Clamping device for tool holders

Abstract

A clamping device for releasably holding a toolholder shank (61) includes a housing (2), a drawbar (5) axially movable in a bore (3) in the housing between an advanced release position and a retracted locking position, a mating member (20) movable under the influence of the drawbar into locking engagement with the toolholder shank, a sleeve (30) disposed about a wall (14) of the housing and axially movable relative thereto, a first wedge (40) received in a first aperture (45) in the wall and configured to move the drawbar rearwardly in the bore when urged radially inwardly at the aperture by first axial movement of the sleeve, and a second wedge (50) received in a second aperture (55) in the wall and configured to move the drawbar forwardly in the bore when urged radially inwardly at the aperture by an opposite axial movement of the sleeve.

Description

[Technical field]

[0001] The invention relates to a clamping device according to the preamble of claim 1, which is intended to be used for connecting a tool holder to a machine tool. [Background technology]

[0002] Within the field of machine tools for metal cutting, cutting tools used for machining workpieces of metallic material, for example in the form of drills, milling tools or lathe tools, are often fixed in a tool holder, which may then be removably fixed in a clamping device mounted on the machine tool. It has been known for some time to clamp the shank of such a tool holder to a housing of a clamping device by means of a clamping mechanism arranged in said housing. Tool holders for cutting tools in the form of drills and milling tools are usually clamped to a rotatable housing in the form of a spindle, while tool holders for lathe tools may be clamped to a non-rotatably arranged housing. When a cutting tool needs to be exchanged, the tool holder is released from the housing of the clamping device and a new tool holder with a different cutting tool is clamped to the housing. A clamping device of this type may for example be removably fixed to the outer edge of a tool turret contained in the machine tool.

[0003] A clamping device comprising a spindle with a clamping mechanism adapted for automatic tool changing operations is previously known from EP 1 468 767 B1. In the clamping device according to EP 1 468 767 B1, an actuating member in the form of a first drawbar is slidably mounted inside the spindle, which is arranged to achieve an axial displacement of a second drawbar via a force amplification mechanism comprising a number of cooperating wedges arranged between them. A gas spring inside the spindle is arranged to bias the two drawbars into a retracted locking position, in which a tool holder is clamped to the spindle. A hydraulic piston may be arranged to act on the piston at the rear end of the gas spring in order to achieve a displacement of the two drawbars into an advanced release position in which the tool holder may be released from the spindle. However, this previously known clamping device has a relatively long axial extent and is therefore not suitable for use when the tool holder is removably fixed at the outer edge of a tool turret, where the axial space available for the clamping device is limited.

[0004] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide a clamping device of the above mentioned type which has a new and favourable design and which is suitable for use with a tool turret of a machine tool. Summary of the Invention

[0005] According to the invention, this object is achieved by means of a clamping device having the features defined in claim 1.

[0006] The clamping device according to the invention comprises: a housing having a forward end, a rearward end and a bore extending rearwardly across the forward end, a mounting site provided at the forward end of the bore for receiving a toolholder shank; a drawbar slidably mounted within the bore and adapted to be reciprocally movable in the bore along its longitudinal axis between an advanced release position and a retracted locking position; a mating member disposed about the draw bar at its forward end, the mating member being movable under the influence of movement of the draw bar from an advanced release position to a retracted locking position from a first position in which the mating member enables the toolholder shank to move into and out of a mounting portion of the bore to a second position in which the mating member is in locking engagement with the toolholder shank and keeps it fixed to the housing; a first wedge slidably received in a first aperture extending radially through a peripheral wall of the housing, the first wedge including a first wedge surface facing toward a rear end of the housing and in contact with a first sliding surface on the drawbar facing toward a front end of the housing, and a first pressure surface facing outwardly from the housing, the first wedge configured to urge the drawbar toward a retracted, locking position when urged radially inward in the first aperture; a second wedge slidably received in a second aperture extending radially through the peripheral wall, the second wedge including a second wedge surface facing toward the front end of the housing and in contact with a second slide surface on the drawbar facing toward the rear end of the housing, and a second pressure surface facing outwardly from the housing, the second wedge configured to urge the drawbar toward an advanced release position when urged radially inward in the second aperture; an actuation sleeve disposed around the peripheral wall and slidably mounted thereon, adapted to be movable axially relative to the housing in a first axial direction to effect movement of the drawbar from the advanced release position to the retracted locking position, and in an opposite second axial direction to effect movement of the drawbar from the retracted locking position to the advanced release position, the actuation sleeve being provided on its inner side with a first pressure surface facing inwardly for contact with the first pressure surface and having a radial distance to the longitudinal axis that is longer as viewed in the first axial direction, and a second pressure surface facing inwardly for contact with the second pressure surface and having a radial distance to the longitudinal axis that is longer as viewed in the second axial direction; Includes.

[0007] The first pressure surface of the actuation sleeve is configured to press the first wedge radially inward at the first aperture by pressing against the first pressure surface when the actuation sleeve is moved in the first axial direction. The second pressure surface of the actuation sleeve is configured to press the second wedge radially inward at the second aperture by pressing against the second pressure surface when the actuation sleeve is moved in the second axial direction. Thus, the drawbar is movable from an advanced release position to a retracted locking position by movement of the actuation sleeve in the first axial direction under the influence of the actuation sleeve and the first wedge, and the drawbar is movable from a retracted locking position to an advanced release position by movement of the actuation sleeve in the second axial direction under the influence of the actuation sleeve and the second wedge.

[0008] The first pressure surface of the actuation sleeve has a radial distance to the longitudinal axis that increases in the first axial direction, so that movement of the actuation sleeve in the first axial direction causes the first pressure surface to apply a pressure to the first pressure surface of the first wedge, the pressure having a radial component such that the first wedge is forced radially inward toward the longitudinal axis.

[0009] The second pressure surface of the actuation sleeve has a radial distance to the longitudinal axis that increases in the second axial direction, so that movement of the actuation sleeve in the second axial direction causes the second pressure surface to apply a pressure to the second pressure surface of the second wedge, the pressure having a radial component such that the second wedge is forced radially inward toward the longitudinal axis.

[0010] By using the actuating sleeve described above to control the axial movement of the drawbar, no gas spring or similar, which takes up a lot of space in the axial direction, is needed to control the axial movement of the drawbar, which implies that the clamping device can be made axially compact. The clamping device is therefore suitable for use in tool turrets. Furthermore, the use of separate wedges to control the axial movement of the drawbar in two different directions implies that the design of the first wedge can be optimized to meet the specific requirements associated with the movement of the drawbar from the advanced release position to the retracted locking position, and the design of the second wedge can be optimized to meet the specific requirements associated with the opposite movement of the drawbar from the retracted locking position to the advanced release position.

[0011] The above-mentioned housing of the clamping device may have the form of a rotatable spindle. It may be connected or connectable to a drive mechanism in the tool turret of the machine tool. However, the clamping device of the invention is not limited to use in a tool turret, and such a housing in the form of a rotatable spindle may alternatively constitute the main spindle of the machine tool or may be connected to such a main spindle without any intermediate tool turret. If the housing has the form of a rotatable spindle, the clamping device may be used to clamp a tool holder to which a drilling or milling tool or other type of rotating tool is provided. The housing included in the clamping device of the invention may, as a further alternative, be a non-rotatable housing. In the latter case, the clamping device may be used to clamp a tool holder to which a lathe tool or other type of non-rotating tool is provided.

[0012] According to an embodiment of the invention, when the drawbar is forced into the retracted locking position under the influence of the actuation sleeve and the first wedge, the actuation sleeve is configured to assume a self-locking axial position on the peripheral wall of the housing, thereby maintaining the drawbar in the retracted locking position. The actuation sleeve is thereby able to maintain the drawbar in the retracted locking position without requiring any external force from the actuator. This implies that in connection with a tool changing operation, the actuation sleeve only needs to be subjected to external forces from an actuator, for example in the form of a hydraulic or pneumatic actuator.

[0013] According to another embodiment of the invention, the first pressure surface and the first pressure surface are inclined with respect to the longitudinal axis at such an angle α that the first wedge maintains the actuation sleeve in a self-locking axial position at the circumferential wall when the drawbar is forced into the retracted locking position under the influence of the actuation sleeve and the first wedge. In this case, both the first pressure surface and the first pressure surface extend in the same direction when viewed in a longitudinal section through the housing. The angle α is chosen to be less than the self-locking threshold angle so that the actuation sleeve is in a self-locking axial position relative to the first wedge when the drawbar is displaced inside the bore into the retracted locking position. To obtain a self-locking axial position, the angle α should be sufficiently small, i.e. less than the self-locking threshold angle. The self-locking axial position refers to the axial position. Here, the static friction force between the first pressure surface of the first wedge and the first pressure surface of the actuation sleeve is greater than the opposing force in the plane of friction caused by the force applied to the first wedge in a radial direction perpendicular to the longitudinal axis. The axial position of the self-locking is thus obtained within an angle range that depends on the coefficient of friction between the first pressure surface of the first wedge and the first pressure surface of the actuation sleeve. This coefficient of friction depends on various parameters such as the material used, the surface coating, the use of lubricants, etc. The self-locking threshold angle is therefore determined by such parameters. A person skilled in the art will be able to determine the self-locking threshold angle that applies in each particular case by using common general knowledge and / or routine experimentation, or at least by predicting or assessing whether a particular angle is below such a self-locking threshold angle. In general, it is preferable to choose an angle α that is sufficiently below the self-locking threshold angle, thereby ensuring a self-locking configuration. A further benefit of using a small angle α is that a force multiplying effect is achieved, thanks to the fact that a small angle α implies that a relatively long axial displacement of the working sleeve results in a relatively short axial displacement of the drawbar.However, a too small angle α may be inefficient and may not function well in practice. For example, a very small angle α may indicate that it is difficult to release the actuation sleeve from the self-locking axial position. The angle α is preferably between 2° and 10°. If the angle α is within this range, the self-locking effect may be achieved, as well as a suitable force amplifying effect.

[0014] Another embodiment of the present invention comprises: the first wedge includes a third pressure surface facing outwardly from the housing; the actuation sleeve is provided on its interior side with a third pressure surface facing inwardly for contact with the third pressure surface, the third pressure surface having a radial distance to the longitudinal axis that is greater in the first axial direction; the third pressure surface and the third pressure surface are inclined at an angle β with respect to the longitudinal axis that is greater than the angle α; The first and third pressure surfaces and the first and third pressure receiving surfaces are respectively arranged consecutively in the first wedge in the actuating sleeve, and are characterized in that after movement of the actuating sleeve in the first axial direction, the third pressure surface is configured to slide over and press against the third pressure receiving surface in the first wedge during a first phase of the movement, and the first pressure surface is configured to slide over and press against the first pressure receiving surface in the first wedge during a subsequent second phase of the movement.

[0015] Thereby, the drawbar may be moved axially quickly during the initial phase of clamping under the effect of a larger angle β. This initial clamping phase does not require a large force. However, during the final phase of clamping, a large force is required to displace the drawbar a short distance. Once the actual clamping occurs, i.e. when the mating members assume the above-mentioned first position, the drawbar is moved axially under the effect of a smaller angle α, so that the axial movement of the drawbar is small compared to the axial movement of the working sleeve, which provides a force multiplying effect, also called "power boost". The angle β is preferably between 10° and 75°, preferably between 35° and 65°, which provides an efficient initial axial movement of the drawbar. By using a tight angle β for the initial axial movement of the drawbar and a small angle α for the actual clamping, the working sleeve (and therefore the entire clamping device) can be made relatively short in the axial direction, while still providing a self-locking clamping mechanism with a large force multiplying effect.

[0016] According to another embodiment of the invention, the first and third pressure surfaces and the first and third pressure receiving surfaces are curved as viewed in a cross section perpendicular to the longitudinal axis, which facilitates manufacturing of the actuation sleeve.

[0017] According to another embodiment of the invention, the first and second pressure surfaces partially overlap each other in the axial direction of the actuation sleeve and are spaced apart from each other in the circumferential direction of the actuation sleeve. The length of the actuation sleeve may be shortened thereby. Furthermore, the second pressure surface is preferably provided in a recess formed in the rotationally symmetric inner wall surface of the actuation sleeve.

[0018] According to another embodiment of the invention, the clamping device comprises two or more such first wedges spaced apart in the circumferential direction of the peripheral wall, each first wedge being received in a first aperture extending radially through the peripheral wall. The clamping device may also comprise two or more such second wedges spaced apart in the circumferential direction of the peripheral wall, each second wedge being received in a second aperture extending radially through the peripheral wall. The first apertures and the associated first wedges, as well as the second apertures and the associated second wedges, are preferably distributed equidistantly in the circumferential direction of the peripheral wall. This results in a well-balanced clamping device with good distribution of forces. A large number of wedges and associated apertures may however be undesirable due to the fact that each aperture reduces the strength of the housing. The three first wedges, three second wedges and associated apertures provide a balanced clamping device with an appropriate level of force distribution while still maintaining sufficient strength of the housing. The first and second wedges are preferably arranged in an alternating manner in the circumferential direction of the peripheral wall, such that each one of the first wedges is followed by one of the second wedges in the circumferential direction of the peripheral wall, and each one of the second wedges is followed by one of the first wedges in the circumferential direction of the peripheral wall.

[0019] Further advantageous features of the clamping device according to the invention will emerge from the following description and from the dependent claims.

[0020] A specific description of embodiments of the present invention follows, given by way of example with reference to the accompanying drawings in which: [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a side view of a clamping device according to one embodiment of the present invention, in which a tool holder is clamped to a housing of the clamping device. [Diagram 2] 2 is a longitudinal cross-sectional view through the clamping device and tool holder shown in FIG. 1 with the drawbar of the clamping device in a retracted, locking position and the tool holder clamped to the housing. [Diagram 3] FIG. 2 is a partial cutaway perspective view of the clamping device of FIG. 1; [Figure 4] FIG. 3 is a longitudinal cross-sectional view corresponding to FIG. 2. [Diagram 5] FIG. 2 is a longitudinal section through the clamping device and tool holder shown in FIG. 1 with the drawbar in an advanced release position. [Figure 6] 2 is a longitudinal cross-sectional view through the clamping device and tool holder shown in FIG. 1 with the drawbar in an intermediate position between the advanced release position and the retracted locking position. [Figure 7] FIG. 2 is an exploded view of the clamping device and tool holder of FIG. 1; [Figure 8] FIG. 2 is an exploded view of the clamping device and tool holder of FIG. 1 from another angle. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 5 is a cross-sectional view taken along line XX in FIG. [Figure 11] FIG. 5 is a cross-sectional view taken along line XI-XI in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A clamping device 1 according to one embodiment of the present invention is shown in Figures 1 to 10. The clamping device 1 is configured to releasably clamp a tool holder 60 (shown very diagrammatically in the figures) to a clamping device housing 2 to enable machining of a workpiece with a cutting tool (not shown) fixed to the tool holder 60.

[0023] The housing 2 has a forward end 2a, a rearward end 2b and a bore 3 intersecting the forward end 2a and extending rearwardly therefrom. The bore 3 thus has an inlet opening 3a (see FIG. 3) at the housing's forward end 2a. The housing 2 is connectable to a tool turret of a machine tool via a connecting member 4 extending from the housing 2 at its rearward end.

[0024] In the embodiment shown, the housing 2 has the form of a machine spindle, which may be rotatably mounted by means of rolling bearings in a surrounding casing. In this case, the housing 2 may be connectable via the connecting member 4 to a drive mechanism of a machine tool, such as a drive mechanism in a tool turret of the machine tool, in order that the housing 2 can be rotationally driven by the drive mechanism. However, the housing 2 may alternatively be designed as a non-rotatable housing.

[0025] The drawbar 5 is slidably mounted inside the bore 3 of the housing 2 and is reciprocally movable therein along its longitudinal axis L between an advanced release position (see FIG. 5) and a retracted locking position (see FIGS. 2 and 4). The drawbar 5 has a front end facing the entrance opening 3a of the bore 3 and an opposite rear end. A head section 6 and a neck section 7 are provided at the front end of the drawbar 5. The head section 6 is located in front of the neck section 7 in the longitudinal direction of the drawbar and is connected to the neck section 7 via an inclined surface 8 at the head section 6 facing rearwards. A sealing ring 9 is arranged between the drawbar 5 and the inner surface of the bore 3. In the example shown, this sealing ring 9 is received in an outer groove of the drawbar 5.

[0026] The drawbar 5 is prevented from rotating relative to the housing 2. In the embodiment shown, two planar wall sections 5c, 5d (see Figures 2 and 9) are provided on both opposite sides of the drawbar 5 at a portion of the drawbar located behind the neck region 7, which planar wall sections 5c, 5d are in sliding contact with respective planar surfaces 3c, 3d in the bore 3 to prevent mutual rotation between the drawbar 5 and the housing 2. However, mutual rotation between the drawbar 5 and the housing 2 could be prevented in any other suitable manner.

[0027] A mounting site 10 for receiving a mounting shank 61 in a toolholder 60 is provided at the front end of the bore 3. This mounting shank 61 is referred to herein as the toolholder shank.

[0028] In the embodiment shown, the housing 2 comprises a base part 12 and an end piece 13 mounted on the base part 12 at the front end 2a of the housing. The end piece 13 has the form of a sleeve with an axial through hole forming part of the aforementioned bore 3. In this case, the aforementioned mounting area 10 is located in the through hole of the end piece 13. Alternatively, the part of the housing 2 which contains the bore 3 may be formed in one piece without any end piece of the aforementioned type.

[0029] The toolholder shank 61 can be inserted into the mounting area 10 of the bore 3 through an inlet opening 3a at the front end 2a of the housing 2. The head part 6 of the drawbar is received in a mating bore 62 in the toolholder shank 61, the tubular wall 63 of which is received in the space between the head part 6 and the inner surface of the end piece 13. In the embodiment shown here, the mounting area 10 is conical in shape and has a somewhat "triangular" or polygonal, non-circular cross-sectional shape adapted to receive a similarly shaped toolholder shank 61. This conical shape ensures a play-free connection between the toolholder shank 61 and the housing 2 in the radial as well as the axial direction, while this non-circular cross-section ensures a non-rotatable fixation of the toolholder shank 61 to the housing 2. However, the mounting area 10 may also have any other suitable shape for receiving other types of toolholder shanks.

[0030] A mating member 20 in the form of a segment is arranged around the drawbar 5 at its front end. Under the effect of movement of the drawbar 5 from an advanced release position to a retracted locking position, the mating member 20 is movable from a first position (see FIG. 5 ), in which the mating member 20 allows the toolholder shank 61 to move into and out of the resting portion 10 of the bore 3, to a second position (see FIGS. 2 and 4 ), in which the mating member 20 is in locking engagement with a mating groove 64 in a mating bore 62 in the toolholder shank 61, thereby keeping the toolholder shank 61 fixed to the housing 2.

[0031] In the illustrated embodiment, the mating members 20 are disposed about the neck portion 7 of the drawbar 5 and are held thereabout by means of a retainer ring 21 and a resilient O-ring 22 disposed in the bore 3 and surrounding the neck portion 7. Each of the mating members 20 has an outwardly facing flange portion 23 that engages in an internal groove in the retainer ring 21. The O-ring 22 is received in the outwardly facing groove at the rear end of each of the mating members 20. A compression spring 24 is also disposed in the bore 3 and is configured to surround the drawbar 5. The compression spring 24 rests between a shoulder on the drawbar 5 and the retainer ring 21 and is configured to bias the retainer ring 21 and the mating members 20 forwardly. Forward movement of the retainer ring 21 toward the entrance opening of the bore 3 is limited by a shoulder 25 provided in the bore 3. In the example shown, this shoulder 25 is formed by the rearward facing end face of the end piece 13 .

[0032] At its front end, each of the mating members 20 is provided with an outwardly directed mating flange 27 that is adapted to engage with a mating groove 64 in the toolholder shank 61 when the mating member 20 is in the second position described above. When the drawbar 5 is in the advanced release position, each of the front ends of the mating members 20 is located behind the head portion 6 of the drawbar 5 and the mating flange 27 is out of engagement with the mating groove 64 in the toolholder shank 61, as shown in FIG. 5. When the drawbar 5 is moved axially rearward in the bore 3 along its longitudinal axis L, the inclined surface 8 in the head portion 6 of the drawbar comes into contact with each of the front ends of the mating members 20. Each of the front ends of the mating members 20 slides over this inclined surface 8 and is forced outwardly so that the mating flange 27 of the mating member comes into engagement with the mating groove 64 in the toolholder shank 61. Thereafter, the tool holder shank 61 is pulled by the draw bar 5 and comes into close contact with the inner surface of the end piece 13 at the mounting portion 10 described above.

[0033] The clamping device 1 further comprises an actuation sleeve 30 arranged around a peripheral wall 14 of the housing 2, slidably mounted on said peripheral wall 14 and adapted to be axially movable relative to the housing 2 along a longitudinal axis L. The actuation sleeve 30 is non-rotatably mounted on the housing 2, i.e. prevented from rotating relative to the peripheral wall 14. In the example shown, balls 15 (see Figures 7 and 8) are arranged between the actuation sleeve 30 and the housing 2. The balls 15 are distributed around the peripheral wall 14, each of them being partially housed in a recess in the peripheral wall 14 and partially in a longitudinal groove 38 in the actuation sleeve 30. The balls 15 are fixed in their axial position relative to the peripheral wall 14 by being received in a recess on the outer side of the peripheral wall. The ball 15 is slidably received in a longitudinal groove 38 on the inside of the actuation sleeve 30, which allows the actuation sleeve 30 to move axially relative to the ball 15 as the actuation sleeve is moved axially relative to the peripheral wall 14. The ball 15 prevents mutual rotation between the actuation sleeve 30 and the peripheral wall 14.

[0034] The one or more first wedges 40 are mounted on the housing 2 and configured to transmit an axial movement of the actuating sleeve 30 in a first axial direction D1 relative to the housing 2 to a movement of the drawbar 5 from an advanced release position to a retracted locking position. Furthermore, the one or more second wedges 50 are mounted on the housing 2 and configured to transmit an axial movement of the actuating sleeve 30 in an opposite second axial direction D2 relative to the housing 2 to a movement of the drawbar 5 from a retracted locking position to an advanced release position. In the embodiment shown here, the first axial direction D1 is toward the front end 2a of the housing 2, and the second axial direction D2 is toward the rear end 2b of the housing 2. Thus, in this case, the movement of the drawbar 5 from the advanced release position to the retracted locking position is achieved by a forward axial movement of the actuating sleeve 30 along the peripheral wall 14, while the movement of the drawbar 5 from the retracted locking position to the advanced release position is achieved by a rearward axial movement of the actuating sleeve 30 along the peripheral wall 14. However, as an alternative, the actuating sleeve 30 and the first and second wedges 40, 50 can be arranged to cooperate such that the movement of the drawbar 5 from the advanced release position to the retracted locking position is achieved by a rearward axial movement of the actuating sleeve 30 along the peripheral wall 14, while the movement of the drawbar 5 from the retracted locking position to the advanced release position is achieved by a forward axial movement of the actuating sleeve 30 along the peripheral wall 14. Thus, in the latter case, the first axial direction D1 is towards the rear end 2b of the housing 2, and the second axial direction D2 is towards the front end 2a of the housing 2.

[0035] In the illustrated embodiment, the clamping device 1 includes three first wedges 40 spaced circumferentially about the peripheral wall 14. Each of the first wedges 40 is slidably received in a respective first aperture 45 extending radially through the peripheral wall 14. The first wedges 40 are configured to together urge the drawbar 5 toward a retracted, locking position when they are urged radially inward in their associated first apertures 45.

[0036] The clamping device 1 may include any suitable number of first wedges 40 disposed in the peripheral wall 14 of the housing 2 and extending through a corresponding number of first apertures 45. The first wedges 40 and associated first apertures 45 are preferably distributed equidistantly circumferentially about the peripheral wall 14.

[0037] Each of the first wedges 40 includes a first pressure surface 41 facing outward from the peripheral wall 14 of the housing 2, and the actuation sleeve 30 is provided on its inside with a first pressure surface 31 facing inward for contacting the first pressure surface 41 of the first wedge. Each of the first pressure surfaces 31 has a radial distance to the longitudinal axis L that is longer in the above-mentioned first axial direction D1. The first pressure surface 31 is configured to press the first wedge 40 radially inward at the first aperture 45 by pressing the first pressure surface 41 of the first wedge when the actuation sleeve 30 is moved in the first axial direction D1.

[0038] Each of the first wedges 40 also includes a wedge surface 46 facing the rear end 2b of the housing 2 and in contact with the first slide surface 16 on the drawbar 5 facing the front end 2a of the housing. When the first wedges 40 are pushed radially inwardly at the first aperture 45 by the actuation sleeve 30, the wedge surface 46 of each of the first wedges 40 slides over and presses against the corresponding first slide surface 16 on the drawbar, thereby moving the drawbar 5 toward the retracted, locking position.

[0039] In the embodiment shown, the wedge surface 46 of each of the first wedges and the associated first slide surface 16 of the drawbar 5 are formed as planes. They are inclined with respect to the longitudinal axis L as seen in a longitudinal section through the housing 2 perpendicular to the longitudinal axis L. In this case, the surfaces 16, 46 are linear as seen in a section perpendicular to the longitudinal axis L, as shown in FIG. 10. The wedge surface 46 of each of the first wedges and the associated first slide surface 16 of the drawbar 5 may alternatively be curved as seen in a section perpendicular to the longitudinal axis L. In the latter case, the surfaces 16, 46 are not planar. As a further alternative, one of the surfaces 16, 46 may be curved as seen in a longitudinal section through the housing 2 perpendicular to the longitudinal axis L.

[0040] When the drawbar 5 is forced into the retracted locking position under the influence of the actuation sleeve 30 and the first wedge 40, the actuation sleeve 30 is preferably configured to assume a self-locking axial position on the peripheral wall 14, such that the actuation sleeve 30 is able to maintain the drawbar 5 in the retracted locking position. In the self-locking axial position, frictional forces between the actuation sleeve 30 and the first wedge 40 and / or the peripheral wall 14 parts in contact with the actuation sleeve 30 prevent the actuation sleeve from being displaced axially in the second axial direction D2.

[0041] The first pressure surface 31 and the first pressure receiving surface 41 are preferably inclined with respect to the longitudinal axis L by such an angle α (see FIG. 4 ) that when the drawbar 5 is forced into the retracted locking position under the influence of the operating sleeve 30 and the first wedge 40, the first wedge 40 maintains the operating sleeve 30 in a self-locking axial position at the peripheral wall 14.

[0042] In the illustrated embodiment, the clamping device 1 includes three second wedges 50 spaced circumferentially about the peripheral wall 14. Each of the second wedges 50 is slidably received in a respective second aperture 55 extending radially through the peripheral wall 14. The second wedges 50 are configured to together urge the drawbar 5 toward an advanced release position when they are urged radially inward in their associated second apertures 55.

[0043] The clamping device 1 may include any suitable number of second wedges 50 disposed in the peripheral wall 14 of the housing 2 and extending through a corresponding number of second apertures 55. The second wedges 50 and associated second apertures 55 are preferably distributed equidistantly circumferentially about the peripheral wall 14.

[0044] Each of the second wedges 50 includes a second pressure surface 52 facing outward from the peripheral wall 14 of the housing 2, and the actuation sleeve 30 is provided on its inside with a second pressure surface 32 facing inward for contacting the second pressure surface 52 of the second wedge. Each of the second pressure surfaces 32 has a radial distance to the longitudinal axis L that is longer in the above-mentioned second axial direction D2. The second pressure surface 32 is configured to press the second wedge 50 radially inward at the second aperture 55 by pressing the second pressure surface 52 of the second wedge when the actuation sleeve 30 is moved in the second axial direction D2.

[0045] Each of the second wedges 50 also includes a wedge surface 57 facing the front end 2a of the housing 2 and in contact with the second slide surface 17 on the drawbar 5 facing the rear end 2b of the housing. When the second wedges 50 are pushed radially inwardly at the second aperture 55 by the actuation sleeve 30, the wedge surface 57 of each of the second wedges 50 slides over and presses against the corresponding second slide surface 17 on the drawbar, thereby moving the drawbar 5 towards the advanced locking position.

[0046] In the embodiment shown, the wedge surface 57 of each of the second wedges and the associated second slide surface 17 at the drawbar 5 are formed as planes. They are inclined with respect to the longitudinal axis L as seen in a longitudinal section through the housing 2 perpendicular to the longitudinal axis L. In this case, the surfaces 17, 57 are linear as seen in a section perpendicular to the longitudinal axis L, as shown in FIG. 11. The wedge surface 57 of each of the second wedges and the associated second slide surface 17 at the drawbar 5 may alternatively be curved as seen in a section perpendicular to the longitudinal axis L. In the latter case, the surfaces 17, 57 are not planar. As a further alternative, one of the surfaces 17, 57 may be curved as seen in a longitudinal section through the housing 2 perpendicular to the longitudinal axis L.

[0047] Each of the first wedges 40 may also include a third pressure surface 43 facing outward from the peripheral wall 14 of the housing 2, and the actuation sleeve 30 is provided on its inside with a third pressure surface 33 facing inward for contacting the third pressure surface 43 of each of the first wedges. The third pressure surface 33 has a radial distance to the longitudinal axis L that is longer as seen in the first axial direction D1. The third pressure surface 33 and the third pressure surface 43 are inclined with respect to the longitudinal axis L by an angle β (see FIG. 6 ) that is greater than the above-mentioned angle α. The first and third pressure surfaces 31, 33 and the first and third pressure receiving surfaces 41, 43 are arranged consecutively on the actuating sleeve 30 and each of the first wedges 40, such that after movement of the actuating sleeve 30 in the first axial direction D1, the third pressure surface 33 is configured to slide over and press against the associated third pressure receiving surface 43 during an initial first phase of movement, and thereafter the first pressure surface 31 is configured to slide over and press against the associated first pressure receiving surface 41 during a subsequent second phase of movement.

[0048] In the embodiment shown, the third pressure surface 33 on the actuation sleeve 30 has the form of an annular, rotationally symmetric surface. In this case, there is only one third pressure surface 33 on the actuation sleeve 30. However, the actuation sleeve 30 may alternatively be provided with a number of separate third pressure surfaces 33 corresponding to the number of first wedges 40, with the third pressure receiving surface 43 on each of the first wedges 40 being associated with its own third pressure surface 33 on the actuation sleeve 30.

[0049] The first and third pressure surfaces 31, 33 and the first and third pressure receiving surfaces 41, 43 are preferably curved as viewed in a cross section perpendicular to the longitudinal axis L. The second pressure surface 32 and the second pressure receiving surface 52 may also be curved as viewed in a cross section perpendicular to the longitudinal axis L. However, one or more of the pressure surfaces 31, 32, 33 and the pressure receiving surfaces 41, 52, 43 may alternatively have a planar form and, as a result, be linear as viewed in a cross section perpendicular to the longitudinal axis L. In the embodiment shown, each of the second pressure surfaces 32 is provided in a recess 34 formed in the rotationally symmetric inner wall surface 35 of the actuation sleeve 30. Furthermore, in the embodiment shown, a portion 39 of this rotationally symmetric inner wall surface 35 on the inside of the actuation sleeve is conical, and the first pressure surfaces 31 are provided in different parts of this conical wall portion 39.

[0050] The first wedges 40 and the second wedges 50 are preferably arranged alternately in the circumferential direction of the peripheral wall 14, such that each one of the first wedges 40 is followed by one of the second wedges 50 in the circumferential direction of the peripheral wall 14, and each one of the second wedges 50 is followed by one of the first wedges 40 in the circumferential direction of the peripheral wall 14.

[0051] In the embodiment shown, the first pressure surface 31 and the second pressure surface 32 partially overlap each other in the axial direction of the actuation sleeve 30 and are spaced apart from each other in the circumferential direction of the actuation sleeve 30 .

[0052] The first and second wedges 40, 50 are received in a non-rotatable manner in the associated first and second apertures 45, 55 in the peripheral wall 14 of the housing 2, i.e. each wedge is prevented from rotating in its associated aperture. In the embodiment shown, each wedge 40, 50 and each associated aperture 45, 55 in the peripheral wall 14 have mutual contact surfaces with a circular cross-sectional shape. In this case, a ball 18 (see Figures 10 and 11) is arranged between each wedge 40, 50 and the inner surface of the associated aperture 45, 55, said ball 18 being partially received in a recess 48, 58 in the envelope surface of the wedge and partially in an elongated groove 19 in the inner surface of the aperture. By being received in the recess 48, 58 in its envelope surface, the ball 18 remains fixed in position relative to the associated wedge 40, 50. The ball 18 is slidably received in an elongated groove 19 in the associated aperture 45, 55, allowing the wedge 40, 50 to move axially in the associated aperture 45, 55 while the ball 18 prevents the wedge from rotating in the aperture. Alternatively, the envelope surface of the wedge 40, 50 and the inner surface of the aperture 45, 55 may have a non-circular cross-sectional shape, such as an elliptical cross-sectional shape, to prevent the wedge from rotating in the associated aperture.

[0053] The clamping device 1 may also include additional components, such as one or more hydraulic or pneumatic actuators, to achieve movement of the actuation sleeve 30 in the first and second axial directions D1, D2. The control of the clamping device 1 may be easily automated using actuators or the like, making the clamping device 1 according to the invention suitable for use in automated tool changing operations. However, the clamping device 1 according to the invention may also be adapted for manual operation.

[0054] When the toolholder 60 is clamped in the housing 2, the toolholder shank 61 is inserted into the resting portion 10 of the bore 3, with the drawbar 5 in the advanced release position, as shown in FIG. 5. The head portion 6 of the drawbar is thus received in the mating bore 62 in the toolholder shank 61, and the mating groove 64 in the toolholder shank 61 is located outside the mating flange 27 of the mating member 20. The actuation sleeve 30 is then moved in the first axial direction D1, for example by means of a hydraulic or pneumatic actuator or by manual operation. During this first phase of the axial movement of the actuation sleeve 30, the third pressure surface 33 of the actuation sleeve 30 slides over and presses against the third pressure surface 43 of the first wedge 40. This causes the first wedge 40 to be pressed radially inwards, displacing the drawbar 5 axially towards the retracted locking position. The relatively steep inclination β of the third pressure and pressure surfaces 33, 43 causes the first wedge 40 to move inwards rather quickly initially, which results in a relatively rapid displacement of the drawbar 5. The relatively steep angle β is preferred because it does not require large forces for the initial displacement of the drawbar 5. The first and third pressure surfaces 31, 33 and the first and third pressure surfaces 41, 43 are arranged such that when the operating sleeve 30 is moved a distance such that the third pressure surface 33 passes the third pressure surface 43 and the first pressure surface 31 reaches the first pressure surface 41, i.e. at the transition between these respective surfaces, the drawbar 5 reaches approximately its final retracted position in the bore 3. Thus, for the final clamping phase, where large forces are beneficial, the first pressure and pressure surfaces 31, 41 are active. In this phase, the relatively large movement of the working sleeve 30 results in a very small radial displacement of the first wedge 40 and an even smaller axial displacement of the drawbar 5, which in turn provides a force multiplying effect, enabling the drawbar 5 to pull the toolholder shank 61 with great force into firm engagement with the housing 2.Furthermore, the small inclination α of the first pressure and pressure surfaces 31, 41 provides a self-locking effect, ensuring that the clamping device remains clamped without the need for any additional locking means, whereby the force on the actuation sleeve 30 may be released when the drawbar 5 reaches the retracted, locked position.

[0055] When a tool change operation is performed and the tool holder 60 is released from the housing 2, the actuation sleeve 30 is moved in the second axial direction D2. When the actuation sleeve 30 is subjected to a sufficient force in the second axial direction D2, the self-locking friction engagement between the first pressure surface 31 of the actuation sleeve 30 and the first pressure surface 41 of the first wedge 40 is released, after which the actuation sleeve 30 can move in the second axial direction relative to the housing 2. When the actuation sleeve 30 is moved in this direction, the second pressure surface 32 of the actuation sleeve 30 slides over and presses against the second pressure surface 52 of the second wedge 50. This causes the second wedge 50 to be pressed radially inwards, displacing the drawbar 5 axially towards the advanced release position. As the drawbar 5 is moved towards the advanced release position, the outer end of the head portion 6 of the drawbar 5 abuts against a surface 65 in the mating bore 62 in the toolholder shank 61, thereby releasing the toolholder shank 61 from the housing 2. During movement of the drawbar 5 towards the advanced release position, the first slide surface 16 on the drawbar 5 presses against the wedge surface 46 on the first wedge 40, thereby pushing the first wedge 40 radially outward. The radially outward movement of the first wedge 40 is limited by a stop ring 36 fixed in an annular groove 37 on the inside of the working sleeve 30.

[0056] The present invention is of course not in any way limited to the embodiments described above: on the contrary, many possibilities for modification thereof will become apparent to those skilled in the art without departing from the basic concept of the invention as defined in the appended claims.

Claims

1. 1. A clamping device for releasably retaining a tool holder shank, comprising: a housing (2) having a front end (2a), a rear end (2b) and a bore (3) intersecting said front end (2a) and extending rearwardly therefrom, said bore (3) being provided at its front end with a mounting portion (10) for receiving said toolholder shank (61); a drawbar (5) slidably mounted within said bore (3) and adapted to be reciprocally movable therein along its longitudinal axis (L) between an advanced release position and a retracted locking position; a mating member (20) arranged at its front end around the drawbar (5), the mating member (20) being movable under the effect of movement of the drawbar (5) from the advanced release position to the retracted locking position from a first position in which the mating member (20) enables the toolholder shank (61) to move in and out of the mounting portion (10), to a second position in which the mating member (20) is in locking engagement with the toolholder shank (61) and keeps it fixed to the housing (2); a first wedge (40) including a wedge surface (46) facing the rear end (2b) of the housing and a first pressure receiving surface (41); A clamping device (1) comprising: the first wedge (40) is slidably received in a first aperture (45) extending radially through the peripheral wall (14) of the housing (2), the first pressure surface (41) of the first wedge facing outwardly from the housing (2) and the wedge surface (46) of the first wedge contacting a first slide surface (16) of the drawbar facing toward the front end (2a) of the housing, the first wedge (40) being configured to urge the drawbar (5) toward the retracted locking position when urged radially inwardly in the first aperture (45); the clamping device (1) includes a second wedge (50) slidably received in a second aperture (55) extending radially through the peripheral wall (14), the second wedge (50) including a second wedge surface (57) facing toward the front end (2a) of the housing and in contact with a second slide surface (17) of the drawbar facing toward the rear end (2b) of the housing, and a second pressure surface (52) facing outwardly from the housing (2), the second wedge (50) being configured to urge the drawbar (5) toward the advanced release position when urged radially inward in the second aperture (55); the clamping device (1) is arranged around the peripheral wall (14) and comprises an actuating sleeve (30) slidably mounted thereon and adapted to be axially movable relative to the housing (2) in a first axial direction (D1) for effecting movement of the drawbar (5) from the advanced release position to the retracted locking position and in an opposite second axial direction (D2) for effecting movement of the drawbar (5) from the retracted locking position to the advanced release position, the actuating sleeve (30) being provided on its inner side with a first pressure surface (31) facing inwardly for contact with the first pressure surface (41) and having a radial distance to the longitudinal axis (L) and a second pressure surface (32) facing inwardly for contact with the second pressure surface (52) and having a radial distance to the longitudinal axis (L), the first pressure surface (31) is configured to press the first pressure surface (41) and thereby press the first wedge (40) radially inwardly at the first aperture (45) when the operating sleeve (30) is moved in the first axial direction (D1); the second pressure surface (32) is configured to push the second wedge (50) radially inwardly at the second aperture (55) by pushing the second pressure surface (52) when the operating sleeve (30) is moved in the second axial direction (D2). Clamping device (1).

2. 2. The clamping device according to claim 1, characterized in that when the drawbar (5) is forced into the retracted locking position under the influence of the actuating sleeve (30) and the first wedge (40), the actuating sleeve (30) is configured to assume a self-locking axial position on the peripheral wall (14), thereby maintaining the drawbar (5) in the retracted locking position.

3. A clamping device as described in claim 2, characterized in that when the drawbar (5) is pushed into the retracted locking position under the influence of the operating sleeve (30) and the first wedge (40), the first pressure surface (31) and the first pressure receiving surface (41) are inclined relative to the longitudinal axis (L) at an angle α such that the first wedge (40) maintains the operating sleeve (30) in a self-locking axial position on the peripheral wall (14).

4. The first wedge (40) includes a third pressure surface (43) facing outward from the housing (2); the actuation sleeve (30) is provided on its inner side with a third pressure surface (33) facing inwards for contact with the third pressure surface (43), the third pressure surface (33) having a radial distance to the longitudinal axis (L); The third pressure surface (33) and the third pressure receiving surface (43) are inclined at an angle β with respect to the longitudinal axis (L) that is greater than the angle α, the first and third pressure surfaces (31, 33) and the first and third pressure receiving surfaces (41, 43) are arranged successively on the actuation sleeve (30) and on the first wedge (40), respectively, and after a movement of the actuation sleeve (30) in the first axial direction (D1), the third pressure surface (33) is configured to slide over and press against the third pressure receiving surface (43) during a first phase of the movement, and the first pressure surface (31) is configured to slide over and press against the first pressure receiving surface (41) during a subsequent second phase of the movement. The clamping device of claim 3 .

5. 5. The clamping device according to claim 1, wherein the first and third pressure surfaces (31, 33) and the first and third pressure receiving surfaces (41, 43) are curved when viewed in a cross section perpendicular to the longitudinal axis (L).

6. The clamping device according to any one of claims 1 to 5, characterized in that the first pressure surface (31) and the second pressure surface (32) partially overlap each other in the axial direction of the operating sleeve (30) and are spaced apart from each other in the circumferential direction of the operating sleeve (30).

7. 7. The clamping device according to claim 6, characterized in that the second pressure surface (32) is provided in a recess (34) formed in a rotationally symmetric inner wall surface (35) of the actuating sleeve (30).

8. 8. The clamping device according to claim 1, wherein the clamping device (1) comprises two or more first wedges (40) spaced circumferentially about the peripheral wall (14), each first wedge (40) being received in a first aperture (45) extending radially through the peripheral wall (14).

9. 9. The clamping device according to claim 8, characterized in that the first wedges (40) are three in number.

10. 10. A clamping device according to claim 8 or 9, characterized in that the first wedges (40) are distributed equidistantly in the circumferential direction of the peripheral wall (14).

11. 11. The clamping device according to any one of claims 8 to 10, characterized in that the clamping device (1) includes two or more such second wedges (50) spaced circumferentially about the peripheral wall (14), each second wedge (50) being received in a second aperture (55) extending radially through the peripheral wall (14).

12. Clamping device according to claim 11, characterized in that the second wedges (50) are three in number.

13. Clamping device according to claim 11 or 12, characterized in that the second wedges (50) are distributed equidistantly in the circumferential direction of the peripheral wall (14).

14. 14. The clamping device according to claim 11, wherein the first wedges (40) and the second wedges (50) are arranged alternately in the circumferential direction of the peripheral wall (14), such that each one of the first wedges (40) is followed by each one of the second wedges (50) in the circumferential direction of the peripheral wall (14) and each one of the second wedges (50) is followed by each one of the first wedges (40) in the circumferential direction of the peripheral wall (14).

15. Clamping device according to any one of the preceding claims, characterized in that the housing (2) is a machine spindle.

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