Clamping device for tool holders

Abstract

A clamping device for releasably holding a toolholder shank (81), comprising: a spindle (2) rotatably mounted inside a housing (3); a drawbar (8) axially movable in a bore (5) in the housing between a forward release position and a retracted locking position; an engagement member (20) movable under the influence of the drawbar into locking engagement with the toolholder shank; an actuating member (13) slidably mounted on the spindle; a motion transmission mechanism (30) for transmitting axial movement of the actuating member to movement of the drawbar; and a cylinder housing (60) and associated piston member (70) for moving the actuating member relative to the spindle. The cylinder housing (60) is arranged in the housing (3) in an axially floating manner. The actuating member (13) is rotatable together with the spindle (2) relative to the cylinder housing (60) and piston member (70).

Description

[Technical Field]

[0001] Field of the Invention and Prior Art 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.

[0002] In the field of machine tools for metal cutting, cutting tools, e.g., in the form of drills or milling cutters, used to machine workpieces of metallic material are often fixed to and rotated with a tool holder, which may be releasably clamped to a rotating spindle of the machine tool for rotation therewith. It is conventionally known to clamp the shank of such a tool holder to the rotating spindle by a clamping mechanism located within the spindle. When the cutting tool needs to be replaced, the tool holder is released from the spindle and a new tool holder with a different cutting tool is clamped to the spindle.

[0003] A clamping device comprising a spindle with a clamping mechanism suitable for automatic tool changing operations is already known from EP 1 468 767 B1, in which an actuating member in the form of a first drawbar is slidably mounted inside the spindle and is configured to bring about axial displacement of a second drawbar via a force amplification mechanism comprising a plurality of cooperating wedges arranged between the drawbars. A gas spring inside the spindle is configured to bias the two drawbars into a retracted locking position in which the tool holder is clamped to the spindle, and a hydraulic piston may be configured to act on a piston at the rear end of the gas spring to effect displacement of the two drawbars into an advanced releasing position in which the tool holder can be released from the spindle. However, this already known clamping device has a relatively long axial extent and therefore it is not suitable to use a clamping device of this type when the tool holder is to be releasably fixed around the periphery of the tool turret where the available axial space for the clamping device is limited.

[0004] A clamping device according to the preamble of claim 1 is already known from EP 3 825 047 A1.

[0005] Object of the invention SUMMARY OF THE INVENTION It is an object of the present invention to provide a clamping device of the type described above which has a new and preferred design and which is suitable for use with a tool turret of a machine tool. Summary of the Invention

[0006] According to the present invention, the above object is achieved by a clamping device having the features defined in claim 1.

[0007] The clamping device according to the present invention comprises: - Housing and a spindle rotatably mounted within the housing and having a forward end, a rearward end, and a bore intersecting the forward end and extending rearwardly from the forward end, the bore having a mounting portion at the forward end for receiving a toolholder shank; a drawbar slidably mounted inside the bore so as to be reciprocally movable within the bore along the longitudinal axis of the bore between a forward release position and a rearward locking position; - an engagement member disposed about the drawbar at a forward end thereof, the engagement member being movable from a first position to a second position under the influence of movement of the drawbar from a forward released position to a rearward locked position, the engagement member in the first position allowing the toolholder shank to move in and out of the mounting portion of said bore, and in the second position being in locking engagement with the toolholder shank to securely secure the toolholder shank to the spindle; an actuating member disposed inside the housing, the actuating member being slidably mounted on the spindle so as to be movable relative to the spindle in an axial direction of the spindle; - a motion transmission mechanism disposed inside the housing, the motion transmission mechanism being attached to the spindle and configured to transmit axial movement of the actuating member in a first axial direction relative to the spindle to movement of the drawbar from a forward released position to a rearward locked position; - a hydraulic actuator for axially moving the actuating member relative to the spindle, the hydraulic actuator being disposed within the housing and comprising a cylinder housing and a piston member, the piston member extending around the spindle and slidably mounted to the cylinder housing so as to be hydraulically movable axially relative to the spindle to enable the hydraulic actuator to exert a pulling or pushing force on the actuating member in a first axial direction to effect movement of the drawbar from a forward released position to a rearward locked position; Equipped with.

[0008] The actuating member is rotatable relative to the cylinder housing and piston member together with the spindle, meaning that the hydraulic actuator can remain stationary during machining operations in which the tool holder is rotated with the spindle. The avoidance of rotating parts in the hydraulic actuator facilitates assembly of the hydraulic actuator and associated hydraulic system and also eliminates the need for rotary seals at the interface between the housing and spindle which would limit the potential rotational speed of the spindle. The use of a hydraulic actuator to move the actuating member and thereby achieve movement of the drawbar means that the clamping device according to the present invention is suitable for use in automatic tool changing operations.

[0009] The cylinder housing extends around the spindle and is slidably mounted inside the housing of the clamping device so as to be axially movable relative to the spindle between first and second end positions, wherein in the first position the cylinder housing abuts against a first shoulder on the spindle that limits movement of the cylinder housing relative to the spindle in said first axial direction, and in the second end position the cylinder housing abuts against a second shoulder on the spindle that limits movement of the cylinder housing relative to the spindle in an opposite second axial direction. The piston member has an annular piston head slidably received in a space within the cylinder housing, a first hydraulic chamber formed in the space on a first side of the piston head, and by supplying hydraulic fluid into the first hydraulic chamber, the cylinder housing is movable to the second end position and the piston member is movable in the first axial direction.

[0010] The cylinder housing is mounted inside the clamping device housing in an axially floating manner so as to be axially movable a short distance relative to the housing and the spindle. When the drawbar is to be moved to the rearward locking position, hydraulic fluid is supplied into the first hydraulic chamber, which causes the cylinder housing to move to its second end position and abuts against a second shoulder on the spindle. The second shoulder on the spindle acts as a stop member for the cylinder housing, and further supply of hydraulic fluid into the first hydraulic chamber pushes the piston member in the first axial direction, thereby causing the actuating member to move the drawbar to the rearward locking position. During this axial movement of the piston member and the drawbar, the piston member exerts a force on the actuating member in the first axial direction, while the cylinder housing exerts a corresponding reaction force on the spindle via the second shoulder on the spindle. As a result, no forces are transmitted to the housing of the clamping device during the movement of the drawbar to the retracted locking position, and therefore the rotary bearing between the spindle and the housing of the clamping device is not subjected to any axial forces during operation of this hydraulic actuator, which means reduced stress on the rotary bearing. Compared to prior art solutions in which the rotary bearing between the spindle and the housing of the clamping device is subjected to axial stress during the movement of the drawbar, the solution according to the invention makes it possible to use a smaller size rotary bearing without shortening its expected service life, or to obtain a longer expected service life of the rotary bearing when using rotary bearings of the same size.

[0011] The clamping device according to the present invention can be mounted on a tool turret of a machine tool, where the rotating spindle of the clamping device is connected or connectable to a drive mechanism within the tool turret. However, the clamping device is not limited to use in a tool turret. Instead, the rotating spindle of the clamping device can constitute the main spindle of the machine tool or can be connected to such a main spindle without an intermediate tool turret.

[0012] According to one embodiment of the present invention, the actuating member is configured to maintain the drawbar in the rear-locked position by assuming a self-locking axial position on the spindle when the drawbar is forced to the rear-locked position under the influence of the actuating member and the motion transmission mechanism. As a result, the actuating member is able to maintain the drawbar in the rear-locked position during rotation of the spindle without requiring any external force from the piston member, which means that the piston member only needs to exert a pulling or pushing force on the actuating member in connection with a tool changing operation in which the spindle and actuating member are in a stationary position. As a result, frictional forces between the actuating member and the piston member during rotation of the spindle, and between the cylinder housing and the spindle, can be avoided or at least reduced to a very low level.

[0013] According to another embodiment of the present invention, a second hydraulic chamber is formed in the aforementioned space in the cylinder housing on a second side opposite the piston head, and the cylinder housing is movable to the first end position and the piston member is movable in the second axial direction by supplying hydraulic fluid into this second hydraulic chamber to enable the piston member to exert a pulling or pushing force on the actuating member in the second axial direction. As a result, a double-acting piston member is obtained, and therefore the same piston member can be used to move the actuating member in the first axial direction when the drawbar is to be moved from the forward release position to the rearward locking position, and to move the actuating member in the opposite direction when the drawbar is to be moved from the rearward locking position to the forward release position, which means that the clamping device can be made very compact. When the drawbar is to be moved to the forward release position, hydraulic fluid is supplied into the second hydraulic chamber, which causes the cylinder housing to move to its first end position and abuts the cylinder housing against a first shoulder on the spindle. The first shoulder on the spindle acts as a stop member for the cylinder housing, and further supply of hydraulic fluid into the second hydraulic chamber pushes the piston member in the second axial direction, causing the actuating member to move the drawbar to the forward, released position. During this axial movement of the piston member and the drawbar, the piston member exerts a force on the actuating member in the second axial direction, while the cylinder housing exerts a corresponding reaction force on the spindle via the first shoulder on the spindle. As a result, no force is transmitted to the clamping device housing during the movement of the drawbar to the forward, released position, and therefore the rotary bearing between the spindle and the clamping device housing is not subjected to any axial force during operation of the hydraulic actuator, which means reduced stress on the rotary bearing.

[0014] According to another embodiment of the invention, the cylinder housing comprises a first cylindrical wall radially outwardly limiting the space within the cylinder housing and an opposite second cylindrical wall radially inwardly limiting the space within the cylinder housing, such that the piston head of the piston member is slidably received between the cylinder walls.

[0015] According to another embodiment of the invention, an internal protrusion is provided on the inner side of the cylinder housing, and the cylinder housing is configured to abut against a first shoulder on the spindle via said internal protrusion in said first end position and against a second shoulder on the spindle via said internal protrusion in said second end position, the internal protrusion on the cylinder housing being received with play in a gap formed between the first and second shoulders on the spindle, so that the connection between the cylinder housing and the spindle can be achieved in a simple and reliable manner during a tool change operation.

[0016] According to another embodiment of the invention, the cylinder housing is configured to avoid contact with the spindle when it is in an intermediate axial position between the aforementioned first and second end positions. The cylinder housing is intended to be in this intermediate axial position during tool change operations, i.e., during machining operations in which the tool holder is rotated together with the spindle. As a result, frictional forces between the cylinder housing and the spindle during spindle rotation can be avoided.

[0017] According to another embodiment of the invention, the clamping device comprises a spring-loaded return mechanism configured to act on the cylinder housing, - the cylinder housing is movable from the intermediate axial position to the first end position against the action of a spring force of the return mechanism, and is movable from the first end position to the intermediate axial position under the action of this spring force; The cylinder housing is movable from the aforementioned intermediate axial position to the second end position against the action of the spring force of the return mechanism, and is movable from the second end position to the intermediate axial position under the action of this spring force.

[0018] Thus, the cylinder housing is biased toward the neutral axial position by the spring force of the return mechanism. The spring-loaded return mechanism can ensure that the cylinder housing is automatically removed from contact with the spindle after the tool change operation is completed, so that frictional heat is not generated at the contact surface between the cylinder housing and the spindle when the spindle is rotated at high speed relative to the cylinder housing after the tool change operation.

[0019] According to another embodiment of the invention, the piston member comprises a sleeve-shaped piston stem fixed to the piston head, the piston member being configured to exert the aforementioned pulling or pushing force on the actuating member through the piston stem, the piston stem being advantageously configured to radially inwardly delimit a first hydraulic chamber.

[0020] According to another embodiment of the invention, the actuating member has the form of a sleeve, which is arranged around a peripheral wall of the spindle and is slidably mounted on said peripheral wall so as to be axially movable relative to the spindle.

[0021] Another embodiment of the present invention is the motion transmission mechanism includes a first wedge slidably received within a first opening radially penetrating a peripheral wall of the spindle, the first wedge being configured to urge the pull rod toward the retracted locking position when urged radially inward within the first opening; the first wedge having a first pressure-receiving surface facing away from the spindle; - the actuating member comprises a first pressure applying surface on an inner side thereof, the first pressure applying surface facing inwardly for contact with the first pressure receiving surface and having an increasing radial distance to the longitudinal axis when viewed in the first axial direction; and the first pressure applying surface is configured to press against the first pressure receiving surface to urge the first wedge radially inward within the first opening when the actuating member is moved in the first axial direction; It is characterized by:

[0022] The drawbar is movable from an advanced release position to a retracted locking position under the influence of the actuating member and the first wedge by movement of the actuating member in the first axial direction. Because the first pressure applying surface has a radial distance to the longitudinal axis that increases in the first axial direction, movement of the actuating member in the first axial direction causes pressure to be applied by the first pressure applying surface onto a first pressure receiving surface on the first wedge. This pressure has a radial component such that the first wedge is forced radially inward toward the longitudinal axis.

[0023] The first pressure-applying surface and the first pressure-receiving surface are preferably inclined relative to the longitudinal axis by an angle α such that when the drawbar is forced to the rearward-locking position under the influence of the actuating member and the first wedge, the first wedge maintains the actuating member in a self-locking axial position on the peripheral wall. In this case, both the first pressure-applying surface and the first pressure-receiving surface extend in the same direction through the spindle when viewed in longitudinal cross section. The angle α is selected to be below a self-locking threshold angle so that the actuating member reaches a self-locking axial position relative to the first wedge when the drawbar is displaced to the rearward-locking position inside the bore. To obtain the self-locking axial position, the angle α should be sufficiently small, i.e., below the self-locking threshold angle. The self-locking axial position refers to the axial position where the static friction force between the first pressure-receiving surface on the first wedge and the first pressure-applying surface on the actuating member exceeds the opposing force at the friction surface caused by a force applied to the first wedge in a radial direction perpendicular to the longitudinal axis. Thus, the self-locking axial position is obtained within an angular range that depends on the coefficient of friction between the first pressure-receiving surface on the first wedge and the first pressure-applying surface on the actuating member. This coefficient of friction depends on various parameters, such as the materials used, coatings on the surfaces, the use of lubricants, etc. Thus, the self-locking threshold angle depends on such parameters. Those skilled in the art will be able to identify the self-locking threshold angle applicable to each particular case by using common general knowledge and / or routine experimentation, or at least predict or estimate whether a certain angle is below such a self-locking threshold angle. Generally, it is preferable to ensure a self-locking configuration by selecting an angle α that is well below the self-locking threshold angle. An additional benefit of using a small angle α is that a force amplification effect is obtained due to the fact that a small angle α means that a relatively long axial displacement of the actuating member results in a relatively short axial displacement of the drawbar. However, an excessively small angle α can be inefficient and may not work well in practice. For example, a very small angle α may make it difficult to release the actuating member from a self-locking axial position. The angle α is advantageously between 2° and 10°.An angle α within this range provides a self-locking effect as well as a suitable force multiplication effect.

[0024] According to another embodiment of the invention, the first wedge comprises a wedge surface that faces the rear end of the spindle and that contacts a first sliding surface on the drawbar that faces the front end of the spindle.

[0025] Another embodiment of the present invention is - the motion transmission mechanism includes a second wedge slidably received within a second opening radially penetrating the peripheral wall of the spindle, the second wedge including a wedge surface and a second pressure-receiving surface, the wedge surface facing the forward end of the spindle and in contact with a second sliding surface on the drawbar facing the rearward end of the spindle, the second pressure-receiving surface facing outward from the spindle, the second wedge configured to urge the drawbar toward the forward release position when urged radially inward within the second opening; - the actuating member comprises a second pressure applying surface on an inner side thereof, the second pressure applying surface facing inwardly for contact with the second pressure receiving surface and having an increasing radial distance to the longitudinal axis when viewed in the second axial direction; and the second pressure applying surface is configured to press against the second pressure receiving surface to urge the second wedge radially inward within the second opening when the actuating member is moved in the second axial direction; It is characterized by:

[0026] The drawbar is movable from a retracted, locked position to an advanced, released position under the influence of the actuating member and the second wedge by movement of the actuating member in the second axial direction. Because the second pressure-applying surface has a radial distance to the longitudinal axis that increases in the second axial direction, movement of the actuating member in the second axial direction causes pressure to be applied by the second pressure-applying surface onto a second pressure-receiving surface on the second wedge. This pressure has a radial component such that the second wedge is forced radially inward toward the longitudinal axis.

[0027] According to another embodiment of the present invention, the clamping device includes two or more such first wedges spaced apart circumferentially around the peripheral wall, with each first wedge received in a respective first opening radially through the peripheral wall. The clamping device can also include two or more such second wedges spaced apart circumferentially around the peripheral wall, with each second wedge received in a respective second opening radially through the peripheral wall. The first openings and associated first wedges, and the second openings and associated second wedges, are preferably evenly distributed circumferentially around the peripheral wall. This results in a balanced clamping device with good force distribution. However, a large number of wedges and associated openings may be undesirable due to the fact that each opening reduces the strength of the housing. Three first wedges and three second wedges with associated openings provide a balanced clamping device with an appropriate level of force distribution while still maintaining sufficient strength of the housing. The first wedges and second wedges are advantageously arranged alternately when viewed in the circumferential direction of the peripheral wall, wherein each of the first wedges is followed by one of the second wedges when viewed in the circumferential direction of the peripheral wall, and wherein each of the second wedges is followed by one of the first wedges when viewed in the circumferential direction of the peripheral wall.

[0028] Further advantageous features of the clamping device according to the invention will become apparent from the description that follows.

[0029] A detailed description of embodiments of the invention, given by way of example, follows below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a plan view of a clamping device and a tool holder according to an embodiment of the present invention; [Figure 2] 2 is a partially cutaway perspective view of the clamping device and tool holder of FIG. 1, with the tool holder separated from the clamping device; FIG. [Figure 3a]2 is a longitudinal cross-sectional view of the clamping device and tool holder of FIG. 1, with the drawbar of the clamping device shown in an advanced release position and the cylinder housing shown in a first end position; [Figure 3b] 3b is a longitudinal section corresponding to FIG. 3a, with the drawbar shown in the retracted locking position and the cylinder housing shown in a second end position; FIG. [Figure 3c] 3b is a longitudinal section corresponding to FIG. 3a, with the drawbar shown in the retracted locking position and the cylinder housing shown in the intermediate axial position; FIG. [Figure 4] 2 is a perspective view, partially cut away, of components included in the clamping device of FIG. 1; [Figure 5] 5 is a longitudinal section through the tool holder and parts of the clamping device shown in FIG. 4, with the tool holder in a clamped state. [Figure 6] FIG. 6 is a longitudinal section corresponding to FIG. 5, with the tool holder in an unclamped state. [Figure 7] FIG. 5 is an exploded view of the tool holder and parts of the clamping device shown in FIG. 4. [Figure 8] 5 is another exploded view of the tool holder and parts of the clamping device shown in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0031] Detailed Description of Embodiments of the Invention A clamping device 1 according to one embodiment of the present invention is shown in Figures 1 to 8. The clamping device 1 is configured to releasably clamp a tool holder 80 (shown very diagrammatically in the drawings) to a rotating spindle 2 of the clamping device and to allow machining of a workpiece with a cutting tool (not shown) fixed to the tool holder 80.

[0032] The spindle 2 is rotatably mounted in the housing 3 of the clamping device 1 by means of a rolling bearing 4, for example in the form of a tapered roller bearing or any other suitable type of roller bearing. The spindle 2 has a front end 2 a, a rear end 2 b, and a bore 5 that intersects with and extends rearwardly from the front end 2 a. The bore 5 therefore has an inlet opening at the front end 2 a of the spindle. The spindle 2 is connectable to a drive mechanism of a machine tool, for example a drive mechanism in a tool turret of the machine tool, via a connecting pin 6 at the rear end 2 b of the spindle, to enable the spindle to be rotationally driven by the drive mechanism.

[0033] A mounting portion 7 (see Figures 2 and 4) is provided at the forward end of the bore 5 for receiving a mounting shank 81 on a tool holder 80. This mounting shank 81 is referred to herein as the tool holder shank.

[0034] A drawbar 8 is slidably mounted inside the bore 5 so as to be reciprocally movable within the bore 5 along the longitudinal axis L of the bore 5 between a forward, released position (see FIGS. 3a and 6) and a rearward, locked position (see FIGS. 3b, 3c, and 5). The drawbar 8 has a forward end facing the entrance opening of the bore 5 and an opposite rearward end. A head portion 9 and a neck portion 10 are provided at the forward end of the drawbar 8. The head portion 9 is located forward of the neck portion 10 when viewed in the longitudinal direction of the drawbar, and the head portion 9 is connected to the neck portion 10 via a rearward-facing inclined surface 11 on the head portion 9. A sealing ring 12 is disposed between the drawbar 8 and the inner surface of the bore 5. In the example shown, the sealing ring 12 is received in a groove on the outer side of the drawbar 8.

[0035] A toolholder shank 81 is insertable into the mounting portion 7 of the bore 5 through an entrance opening at the forward end 2a of the spindle 2. The head portion 9 of the drawbar is received in an engagement bore 82 in the toolholder shank 81, with the tubular wall 83 of the toolholder shank being received in the space between the head portion 9 and the inner surface of the bore 5. In the embodiment shown, the mounting portion 7 of the bore 5 is conically shaped and has a somewhat "triangular" or polygonal non-circular cross-sectional shape adapted to receive a similarly shaped toolholder shank 81. The conical shape ensures a radially and axially play-free connection between the toolholder shank 81 and the spindle 2, while the non-circular cross-section ensures non-rotatable fixation of the toolholder shank 81 relative to the spindle 2. However, the mounting portion 7 of the bore 5 could also have any other suitable shape for receiving other types of toolholder shanks.

[0036] An engagement member 20 in the form of a segment is disposed around the drawbar 8 at its forward end. Under the influence of movement of the drawbar 8 from a forward released position to a rearward locked position, the engagement member 20 is movable from a first position (see Figures 3a and 6) to a second position (see Figures 3b, 3c and 5), in which in the first position the engagement member 20 allows the toolholder shank 81 to move in and out of the mounting portion of the bore 5, and in the second position the engagement member 20 keeps the toolholder shank 81 fixed to the spindle 2 by locking engagement with an engagement groove 84 in an engagement bore 82 in the toolholder shank 81.

[0037] In the embodiment shown, the engagement members 20 are disposed around the neck portion 10 of the draw rod 8 and are held in place around the neck portion by a retaining ring 21 (see FIG. 6 ) and a resilient O-ring 22, which are disposed within the bore 5 and surround the neck portion 10. Each engagement member 20 has an outwardly facing flange portion 23 that is engaged within an internal groove in the retaining ring 21. The O-ring 22 is received within the outwardly facing groove at the rearward end of each engagement member 20. A compression spring 24, a thrust ring 25, and a stop ring 26 are also disposed within the bore 5 and configured to surround the draw rod 8. The compression spring 24 is attached between a shoulder on the draw rod 8 and the thrust ring 25, and is configured to bias the thrust ring 25, the retaining ring 21, and the engagement members 20 forward. Forward movement of the retaining ring 21 towards the entrance opening of the bore 5 is limited by a stopper ring 26 mounted in a groove in the inner surface of the bore 5 .

[0038] Each engagement member 20 includes an outwardly directed engagement flange 27 at its forward end that is configured to engage an engagement groove 84 in the toolholder shank 81 when the engagement members 20 are in the second position described above. As shown in Figures 3a and 6, when the drawbar 8 is in the forward release position, the forward end of the engagement member 20 is located rearward of the head portion 9 of the drawbar 8 and the engagement flange 27 is out of engagement with the engagement groove 84 in the toolholder shank 81. As the drawbar 8 is moved axially rearward within the bore 5 along the longitudinal axis L of the bore 5, the inclined surface 11 on the head portion 9 of the drawbar comes into contact with the forward end of the engagement member 20, which now slides over this inclined surface 11 and is forced outward such that the engagement flange 27 on the engagement member engages with the engagement groove 84 in the toolholder shank 81, with the result that the toolholder shank 81 is pulled by the drawbar 8 into firm contact with the inner surface of the spindle 2 within the mounting portion of the bore 5.

[0039] The clamping device 1 further comprises an actuating member 13, which is concentric with the spindle 2 and slidably mounted thereon such that it is axially movable relative to the spindle 2 along the longitudinal axis L. The actuating member 13 is non-rotatably mounted on the spindle 2, i.e., prevented from rotating relative to the spindle 2, and is therefore configured to rotate together with the spindle 2. A motion transmission mechanism 30 is mounted on the spindle 2 and configured to translate axial movement of the actuating member 13 in a first axial direction D1 relative to the spindle 2 into movement of the drawbar 8 from the forward release position to the rearward locking position. In the embodiment shown, this first axial direction D1 is toward the front end 2a of the spindle 2. Thus, in this case, movement of the drawbar 8 from the forward release position to the rearward locking position is brought about by axial movement of the actuating member 13 forward along the spindle 2. However, alternatively, the actuating member 13 and the motion transmission mechanism 30 may be arranged to cooperate in such a manner that movement of the drawbar 8 from the forward released position to the rearward locked position is effected by axial movement of the actuating member 13 rearward along the spindle 2.

[0040] The clamping device 1 further comprises a hydraulic actuator 17 for axially moving the actuating member 13 relative to the spindle 2. The hydraulic actuator 17 is disposed within the housing 3 and comprises a cylinder housing 60 and a piston member 70. The cylinder housing 60 is configured to surround a portion of the spindle 2. The cylinder housing 60 is slidably mounted within the interior space of the housing 3 so as to be axially movable relative to the housing 3 and the spindle 2 between a first end position (see FIG. 3a) and a second end position (see FIG. 3b). In the first end position, the cylinder housing 60 abuts against a first shoulder 61a on the spindle 2, which limits movement of the cylinder housing 60 relative to the spindle 2 in a first axial direction D1. In the second position, the cylinder housing 60 abuts against a second shoulder 61b on the spindle 2, which limits movement of the cylinder housing 60 relative to the spindle 2 in an opposite, second axial direction D2. As shown in Figure 3c, the cylinder housing 60 is preferably configured so as not to come into contact with the spindle 2 when it is in an intermediate axial position between the first and second end positions described above.

[0041] In the illustrated embodiment, an internal protrusion 62 is provided on the inner side of the cylinder housing 60, which is configured to abut against a first shoulder 61 a on the spindle 2 via this internal protrusion 62 in a first end position and against a second shoulder 61 b ​​on the spindle 2 via this internal protrusion 62 in a second end position. Thus, in this case, the internal protrusion 62 is configured to function as an abutment member through which the cylinder housing 60 abuts against the respective shoulders 61 a, 61 b ​​on the spindle 2 in the aforementioned end positions. The internal protrusion 62 is received with play in the gap between the first and second shoulders 61 a, 61 b ​​on the spindle 2, thereby preventing the cylinder housing from coming into contact with the spindle 2 when it is in an intermediate axial position between the first and second end positions. In the illustrated example, the internal protrusion 62 has the form of a locking ring mounted in an annular groove provided in the cylinder housing 60, but it may alternatively be formed as an integral part of the cylinder housing. In the embodiment shown, the first shoulder 61 a and the second shoulder 61 b ​​on the spindle are formed by mutually facing surfaces in an annular groove provided on the outer side of the spindle 2. However, the first shoulder 61 a and the second shoulder 61 b ​​on the spindle and the associated abutment member 62 on the cylinder housing may also be designed in any other suitable manner.

[0042] The piston member 70 is also configured to surround a portion of the spindle 2. The piston member 70 is slidably mounted in the cylinder housing 60 so as to be hydraulically movable axially relative to the spindle 2 to enable the piston member 70 to exert a pulling or pushing force on the actuating member 13 in the first axial direction D1, thereby effecting movement of the drawbar 8 from the forward released position to the rearward locked position. In the illustrated embodiment, the piston member 70 is configured to exert an axially directed pulling force on the actuating member 13, thereby moving the actuating member 13 in the first axial direction D1. Alternatively, the piston member 70 may be configured to exert an axially directed pushing force on the actuating member 13, thereby moving the actuating member 13 in the first axial direction D1. The piston member 70 includes an annular piston head 71 slidably received in a space within the cylinder housing 60, with a first hydraulic chamber 63 a formed within the space on a first side of the piston head 71. By supplying hydraulic fluid into the first hydraulic chamber 63a, the cylinder housing 60 can be moved to the second end position, and the piston member 70 can be moved in the first axial direction D1.

[0043] In the embodiment shown, the cylinder housing 60 comprises a first cylindrical wall 64 that radially outwardly limits the aforementioned space within the cylinder housing, and an opposite second cylindrical wall 65 that radially inwardly limits the aforementioned space within the cylinder housing. In the example shown, the cylinder housing 60 is formed by a first cylinder housing part 60a and a second cylinder housing part 60b (see FIG. 6 ), which can be fixed to one another by a threaded joint 66 or in any other suitable manner, with the first cylindrical wall 64 forming part of the first cylinder housing part 60a and the second cylindrical wall 65 forming part of the second cylinder housing part 60b. Sealing rings 72a, 72b are arranged on either side of the piston head 71, with the first sealing ring 72a mounted in a groove in the outwardly facing surface of the piston head so as to be in sealing contact with the first cylindrical wall 64, and the second sealing ring 72b mounted in a groove in the inwardly facing surface of the piston head so as to be in sealing contact with the second cylindrical wall 65. Of course, the cylinder housing 60 may be designed in any other suitable manner.

[0044] In the embodiment shown, a second hydraulic chamber 63b is formed in the aforementioned space in the cylinder housing 60 on a second side opposite the piston head 71, and the cylinder housing 60 is movable to a first end position and the piston member 70 is movable in the second axial direction D2 by supplying hydraulic fluid into this second hydraulic chamber 63b to enable the piston member 70 to exert a pulling force or a pushing force on the actuating member 13 in the second axial direction D2. In the embodiment shown, the piston member 70 is configured to exert an axially directed pushing force on the actuating member 13, thereby moving the actuating member 13 in the second axial direction D2. Alternatively, the piston member 70 may be configured to exert an axially directed pulling force on the actuating member 13, thereby moving the actuating member 13 in the second axial direction D2.

[0045] In the embodiment shown, the piston member 70 comprises a sleeve-shaped piston stem 73 fixed to the piston head 71, and is configured to exert the aforementioned pulling or pushing force on the actuating member 13 via the piston stem 73. The piston stem 73 is preferably concentric with the actuating member 13 and extends around the spindle 2. The piston stem 73 radially inwardly delimits a first hydraulic chamber 63a, while the second hydraulic chamber 63b is radially inwardly delimited by the aforementioned second cylindrical wall 65. In the example shown, the second cylindrical wall 65 extends into a gap provided between an inner surface of the piston stem 73 and an outer surface of the actuating member 13.

[0046] The piston stem 73 may be configured to exert the above-mentioned force on the actuating member 13 by acting on an annular external protrusion 15 and a lock ring 16 provided on an outer side surface of the actuating member 13, the external protrusion 15 and the lock ring 16 being spaced apart in the axial direction of the actuating member 13. In the illustrated embodiment, an annular internal protrusion 74 is provided on an inner side surface of the piston stem 73. The internal protrusion 74 on the piston stem 73 is received with play in a gap formed between the external protrusion 15 and the lock ring 16. In this case, when the piston member 70 moves the actuating member in the first axial direction D1, the axial force is transmitted from the piston member 70 to the actuating member 13 via the internal protrusion 74 and the external protrusion 15, and when the piston member 70 moves the actuating member in the second axial direction D2, the axial force is transmitted from the piston member 70 to the actuating member 13 via the external protrusion 74 and the lock ring 16. It should be understood that the piston member 70 and the contact surfaces between the piston member and the actuating member 13 may be designed in any other suitable manner.

[0047] The actuating member 13 is rotatable together with the spindle 2 relative to the cylinder housing 60 and piston member 70, while the cylinder housing 60 and piston member 70 are configured to remain stationary within the housing 3 when the spindle 2 is rotated relative to the housing 3.

[0048] Preferably, the cylinder housing 60 and the piston member 70 are concentric with the actuating member 13 and the spindle 2, although it would also be possible to use a cylinder housing 60 and a piston member 70 having their respective central axes arranged parallel to but somewhat eccentric to the central axis of the spindle 2. In order to save space in the longitudinal direction of the clamping device 1, the cylinder housing 60 and the piston member 70 are advantageously arranged to at least partially overlap the actuating member 13.

[0049] The actuating member 13 is preferably configured to assume a self-locking axial position on the spindle 2 when the drawbar 8 is forced into the rear locking position under the influence of the actuating member 13 and the motion transmission mechanism 30, such that the actuating member 13 holds the drawbar 8 in the rear locking position. As a result, the piston member 70 only needs to exert a force on the actuating member 13 for tool changing operations in which the spindle 2 is stationary and the drawbar 8 must be moved from the rear locking position to the forward release position and then returned to the rear locking position. In the self-locking axial position, frictional forces between the actuating member 13 and parts of the motion transmission mechanism 30 and / or spindle 2 in contact with the actuating member 13 prevent the actuating member from being axially displaced in the second axial direction D2.

[0050] Due to the fact that during the machining operation the working member 13 rotates at high speed together with the spindle 2 while the piston member 70 and the cylinder housing 60 remain stationary, it is important to avoid or at least keep as low as possible frictional forces between the working member 13 and the piston member 70 and between the spindle 2 and the cylinder housing 60 during the machining operation. In the embodiment shown, frictional forces at the interface between the piston member 70 and the working member 13 are avoided by providing slight radial and axial play between the working member and the piston member at the connection formed by the above-mentioned cooperating parts 15, 16, 74 of the working member and the piston member. Similarly, frictional forces at the interface between the cylinder housing 60 and the spindle 2 are avoided by providing slight radial and axial play between the cylinder housing and the spindle at the connection formed by the above-mentioned cooperating parts 62, 61a, 61b of the cylinder housing and the spindle.

[0051] The clamping device 1 advantageously comprises a spring-loaded return mechanism 90 acting on the cylinder housing 60, the cylinder housing 60 is movable from the intermediate axial position to the first end position against the action of the spring force of the return mechanism 90, and is movable from the first end position to the intermediate axial position under the action of this spring force; the cylinder housing 60 is movable from the intermediate axial position to the second end position against the action of the spring force of the return mechanism 90, and from the second end position to the intermediate axial position under the action of this spring force.

[0052] In the illustrated embodiment, the return mechanism 90 comprises two or more spheres 91 distributed in the circumferential direction of the cylinder housing 60, which are received in annular grooves 92 on the outer side surface of the cylinder housing. The grooves 92 have a cross-sectional shape adapted to the shape of the spheres 91, so that the opposing side walls of the grooves 92 guide the spheres toward a central position within the groove. Each sphere 91 passes through a respective opening 93 (see FIG. 3a) in the housing 3 of the clamping device 1, which opening 93 opens into an associated cavity 94 in the housing. A spring unit 95 is accommodated in this cavity 94, against which the spheres 91 rest and which is configured to act on the spheres 91 to urge them radially inward into the annular groove 92. In the illustrated example, each spring unit 95 comprises a compression spring element formed by a stack of disc springs. The spring-loaded return mechanism 90 may also be designed in any other suitable manner.

[0053] In the embodiment shown, the actuating member 13 has the form of a sleeve, in which case it is arranged around a peripheral wall 14 of the spindle 2 and slidably mounted on this wall so as to be axially movable relative to the spindle.

[0054] The motion transmission mechanism 30 can be designed in many different ways. For example, the motion transmission mechanism 30 can comprise one or more first wedges 40 for transmitting the axial movement of the actuating member 13 in the first axial direction D1 relative to the spindle 2 to the movement of the drawbar 8 from the forward release position to the rearward locking position, and one or more second wedges 50 for transmitting the axial movement of the actuating member 13 in the second axial direction D2 relative to the spindle 2 to the movement of the drawbar 8 from the rearward locking position to the forward release position.

[0055] In the embodiment shown, the motion transmission mechanism 30 includes three first wedges 40 spaced circumferentially about the peripheral wall 14. Each first wedge 40 is slidably received within a respective first opening 45 extending radially through the peripheral wall 14. The first wedges 40 are configured to collectively urge the drawbar 8 toward the retracted, locked position when they are urged radially inward within their associated first openings 45.

[0056] Each first wedge 40 includes a first pressure-receiving surface 41 facing outward from the peripheral wall 14 of the spindle 2, and the actuating member 13 includes an inward-facing first pressure-applying surface 31 on its inner side for contacting the first pressure-receiving surface 41 on the first wedge. Each first pressure-applying surface 31 has an increasing radial distance to the longitudinal axis L when viewed in the first axial direction D1. The first pressure-applying surface 31 is configured to press against the first pressure-receiving surface 41 on the first wedge, thereby pushing the first wedge 40 radially inward within the first opening 45, when the actuating member 13 is moved in the first axial direction D1. The first pressure applying surface 31 and the first pressure receiving surface 41 are preferably inclined relative to the longitudinal axis L by an angle α (see FIG. 5 ) such that when the pull rod 8 is forced into the retracted locking position under the influence of the actuating member 13 and the first wedge 40, the first wedge 40 maintains the actuating member 13 in a self-locking axial position on the peripheral wall 14.

[0057] Each first wedge 40 also includes a wedge surface 48 that faces the rearward end 2 b of the spindle 2 and contacts a first sliding surface 18 on the drawbar 8 that faces the forward end 2 a of the housing. When the first wedges 40 are pushed radially inward within the first opening 45 by the actuating member 13, the wedge surface 48 of each first wedge 40 slides against a corresponding first sliding surface 18 on the drawbar, thereby forcing the drawbar 8 to move toward the rear locked position.

[0058] In the embodiment shown, clamping device 1 includes three second wedges 50 spaced circumferentially about peripheral wall 14. Each second wedge 50 is slidably received within a respective second opening 55 extending radially through peripheral wall 14. Second wedges 50 are configured to collectively urge drawbar 8 toward the advanced release position when they are urged radially inward within their associated second openings 55.

[0059] Each second wedge 50 includes a second pressure-receiving surface 52 facing outward from the peripheral wall 14 of the spindle 2, and the actuating member 13 includes an inward-facing second pressure-applying surface 32 on its inner side for contacting the second pressure-receiving surface 52 on the second wedge. Each second pressure-applying surface 32 has an increasing radial distance to the longitudinal axis L when viewed in the second axial direction D2. The second pressure-applying surface 32 is configured to press against the second pressure-receiving surface 52 on the second wedge, thereby pushing the second wedge 50 radially inward within the second opening 55, when the actuating member 13 is moved in the second axial direction D2.

[0060] Each second wedge 50 also includes a wedge surface 59 that faces the forward end 2 a of the spindle 2 and contacts a second sliding surface 19 on the drawbar 8 that faces the rearward end 2 b of the housing. When the second wedges 50 are pushed radially inward within the second opening 55 by the actuating member 13, the wedge surface 59 of each second wedge 50 slides against the corresponding second sliding surface 19 on the drawbar, thereby forcing the drawbar 8 to move toward the forward locked position.

[0061] Each first wedge 40 may also have a third pressure-receiving surface 43 (see FIG. 6) facing outward from the peripheral wall 14 of the spindle 2, and the actuating member 13 has an inward-facing third pressure-applying surface 33 on its inner side for contacting the third pressure-receiving surface 43 on each first wedge. Each third pressure-applying surface 33 has an increasing radial distance to the longitudinal axis L when viewed in the first axial direction D1. The third pressure-applying surface 33 and the third pressure-receiving 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 applying surfaces 31, 33 and the first and third pressure receiving surfaces 41, 43 are arranged consecutively on the actuating member 13 and each first wedge 40, respectively, so that during movement of the actuating member 13 in the first axial direction D1, the third pressure applying surface 33 is configured to slide against the associated third pressure receiving surface 43 during an initial first movement stage, and the first pressure applying surface 31 is configured to slide against the associated first pressure receiving surface 41 during a subsequent second movement stage. As a result, the pull rod 8 can be moved rapidly in the first axial direction D1 during the initial clamping stage under the influence of a larger angle β. This initial clamping stage does not require much force. However, during the final clamping stage, a large force is required to displace the pull rod 8 a short distance. When the actual clamping occurs, i.e., when the engagement member 20 assumes the above-mentioned first position, the drawbar 8 is moved in the first axial direction D1 under the influence of a smaller angle α so that the axial movement of the drawbar 8 is small compared to the axial movement of the actuating member 13, thereby providing a force amplification effect also referred to as "power boost." The angle β is suitably between 10° and 75°, preferably between 35° and 65°, which provides an efficient initial axial movement of the drawbar 8. By using a steep angle β for the initial axial movement of the drawbar 8 and a small angle α for the actual clamping, the actuating member 13 (and therefore the entire clamping device 1) can be made relatively short in the axial direction while still providing a significant force amplification effect to the self-locking clamping mechanism.

[0062] The first and second wedges 40, 50 are non-rotatably received within associated first and second openings 45, 55 in the peripheral wall 14 of the spindle 2, i.e., each wedge is prevented from rotating within its associated opening.

[0063] 6, when the toolholder 80 is to be clamped to the spindle 2, the toolholder shank 81 is inserted into the mounting portion 7 of the bore 5 with the spindle 2 held stationary and the drawbar 8 positioned in the forward release position. As a result, the head portion 9 of the drawbar is received in the engagement bore 82 in the toolholder shank 81, and the engagement groove 84 in the toolholder shank 81 is positioned on the outer side surface of the engagement flange 27 of the engagement member 20. Immediately thereafter, hydraulic oil is supplied into the first hydraulic chamber 63a to move the cylinder housing 60 a short distance in the second axial direction D2 to engage with the second shoulder 61b on the spindle 2, as shown in FIG. 3b, and move the piston member 70 in the first axial direction D1, thereby achieving corresponding axial movement of the working member 13 in the first axial direction D1. During this first stage of axial movement of the actuating member 13, the third pressure-applying surface 33 on the actuating member 13 slides against the third pressure-receiving surface 43 on the first wedge 40. As a result, the first wedge 40 is forced radially inward and the drawbar 8 is displaced axially toward the retracted, locked position. The relatively steep slope β of the third pressure-applying surface 33 and the third pressure-receiving surface 43 causes the first wedge 40 to move inwardly fairly quickly initially, thereby resulting in a relatively rapid displacement of the drawbar 8. The relatively steep angle β is advantageous because the initial displacement of the drawbar 8 does not require much force. The first and third pressure applying surfaces 31, 33 and the first and third pressure receiving surfaces 41, 43 are arranged so that when the actuating member 13 is moved a distance such that the third pressure applying surface 33 passes the third pressure receiving surface 43 and the first pressure applying surface 31 reaches the first pressure receiving surface 41, i.e., when transitioning between these respective surfaces, the drawbar 8 has nearly reached its final retracted position within the bore 5. Thus, for the final clamping stage where high forces are beneficial, the first pressure applying surface 31 and the first pressure receiving surface 41 are effective.At this stage, the relatively large movement of the actuating member 13 results in a very small radial displacement of the first wedge 40 and an even smaller axial displacement of the drawbar 8, which consequently provides a force amplification effect that allows the drawbar 8 to pull the toolholder shank 81 with a large force into firm engagement with the spindle 2. Furthermore, the small inclination α of the first pressure-applying surface 31 and the first pressure-receiving surface 41 provides a self-locking effect and ensures that the clamping device remains clamped without the need for any additional locking means. As a result, when the drawbar 8 reaches the retracted locking position, the hydraulic pressure in the first hydraulic chamber 63a can be released. Once the hydraulic pressure in the first hydraulic chamber 63a is released, the return mechanism 90 automatically moves the cylinder housing 60 a short distance in the first axial direction D1 to return the cylinder housing 60 to the intermediate axial position shown in FIG. 3c, which means that the cylinder housing is released from contact with the spindle 2. During movement of the drawbar 8 towards the retracted locked position, the second sliding surface 19 on the drawbar 8 bears against the wedge surface 59 on the second wedge 50, thereby pushing the second wedge 50 radially outward.

[0064] When a tool changing operation is to be performed and the tool holder 80 is to be released from the spindle 2, rotation of the spindle 2 is stopped and hydraulic oil is supplied into the second hydraulic chamber 63b to move the cylinder housing 60 a short distance in the first axial direction D1 to engage a first shoulder 61a on the spindle 2 and move the piston member 70 in the second axial direction D2, as shown in Figure 3a, thereby achieving corresponding axial movement of the actuating member 13 in the second axial direction D2. When the actuating member 13 is subjected to a sufficient force in the second axial direction D2, the self-locking frictional engagement between the first pressure applying surface 31 on the actuating member 13 and the first pressure receiving surface 41 on the first wedge 40 is released, so that the actuating member 13 is movable relative to the spindle 2 in the second axial direction D2. As the actuating member 13 is moved in this direction, the second pressure-applying surface 32 on the actuating member 13 slides and bears against the second pressure-receiving surface 52 on the second wedge 50. As a result, the second wedge 50 is forced radially inward and the drawbar 8 is displaced axially toward the forward release position. As the drawbar 8 is moved toward the forward release position, the outer end of the head portion 9 of the drawbar 8 abuts a surface 85 within an engagement bore 82 in the toolholder shank 81, thereby releasing the toolholder shank 81 from the spindle 2. During movement of the drawbar 8 toward the forward release position, the first sliding surface 18 on the drawbar 8 presses against the wedge surface 48 on the first wedge 40, thereby forcing the first wedge 40 radially outward.

[0065] Naturally, the present invention is in no way limited to the above-described embodiments: on the contrary, many possibilities for modifying the present invention will become apparent to those skilled in the art without departing from the basic idea of ​​the present invention as defined in the appended claims.

Claims

1. A clamping device for releasably holding a tool holder shank, said clamping device (1) comprising: a housing (3), a spindle (2) rotatably mounted inside said housing (3) and having a forward end (2a), a rearward end (2b) and a bore (5) intersecting said forward end (2a) and extending rearwardly from said forward end (2a), said bore (5) being provided at its forward end with a mounting portion (7) for receiving a toolholder shank (81); a drawbar (8) slidably mounted inside said bore (5) so as to be reciprocally movable within said bore along the longitudinal axis (L) of said bore between a forward release position and a rearward locking position; an engagement member (20) arranged around the drawbar (8) at its forward end, the engagement member (20) being movable from a first position to a second position under the influence of movement of the drawbar (8) from the forward release position to the rearward locking position, the engagement member (20) in the first position allowing the toolholder shank (81) to move in and out of the mounting portion (7) of the bore (5) and in the second position being in locking engagement with the toolholder shank (81) to securely fasten the toolholder shank (81) to the spindle (2); an actuating member (13) arranged inside the housing (3) and slidably mounted on the spindle (2) so as to be movable relative to the spindle (2) in the axial direction of the spindle (2); a motion transmission mechanism (30) arranged inside the housing (3), attached to the spindle (2) and configured to transmit an axial movement of the actuating member (13) in a first axial direction (D1) relative to the spindle (2) to a movement of the drawbar (8) from the forward release position to the backward lock position; Equipped with - said clamping device (1) comprises a hydraulic actuator (17) for axially moving said actuating member (13) relative to said spindle, said hydraulic actuator (17) being arranged in said housing (3) and comprising a cylinder housing (60) and a piston member (70); the cylinder housing (60) extends around the spindle (2) and is slidably mounted inside the housing (3) so as to be axially movable relative to the spindle (2) between a first end position and a second end position, wherein in the first end position the cylinder housing (60) abuts against a first shoulder (61 a) on the spindle (2) that limits the movement of the cylinder housing (60) relative to the spindle (2) in the first axial direction (D1), and in the second end position the cylinder housing (60) abuts against a second shoulder (61 b) on the spindle (2) that limits the movement of the cylinder housing (60) relative to the spindle (2) in an opposite second axial direction (D2); - the piston member (70) extends around the spindle (2) and is slidably mounted in the cylinder housing (60) so as to be hydraulically movable axially relative to the spindle (2) to enable the piston member (70) to exert a pulling or pushing force on the actuating member (13) in the first axial direction (D1) thereby effecting movement of the drawbar (8) from the forward release position to the rearward locking position; the piston member (70) comprises an annular piston head (71) slidably received in a space within the cylinder housing (60), a first hydraulic chamber (63 a) being formed in the space on a first side of the piston head (71), and by supplying hydraulic fluid into the first hydraulic chamber (63 a), the cylinder housing (60) is movable to the second end position and the piston member (70) is movable in the first axial direction (D1); - said actuating member (13) is rotatable together with said spindle (2) relative to said cylinder housing (60) and said piston member (70); A clamping device comprising:

2. 2. The clamping device according to claim 1, wherein the actuating member (13) is configured to keep the pull rod (8) in the retracted locking position by assuming a self-locking axial position on the spindle (2) when the pull rod (8) is forced to the retracted locking position under the influence of the actuating member (13) and the motion transmission mechanism (30).

3. 3. The clamping device according to claim 1 or 2, characterized in that a second hydraulic chamber (63b) is formed in the space within the cylinder housing (60) on a second side opposite to the piston head (71), and the cylinder housing (60) is movable to the first end position and the piston member (70) is movable in the second axial direction (D2) by supplying hydraulic fluid into the second hydraulic chamber (63b) to enable the piston member (70) to exert a pulling force or a pushing force on the actuating member (13) in the second axial direction (D2).

4. 4. A clamping device according to claim 1, wherein the cylinder housing (60) comprises a first cylindrical wall (64) limiting the space within the cylinder housing radially outward and an opposite second cylindrical wall (65) limiting the space within the cylinder housing radially inward.

5. - an internal projection (62) is provided on the inner side of the cylinder housing (60), said cylinder housing (60) being configured to abut via said internal projection (62) against said first shoulder (61 a) on said spindle (2) in said first end position and to abut via said internal projection (62) against said second shoulder (61 b) on said spindle (2) in said second end position; and the internal projection (62) on the cylinder housing (60) is received with play in the gap formed between the first shoulder (61a) and the second shoulder (61b) on the spindle (2); 5. A clamping device according to any one of claims 1 to 4, characterized in that

6. 6. A clamping device according to any one of claims 1 to 5, characterized in that the cylinder housing (60) is configured not to come into contact with the spindle (2) when it is in an intermediate axial position between the first end position and the second end position.

7. the clamping device (1) comprises a spring-loaded return mechanism (90) configured to act on the cylinder housing (60); the cylinder housing (60) is movable from the intermediate axial position to the first end position against the action of the spring force of the return mechanism (90) and from the first end position to the intermediate axial position under the action of the spring force; and the cylinder housing (60) is movable from the intermediate axial position to the second end position against the action of the spring force of the return mechanism (90) and from the second end position to the intermediate axial position under the action of the spring force; 7. The clamping device according to claim 6, wherein:

8. 8. A clamping device according to any one of claims 1 to 7, characterized in that the piston member (70) comprises a sleeve-shaped piston stem (73) fixed to the piston head (71), and the piston member (70) is configured to exert the pulling force or the pushing force on the actuating member (13) through the piston stem (73).

9. 9. A clamping device according to claim 8, characterized in that the piston stem (73) is configured to delimit the first hydraulic chamber (63a) radially inwardly.

10. 10. A clamping device according to any one of claims 1 to 9, characterized in that the actuating member (13) has the form of a sleeve, the actuating member (13) being arranged around a peripheral wall (14) of the spindle (2) and slidably mounted on said peripheral wall so as to be axially movable relative to the spindle.

11. the motion transmission mechanism (30) comprises a first wedge (40) slidably received in a first opening (45) extending radially through the peripheral wall (14) of the spindle (2), the first wedge (40) being configured to push the pull rod (8) towards the retracted locking position when pushed radially inward in the first opening (45); - said first wedge (40) comprises a first pressure-receiving surface (41) facing away from said spindle (2); - said actuating member (13) comprises on its inner side a first pressure-applying surface (31) facing inwards for contact with said first pressure-receiving surface (41) and having an increasing radial distance to said longitudinal axis (L) when viewed in said first axial direction (D1); the first pressure application surface (31) is configured to press the first wedge (40) radially inward within the first opening (45) by pressing against the first pressure receiving surface (41) when the actuating member (13) is moved in the first axial direction (D1), the first pressure application surface (31) and the first pressure receiving surface (41) being preferably inclined with respect to the longitudinal axis (L) by an angle α such that the first wedge (40) keeps the actuating member (13) in a self-locking axial position on the peripheral wall (14) when the pull rod (8) is forced into the retracted locking position under the influence of the actuating member (13) and the first wedge (40); The clamping device according to claim 10, characterized in that

12. 12. The clamping device according to claim 11, characterized in that the first wedge (40) comprises a wedge surface (48) facing the rear end (2b) of the spindle (2) and in contact with a first sliding surface (18) on the drawbar facing the front end (2a) of the spindle.

13. the motion transmission mechanism (30) comprises a second wedge (50) slidably received in a second opening (55) radially penetrating the peripheral wall (14) of the spindle (2), the second wedge (50) comprising a wedge surface (59) and a second pressure-receiving surface (52), the wedge surface (59) facing the front end (2a) of the spindle (2) and in contact with a second sliding surface (19) on the pull rod facing the rear end (2b) of the spindle, the second pressure-receiving surface (52) facing outward from the spindle (2), the second wedge (50) being configured to push the pull rod (8) towards the forward release position when pushed radially inward in the second opening (55); - said actuating member (13) comprises on its inner side a second pressure-applying surface (32) facing inwards for contact with said second pressure-receiving surface (52) and having an increasing radial distance to said longitudinal axis (L) when viewed in said second axial direction (D2); the second pressure-applying surface (32) is configured to press against the second pressure-receiving surface (52) and thereby push the second wedge (50) radially inwards within the second opening (55) when the actuating member (13) is moved in the second axial direction (D2); 13. The clamping device according to claim 12, wherein:

14. 14. A clamping device according to claim 13, characterized in that the clamping device (1) comprises two or more, preferably three, second wedges (50) spaced apart in the circumferential direction of the peripheral wall (14), each second wedge (50) being received in a respective second opening (55) radially penetrating the peripheral wall (14).

15. 15. A clamping device according to any one of claims 11 to 14, characterized in that the clamping device (1) comprises two or more, preferably three, first wedges (40) spaced apart in the circumferential direction of the peripheral wall (14), each first wedge (40) being received in a respective first opening (45) radially penetrating the peripheral wall (14).

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