. 8 is a side view of the cam shaft according to FIGS. 6 and 7.

(7) FIG. 9 is a view from below of the cam shaft in FIGS. 6-8.

(8) FIG. 10 is a plan view of a drawbar of the clamping device.

(9) FIG. 11 is a side view of the drawbar in FIG. 10.

(10) FIG. 12 is a longitudinal cross-section through the clamping device and the tool holder, along the center line, in an initial, unlocked stage.

(11) FIG. 13 is a side view of the clamping device.

(12) FIG. 14 is a longitudinal cross-section along the line XIV-XIV in FIG. 13 in the unlocked stage.

(13) FIG. 15 is a longitudinal cross-section along the line XV-XV in FIG. 13 in the unlocked stage.

(14) FIG. 16 is a longitudinal cross-section along the line XVI-XVI in FIG. 13 in the unlocked stage.

(15) FIG. 17 is a cross-section along the line XVII in FIG. 13 in the unlocked stage;

(16) FIG. 18 is a longitudinal cross-section through the clamping device and the tool holder, along the center line, in an activated, locked stage.

(17) FIG. 19 is a side view of the clamping device.

(18) FIG. 20 is a longitudinal cross-section along the line XX-XX in FIG. 13 in the locked stage.

(19) FIG. 21 is a longitudinal cross-section along the line XXI-XXI in FIG. 13 in the locked stage.

(20) FIG. 22 is a longitudinal cross-section along the line XXII-XXII in FIG. 13 in the locked stage.

(21) FIG. 23 is a cross-section along the line XVIII-XVIII in FIG. 13 in the locked stage.

DETAILED DESCRIPTION

(22) Referring to FIGS. 4 and 5, a clamping device 10 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 herein 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 a rotating spindle of a working machine or the like (not shown).

(23) The clamping device includes a somewhat elongated, cylindrical shaped housing 13 having an inner bore 14. On its envelope surface the housing is provided with a hole 15 for mounting of a cam shaft 16 into 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.

(24) 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, the tool holder is also 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 or polygonal shape ensures an unrotatably fixation of the mounting shank in relation to the mounting bore.

(25) 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 having a drawbar 19, a compression spring 20, a thrust ring 21, an elastic o-ring 22, a plurality of engagement segments 23, a retainer ring 24 which is split into two pieces and a stop ring 25 arranged within the bore 14 of the cylindrically formed housing 13.

(26) A sealing ring 26 is also arranged between the drawbar and the inner bore of the housing. The hole 15 is formed through the housing wall perpendicular to its center axis 27 and in an assembled state the cam shaft 16 is inserted into the hole and through an aperture 28 in the drawbar. After insertion of the cam shaft into the hole 15, a cover 29 is positioned over the hole and secured by means of screws in order to prevent removal of the cam shaft, wherein the cover 29 in its turn is provided with a through hole 30 to allow access to the hex socket drive 17 of the cam shaft for insertion of a hex socket wrench for setting of the cam shaft in the assembled state.

(27) The cam shaft 16 is illustrated in more detail in a perspective view from above and below according to FIGS. 6 and 7, respectively, a side view according to FIG. 8 and an end view according to FIG. 11, which is seen from below in FIGS. 6-8. In the upper end the cam shaft has a head formed with the hex socket drive 17. Around a part of the hex socket drive the head is provided with a flange 31 which defines the depth of insertion into the housing and is provided with a stop lug 32, which is arranged to interact with stop surfaces within the hole 15 of the housing for restriction of the maximal turning angle of the cam shaft.

(28) Reference is now made to FIGS. 10 and 11, in which the drawbar 19 is illustrated in a plan view and a side view, respectively. Since the cam shaft 16 is to be inserted through the aperture 28 from one side of the drawbar, the aperture has to have a sufficient large cross-sectional dimension in order to let the cam shaft through. That condition is one of the determinant factors for how large the largest cross-sectional dimension of the drawbar will be, since two leg portions 33, which interconnect the forward and rear portions of the drawbar with each other, has to have a sufficient cross sectional dimension in order to withstand the large forces that the drawbar is subjected to during clamping of a tool holder.

(29) Accordingly, in order to restrict the cross-sectional dimension of the drawbar to such an extent that it can be inserted into the housing through the clamping bore 14 from the forward end of the housing, it is also necessary to restrict the largest cross-sectional dimension of the cam shaft. Accordingly, this is achieved by providing the cam shaft with two cam formations and more precisely a first, large cam formation 34 positioned adjacent the flange 31 and a second, small cam formation 35 positioned at the other end of the cam shaft and being spaced apart by a circular cylindrical portion 36.

(30) The cam formations are arranged to be journalled in first and second seating apertures 37, 38, respectively, in the housing on opposite sides of the drawbar, as is best seen from FIGS. 13, 15, 19 and 21. The cam formations 34 and 35 have different sizes, but are similarly shaped to that extent that they each is formed with a first cam surface 34, 35, each having the same cam pitch per angular measure, as well as a second cam surface 34, 35, each having the same cam pitch per angular measure.

(31) The intermediate circular cylindrical portion 36 is, in the assembled state of the clamping device, positioned within the aperture 28 of the drawbar. This has the result that the end of the cam shaft having the small cam formation 35 can pass through an aperture of the drawbar having a relatively small width in a direction perpendicular to its centre axis 27. In this way, the maximum width of the drawbar can be restricted to such an extent that it can be inserted through the clamping bore 14 from the forward end of the clamping device and yet the cross sectional dimensions of the leg portions 33 can be sufficient large to withstand the occurring forces during clamping of a tool holder.

(32) As is evident from FIG. 10, aperture 28 of the drawbar has a mainly circular shape. However, on a part of the aperture facing in a forward direction the aperture is formed with an extended portion 39 in the direction of its center axis 27. During insertion of the cam shaft 16 through the aperture 28 the largest cross-sectional dimension of the second cam formation 35 can thus be located in parallel with the center axis and pass through the extended portion 39 of the aperture, which makes it possible to restrict the width of the aperture in a direction perpendicular to the centre axis and accordingly also the overall width of the drawbar 19.

(33) As can be further seen from FIGS. 10 and 11, the aperture of the drawbar 19 is formed in a relatively flat and thin body portion 40 at the rear part of the drawbar. In its forward end it is formed with a drawhead 41, which is connected to the body portion via a neck portion 42. Between the neck portion and the body portion the drawbar is also formed with a circular flange 43 and a groove 44 for accommodating the sealing ring 26.

(34) Reference is now made to FIGS. 12-17 in which is illustrated an unlocked state when the tool holder just has been inserted with its mounting shank 18 into the mounting bore 14 of the clamping device or is to be removed from the clamping device. FIG. 12 is a section along the center line 27 of the assembled tool holder 11 and the clamping device 10 with all its components mounted in place. FIG. 13 is a side view of the clamping device in parallel to the cam shaft and here is indicated the longitudinal and cross-sections in which the FIGS. 14-17 are viewed in the unclamped state of the cam shaft 16 and the drawbar 19. For the sake of simplicity, the clamping device is shown without the tool holder and the coupling mechanism in FIGS. 14-17.

(35) In FIGS. 12-17 the clamping device is in an initial state with the cam shaft 16 rotated to a counter clockwise end position in which the tool holder is unlocked from the clamping device. As can be seen, the engagement segments 23 are mounted around the neck portion 42 of the drawbar in a space formed between the neck portion and an inner surface of an engagement bore within the mounting shank 18 of the tool holder. The engagement segments 24 are held in place by an outward extending flange portion 45 of each engagement segment being in engagement with an inner groove inside the two-part retainer ring 24, and the elastic o-ring 22 is positioned in an outward facing groove formation in the rear end of the engagement segments.

(36) The forward ends of the engagement segments are formed with outward directed engagement flanges 46, which are arranged to engage with an inner engagement groove 47 inside the engagement bore of the tool holder, but are in this initial state out of engagement with the engagement groove. Moreover, the compression spring 20 is mounted between a shoulder face 48 of the housing and the thrust ring 21 and forces it as well as the retainer ring 24 and the engagement segments 23 in the forward direction against the stop ring 25.

(37) In this unlocked state the cam shaft is rotated such that the second cam surfaces 34, 35 of the first and second cam portions 34, 35 act on rear bearing surfaces 37 and 38, respectively, of the bearing apertures 37, 38 (FIGS. 14 and 16) such that the cam shaft 16 is displaced in a direction forward, and the cylindrical portion 36 act on a forward surface of the aperture in the drawbar and, accordingly, the drawbar will be displaced in a forward direction.

(38) Reference is now made to the FIGS. 19-23 which are similar to the FIGS. 12-17. However, here the clamping device is in a locked or clamped state in which the mounting shank 18 is coupled to the clamping device by the coupling mechanism and drawn by the drawbar 19 and the cam shaft 16 with a large force into firm engagement within the mounting bore 14.

(39) This is accomplished in that the cam shaft, from the initial state according to FIGS. 12-17, is rotated clockwise about 180 from the unlocked position to a locked position, in which the first cam surfaces 34, 35 of the first and second cam formations 34, 35 act on forward bearing surfaces 37, 38 of the seating apertures 37, 38 of the housing, which will displace the cam shaft 16 rearward, whereas the cylindrical portion 36 act on a rear surface of the aperture in the drawbar and, accordingly, the drawbar will be displaced in a rearward direction.

(40) This locked position is illustrated in a longitudinal cross=section along the center axis according to FIG. 18. As can be seen, the thrust ring 21, the retainer ring 23 and the engagement segments 23 are still pushed forward toward the stop ring 25 by the compression spring 20, while the drawbar 19 is drawn rearward by the cam shaft 16 as described above. This has the effect that the drawhead 41 will be displaced inwards in relation to the engagement segments 23 such that their forward ends will slide on a rearward facing bevelled surface 49 of the drawhead 41. In this way the engagement flanges 46 on the forward ends of the engagement segments will be displaced outwards and engage with the engagement groove 47 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 14 in the housing.

(41) A further advantage with the clamping device as disclosed herein is that it is provided with a fluid channel 50 for distribution of cooling medium, liquid or gas, from the rear end of the clamping device to the tool holder. One difficulty with providing such a cooling system is that it is not desired that the fluid passes through the space where the cam shaft 16 is accommodated. For one reason it could be difficult to seal the cam shaft for preventing leakage of cooling fluid. Another problem is that some form of lubricant is normally used between the sliding surfaces of the cam shaft and the drawbar, which lubricant could be washed away if a cooling medium flows through there. These problems have been overcome by forming the drawbar 19 with a relatively flat and thin body portion 40 at the area around the aperture 28, as well as making the cam shaft 16 so short such that it does not reach through the housing 13. In this way the fluid channel can pass by the cam shaft within the housing in the area between the end of the second cam formation 35 and the outer circumference of the housing 13.

(42) The fluid channel can be formed by drilling a straight hole from the mounting bore 14 in the forward end as well as a straight hole from an engagement bore 51 within the mounting shank 12 in the rear end of the clamping device, wherein the straight holes meet at an angle in the area between the cam shaft and the outer circumference of the housing.

(43) 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.