Clamping device for tool holders

Abstract

A clamping device for releasably holding a toolholder shank (71), the clamping device comprising: a spindle (2) rotatably mounted inside a housing (3), a drawbar (8) axially movable in a bore (5) in the housing, 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 hydraulic actuator (50) having a piston unit (52) for moving the actuating member. A valve assembly (83) having two parallel, oppositely directed check valves (85a, 85b) provides residual hydraulic pressure in a hydraulic chamber (83b) of the hydraulic actuator to cause automatic return movement of the piston unit after movement of the drawbar to a rearward, locking position.

Description

[Technical Field]

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

[0002] Within the field of machine tools for metal cutting, cutting tools, for example in the form of drills or milling tools, used to machine workpieces of metallic material are often fixed to and rotate with a tool holder, which may be removably clamped to a rotatable spindle of the machine tool for rotation therewith. It has previously been known to clamp the shank of such a tool holder to the rotatable spindle by a clamping mechanism located in the spindle. When the cutting tool needs to be replaced, the tool holder is removed 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 adapted for automatic tool changing operations has previously been known from EP 1 468 767 B1. In the clamping device described in EP 1 468 767 B1, an actuating member in the form of a first drawbar is slidably mounted inside the spindle and is configured to effect axial displacement of a second drawbar via a force amplification mechanism comprising several cooperating wedges arranged between the drawbars. A gas spring inside the spindle is configured to place the two drawbars into a retracted locking position in which a tool holder is clamped to the spindle, and a hydraulic piston can be configured to act on a piston at the rear end of the gas spring to effect displacement of the two drawbars to an advanced releasing position in which the tool holder can be released from the spindle.

[0004] Object of the invention The object of the present invention is to achieve a further development of a clamping device of the type mentioned above, in order to provide a clamping device adapted for automatic tool changing operations, which is improved in at least some respects. Summary of the Invention

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

[0006] The clamping device according to the invention comprises: - Housing and a spindle rotatably mounted inside the housing and having a forward end, a rearward end, and a bore intersecting the forward end and extending rearwardly therefrom, the forward end of the bore being provided with a mounting portion for receiving a toolholder shank; a drawbar slidably mounted inside the bore for reciprocal movement within the bore along a longitudinal axis of the drawbar between a forward release position and a rearward locking position; an engaging member disposed about the draw bar at a forward end of said engaging member, the engaging member being movable under the influence of movement of the draw bar from a forward releasing position to a rearward locking position from a first position at which the engaging member allows the toolholder shank to move into and out of said mounting portion of the bore to a second position at which the engaging member is in locking engagement with the toolholder shank, maintaining the engaging member fixed to the spindle; - an actuating member disposed inside the housing, the actuating member being slidably mounted on the spindle such that the actuating member is movable relative to the spindle in an axial direction thereof; - 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 disposed in or mounted on a housing and configured to move an actuating member axially relative to the spindle, the hydraulic actuator comprising a piston unit configured to be slidably received in a space in the hydraulic actuator and divide the space into a first hydraulic chamber and a second hydraulic chamber; - a first hydraulic line connected to the first hydraulic chamber, wherein hydraulic fluid can be supplied to and discharged from the first hydraulic chamber via the first hydraulic line; - a second hydraulic line connected to the second hydraulic chamber, wherein hydraulic fluid can be supplied to and discharged from the second hydraulic chamber via the second hydraulic line; and Equipped with.

[0007] The piston unit is movable in a first direction by supplying hydraulic fluid into a first hydraulic chamber via a first hydraulic line, and the piston unit is movable in an opposite second direction by supplying hydraulic fluid into a second hydraulic chamber via a second hydraulic line, to enable the piston unit to apply, directly or through a connecting element, a pulling or pushing force to the actuating member in said first axial direction, thereby effecting movement of the drawbar from a forward released position to a rearward locked position.

[0008] The clamping device further comprises a valve assembly, hereinafter referred to as a first valve assembly, the first valve assembly being disposed in the second hydraulic line; - a first flow path and a second flow path arranged in parallel with each other; - a first check valve, preferably in the form of a spring-loaded check valve, disposed in the first flow path and configured to allow hydraulic fluid flow through the first flow path toward the second hydraulic chamber and to obstruct hydraulic fluid flow through the first flow path away from the second hydraulic chamber; - A second check valve is disposed in the second flow path, and the hydraulic pressure in the second hydraulic chamber is equal to the cracking pressure p of the second check valve. C2 a second check valve, preferably in the form of a spring-loaded check valve, configured to permit hydraulic fluid flow through the second flow path away from the second hydraulic chamber and to obstruct hydraulic fluid flow through the second flow path toward the second hydraulic chamber when Equipped with.

[0009] According to the present invention, the actuating member is rotatable relative to the piston unit together with the spindle, which implies that the piston unit and all other parts of the hydraulic actuator can remain stationary during machining operations as the tool holder rotates with the spindle. By avoiding rotating parts in the hydraulic actuator used to move the actuating member in connection with automatic tool changing operations, the construction of the hydraulic actuator and associated hydraulic system is simplified and no rotary seal is required at the interface between the housing and the spindle, which would limit the possible rotational speed of the spindle. The use of a hydraulically operated piston unit to move the actuating member, and thereby achieve movement of the drawbar, implies that the clamping device according to the present invention is suitable for use in automatic tool changing operations.

[0010] The purpose of the first valve assembly is to ensure that a small residual pressure remains in the second hydraulic chamber at the moment hydraulic movement of the piston unit in the first direction is stopped and the hydraulic pressure in the first hydraulic chamber is released after movement of the drawbar to the rear locking position. The magnitude of this residual pressure is equal to the cracking pressure p of the second check valve. C2The residual pressure is required to cause a short return movement of the piston unit in the second direction to release any possible residual frictional contact between the piston unit and the actuating member or possible connecting element. Such contact may remain due to frictional forces between the piston unit and the associated sliding surface in the hydraulic actuator. By selecting a check valve with a suitable cracking pressure, it is possible to ensure that the piston unit automatically releases contact with the actuating member or connecting element, as the case may be, after the tool change operation is completed, so that there is no frictional heat generation at the interface between the piston unit and the actuating member or connecting element when the actuating member rotates together with the spindle at high speed relative to the piston unit after the tool change operation. Without the above-mentioned type of valve assembly, there is a risk of high frictional heat generation at the interface, which could cause damage to the clamping device. The cracking pressure p of the second check valve C2 is the cracking pressure p C2 and the effective pressure area on the side of the piston unit facing the second hydraulic chamber must be higher than the maximum value of the friction force between the piston unit and the associated sliding surface in the hydraulic actuator, which is preferably about 0.2 to 2 MPa.

[0011] The clamping device according to the invention can be mounted on the tool turret of a machine tool, with the rotatable spindle of the clamping device being 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 can constitute the main spindle of the machine tool or can be connected to such a main spindle without any intermediate tool turret.

[0012] According to one embodiment of the present invention, the actuating member is configured to assume a self-locking axial position on the spindle when the drawbar is put into the rear-locking position under the influence of the actuating member and the motion transmission mechanism, thereby keeping the drawbar in the rear-locking position, whereby the actuating member is able to keep the drawbar in the rear-locking position during rotation of the spindle without requiring any external force from the piston unit, which implies that the piston unit only needs to apply a pulling or pushing force to the actuating member with a tool changing operation when the spindle and the actuating member are in a rest position.

[0013] Smaller pressure peaks may occasionally occur in the hydraulic system connected to the hydraulic actuator. These pressure peaks may be transmitted to the second hydraulic chamber via the second hydraulic line and the first check valve described above, causing unwanted movement of the piston unit and resulting in accidental movement of the drawbar toward the forward release position. By selecting a check valve with a cracking pressure of at least 0.1 MPa, preferably 0.2 MPa or more, it is possible to prevent such pressure peaks from being transmitted to the second hydraulic chamber.

[0014] According to another embodiment of the invention, the first valve assembly is disposed in or mounted on a housing. This allows all components of the clamping device to be disposed in or mounted on the housing, which makes it possible to provide the clamping device in the form of a compact unit suitable for detachable mounting to a conventional tool turret of a machine tool. However, the first valve assembly may alternatively be disposed remote from the housing of the clamping device, for example, in a tool turret of a machine tool configured to carry the housing.

[0015] According to another embodiment of the present invention, the clamping device includes a hydraulic accumulator, preferably in the form of a spring-loaded accumulator, arranged in fluid communication with the second hydraulic chamber. When the hydraulic actuator is operated to move the drawbar to the rearward locking position, the hydraulic accumulator is preloaded to a pressure corresponding to the residual pressure in the second hydraulic chamber, defined by the cracking pressure of the second check valve. During the short return movement of the piston unit under the influence of the residual pressure in the second hydraulic chamber, the pressurized hydraulic fluid in the hydraulic accumulator contributes to the movement of the piston unit, allowing an increase in the stroke of the piston unit during the return movement for a given value of the maximum residual pressure in the second hydraulic chamber. In this way, by using the hydraulic accumulator, the required cracking pressure p of the second check valve can be reduced. C2 The hydraulic accumulator preferably reduces the cracking pressure p of the second check valve. C2 The cracking pressure of the second check valve, p, corresponds to 80-90% of the C2 Preferably, the pressure vessel is sized for a maximum cumulative pressure less than 100 psi.

[0016] According to another embodiment of the present invention, the clamping device includes a second valve assembly disposed in the first hydraulic line; a third flow path and a fourth flow path arranged parallel to each other; - a third check valve, preferably in the form of a spring-loaded check valve, disposed in the third flow path and configured to allow hydraulic fluid flow through the third flow path toward the first hydraulic chamber and to obstruct hydraulic fluid flow through the third flow path away from the first hydraulic chamber; a fourth check valve, preferably in the form of a spring-loaded check valve, disposed in the fourth flow path and configured to permit hydraulic fluid flow through the fourth flow path away from the first hydraulic chamber and to obstruct hydraulic fluid flow through the fourth flow path toward the first hydraulic chamber when hydraulic pressure in the first hydraulic chamber exceeds a cracking pressure of the fourth check valve; Equipped with Cracking pressure p of the fourth check valve C4 However, the following condition is met: p C4 <p C2 has a value such that A2 / A1 is satisfied, where p C2 is the cracking pressure of the second check valve, and p C4 is the cracking pressure of the fourth check valve, A1 is the effective pressure area on the side of the piston unit facing the first hydraulic chamber, and A2 is the effective pressure area on the side of the piston unit facing the second hydraulic chamber. The second valve assembly is configured to limit the length of the return stroke of the piston unit to prevent said return stroke from causing frictional contact between the piston unit and the actuating member or connecting element, as the case may be, at an interface through which the piston unit is configured to apply a force to the actuating member when the drawbar is to move from the rearward locking position towards the forward release position.

[0017] As mentioned above, smaller pressure peaks may occasionally occur in the hydraulic system connected to the hydraulic actuator. These pressure peaks may be transmitted to the first hydraulic chamber via the first hydraulic line and the third check valve mentioned above, causing unwanted movement of the piston unit. By selecting a check valve with a cracking pressure of at least 0.1 MPa, preferably 0.2 MPa or more, it is possible to prevent such pressure peaks from being transmitted to the first hydraulic chamber.

[0018] According to another embodiment of the invention, the actuating member has the form of a sleeve, which is arranged around the peripheral wall of the spindle and is slidably mounted thereon so as to be axially movable relative to the spindle, whereby the actuating member can be incorporated into the clamping device in a simple and space-saving manner.

[0019] Another embodiment of the present invention is - the motion transmission mechanism comprises two or more wedges spaced apart circumferentially of the spindle, each wedge received in a respective opening extending radially through a peripheral wall of said spindle, the wedges being configured to urge the drawbar towards a rear locking position when the wedge is urged radially inwardly in its associated opening; - each wedge having a first pressure surface facing outward from the spindle; - the actuating member is provided on its interior with a first pressure surface facing inward for contacting a first pressure surface on each wedge, the first pressure surfaces having increasing radial distances to the longitudinal axis when viewed in said first axial direction; the first pressure surface is configured to press against a first pressure surface on each wedge, thereby urging each wedge radially inwardly in an associated opening, when the actuating member moves in the first axial direction; It is characterized by: The first pressure surfaces have radial distances to the longitudinal axis that increase in the first axial direction, so that movement of the actuating member in the first axial direction causes pressure to be exerted by the first pressure surfaces of each wedge by the first pressure surfaces, the pressure having a radial component such that each wedge is forced radially inward toward the longitudinal axis.

[0020] According to another embodiment of the present invention, the first pressure surface and the first pressure surface are inclined relative to the longitudinal axis by an angle α such that when the drawbar is moved to the rear-locking position under the influence of the actuating member and the wedge, the wedge maintains the actuating member in a self-locking axial position on the spindle. In this case, both the first pressure surface and the first pressure surface extend in the same direction when viewed in a longitudinal section through the spindle. The angle α is selected to be below the self-locking threshold angle so that the actuating member reaches the self-locking axial position relative to the wedge when the drawbar is displaced to the rear-locking position inside the bore. To achieve 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 at which the static friction force between the first pressure surface of each wedge and the first pressure surface of the actuating member is greater than the opposing force in the friction surface caused by a force applied to the wedge in a radial direction perpendicular to the longitudinal axis. Therefore, the self-locking axial position is obtained within an angle range that depends on the coefficient of friction between the first pressure surface of each wedge and the first pressure surface of the actuating member. This coefficient of friction depends on various parameters, such as the materials used, the coating on the surfaces, and the use of lubricants. Therefore, the self-locking threshold angle depends on such parameters. Those skilled in the art can identify the self-locking threshold angle that applies to each particular case by using common general knowledge and / or routine experimentation, or at least predict or assess whether an angle falls below such a self-locking threshold angle. Generally, it is preferable to select an angle α that is sufficiently below the self-locking threshold angle, thereby ensuring a self-locking configuration. An additional benefit of using a small angle α is that a small angle α implies that a relatively long axial displacement of the actuating member results in a relatively short axial displacement of the drawbar, thereby achieving a force amplification effect. However, an angle α that is too small may be inefficient and may not actually function well. For example, a very small angle α may make it difficult to release the actuating member from the self-locking axial position. The angle α is advantageously between 2° and 10°. With an angle α within this range, a self-locking effect as well as a suitable force multiplication effect can be achieved.

[0021] Another embodiment of the present invention is - each wedge has a second pressure surface facing away from the spindle; - the actuating member is provided on its interior with second pressure surfaces facing inward for contacting second pressure surfaces on each wedge, the second pressure surfaces having increasing radial distances to the longitudinal axis when viewed in said first axial direction; the second pressure surface and the second pressure surface are inclined relative to the longitudinal axis by an angle β greater than the angle α; the first and second pressure surfaces and the first and second pressure surfaces are successively arranged on the actuating member and each wedge, respectively, such that when the actuating member moves in the first axial direction, the second pressure surface is configured to slide on and press against the second pressure surface on each wedge during a first stage of movement, and the first pressure surface is configured to slide on and press against the first pressure surface on each wedge during a subsequent second stage of movement; It is characterized by: This allows the drawbar to move axially rapidly under the influence of the larger angle β during the initial stage of clamping. This initial clamping stage does not require much force. However, during the final stage of clamping, a large force is required to displace the drawbar a short distance. When actual clamping occurs, i.e., when the engaging member assumes the first position described above, the drawbar moves axially under the influence of the smaller angle α so that the axial movement of the drawbar is small compared to the axial movement of the actuating member, resulting in a force amplification effect also known as a "power boost." The angle β is preferably between 10° and 75°, and more preferably between 35° and 65°, which provides efficient initial axial movement of the drawbar. By using a steep angle β for the initial axial movement of the drawbar and a small angle α for actual clamping, the actuating member (and therefore the entire clamping device) can be made relatively short axially while still providing a self-locking clamping mechanism with a significant force amplification effect.

[0022] According to another embodiment of the invention, the piston unit is annular and extends around the spindle, whereby it can be incorporated in a housing of the clamping device in a space-saving manner.

[0023] Another embodiment of the present invention is - the actuating member is provided on its exterior with an annular external protrusion, the piston unit being configured to exert said pulling or pushing force on the actuating member by acting on said external protrusion; - the piston unit is provided with an annular internal protrusion on the inside; - a lock ring is fixed to the piston unit on its inner side, and the lock ring and the inner protrusion are spaced apart in the axial direction of the piston unit; - the outer projection on the actuating member is received with play in the gap formed between the inner projection and the locking ring; It is characterized by: Thereby, the piston unit can be kept axially in a predetermined position relative to the actuating member during rotation of the spindle in a simple manner without any direct contact between the piston unit and the actuating member.

[0024] Further advantageous features of the clamping device according to the invention will become apparent from the following description.

[0025] A specific description of embodiments of the present invention, cited as examples, follows with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram of a clamping device and tool holder according to an embodiment of the present invention. [Figure 2] 2 is a longitudinal section through components included in the clamping device of FIG. 1, with the drawbar of the clamping device shown in a retracted, locking position; FIG. [Figure 3]FIG. 3 is a longitudinal section corresponding to FIG. 2, with the drawbar shown in the forward release position. [Figure 4] FIG. 2 is a partial cutaway perspective view of the tool holder and components included in the clamping device of FIG. 1, with the tool holder separated from the spindle. [Figure 5] FIG. 5 is a side view of the tool holder and parts of the clamping device shown in FIG. 4, with the tool holder in an unclamped state. [Figure 6] FIG. 5 is a longitudinal section through the tool holder and parts of the clamping device shown in FIG. 4, with the tool holder in an unclamped state. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 5. [Figure 8] 10 is a schematic, partially cut-away side view of components included in a clamping device according to an alternative embodiment of the present invention. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] 10 is a schematic diagram of a clamping device according to another embodiment of the present invention. [Figure 11] 11 is a perspective view of the components included in the clamping device of FIG. 10. [Figure 12] FIG. 12 is a side view of the portion shown in FIG. 11. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. [Figure 14] FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. [Figure 15] FIG. 14 is a cross-sectional view taken along line XV-XV in FIG. [Figure 16] FIG. 11 is a partial cutaway side view of the components included in the clamping device of FIG. 10 with a tool holder clamped to the spindle of the clamping device. [Figure 17] 17 is a partial cutaway perspective view of parts of the clamping device shown in FIG. 16. FIG. [Figure 18] FIG. 17 is a longitudinal section through some of the parts of the tool holder and clamping device shown in FIG. [Figure 19] FIG. 19 is a plan view from above of the tool holder and parts of the clamping device shown in FIG. 18, but with the actuating member removed from the spindle. DETAILED DESCRIPTION OF THE INVENTION

[0027] A clamping device 1 according to a first embodiment of the invention is shown schematically in Figure 1 and a clamping device according to another embodiment of the invention is shown schematically in Figure 10. Clamping device 1 is configured to releasably clamp a tool holder 70 (shown very diagrammatically in the drawings) to a rotatable spindle 2 in the clamping device to enable machining of a workpiece with a cutting tool (not shown) fixed to tool holder 70.

[0028] The spindle 2 is rotatably mounted in a housing 3 of the clamping device 1 by means of a rolling bearing 4. The spindle 2 has a front end 2a, a rear end 2b, and a bore 5 that intersects the front end 2a and extends rearwardly therefrom. The bore 5 thus has an inlet opening 5a at the front end 2a of the spindle (see FIG. 4).

[0029] In the embodiment shown in Figures 1 to 7, the spindle 2 is connectable to a drive mechanism of a machine tool, for example a drive mechanism in a tool turret of a machine tool, via a connecting pin 6 at the rear end 2b of the spindle to enable the spindle to be driven and rotated by the drive mechanism.

[0030] In the embodiment shown in Figures 10 to 19, the clamping device 1 comprises a drive shaft 16 rotatably mounted in the housing 3 by means of rolling bearings 18a, 18b. The drive shaft 16 has a first end 16a facing the spindle 2 and an opposite second end 16b facing away from the spindle. The drive shaft 16 is connectable at its second end 16b via a connecting pin 6' to a drive mechanism of a machine tool, for example, a drive mechanism in a tool turret of the machine tool, so as to enable the drive mechanism to drive and rotate the drive shaft 16. The drive shaft 16 is drivingly connected to the spindle 2 via a bevel gear arrangement 19 consisting of a first bevel gear 19a non-rotatably fixed to the drive shaft 16 at the first end 16a of the drive shaft 16 and a second bevel gear 19b non-rotatably fixed to the spindle 2, engaged with the first bevel gear 19a.

[0031] A mounting portion 7 (see Figure 4) is provided at the forward end of the bore 5 for receiving a mounting shank 71 on a tool holder 70. This mounting shank 71 will be referred to herein as the tool holder shank.

[0032] 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 drawbar 8 between a forward release position (see FIGS. 3 and 6) and a rearward locking position (see FIGS. 2, 13, and 18). The drawbar 8 has a front end facing the entrance 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 located 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 a rearwardly facing beveled surface 11 on the head portion 9.

[0033] A toolholder shank 71 is insertable into the mounting portion of the bore 5 through an entrance opening 5a at the front end 2a of the spindle 2. The head portion 9 of the drawbar is received in an engagement bore 72 in the toolholder shank 71, with a tubular wall 73 of the toolholder shank being received in the space between the head portion 9 and the inner surface of the bore 5. In the illustrated embodiment, the mounting portion 7 of the bore 5 is conical and has a somewhat "triangular" or polygonal non-circular cross-sectional shape adapted to receive a similarly shaped toolholder shank 71. However, the mounting portion of the bore 5 could have any other suitable shape for receiving other types of toolholder shanks.

[0034] An engagement member 20 in the form of a segment is disposed around the draw bar 8 at its front end. Under the influence of movement of the draw bar 8 from a forward release position to a rear locking position, the engagement member 20 is movable from a first position (see Figures 3 and 6) in which the engagement member 20 allows the toolholder shank 71 to move into and out of the mounting portion of the bore 5, to a second position (see Figures 2, 13 and 18) in which the engagement member 20 is in locking engagement with the engagement groove 74 in the engagement bore 72 in the toolholder shank 71, thereby keeping the toolholder shank 71 fixed to the spindle 2.

[0035] In the illustrated embodiment, the engagement members 20 are disposed about the neck portion 10 of the drawbar 8 and are held in place about the neck portion by a retainer ring 21 (see FIG. 18 ) and a resilient O-ring 22, which are disposed in the bore 5 and surround the neck portion 10. Each engagement member 20 has an outwardly facing flange portion 23 that engages an internal groove in the retainer ring 21. The O-ring 22 is received in the outwardly facing groove at the rear end of each engagement member 20. A compression spring 24, a thrust ring 25, and a stop ring 26 are also disposed in the bore 5 and configured to surround the drawbar 8. The compression spring 24 is mounted between a shoulder on the drawbar 8 and the thrust ring 25, and the compression spring 24 is configured to move the thrust ring 25, the retainer ring 21, and the engagement members 20 forward. Forward movement of the retainer ring 21 toward the entrance opening of the bore 5 is limited by a stop ring 26 mounted in a groove in the inner surface of the bore 5.

[0036] At the front end of each engagement member 20, each engagement member 20 is provided with an outwardly directed engagement flange 27 configured to engage with an engagement groove 74 in the toolholder shank 71 when the engagement member 20 is in the above-mentioned second position. When the drawbar 8 is in the forward release position, as shown in FIG. 6, the front end of the engagement member 20 is located behind the head portion 9 of the drawbar 8, and the engagement flange 27 is not engaged with the engagement groove 74 in the toolholder shank 71. When the drawbar 8 moves axially rearward in the bore 5 along its longitudinal axis L, the bevel surface 11 on the head portion 9 of the drawbar contacts the front end of the engagement member 20, which slides over this bevel surface 11 and is pushed outward so that the engagement flange 27 on the engagement member engages with the engagement groove 74 in the toolholder shank 71. Upon engagement, the toolholder shank 71 is brought into firm contact by the drawbar 8 with the inner surface of the spindle 2 within the mounting portion of the bore 5.

[0037] The clamping device 1 further comprises an actuating member 13 concentric with the spindle 2 and slidably mounted thereon for axial movement 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 transmit axial movement of the actuating member 13 in a first axial direction AD1 relative to the spindle 2 to movement of the drawbar 8 from the forward release position to the rearward locking position. In the illustrated embodiment, this first axial direction AD1 is toward the rear end 2b of the spindle 2. Thus, in this case, movement of the drawbar 8 from the forward release position to the rearward locking position is effected by axial movement of the actuating member 13 rearward 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 rear locked position is effected by axial movement of the actuating member 13 forward along the spindle 2.

[0038] At least one hydraulic actuator 50 is disposed in or mounted on the housing 3 and configured to move the actuating member 13 axially relative to the spindle 2. Each hydraulic actuator 50 includes a piston unit 52 configured to be slidably received in the hydraulic actuator space 53 and divide the space into a first hydraulic chamber 53a and a second hydraulic chamber 53b. Hydraulic fluid can be supplied to and discharged from the first hydraulic chamber 53a via a first hydraulic line 81 and can be supplied to and discharged from the second hydraulic chamber 53b via a second hydraulic line 82. The piston unit 52 is movable in a first direction D1 by supplying hydraulic fluid into the first hydraulic chamber 53a to enable the piston unit 52 to apply a pulling or pushing force to the actuating member 13 in said first axial direction AD1, thereby effecting movement of the drawbar 8 from a forward release position to a rearward locking position. The piston unit 52 is movable in an opposite second direction D2 by supplying hydraulic fluid to the second hydraulic chamber 53b.

[0039] In the embodiment shown in FIGS. 1 to 9, the clamping device 1 is provided with a single hydraulic actuator 50 arranged in the housing 3.

[0040] In the embodiment shown in Figures 10 to 19, the clamping device 1 is provided with two hydraulic actuators 50 arranged opposite each other on either side of the spindle 2. It would also be possible to use three or more hydraulic actuators 50 distributed around the spindle 2 in any suitable manner. In the embodiment shown in Figures 10 to 19, each hydraulic actuator 50 comprises a separate actuator casing 51 fixed to the housing 3 on either side thereof. However, the hydraulic actuators 50 may alternatively be integrated into the housing 3. In the embodiment shown in Figures 10 to 19, the clamping device 1 also comprises a connecting element 60 configured to form a connection in the radial direction between the actuating member 13 and the piston unit 52 of the hydraulic actuator 50. The connecting element 60 is configured to transfer axial movement of the piston unit 52 relative to the housing 3 to a corresponding axial movement of the actuating member 13 relative to the spindle 2.

[0041] The actuating member 13 is configured to assume a self-locking axial position on the spindle 2 when the drawbar 8 is put into the rearward locking position under the influence of the actuating member 13 and the motion transmission mechanism 30, thereby making it possible to keep the drawbar 8 in the rearward locking position. Thereby, the piston unit 52 only has to apply a force to the actuating member 13 with a tool change operation when the spindle 2 is stationary and the drawbar 8 is to move from the rearward locking position to the forward release position and then back to the rearward 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 a direction opposite to the first axial direction AD1.

[0042] The clamping device is connected to a hydraulic system 90, which may have the general design shown in Figures 1 and 10, comprising a hydraulic fluid reservoir 91, a pump 92 and a directional control valve 93, the directional control valve being provided with a pressure port P and a return port R. The pump 92 is configured to pump hydraulic fluid from the reservoir 91 to the pressure port P. The return port R is connected to the reservoir 91 to allow hydraulic fluid to be returned from the directional control valve 93 to the reservoir via the return port. The first hydraulic chamber 53a of each hydraulic actuator 50 is connected to the directional control valve 93 through a first hydraulic line 81, and the second hydraulic chamber 53b of each hydraulic actuator is connected to the directional control valve 93 through a second hydraulic line 82.

[0043] The directional control valve 93 is provided with a valve spool 94, which is a first operating position in which the pressure port P is connected to the first hydraulic line 81 and the return port R is connected to the second hydraulic line 82; a second operating position in which the pressure port P is connected to the second hydraulic line 82 and the return port R is connected to the first hydraulic line 81; a normal position in which the pressure port P is disconnected from the first hydraulic line 81 and the second hydraulic line 82 and the return port R is connected to the first hydraulic line 81; It is possible to move between 1 and 10, the valve spool 94 is shown in a normal position. In the example shown in Figures 1 and 10, the valve spool 94 moves from the normal position to the first operating position by moving to the right under the influence of an actuation force acting on the valve spool 94 in a first direction, and moves from the normal position to the second operating position by moving to the left under the influence of an actuation force acting on the valve spool 94 in the opposite direction. The valve spool 94 is configured to automatically return to the normal position when the actuation force is removed.

[0044] The clamping device 1 comprises a first valve assembly 83, the first valve assembly 83 being disposed in the second hydraulic line 82; a first flow path 84a and a second flow path 84b arranged in parallel with each other; a first check valve 85a, preferably in the form of a spring-loaded check valve, disposed in the first flow path 84a and configured to allow hydraulic fluid flow through the first flow path 84a toward the second hydraulic chamber 53b and to obstruct hydraulic fluid flow through the first flow path 84a away from the second hydraulic chamber 53b; The second check valve 85b is provided in the second flow path 84b, and the hydraulic pressure in the second hydraulic chamber is equal to or exceeds the cracking pressure p of the second check valve 85b. C2 a second check valve 85b, preferably in the form of a spring-loaded check valve, configured to permit hydraulic fluid flow through the second flow path 84b away from the second hydraulic chamber 53b and to obstruct hydraulic fluid flow through the second flow path 84b towards the second hydraulic chamber 53b when Equipped with. The first check valve 85a and the second check valve 85b are therefore arranged in parallel and opposite directions to each other. The first valve assembly 83 operates such that the cracking pressure p of the second check valve 83 is reached at the moment when the hydraulically driven movement of the piston unit 52 in the first direction D1 stops and the first hydraulic chamber 53a is connected to the fluid reservoir 91 after the movement of the drawbar 8 to the retracted locking position. C2 This ensures that a residual pressure corresponding to the pressure difference V 1 remains in the second hydraulic chamber 53b, which will result in a short return movement of the piston unit 52 in the second direction D2.

[0045] To be able to bring about the above-mentioned return movement of the piston unit 52, the cracking pressure p of the second check valve 85b must be C2 is satisfied by the following condition: p C2 >F friction / A2 must have a value such that Here, F frictionis the maximum value of the friction force between the piston unit 52 and the associated sliding surface or surfaces in the hydraulic actuator 50, and A2 is the effective pressure area on the side of the piston unit 52 facing the second hydraulic chamber 53b. C2 The value of p must also be adapted depending on the desired length of the return stroke of the piston unit 52. The cracking pressure p of the second check valve 85b C2 is preferably about 0.2 to 2 MPa. The first check valve 85a advantageously has a cracking pressure p of 0.1 MPa or more, preferably 0.2 MPa or more. C1 It has.

[0046] In the embodiment shown in Figures 1 and 10, the clamping device 1 also comprises a second valve assembly 87 disposed in the first hydraulic line 81; a third flow path 84c and a fourth flow path 84d arranged parallel to each other; a third check valve 85c, preferably in the form of a spring-loaded check valve, disposed in the third flow path 84c and configured to allow hydraulic fluid flow through the third flow path 84c towards the first hydraulic chamber 53a and to obstruct hydraulic fluid flow through the third flow path 84c away from the first hydraulic chamber 53a; - A fourth check valve 85d is disposed in the fourth flow path 84d, and the hydraulic pressure in the first hydraulic chamber is equal to or greater than the cracking pressure p of the fourth check valve 85d. C4 a fourth check valve 85d, preferably in the form of a spring-loaded check valve, configured to permit hydraulic fluid flow through the fourth flow path 84d away from the first hydraulic chamber 53a and to obstruct hydraulic fluid flow through the fourth flow path 84d towards the first hydraulic chamber 53a when Equipped with. The third check valve 85c and the fourth check valve 85d are therefore arranged in parallel and in opposite directions. The cracking pressure p C4 is satisfied by the following condition: p C4 <p C2 has a value such that A2 / A1 is satisfied, where pC2 is the cracking pressure of the second check valve 85b, A1 is the effective pressure area on the side of the piston unit 52 facing the first hydraulic chamber 53a, and A2 is the effective pressure area on the side of the piston unit 52 facing the second hydraulic chamber 53b. The third check valve 85c advantageously has a cracking pressure p of 0.1 MPa or more, preferably 0.2 MPa or more. C3 It has.

[0047] A hydraulic accumulator 86, preferably in the form of a spring-loaded accumulator, may be disposed in fluid communication with the second hydraulic chamber 53b for applying hydraulic force to the aforementioned return movement of the piston unit 52. The hydraulic accumulator 86 preferably operates in response to a cracking pressure p of the second check valve 85b. C2 The cracking pressure p of the second check valve 85b corresponds to 80 to 90% of the C2 1, the hydraulic accumulator 86 is connected to the second hydraulic chamber 53b via a second hydraulic line 82.

[0048] The first valve assembly 83 , the second valve assembly 87 and the hydraulic actuator 86 are preferably disposed in or mounted on the housing 3 .

[0049] 10, two hydraulic actuators 50 are connected to the hydraulic system 90 in parallel with one another and are configured to share the same valve assemblies 83, 87. Thus, in this case, the first valve assembly 83 is connected to the second hydraulic chambers 53b of both hydraulic actuators, and the second valve assembly 87 is connected to the first hydraulic chambers 53a of both hydraulic actuators. If the hydraulic actuators 50 were connected to the hydraulic system 90 in other ways, it would also be possible to provide each hydraulic actuator 50 with its own valve assembly 83, 87.

[0050] In the embodiment shown in FIGS. 1-9, the piston unit 52 is annular and configured to surround a portion of the spindle 2. In this case, the piston unit 52 is slidably mounted in the housing 3 such that it is hydraulically movable in the axial direction relative to the housing. In the embodiment shown in FIGS. 1-7, the piston unit 52 is configured to apply an axially directed pulling force to the actuating member 13, thereby moving the actuating member 13 in the first axial direction AD1. In the embodiment shown in FIGS. 8 and 9, the piston unit 52 is configured to apply an axially directed pushing force to the actuating member 13, thereby moving the actuating member 13 in the first axial direction AD1. The annular piston unit 52 is configured to remain stationary in the housing 3 when the spindle 2 rotates relative to the housing 3.

[0051] In the embodiment shown in Figures 1 to 7 and 10 to 19, the actuating member 13 has the form of a sleeve. In this case, the actuating member 13 is arranged around a peripheral wall 14 of the spindle 2 and is slidably mounted on this peripheral wall so as to be axially movable relative to the spindle.

[0052] In the embodiment shown in FIGS. 1 to 7 , the piston unit 52 includes an annular piston head 56 and a sleeve-shaped piston stem 57 fixed to the piston head, and the piston unit 52 is configured to apply the aforementioned pulling or pushing force to the actuating member 13 through the piston stem 57. The piston head 56 and the piston stem 57 are preferably concentric with the actuating member 13 and extend around the spindle 2. The piston stem 57 may be configured to apply the aforementioned force to the actuating member 13 by acting on an annular external protrusion 15 provided on the outside of the actuating member 13. In the embodiment shown in FIGS. 1 to 7 , an annular internal protrusion 58 is provided on the inside of the piston stem 57, and a locking ring 59 is fixed to the piston stem 57 inside thereof, the locking ring 59 and the internal protrusion 58 being spaced apart in the axial direction of the piston stem 57. The external protrusion 15 on the actuating member 13 is received with play in a gap formed between the internal protrusion 58 and the locking ring 59. In this case, the axial force is transmitted from the piston unit 52 to the actuating member 13 via the lock ring 59 when the piston unit 52 moves the actuating member in the first axial direction AD1, and via the internal protrusion 58 when the piston unit 52 moves the actuating member in the opposite direction.

[0053] 10 to 19, the connecting element 60 comprises a central part 61, through which the connecting element is connected to the actuating member 13, and arms 62, one for each hydraulic actuator 50, through which the connecting element 60 is connected to the piston unit 52 of the hydraulic actuator. Each arm 62 is fixed to the central part 61 and projects radially therefrom. The connecting element 60 can, of course, be designed in many different ways, depending on the particular design of the clamping device 1.

[0054] The connecting element 60 may be fixed to the actuating member 13 so as to be movable axially relative to the spindle 2 together with the actuating member 13, and the connecting element is configured to rotate relative to the piston unit 52 together with the actuating member 13 and the spindle. However, in the embodiment shown in FIGS. 10 to 19 , the actuating member 13 is rotatable relative to the connecting element 60 together with the spindle 2. In this case, the sleeve-shaped actuating member 13 may extend into the central part 61 of the connecting element 60 through a recess 63 having a circular cross-sectional shape. In the illustrated embodiment, an annular internal protrusion 66 is provided in said recess 63. Furthermore, an annular external protrusion 15 is provided on the outside of the actuating member 13, and a locking ring 28 is fixed to the actuating member 13 on its outside, the locking ring 28 and the external protrusion 15 being spaced apart in the axial direction of the actuating sleeve 13. The internal protrusion 66 on the connecting element 60 is received with play in a gap formed between the external protrusion 15 and the locking ring 28. In this case, the axial force is transmitted from the connecting element 60 to the operating sleeve 13 via the locking ring 28 when the piston unit 52 moves the operating sleeve 13 in the first axial direction AD1, and via the external protrusion 15 when the piston unit 52 moves the operating sleeve in the opposite direction.

[0055] In the embodiment shown in Figures 1 to 7 and 10 to 19, a release spring 17, preferably in the form of a helical compression spring, is mounted in the interior space of the spindle 2 and is arranged to act on the rear end of the drawbar 8 to move the drawbar towards its forward released position. The drawbar 8 is movable from its forward released position to its rear locked position under the influence of the actuating member 13 and the motion transmission mechanism 30 against the action of the spring force from this release spring 17.

[0056] The motion transmission mechanism 30 can be designed in many different ways. In the embodiment shown in FIGS. 1-7 and 10-19, the motion transmission mechanism includes three wedges 31 spaced apart circumferentially of the spindle 2. Each wedge 31 is received in a respective opening 32 extending radially through the aforementioned peripheral wall 14 of the spindle 2, and the wedges 31 are configured to urge the drawbar 8 toward the rearward locking position when the wedge 31 is urged radially inwardly in the associated opening 32. Each wedge 31 includes a first pressure surface 33 facing outward from the spindle 2, and the actuating member 13 is provided on its interior with an inwardly facing first pressure surface 34 for contacting the first pressure surface 33 on each wedge. The first pressure surfaces 34 have increasing radial distances to the longitudinal axis L when viewed in the aforementioned first axial direction AD1. The first pressure surface 34 is configured to press against the first pressure surface 33 on each wedge, thereby urging the wedges 31 radially inward in the openings 32, as the actuating member 13 moves in the first axial direction AD1. The illustrated motion transmission mechanism 30 also includes three wedge engagement members 35 that protrude radially from the drawbar 8 into each of the openings 32 and are fixed to the drawbar so as to be movable along the longitudinal axis L together with the drawbar. Thus, movement of the wedge engagement members 35 along the longitudinal axis L causes corresponding movement of the drawbar 8. Each wedge engagement member 35 contacts one of the wedges 31. The motion transmission mechanism 30 may include any suitable number of wedges 31 and associated wedge engagement members 35 arranged to extend through a corresponding number of openings 32 in the peripheral wall 14 of the spindle 2.

[0057] Each wedge engaging member 35 has a sliding surface 36 facing the front end 2 a of the spindle 2 (see FIG. 18 ), and each opening 32 has a sliding surface 37 facing the rear end 2 b of the spindle. Furthermore, each wedge 31 has a first wedge surface 38 facing the rear end 2 b of the spindle and a second wedge surface 39 facing the front end 2 a of the spindle, these first and second wedge surfaces 38, 39 approaching each other in the radial direction toward the longitudinal axis L. The first wedge surface 38 of each wedge 31 is in contact with the sliding surface 36 of the associated wedge engaging member 35, and the second wedge surface 39 of each wedge is in contact with the sliding surface 37 of the associated opening 32. When the wedges 31 are forced radially inward in the openings 32 by the actuating member 13, the first wedge surface 38 and second wedge surface 39 of each wedge 31 slide against corresponding sliding surfaces 36, 37 of the associated wedge-engaging member 35 and the opening 32, thereby moving the drawbar 8 toward the rear-locking position. The first pressure surface 34 and the first pressure-receiving surface 33 are preferably inclined relative to the longitudinal axis L by an angle α (see FIG. 6 ) such that when the drawbar 8 is brought into the rear-locking position under the influence of the actuating member 13 and the wedges 31, the wedges 31 maintain the actuating member 13 in a self-locking axial position on the spindle 2.

[0058] Each wedge 31 may also include a second pressure surface 43 facing outward from the spindle 2, and the actuating member 13 is provided on its interior side with an inwardly facing second pressure surface 44 for contacting the second pressure surface 43 on each wedge. The second pressure surfaces 44 have increasing radial distances to the longitudinal axis L when viewed in the first axial direction AD1. The second pressure surfaces 44 and the second pressure surfaces 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 pressure surface 34 and the second pressure surface 44 and the first pressure receiving surface 33 and the second pressure receiving surface 43 are arranged successively on the actuating member 13 and on each wedge 31, respectively, so that when the actuating member 13 moves in the first axial direction AD1, the second pressure surface 44 is configured to slide on each wedge and press against the second pressure receiving surface 43 during an initial first stage of movement, and then the first pressure surface 34 is configured to slide on each wedge and press against the first pressure receiving surface 33 during a subsequent second stage of movement.

[0059] Each wedge engaging member 35 further includes a release pressure surface 40 (see FIG. 18) facing the rear end 2 b of the spindle 2, and the actuating member 13 includes a release pressure surface 41 facing the front end 2 a of the spindle. The release pressure surface 41 of the actuating member 13 is configured to contact the release pressure surface 40 of the wedge engaging member 35 when the actuating member 13 moves in the second axial direction, thereby enabling the actuating member to apply a forwardly directed axial force to the drawbar 8 via the wedge engaging member 35 during the final stage of the drawbar's movement from the rear locking position to the forward released position.

[0060] When the toolholder 70 is to be clamped to the spindle 2, the toolholder shank 71 is inserted into the mounting portion 7 of the bore 5 with the spindle 2 held in a fixed position and the drawbar 8 in an advanced release position, as shown in FIGS. 3 and 6 . This causes the head portion 9 of the drawbar to be received in the engagement bore 72 in the toolholder shank 71, and the engagement groove 74 in the toolholder shank 71 to be positioned on the outer side of the engagement flange 27 of the engagement member 20. Hydraulic oil is then supplied into the first hydraulic chamber 53a of each hydraulic actuator 50 to move the piston unit 52 in the first direction D1, thereby achieving corresponding axial movement of the actuating member 13. During this first stage of axial movement of the actuating member 13, the second pressure surface 44 on the actuating member 13 slides on the wedge 31 and presses against the second pressure surface 43. This forces the wedge 31 radially inward, displacing the drawbar 8 axially toward the rearward locking position. The relatively steep angle β of the second pressure surface 44 and the second pressure surface 43 causes the wedge 31 to initially move inward at a fairly high rate, 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 pressure surface 34 and the second pressure surface 44 and the first pressure surface 33 and the second pressure surface 43 are positioned so that the actuating member 13 has traveled a distance such that the second pressure surface 44 has passed the second pressure surface 43, and by the time the first pressure surface 34 reaches the first pressure surface 33, i.e., at the transition between these respective surfaces, the drawbar 8 has nearly reached its final destination at the aft end of the bore 5. Thus, for the final clamping stage where high forces are beneficial, the first pressure surface 34 and the first pressure surface 33 are active. In this stage, a relatively large movement of the actuating member 13 results in a very small radial displacement of the wedge 31 and an even smaller axial displacement of the draw bar 8, resulting in a force multiplication effect that enables the draw bar 8 to firmly engage the toolholder shank 71 with the spindle 2 with a large force.Furthermore, the small slope α of the first pressure surface 34 and the first pressure-receiving surface 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 on the piston unit 52 to be released when the drawbar 8 reaches the rearward locking position. When the hydraulic pressure on the piston unit 52 is released, the residual pressure remaining in the second hydraulic chamber 53b due to the second check valve 85b automatically moves the piston unit 52 a short distance in the second direction D2. In the embodiment shown in FIGS. 1-7, this return movement of the piston unit 52 implies that the piston unit moves away from contact with the actuating member 13. In the embodiment shown in FIGS. 10-19, the short return movement of the piston unit 52 results in the connecting element 60 moving away from contact with the actuating member 13.

[0061] When a tool change operation is performed and the tool holder 70 is to be released from the spindle 2, rotation of the spindle 2 stops, and hydraulic oil is supplied into the second hydraulic chamber 53b to move the piston unit 52 in the second direction D2, thereby achieving corresponding axial movement of the actuating member 13. When the actuating member 13 is subjected to sufficient force by the piston unit 52 in the second axial direction D2, the self-locking frictional engagement between the first pressure surface 34 on the actuating member 13 and the first pressure surface 33 on the wedge 31 is released, allowing the actuating member 13 to move relative to the spindle 2 in the second axial direction under the influence of the piston unit 52. As the actuating member 13 moves in this direction, the spring force exerted by the release spring 17 on the rear end of the drawbar 8 axially pushes the drawbar toward the forward release position. This causes the wedge engagement member 35 to apply a force to the wedge 31, pushing it radially outward. When the actuating member 13 has moved a certain distance in the second axial direction, the release pressure surface 41 on the actuating member 13 comes into contact with the release pressure surface 40 on the wedge engagement member 35, thereby enabling the actuating member 13 to apply an axial force to the draw bar 8 via the wedge engagement member 35 that presses the outer end of the head portion 9 of the draw bar 8 against a surface 75 in the engagement bore 72 in the toolholder shank 71, thereby releasing the toolholder shank 71 from the spindle 2.

[0062] In the embodiment shown in Figures 8 and 9, the actuating member 13 comprises a base portion 64 having a circular cross-sectional shape that is slidably received in the inner bore 5 of the spindle 2 so as to be movable axially relative to the spindle. In this case, the actuating member 13 also comprises two arms 65a, 65b fixed to the base portion 64 so as to be movable axially relative to the spindle 2 together with the base portion 64. The arms 65a, 65b project radially from the base portion 64 on either side thereof. In the example shown, the arms 65a, 65b constitute opposite end sections of a transverse pin 66 that is fixed to the base portion 64 and extends across the base portion 64 perpendicular to the central axis of the base portion. Openings 67 for the arms 65a, 65b extend radially through the peripheral wall of the spindle 2 on either side of the spindle, with each arm 65a, 65b spanning one of these openings 67. The opening 67 is elongated to allow the arms 65a, 65b to move axially relative to the spindle 2, and extends in the axial direction of the spindle 2. The outer end of each arm 65a, 65b is received with play in an annular groove 68 provided on the inside of the annular piston unit 52, thereby allowing the piston unit 52 to apply a pushing force to the actuating member 13 and allowing the actuating member 13 to rotate relative to the piston unit 52 together with the spindle 2. When hydraulic fluid is supplied to the first hydraulic chamber 53a, the piston unit 52 presses the arms 65a, 65b, thereby pushing the entire actuating member 13 backward in the above-mentioned first axial direction AD1. When hydraulic fluid is supplied to the second hydraulic chamber 53b, the piston unit 52 presses the arms 65a, 65b, thereby pushing the entire actuating member 13 forward in the opposite direction. In this embodiment, the actuating member 13 is fixed to the base part 64 and is configured to act on the motion transmission mechanism 30 via a protrusion 69 that projects from the front face of the base part towards the front end 2a of the spindle 2. The motion transmission mechanism 30 included in the clamping device 1 according to Figures 8 and 9 is of the type described in US Patent No. 6,370,995 (B1).Therefore, the design and function of this motion transmission mechanism 30 is described in more detail in US Pat. No. 6,370,995 B1.

[0063] The present invention is, of course, not limited in any way to the embodiments described above: on the contrary, many possibilities for modification of the invention will become apparent to those skilled in the art without departing from the basic concept thereof 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 front end, a rear end and a bore (5) intersecting said front end and extending rearwardly therefrom, said front end being provided with a mounting portion (7) for receiving said toolholder shank (71); a drawbar (8) slidably mounted inside said bore (5) so as to be reciprocally movable in said bore along its longitudinal axis (L) between a forward release position and a rearward locking position; an engagement member (20) arranged around the draw bar (8) at its front end, the engagement member (20) being movable from a first position to a second position under the influence of movement of the draw bar (8) from the forward release position to the rear locking position, wherein in the first position the engagement member (20) allows the toolholder shank (71) to move in and out of the mounting portion (7) of the bore (5), and in the second position the engagement member (20) is in locking engagement with an engagement groove (74) of the toolholder shank (71) to keep the toolholder shank (71) fixed to the spindle (2); an actuating member (13) arranged inside said housing (3), said actuating member (13) being slidably mounted on said spindle (2) so that said actuating member (13) is movable relative to said spindle (2) in the axial direction of said actuating member; a motion transmission mechanism (30) arranged inside the housing (3), the motion transmission mechanism (30) being attached to the spindle (2) and configured to transmit an axial movement of the actuating member (13) in a first axial direction (AD1) relative to the spindle (2) into a movement of the drawbar (8) from the forward release position to the rearward locking position; Equipped with said clamping device (1) a hydraulic actuator (50) arranged in or mounted on the housing (3) and configured to move the actuating member (13) axially relative to the spindle (2), the hydraulic actuator (50) comprising a piston unit (52) configured to be slidably received in a space (53) of the hydraulic actuator (50) and to divide the space into a first hydraulic chamber (53a) and a second hydraulic chamber (53b); a first hydraulic line (81) connected to the first hydraulic chamber (53 a), wherein hydraulic fluid can be supplied to the first hydraulic chamber (53 a) and can be discharged from the first hydraulic chamber (53 a) via the first hydraulic line (81); a second hydraulic line (82) connected to the second hydraulic chamber (53b), wherein hydraulic fluid can be supplied to and discharged from the second hydraulic chamber (53b) via the second hydraulic line (82); and the piston unit (52) is movable in a first direction (D1) by supplying hydraulic fluid into the first hydraulic chamber (53 a) via the first hydraulic line (81) and in an opposite second direction (D2) by supplying hydraulic fluid into the second hydraulic chamber (53 b) via the second hydraulic line (82) so that the piston unit (52) can exert, directly or via a connecting element (60), a pulling or pushing force on the actuating member (13) in the first axial direction (AD1), thereby bringing about a movement of the drawbar (8) from the forward release position to the backward locking position; - said actuating member (13) is rotatable together with said spindle (2) relative to said piston unit (52); - said clamping device (1) comprises a first valve assembly (83), said first valve assembly (83) being arranged in said second hydraulic line (82); a first flow path (84a) and a second flow path (84b) arranged in parallel with each other; a first check valve (85a) disposed in the first flow path (84a) and configured to allow hydraulic fluid flow through the first flow path (84a) toward the second hydraulic chamber (53b) and to obstruct hydraulic fluid flow through the first flow path (84a) away from the second hydraulic chamber (53b); The hydraulic pressure in the second hydraulic chamber (53b) is arranged in the second flow path (84b), and the hydraulic pressure in the second hydraulic chamber (53b) is equal to or greater than the cracking pressure (p Ｃ２ the second check valve (85b) configured to permit hydraulic fluid flow through the second flow path (84b) away from the second hydraulic chamber (53b) and to obstruct hydraulic fluid flow through the second flow path (84b) towards the second hydraulic chamber (53b) when the pressure difference (P) exceeds the pressure difference (P) of the second check valve (85b); To have A clamping device comprising:

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

3. The cracking pressure (p Ｃ２ 3. The clamping device according to claim 1, wherein the strain is in the range of 0.2 to 2 MPa.

4. The first check valve (85a) is configured to detect a cracking pressure (p Ｃ１ 4. The clamping device according to claim 1, further comprising:

5. 5. The clamping device according to any one of claims 1 to 4, characterized in that the first valve assembly (83) is arranged in or mounted on the housing (3).

6. 6. The clamping device according to claim 1, wherein the clamping device (1) comprises a hydraulic accumulator (86) arranged in fluid communication with the second hydraulic chamber (53b).

7. The hydraulic accumulator (86) supplies the cracking pressure (p Ｃ２ The cracking pressure (p) of the second check valve (85b) corresponds to 80 to 90% of the Ｃ２ 7. The clamping device according to claim 6, characterized in that it is dimensioned for a maximum cumulative pressure lower than 100 psi.

8. the clamping device (1) comprises a second valve assembly (87), the second valve assembly (87) being disposed in the first hydraulic line (81); a third flow channel (84c) and a fourth flow channel (84d) arranged parallel to one another; a third check valve (85c) arranged in said third flow path (84c) and configured to allow hydraulic fluid flow through said third flow path (84c) towards said first hydraulic chamber (53a) and to obstruct hydraulic fluid flow through said third flow path (84c) away from said first hydraulic chamber (53a); - a pressure regulator (84d) is disposed in the fourth flow path (84d) so that the hydraulic pressure in the first hydraulic chamber (53a) is equal to or exceeds the cracking pressure (p Ｃ４ the fourth check valve (85d) configured to permit hydraulic fluid flow through the fourth flow path (84d) away from the first hydraulic chamber (53a) and to obstruct hydraulic fluid flow through the fourth flow path (84d) towards the first hydraulic chamber (53a) when the pressure difference (P) exceeds the pressure difference (P) of the fourth check valve (85d); Equipped with The cracking pressure (p Ｃ４ ) satisfies the following condition, namely, p Ｃ４ <p Ｃ２ ・A ２ / A １ has a value such that Here, p Ｃ２ is the cracking pressure of the second check valve (85b), and p Ｃ４ is the cracking pressure of the fourth check valve (85d), and A １ is the effective pressure area on the side surface of the piston unit (52) facing the first hydraulic chamber (53a), and A ２ 8. The clamping device according to claim 1, wherein the effective pressure area on the side of the piston unit (52) facing the second hydraulic chamber (53b) is .

9. The third check valve (85c) is configured to detect a cracking pressure (p Ｃ３ 9. The clamping device according to claim 8, characterized in that it comprises:

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 two or more wedges (31) spaced apart in the circumferential direction of the spindle (2), each wedge (31) being received in a respective opening (32) extending radially through the peripheral wall (14) of the spindle (2), each wedge (31) being configured to urge the drawbar (8) towards the retracted locking position when each wedge (31) is urged radially inward in its respective opening (32); - each of said wedges (31) comprises a first pressure surface (33) facing away from said spindle (2); the actuating member (13) comprises, on the inside of the actuating member (13), a first pressure surface (34) facing inwards for contacting the first pressure surface (33) on each wedge (31), the first pressure surface (34) having an increasing radial distance to the longitudinal axis (L) when viewed in the first axial direction (AD1); the first pressure surface (34) is configured to press against the first pressure surface (33) on each wedge (31) when the actuating member (13) moves in the first axial direction (AD1), thereby forcing each wedge (31) radially inward in the respective opening (32); The clamping device according to claim 10, characterized in that

12. 12. The clamping device according to claim 11, wherein the first pressure surface (34) and the first pressure receiving surface (33) are inclined with respect to the longitudinal axis (L) by an angle α such that when the drawbar (8) is brought into the retracted locking position under the influence of the actuating member (13) and the wedges (31), the wedges (31) keep the actuating member (13) in a self-locking axial position on the spindle (2).

13. - each of said wedges (31) comprises a second pressure surface (43) facing away from said spindle (2); the actuating member (13) comprises, on the inside of the actuating member (13), a second pressure surface (44) facing inwards for contacting the second pressure surface (43) on each wedge (31), the second pressure surface (44) having an increasing radial distance to the longitudinal axis (L) when viewed in the first axial direction (AD1); - said second pressure surface (44) and said second pressure receiving surface (43) are inclined relative to said longitudinal axis (L) by an angle β greater than said angle α; the first and second pressure surfaces (34) and (44) and the first and second pressure surfaces (33) and (43) are successively arranged on the actuating member (13) and on each wedge (31), respectively, such that, when the actuating member (13) moves in the first axial direction (AD1), the second pressure surface (44) is configured to slide on each wedge (31) and press against the second pressure surface (43) during a first stage of the movement, and the first pressure surface (34) is configured to slide on each wedge (31) and press against the first pressure surface (33) during a subsequent second stage of the movement; 13. The clamping device according to claim 12, wherein:

14. Clamping device according to any one of the preceding claims, characterized in that the piston unit (52) is annular and extends around the spindle (2).

15. - external projections (15) are provided on the outside of said actuating member (13), said piston unit (52) being configured to exert said pulling or pushing force on said actuating member (13) by acting on said external projections (15); - an internal projection (58) is provided on the inside of said piston unit (52); - the locking ring (59) is fixed to the piston unit (52) inside the locking ring (59), and the locking ring (59) and the internal projection (58) are spaced apart in the axial direction of the piston unit (52); the external projection (15) on the actuating member (13) is received with play in the gap formed between the internal projection (58) and the locking ring (59); 15. The clamping device of claim 14.

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