Clamping device for tool holders

Abstract

A clamping device for releasably holding a toolholder shank (81) includes a spindle (2) rotatably mounted within a housing (3), a drawbar (8) axially movable in a bore (5) 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, an actuating sleeve (13) disposed about a peripheral wall (14) of the spindle and axially movable relative thereto, a motion transmission mechanism (30) for transmitting axial movement of the actuating sleeve to movement of the drawbar, and a hydraulic cylinder arrangement for moving the actuating sleeve. The hydraulic cylinder arrangement includes a cylinder casing (51) fixed to the spindle and an annular piston head (54) fixed to or fixedly connected to the actuating sleeve and slidably received in an annular space within the cylinder casing.

Description

Technical Field

[0001] The present 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 Art

[0002] In the field of machine tools for metal cutting, for example, cutting tools used for machining workpieces of metal materials in the form of drills or milling tools are often fixed to a tool holder and rotated therewith. This is then removably clamped to the rotatable spindle of the machine tool and may be rotated with that spindle. It has been previously known to clamp the shank of such a tool holder to the rotatable spindle using a clamping mechanism disposed on the spindle. When it is necessary to change the cutting tool, 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 including a spindle with a clamping mechanism adapted for automatic tool change operations has been previously known from EP1468767B1. In the clamping device according to EP1468767B1, an actuating member in the form of a first drawbar is slidably mounted inside the spindle, which is configured to achieve the axial displacement of a second drawbar via a force amplification mechanism including a number of cooperating wedges arranged between those drawbars. A gas spring inside the spindle is configured to bias the two drawbars into a retracted locking position. Here, the tool holder is clamped to the spindle. A hydraulic piston may be configured to act on the piston at the rear end of the gas spring in order to achieve the displacement of the two drawbars to a forward release position where the tool holder may be released from the spindle. However, this previously known clamping device has a relatively long axial extent and thus is not suitable for use with this type of clamping device 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] The object of the present invention is to provide a clamping device of the above-described type that has a new and preferred design and is suitable for use with a tool turret of a machine tool.

Summary of the Invention

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

[0006] The clamping device according to the present invention comprises a housing, and a spindle rotatably mounted inside the housing, having a front end, a rear end, and a bore intersecting the front end and extending rearward therefrom, and a mounting site for receiving a tool holder shank is provided at the front end of the bore. A drawbar that is slidably placed inside the bore and is capable of reciprocating between an advanced release position and a retracted locking position along its longitudinal axis in the bore, An engaging member disposed around the drawbar at its front end, which, under the influence of the movement of the drawbar from the advanced release position to the retracted locking position, enables the engaging member to move the tool holder shank in and out of the placement site of the bore from a first position where the engaging member allows it, to a second position where the engaging member is in a locking engagement with the tool holder shank and keeps it fixed to the spindle. An actuating sleeve disposed inside the housing and operated by hydraulic pressure, which is disposed around the peripheral wall of the spindle, slidably placed on this peripheral wall, and is capable of moving axially with respect to the spindle. A motion transmission mechanism disposed inside the housing, which is placed on the spindle and is configured to transmit the axial movement of the actuating sleeve in a first axial direction with respect to the spindle to the movement of the drawbar from the advanced release position to the retracted locking position. A hydraulic cylinder arrangement disposed inside the housing and configured to move the actuating sleeve axially with respect to the spindle, A cylinder casing that is concentric with the actuating sleeve, fixed to the outside of the spindle, and is capable of rotating with the spindle with respect to the housing. An annular piston head fixed to or fixedly connected to the actuating sleeve, which is slidably received in the annular space inside the cylinder casing, and this space is configured to be divided into an annular first hydraulic chamber on the first side of the piston head and an annular second hydraulic chamber on the second side opposite to the piston head. A hydraulic cylinder arrangement including including.

[0007] The actuating sleeve, together with the piston head, is movable in a first axial direction by the supply of hydraulic fluid to the first hydraulic chamber and in an opposite second axial direction by the supply of hydraulic fluid to the second hydraulic chamber. Thus, the drawbar is movable to the retracted locking position under the influence of the piston head and the actuating sleeve by the supply of hydraulic fluid to the first hydraulic chamber within the cylinder casing.

[0008] By using the actuating sleeve described above to control the axial movement of the drawbar, a gas spring or the like that occupies a large amount of space axially is not necessary to control the axial movement of the drawbar, which implies that the clamping device can be made axially compact. The clamping device is thus suitable for use in a tool turret. Furthermore, the use of a hydraulically operated piston member for moving the actuating sleeve and thereby achieving the movement of the drawbar implies that the clamping device according to the invention is suitable for use in automatic tool change operations.

[0009] The clamping device according to the invention may be mounted on a tool turret of a machine tool. Here, the rotatable spindle of the clamping device is connected to, or connectable to, a drive mechanism in the tool turret. However, the clamping device is not limited to use in a tool turret. On the contrary, the rotatable spindle of the clamping device may constitute the main spindle of a machine tool or may be connected to such a main spindle without any intermediate tool turret.

[0010] One embodiment of the invention is the spindle and the cylinder casing form part of a rotatable unit rotatably received in the internal space of the housing, The first hydraulic chamber is hydraulically connected at the interface between the housing and the rotatable unit via an annular first hydraulic connection area to the first hydraulic channel in the housing. The second hydraulic chamber is hydraulically connected at that interface via an annular second hydraulic connection area to the second hydraulic channel in the housing. The rotary seal is arranged at that interface on either side of the first hydraulic connection area and on either side of the second hydraulic connection area. It is characterized by this.

[0011] The rotary seal prevents leakage of hydraulic fluid in two hydraulic connections between the housing and the rotatable unit described above.

[0012] According to another embodiment of the present invention, when the drawbar is pushed into the retracted locking position under the influence of the actuating sleeve and the motion transmission mechanism, the actuating sleeve is configured to assume a self-locking axial position on the spindle, whereby the drawbar is maintained in the retracted locking position. Thereby, the actuating sleeve can maintain the drawbar in the retracted locking position during rotation of the spindle without the need for any external force from the hydraulic cylinder arrangement. This implies that when the spindle and the other parts of the rotatable unit described above are in the stationary position, the piston head only needs to be subjected to hydraulic pressure in relation to the tool change operation. Therefore, when the rotatable unit including the spindle and the cylinder casing is rotated, the hydraulic pressure at the piston head and thereby the hydraulic pressure in the rotary seal described above may be kept low or released. Thereby, the rotary seal does not need to be dimensioned to withstand any higher hydraulic pressure during rotation of the rotatable unit, which means that the frictional force caused by the rotary seal during rotation of the rotatable unit can be reduced.

[0013] According to another embodiment of the present invention, the piston head forms part of an annular piston member that is fixed to the actuating sleeve. Such an arrangement of the actuating sleeve and the piston member as two separate parts connected to each other may be preferred to facilitate the assembly of the clamping device. However, alternatively, the piston head and the actuating sleeve may be integrally formed.

[0014] According to another embodiment of the present invention, the cylinder casing is fixed to the spindle through a threaded joint formed by an internal thread in the cylinder casing and a corresponding external thread on the spindle. Thereby, the cylinder casing may be simply and reliably fixed to the spindle.

[0015] Another embodiment of the present invention is that the motion transmission mechanism includes two or more wedges spaced circumferentially on the spindle, each of the wedges is received in a respective aperture extending radially through the circumferential wall of the spindle, the wedges are configured to push the drawbar towards the retracted locking position when they are pushed radially inwards in the associated apertures, each of the wedges includes a first pressure-receiving surface facing outwards from the spindle, the actuating sleeve is provided on its inner side with a first pressurizing surface facing inwards for contacting the first pressure-receiving surface of each of the wedges, the first pressurizing surface has a radial distance to a longitudinal axis that becomes longer when viewed in the first axial direction, the first pressurizing surface is configured to push the first pressure-receiving surface of each of the wedges, thereby pushing each of the wedges radially inwards in the associated aperture when the actuating sleeve is moved in the first axial direction. It is characterized by this.

[0016] Since the first pressure surface has a radial distance to the longitudinal axis that is long in the first axial direction, the operation of the actuating sleeve in the first axial direction causes pressure to be applied to each first pressure-receiving surface of the wedges by the first pressure surface. This pressure will have a radial component, causing each of the wedges to be pushed radially inwards towards the longitudinal axis.

[0017] According to another embodiment of the present invention, when the drawbar is pushed into the retracted locking position under the influence of the actuating sleeve and the wedge, the first pressure surface and the first pressure-receiving surface are inclined at such an angle α that the wedge maintains the actuating sleeve at the axially self-locking position on the spindle with respect to the longitudinal axis. In this case, both the first pressure surface and the first pressure-receiving surface extend in the same direction when viewed in a longitudinal cross-section passing through the spindle. The angle α is selected to be less than the self-lock threshold angle such that when the drawbar is displaced into the retracted locking position inside the bore, the actuating sleeve assumes the axially self-locking position with respect to the wedge. To obtain the axially self-locking position, the angle α should be small enough, that is, less than the self-lock threshold angle. The axially self-locking position refers to the axial position. Here, the static frictional force between each first pressure-receiving surface of the wedge and the first pressure surface of the actuating sleeve is greater than the opposing force on the friction surface caused by the force applied to the wedge in the radial direction perpendicular to the longitudinal axis. Therefore, the axially self-locking position is obtained within an angular range that depends on the coefficient of friction between each first pressure-receiving surface of the wedge and the first pressure surface of the actuating sleeve. This coefficient of friction depends on various parameters such as the materials used, surface coatings, and use of lubricants. Therefore, the self-lock threshold angle is determined by such parameters. A person skilled in the art will be able to specify the self-lock threshold angle applicable to each specific case by using common general knowledge and / or daily experiments or at least predicting or assessing whether a particular angle is less than such a self-lock threshold angle. Generally, it is preferable to choose an angle α that is well below the self-lock threshold angle, thereby ensuring the self-locking configuration. The additional benefit of using a small angle α, thanks to the fact that a relatively long axial displacement of the actuating sleeve results in a relatively short axial displacement of the drawbar, is that the effect of amplifying the force is achieved. However, an angle α that is too small will 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 actuating sleeve from its 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, as well as an appropriate effect of amplifying the force, may be achieved.

[0018] Another embodiment of the present invention is Each of the wedges includes a second pressure-receiving surface facing outward from the spindle, On the inner side of the actuating sleeve, a second pressure-applying surface is provided which faces inward for contacting the second pressure-receiving surface of each of the wedges, The second pressure-applying surface has a radial distance to the longitudinal axis which becomes longer when viewed in the first axial direction, The second pressure-applying surface and the second pressure-receiving surface are inclined at an angle β greater than the angle α with respect to the longitudinal axis, The first and second pressure-applying surfaces and the first and second pressure-receiving surfaces are continuously arranged in the actuating sleeve and each of the wedges, respectively. After the operation of the actuating sleeve in the first axial direction, the second pressure-applying surface is configured to slide on and press the second pressure-receiving surface of each of the wedges during the first phase of the operation, and the first pressure-applying surface is configured to slide on and press the first pressure-receiving surface of each of the wedges during the subsequent second phase of the operation. It is characterized by this.

[0019] As a result, the drawbar may be axially moved quickly during the initial phase of clamping under the influence 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 by a short distance. When actual clamping occurs, i.e., when the engaging member assumes the first position described above, the drawbar is moved axially under the influence of a smaller angle α, and the axial movement of the drawbar becomes smaller compared to the axial movement of the actuating sleeve, which results in an effect of amplifying the force, also known as "power boost". The angle β is preferably between 10° and 75°, more 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 actual clamping, the actuating sleeve (and thus the entire clamping device) can be made relatively short axially while still providing a self-locking clamping mechanism with a large force amplification effect.

[0020] According to another embodiment of the present invention, the drawbar is movable against the action of a spring force from a release spring disposed inside the spindle from a forward release position to a retracted locking position under the influence of the actuating sleeve and the motion transmission mechanism. Thus, the release spring is configured to move the drawbar towards the forward release position when the actuating sleeve is moved in a second axial direction opposite to the first axial direction. The release spring may ensure that the drawbar is pushed towards the forward release position as soon as the actuating sleeve is moved in the second axial direction. The release spring may also ensure that different components of the motion transmission mechanism are always maintained under a specific axial pressure, thereby keeping them in close contact with each other and maintaining the correct positions relative to each other and relative to the actuating sleeve and the drawbar.

[0021] Further preferred features of the clamping device according to the present invention will become apparent from the following description and the dependent claims.

[0022] A specific description of embodiments of the present invention, shown by way of example, follows with reference to the following attached drawings.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

DETAILED DESCRIPTION OF THE INVENTION

[0024] A clamping device 1 according to one embodiment of the present invention is shown in FIGS. 1 and 2 in a longitudinal cross-sectional view passing through its longitudinal axis. The clamping device 1 is configured to releasably clamp a tool holder 80 (shown very schematically in these drawings) to a rotatable spindle 2 in the clamping device, enabling machining of a workpiece using a cutting tool (not shown) fixed to the tool holder 80.

[0025] The spindle 2 is rotatably mounted in the housing 3 of the clamping device 1 using, for example, a tapered roller bearing, or a rolling bearing 4 in the form of any other suitable type of roller bearing. The spindle 2 has a front end 2a, a rear end 2b, and a bore 5 that intersects the front end 2a and extends rearward therefrom. Thus, the bore 5 has an inlet opening 5a (see FIG. 9) at the front end 2a of the spindle. The spindle 2 is connectable to a drive mechanism of a machine tool, such as a drive mechanism in a tool turret of the machine tool, at the rear end 2b of the spindle via a connection pin 6 so that the spindle can be rotationally driven by the drive mechanism.

[0026] A mounting site 7 (see FIG. 9) for receiving a mounting shank 81 in the tool holder 80 is provided at the front end of the bore 5. This mounting shank 81 is herein referred to as a tool holder shank.

[0027] The drawbar 8 is slidably mounted inside the bore 5 and is reciprocable in the bore 5 along its longitudinal axis L between a forward release position (see FIGS. 2 and 11) and a retracted locking position (see FIGS. 1 and 7). The drawbar 8 has a front end facing the inlet opening 5a of the bore 5 and an opposite rear end. A head portion 9 and a neck portion 10 are provided at the front end of the drawbar 8. The head portion 9 is placed in front 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 an inclined surface 11 facing rearward at 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 here, this sealing ring 12 is received in a groove on the outside of the drawbar 8.

[0028] The tool holder shank 81 is insertable into the mounting portion of the bore 5 through the inlet opening 5a at the front end 2a of the spindle 2. The head portion 9 of the drawbar is received in an engagement bore 82 in the tool holder shank 81, and the tubular wall 83 of the tool holder shank is received in the space between the head portion 9 and the inner surface of the bore 5. In the embodiment shown here, the mounting portion 7 of the bore 5 is conical and is adapted to receive the similarly formed tool holder shank 81 having some "triangular" or polygonal, non-circular cross-sectional shape. This conical shape ensures a play-free connection between the tool holder shank 81 and the spindle 2, both radially and axially, while this non-circular cross-section ensures a non-rotatable fixation of the tool holder shank 81 to the spindle 2. However, the mounting portion of the bore 5 may also have any other suitable shape for receiving other types of tool holder shanks.

[0029] The engagement member 20 in the form of a segment is disposed around the drawbar 8 and at its front end. Under the influence of the movement of the drawbar 8 from the advanced release position to the retracted locking position, the engagement member 20 enables the toolholder shank 81 to enter and exit the seating portion of the bore 5 from a first position (see FIGS. 2 and 11) where the engagement member 20 allows this, to a second position (see FIGS. 1 and 7) where the engagement member 20 is in a locking engagement with the engagement groove 84 in the engagement bore 82 in the toolholder shank 81, thereby keeping the toolholder shank 81 fixed to the spindle 2.

[0030] In the embodiment shown here, the engagement member 20 is disposed around the neck portion 10 of the drawbar 8, and around the neck portion, it is disposed in the bore 5 and is held using a retainer ring 21 (see FIG. 7) that surrounds the neck portion 10 and an elastic O-ring 22. Each of the engagement members 20 has an outward-facing flange portion 23 that engages in an inner groove in the retainer ring 21. The O-ring 22 is received in an outward-facing groove at the rear end of each of the engagement members 20. A compression spring 24, a thrust ring 25, and a stop ring 26 are also disposed in the bore 5 and are configured to surround the drawbar 8. The compression spring 24 is seated between a shoulder in the drawbar 8 and the thrust ring 25 and is configured to bias the thrust ring 25, the retainer ring 21, and the engagement member 20 forward. The forward movement of the retainer ring 21 toward the inlet opening of the bore 5 is restricted by the stop ring 26 seated in a groove on the inner surface of the bore 5.

[0031] At its front end, each of the engagement members 20 is provided with an outward-facing engagement flange 27 configured to engage with the engagement groove 84 in the tool holder shank 81 when the engagement member 20 is in the second position described above. When the drawbar 8 is in the advanced release position, the front ends of the engagement members 20 are each located behind the head portion 9 of the drawbar 8, and the engagement flange 27 is disengaged from engagement with the engagement groove 84 in the tool holder shank 81, as shown in FIGS. 2 and 11. When the drawbar 8 is axially moved rearward along its longitudinal axis L in the bore 5, the inclined surface 11 at the head portion 9 of the drawbar will contact each of the front ends of the engagement members 20. Each of the front ends of the engagement members 20 slides on this inclined surface 11 and is pushed outward, causing the engagement flange 27 on the engagement member to engage with the engagement groove 84 in the tool holder shank 81. Thereafter, the tool holder shank 81 is pulled by the drawbar 8 and brought into close contact with the inner surface of the spindle 2 within the mounting portion of the bore 5.

[0032] The clamping device 1 is concentric with the spindle 2 and further includes an actuating sleeve 13 arranged around the peripheral wall 14 of the spindle 2. The actuating sleeve 13 is slidably mounted on this peripheral wall 14 and is adapted to be axially movable along the longitudinal axis L with respect to the spindle 2. The actuating sleeve 13 is non-rotatably mounted on the spindle 2, that is, rotation with respect to the spindle 2 is prevented, and as a result, it is configured to rotate with the spindle 2. The motion transmission mechanism 30 is mounted on the spindle 2 and is configured to transmit the axial motion of the actuating sleeve 13 in the first axial direction D with respect to the spindle 2 to the motion of the drawbar 8 from the advanced release position to the retracted locking position. In the embodiment shown here, this first axial direction D is the direction towards the rear end 2b of the spindle 2. Therefore, in this case, the motion of the drawbar 8 from the advanced release position to the retracted locking position is achieved by the axial motion of the actuating sleeve 13 rearward along the spindle 2. However, as an alternative, the actuating sleeve 13 and the motion transmission mechanism 30 may be arranged to cooperate such that the motion of the drawbar 8 from the advanced release position to the retracted locking position is achieved by the axial motion of the actuating sleeve 13 forward along the spindle 2.

[0033] Furthermore, the clamping device 1 includes a hydraulic cylinder arrangement 50 for axially moving the actuating sleeve 13 with respect to the spindle 2. This hydraulic cylinder arrangement 50 is concentric with the actuating sleeve 13 and includes a cylinder casing 51 fixed to the outside of the spindle 2 and adapted to be rotatable with the spindle 2 with respect to the housing 3. In the embodiment shown here, the cylinder casing 51 is fixed to the spindle 2 through a threaded joint formed by an internal thread 52 in the cylinder casing 51 and a corresponding external thread 53 in the spindle 2. However, the cylinder casing 51 may of course be fixed to the spindle 2 in any other suitable manner.

[0034] The hydraulic cylinder array 50 also includes an annular piston head 54 that is fixed to or fixedly connected to the actuating sleeve 13. In the embodiment shown here, the piston head 54 forms part of an annular piston member 55 that is concentric with the actuating sleeve 13 and configured to surround a part thereof. This piston member 55 includes a sleeve-shaped base portion 56 that is fixed to the outside of the actuating sleeve 13. The base portion 56 is received in an annular groove on the outside of the actuating sleeve 13 and is fixed to the actuating sleeve 13 using a locking ring 57 that prevents the actuating sleeve 13 and the piston member 55 from moving axially relative to each other. In this case, the piston head 54 is formed as an annular external protrusion in the piston member 55. In the embodiment shown here, the base portion 56 of the piston member 55 covers the radial through holes 58 in the actuating sleeve 13. Those through holes 58 provide access to the spindle 2 and the drawbar 8 for the insertion of different components of the motion transmission mechanism 30 during the assembly of the clamping device 1. Sealing rings 59a, 59b are arranged on both opposite sides of the through holes 58 between the actuating sleeve 13 and the base portion 56 of the piston member.

[0035] Alternatively, the piston head 54 and the actuating sleeve 13 may be integrally formed, for example, with a piston head formed as an annular external protrusion in the actuating sleeve.

[0036] The piston head 54 is slidably received in an annular space 60 inside the cylinder casing 51, and this space is configured to be divided into an annular first hydraulic chamber 61a on the first side of the piston head 54 and an annular second hydraulic chamber 61b on the second side opposite to the piston head. The actuating sleeve 13, together with the piston head 54, is movable in the first axial direction D described above to achieve the movement of the drawbar 8 from the advanced release position to the retracted locking position by supplying hydraulic fluid to the first hydraulic chamber 61a, and the actuating sleeve 13, together with the piston head 54, is movable in the opposite second axial direction by supplying hydraulic fluid to the second hydraulic chamber 61b. The sealing ring 62 is placed in an annular groove on the outward-facing surface of the piston head 54 and is in close contact with the wall 63 of the cylinder casing 51 that radially outwardly delimits the above-described space 60.

[0037] When the drawbar 8 is pushed into the retracted locking position under the influence of the actuating sleeve 13 and the motion transmission mechanism 30, the actuating sleeve 13 is preferably configured to assume a self-locking axial position on the spindle 2, whereby the actuating sleeve 13 can maintain the drawbar 8 in the retracted locking position. Thereby, the piston head 54 only needs to receive hydraulic pressure when the spindle 2 is stationary and the drawbar 8 is moved from the retracted locking position to the advanced release position and then back to the retracted locking position in relation to the tool change operation. In the self-locking axial position, the frictional force between the actuating sleeve 13 and the parts of the motion transmission mechanism 30 and / or the spindle 2 that are in contact with the actuating sleeve 13 prevents the actuating sleeve from being displaced axially in a direction opposite to the first axial direction D.

[0038] The spindle 2 and the cylinder casing 51 form part of a rotatable unit 64 that is rotatably received in the internal space 18 of the housing 3. This rotatable unit 64 also includes other components such as the actuating sleeve 13, the drawbar 8, the piston member 55, and the motion transmission mechanism 30, which are mounted on the spindle 2 and configured to rotate therewith. The first hydraulic chamber 61a is hydraulically connected at the interface between the housing 3 and the rotatable unit 64 to the first hydraulic channel 65a in the housing 3 via an annular first hydraulic connection area 66a, and the second hydraulic chamber 61b is hydraulically connected at that interface to the second hydraulic channel 65b in the housing 3 via an annular second hydraulic connection area 66b. The rotary seals 67a, 67b, 67c are arranged at that interface on either side of the first hydraulic connection area 66a and on either side of the second hydraulic connection area 66b. In the example shown here, there are three rotary seals, and one of them, 67b, is arranged between the first and second hydraulic connection areas 66a, 66b.

[0039] In the embodiment shown here, the rotatable unit 64 described above also includes a sleeve-shaped connection piece 68 that is clamped between the front end of the cylinder casing 51 and the inner part 4a of the rolling bearing 4 provided at the front end 2a of the spindle between the spindle 2 and the housing 3. In this case, the first hydraulic chamber 61a is connected to the first hydraulic connection area 66a through a channel 69 provided in the connection piece 68. There is a small amount of play between the outer surface of the cylinder casing 51, the connection piece 68, and the opposing inner surface of the housing 3.

[0040] The cylindrical outer surface of the actuating sleeve 13 is in sliding contact at its front end, i.e., at the end of the actuating sleeve facing the front end 2a of the spindle 2, with the cylindrical inner surface of the connecting piece 68. The sealing ring 70 is placed in an annular groove in the cylindrical outer surface of the actuating sleeve so as to be in close contact with the opposing inner surface of the connecting piece 68. Another sealing ring 71 is placed in an annular groove in the cylindrical inner surface of the actuating sleeve at its rear end, i.e., at the end of the actuating sleeve facing the rear end 2b of the spindle 2, and this sealing ring 71 is in close contact with the opposing peripheral wall 14 of the spindle 2.

[0041] Each of the rotary seals 67a, 67b, 67c is preferably arranged in each of the annular grooves 72 provided at the above-described interface on the inner surface of the housing 3. However, each of the rotary seals 67a, 67b, 67c can alternatively be arranged in each of the annular grooves provided on the outer surface of the rotatable unit 64. In the embodiment shown here, each of the rotary seals 67a, 67b, 67c includes an inner seal ring 73 and an outer elastic O-ring 74 that surrounds the seal ring 73, is in a radially compressed state, and is configured to press the seal ring 73 against the outer surface of the rotatable unit 64.

[0042] In the embodiment shown here, preferably, a release spring 17 in the form of a helical compression spring is placed in the space inside the spindle 2 and is configured to act on the rear end of the drawbar 8 in order to bias the drawbar towards the advanced release position. The drawbar 8 is movable under the influence of the actuating sleeve 13 and the motion transmission mechanism 30 against the action of the spring force from this release spring 17 from the advanced release position to the retracted locking position. The release spring 17 is preferably arranged behind the drawbar 8 along the longitudinal axis L.

[0043] The motion transmission mechanism 30 may be designed in many different ways. In the embodiment shown here, the motion transmission mechanism includes three wedges 31 that are circumferentially spaced apart on the spindle 2. Each of the wedges 31 is received in a respective aperture 32 that extends radially through the aforementioned circumferential wall 14 of the spindle 2, and the wedges 31 are configured to push the drawbar 8 toward the retracted locking position when they are pushed radially inward in the associated apertures 32. Each of the wedges 31 includes a first pressure-receiving surface 33 that faces outward from the spindle 2 (see FIGS. 7 and 9), and the actuating sleeve 13 is provided, on its inner side, with a first pressurizing surface 34 that faces inward to contact the first pressure-receiving surface 33 of each of the wedges. The first pressurizing surface 34 has a radial distance to the longitudinal axis L that increases as seen in the first axial direction D described above. The first pressurizing surface 34 is configured to push the first pressure-receiving surface 33 of each of the wedges, thereby pushing each of the wedges 31 radially inward in the aperture 32 when the actuating sleeve 13 is moved in the first axial direction D.

[0044] The motion transmission mechanism 30 shown here also includes three wedge engagement members 35 that project radially from the drawbar 8 into respective ones of the apertures 32 and are fixed to the drawbar so as to be movable along the longitudinal axis L together with the drawbar. Thus, the movement of the wedge engagement members 35 along the longitudinal axis L will cause a corresponding movement of the drawbar 8. Each of the wedge engagement members 35 contacts one of the wedges 31. To facilitate the assembly of the clamping device 1, the wedge engagement members 35 shown here are formed as separate elements that are seated in respective radial recesses in the drawbar 8. However, alternatively, the wedge engagement members 35 may be seated in any other suitable manner on the drawbar 8 or may be formed integrally with the drawbar.

[0045] The motion transmission mechanism 30 may include any suitable number of wedges 31 and associated wedge engagement members 35 that are disposed to extend through a corresponding number of apertures 32 in the peripheral wall 14 of the spindle 2. The apertures 32, the associated wedges 31, and the wedge engagement members 35 are preferably evenly distributed in the circumferential direction of the peripheral wall 14.

[0046] Each of the wedge engagement members 35 has a sliding surface 36 facing the front end 2a of the spindle 2, and each of the apertures 32 has a sliding surface 37 facing the rear end 2b of the spindle. Further, each of the wedges 31 has a first wedge surface 38 facing the rear end 2b of the spindle and a second wedge surface 39 facing the front end 2a of the spindle, and the first and second wedge surfaces 38, 39 thereof approach each other radially toward the longitudinal axis L. The first wedge surface 38 of each of the wedges 31 is in contact with the sliding surface 36 of the associated wedge engagement member 35, and the second wedge surface 39 of each of the wedges is in contact with the sliding surface 37 of the associated aperture 32. When the wedge 31 is radially inwardly pressed in the aperture 32 by the actuating sleeve 13, the first and second wedge surfaces 38, 39 of each of the wedges 31 slide on the corresponding sliding surfaces 36, 37 of the associated wedge engagement member 35 and aperture 32 to push them, thereby moving the drawbar 8 toward the retracted locking position.

[0047] The first pressure surface 34 and the first pressure-receiving surface 33 are preferably at such an angle α (see FIG. 11) with respect to the longitudinal axis L that when the drawbar 8 is pushed into the retracted locking position under the influence of the actuating sleeve 13 and the wedge 31, the wedge 31 inclines to maintain the actuating sleeve 13 at the axially self-locking position in the spindle 2.

[0048] Each of the wedges 31 may also include a second pressure-receiving surface 43 facing outward from the spindle 2, and the actuating sleeve 13 is provided, on its inner side, with a second pressing surface 44 facing inward for contacting the second pressure-receiving surface 43 of each of the wedges. The second pressing surface 44 has a radial distance to the longitudinal axis L that increases as seen in the first axial direction D. The second pressing surface 44 and the second pressure-receiving surface 43 are inclined at an angle β (see FIG. 11) that is greater than the angle α described above with respect to the longitudinal axis L. The first and second pressing surfaces 34, 44 and the first and second pressure-receiving surfaces 33, 43 are each arranged continuously in the actuating sleeve 13 and in each of the wedges 31, and after the movement of the actuating sleeve 13 in the first axial direction D, the second pressing surface 44 is configured to slide on and press the second pressure-receiving surface 43 of each of the wedges during the initial first phase of the movement, and then the first pressing surface 34 is configured to slide on and press the first pressure-receiving surface 33 of each of the wedges during the subsequent second phase of the movement.

[0049] Each of the wedge engagement members 35 further includes a release pressure-receiving surface 40 facing the rear end 2b of the spindle 2, and the actuating sleeve 13 includes a release pressing surface 41 facing the front end 2a of the spindle. The release pressing surface 41 of the actuating sleeve 13 is configured to contact the release pressure-receiving surface 40 of the wedge engagement member 35 when the actuating sleeve 13 is moved in the second axial direction described above, thereby enabling the actuating sleeve to exert an axially directed force, during the final phase of the movement of the drawbar from the retracted locking position to the advanced release position, onto the drawbar 8 via the wedge engagement member 35.

[0050] In the embodiment shown here, the support segment 45 and the pins 46 are arranged between the actuating sleeve 13 and the spindle 2. The support segment 45 is arranged inside the actuating sleeve 13 as shown in FIG. 12 and is fixed to the actuating sleeve using the screw 47. The support segment 45 supports the wedges 31 and is designed to keep them maintained and prevent their positions from shifting circumferentially relative to the actuating sleeve 13. Each of the pins 46 is partially received in the recess 48 in the spindle 2 and is partially received in the longitudinal groove 49 in the actuating sleeve 13. The pin 46 is fixed in the axial position relative to the spindle 2 by being received in the recess 48 on the outside of the spindle. The pin 46 is slidably received in the longitudinal groove 49 inside the actuating sleeve 13, and as a result, when the actuating sleeve 13 is axially moved relative to the spindle 2, the actuating sleeve 13 can move axially relative to the pin 46. If the actuating sleeve 13 is in the advanced release position, the rear end of each of the pins 46 is partially received in the recess 42 in the support segment 45 as shown in FIG. 11. The pins 46 prevent relative rotation between the actuating sleeve 13 and the spindle 2. As a result, when the spindle 2 is rotated, the actuating sleeve 13 will rotate at the same rotational speed as the spindle 2 and cannot be displaced circumferentially relative to the spindle 2.

[0051] When the tool holder 80 is clamped to the spindle 2, as shown in FIGS. 2 and 11, with the spindle 2 in the stationary position and the drawbar 8 advanced to the release position and remaining there, the tool holder shank 81 is inserted into the seating portion 7 of the bore 5. Thereby, the head portion 9 of the drawbar is received in the engagement bore 82 in the tool holder shank 81, and the engagement groove 84 in the tool holder shank 81 is placed outside the engagement flange 27 of the engagement member 20. Thereafter, hydraulic fluid is supplied to the first hydraulic chamber 61a to move the actuating sleeve 13 in the first axial direction D. During the first phase of this axial movement of the actuating sleeve 13, the second pressure surface 44 on the actuating sleeve 13 slides over and presses on the second pressure-receiving surface 43 on the wedge 31. Thereby, the wedge 31 is pushed radially inwardly, and the drawbar 8 is displaced axially toward the retracted locking position. Due to the relatively steep inclination β of the second pressure surface and the pressure-receiving surfaces 44, 43, the wedge 31 initially moves inwardly rather quickly, which results in a relatively rapid displacement of the drawbar 8. The relatively steep angle β is suitable because a large force is not required for the initial displacement of the drawbar 8. The first and second pressure surfaces 34, 44 and the first and second pressure-receiving surfaces 33, 43 are arranged such that when the actuating sleeve 13 is moved, i.e., at the transition between their respective surfaces, the drawbar 8 is positioned to almost reach its final destination at the rear end of the bore 5. Thus, for the final clamping phase where a large force is beneficial, the first pressure surface and the pressure-receiving surfaces 34, 33 are active. In this phase, the relatively large movement of the actuating sleeve 13 results in a very small radial displacement of the wedge 31 and an even smaller axial displacement of the drawbar 8, which, as a result, provides an effect of amplifying the force, whereby the drawbar 8 can pull the tool holder shank 81 with a large force and make a firm engagement with the spindle 2.Furthermore, the small inclination α of the first pressure surface and the pressure-receiving surface 34, 33 provides a self-locking effect, ensuring that the clamping device remains clamped without the need for any additional locking means. This allows the hydraulic pressure at the piston head 54 to be released when the drawbar 8 reaches the locked position where it is retracted.

[0052] When a tool change operation is performed and the tool holder 80 is released from the spindle 2, the rotation of the spindle 2 is stopped, and hydraulic oil is supplied to the second hydraulic chamber 61b to move the actuating sleeve 13 in a second axial direction opposite to the first axial direction D. When the actuating sleeve 13 receives sufficient force in the second axial direction due to the hydraulic pressure in the second hydraulic chamber 61b, the self-locking frictional engagement between the first pressure surface 34 on the actuating sleeve 13 and the first pressure-receiving surface 33 on the wedge 31 is released, and then the actuating sleeve 13 becomes movable in the second axial direction relative to the spindle 2 under the influence of the hydraulic pressure in the second hydraulic chamber 61b. When the actuating sleeve 13 is moved in this direction, the spring force exerted by the release spring 17 at the rear end of the drawbar 8 pushes the drawbar axially toward the advanced release position. As a result, the wedge engagement member 35 exerts a force on the wedge 31 and pushes them radially outward. When the actuating sleeve 13 is moved a certain distance in the second axial direction, the release pressure surface 41 on the actuating sleeve 13 comes into contact with the release pressure-receiving surface 40 on the wedge engagement member 35. This enables the actuating sleeve 13 to exert an axial force on the drawbar 8 via the wedge engagement member 35, which presses the outer end of the head portion 9 of the drawbar 8 against the surface 85 in the engagement bore 82 of the tool holder shank 81, thereby releasing the tool holder shank 81 from the spindle 2.

[0053] The present invention is of course not limited to the above-described embodiments by any means. On the contrary, many possibilities for its variations will be apparent to those skilled in the art without departing from the basic concept of the present invention as defined in the appended claims.

Claims

1. 1. A clamping device for releasably retaining a tool holder shank, comprising: A housing (3); a spindle (2) rotatably mounted within said housing (3), said spindle (2) having a front end, a rear end and a bore (5) intersecting said front end and extending rearwardly therefrom, said bore (5) being provided at its front end with a mounting portion (7) for receiving said toolholder shank (81); a drawbar (8) slidably mounted within said bore (5) 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 around the drawbar (8) at its front end, the mating member (20) being movable under the effect of movement of the drawbar (8) from the advanced release position to the retracted locking position from a first position in which the mating member (20) enables the toolholder shank (81) to move into and out of said mounting portion of the bore (5), to a second position in which the mating member (20) is in locking engagement with the toolholder shank (81) and keeps it fixed to the spindle (2); A clamping device (1) comprising: a hydraulically operated actuating sleeve (13) disposed inside the housing (3), the actuating sleeve (13) being disposed around a peripheral wall (14) of the spindle (2) and slidably mounted on said peripheral wall (14) so ​​as to be axially movable relative to the spindle (2); a motion transmission mechanism (30) disposed inside the housing (3), the motion transmission mechanism (30) being mounted on the spindle (2) and configured to transmit an axial movement of the actuating sleeve (13) relative to the spindle (2) in a first axial direction (D) to a movement of the drawbar (8) from the advanced release position to the retracted locking position; a hydraulic cylinder arrangement (50) arranged inside the housing (3) and configured to axially move the actuating sleeve (13) relative to the spindle (2), a cylinder casing (51) concentric with the actuating sleeve (13) and fixed to the spindle (2) at its outer side so as to be rotatable together with the spindle (2) relative to the housing (3); an annular piston head (54) fixedly attached to or fixedly connected to the actuating sleeve (13), the piston head (54) being slidably received in an internal annular space (60) of the cylinder casing (51) and configured to divide the space into an annular first hydraulic chamber (61 a) on a first side of the piston head and an annular second hydraulic chamber (61 b) on an opposite second side of the piston head; a hydraulic cylinder arrangement (50) including: Further comprising: the actuating sleeve (13) together with the piston head (54) is movable in the first axial direction (D) by supplying hydraulic fluid to the first hydraulic chamber (61 a) and in the opposite second axial direction by supplying hydraulic fluid to the second hydraulic chamber (61 b), Clamping device (1).

2. the spindle (2) and the cylinder casing (51) form part of a rotatable unit (64) rotatably received in the interior space (18) of the housing (3); the first hydraulic chamber (61 a) is hydraulically connected to a first hydraulic channel (65 a) in the housing (3) via an annular first hydraulic connection area (66 a) at the interface between the housing (3) and the rotatable unit (64); the second hydraulic chamber (61b) is hydraulically connected to a second hydraulic channel (65b) in the housing (3) via an annular second hydraulic connection area (66b) at said interface, characterised in that rotary seals (67a, 67b, 67c) are arranged at said interface on both sides of the first hydraulic connection area (66a) and on both sides of the second hydraulic connection area (66b). The clamping device of claim 1 .

3. 3. The clamping device according to claim 2, characterized in that each of the rotary seals (67a, 67b, 67c) is arranged at the interface in a respective annular groove (72) arranged in the housing (3).

4. 4. The clamping device according to claim 2 or 3, characterized in that each of the rotary seals (67a, 67b, 67c) comprises an inner seal ring (73) and an outer resilient O-ring (74) surrounding the inner seal ring (73) and configured to be in a radially compressed state and to press the inner seal ring (73) against an outer surface of the rotatable unit (64).

5. 5. The clamping device according to claim 1, wherein the actuating sleeve (13) is configured to assume a self-locking axial position on the spindle (2) when the drawbar (8) is forced into the retracted locking position under the influence of the actuating sleeve (13) and the motion transmission mechanism (30), thereby maintaining the drawbar (8) in the retracted locking position.

6. 6. A clamping device according to claim 1, wherein the piston head (54) forms part of an annular piston member (55) fixed to the actuation sleeve (13).

7. 6. The clamping device according to claim 1, wherein the piston head (54) and the actuating sleeve (13) are formed in one piece.

8. 8. The clamping device according to claim 1, wherein the cylinder casing (51) is fixed to the spindle (2) through a threaded joint formed by an internal thread (52) on the cylinder casing (51) and a corresponding external thread (53) on the spindle (2).

9. The motion transmission mechanism (30) includes two or more wedges (31) spaced circumferentially about the spindle (2); Each of the wedges (31) is received in a respective aperture (32) extending radially through the peripheral wall (14) of the spindle (2); the wedges (31) are configured to urge the drawbar (8) towards the retracted locking position when they are forced radially inwardly in the associated aperture (32); Each of the wedges (31) includes a first pressure surface (33) facing away from the spindle (2); said actuation sleeve (13) being provided on its inside with a first pressure surface (34) facing inwards for contacting said first pressure receiving surface (33) of each of said wedges; the first pressure surface (34) has a radial distance to the longitudinal axis (L) that is greater in the first axial direction (D); the first pressure surface (34) is configured to press the first pressure surface (33) of each of the wedges (31) radially inwardly at the associated aperture (32) when the actuation sleeve (13) is moved in the first axial direction (D), thereby pressing against the first pressure surface (33) of each of the wedges. A clamping device according to any one of the preceding claims.

10. 10. The clamping device according to claim 9, characterized in that the first pressure surface (34) and the first pressure surface (33) are inclined at an angle α with respect to the longitudinal axis (L) in such a way that when the drawbar (8) is forced into the retracted locking position under the influence of the operating sleeve (13) and the wedge (31), the wedge (31) maintains the operating sleeve (13) in a self-locking axial position on the spindle (2).

11. Each of the wedges (31) includes a second pressure surface (43) facing away from the spindle (2); said actuation sleeve (13) is provided on its inner side with a second pressure surface (44) facing inwards for contacting said second pressure surfaces (43) of each of said wedges (31); the second pressure surface (44) has a radial distance to the longitudinal axis (L) that is greater in the first axial direction (D); The second pressure surface (44) and the second pressure receiving surface (43) are inclined with respect to the longitudinal axis (L) at an angle β that is greater than the angle α, the first and second pressure surfaces (34, 44) and the first and second pressure surfaces (33, 43) are respectively arranged in succession on the working sleeve (13) and on each of the wedges (31), such that after a movement of the working sleeve (13) in the first axial direction (D), the second pressure surface (44) is configured to slide over and press against the second pressure surfaces (43) of each of the wedges during a first phase of the movement, and the first pressure surface (34) is configured to slide over and press against the first pressure surfaces (33) of each of the wedges during a subsequent second phase of the movement. The clamping device of claim 10.

12. 12. The clamping device according to claim 1, wherein the drawbar (8) is movable from the advanced release position to the retracted locking position under the influence of the actuating sleeve (13) and the motion transmission mechanism (30) against the action of a spring force from a release spring (17) arranged inside the spindle (2).

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