Motorized spindle with integrated feed with automatic tool holder change

Abstract

The present invention relates to a spindle for a machine tool comprising a toolholder shaft (2), a first actuator connected to a coupling member (11) slidably connected to a first section (21) of the shaft for rotating the shaft, a second actuator connected to a nut helically connected to a second section (22) of the shaft for axially moving the shaft, and a control rod (24) of a toolholder mounting system connected to the second section by full coupling. The spindle comprises locking means (40) mounted movably between the first and second sections via switching means (50) between a first position in which the first and second sections are fully coupled and a second position allowing axial movement of the second section relative to the first section, whereby the control rod is axially movable under the action of the second actuator for controlling the mounting system in a release position of the toolholder.

Description

[Technical field]

[0001] The present invention relates to the field of machine tools, in particular to numerically controlled machine tools, and more particularly to motorized spindles for such machine tools. [Background technology]

[0002] A motorized spindle is a spindle equipped with at least one electric motor and a tool holder, which constitutes an interface between a machine tool and a cutting tool set in rotation. Spindles are also known from the prior art that differ from conventional spindles, which have an architecture known as the integrated feed architecture. In this architecture, the spindle is equipped with a drive shaft that exhibits two independent movements, namely a movement in rotation and a movement in translation. Each of these movements can be realized by an actuation chain.

[0003] Such a spindle architecture is known from its embodiment described in document FR3018712. The spindle described in that document comprises a toolholder shaft mounted so as to be rotatable about an axis of rotation and axially displaceable along the axis of rotation. To that end, the shaft is connected to two rotary motors, a first motor connected to a coupling member slidably connected to a first part of the shaft for driving the shaft in rotation, and a second motor connected to a nut screwed to a second part of the shaft for moving the shaft axially. These two motors are connected to a control unit designed to control each motor independently of the other. In said architecture, the toolholder shaft is thus formed in two parts. That is, a splined first part is located at the front of the spindle and is slidably connected to a coupling member actuated by a first motor, the assembly of the coupling member and the first motor constituting an operating module for rotational movement of the tool holder shaft, and a threaded second part is located at the rear of the spindle and is threadedly connected to a nut actuated by a second motor, the assembly of the nut and the second motor constituting an operating module for feed movement of the tool holder shaft. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] French Patent No. 3018712 Summary of the Invention [Problem to be solved by the invention]

[0005] The rotational speed and the translating speed can therefore be adjusted independently of each other by each motor, the coaxial arrangement also ensuring the relative compactness of the machine tool, which is also optimised when the first and second motors are coaxial with the tool holder shaft.

[0006] FIG. 1 is a cross-sectional view of a spindle 1 according to the above architecture.

[0007] The tool holder shaft 2 of the spindle 1 has a front end on which a tool holder 3 is mounted by means of a mounting system 4. This system 4 is standardized as an HSK-TYPE system known as the Taper / Face system. Such a Taper / Face system is particularly suitable for both automatic and manual tool changing. However, the interface between the tool holder and the spindle may be covered by different suitable standards.

[0008] The toolholder shaft 2 is mounted to rotate about and move axially along a rotation axis 20. The shaft 2 is connected to two rotary electric motors, a first motor 10 for driving the rotation and a second motor 30 for moving axially. More particularly, the first motor 10 has a rotor fixed for rotation to a coupling member 11 designed to be slidably connected to a first portion 21 of the shaft 2 for driving the rotation of the toolholder shaft 2. The coupling member 11 is, for example, an internally splined sleeve. The first portion is a splined portion. In other words, the sleeve 11 is rotatably connected to the frame of the machine tool and is slidably connected to the splined portion 21 of the toolholder shaft 2. The sleeve 11 is axially fixed.

[0009] The second motor 30 has a rotor fixed for rotation to a nut 31 which is fitted to the second portion of the toolholder shaft 2, consisting of the threaded portion 22. This results in a helical coupling being formed with respect to the axially rotating shaft 2 when a relative speed is imposed between the coupling member 11 and the nut 31, i.e. when these two elements are rotated at different speeds.

[0010] The toolholder shaft is therefore designed in such a way that the splined section 21 and the threaded section 22 are separate and continuous with each other along the axis of rotation 20, respectively from front to rear. The two parts 21, 22 of the drive shaft are connected together by means of a connecting bush 23, which in this case is fixed at each end adjacent to the splined section 21 and the threaded section 22. In other words, the splined section 21 of the shaft 2 is rigidly connected (with a built-in connection) to the threaded section 22 of the toolholder shaft. From a dynamic point of view, the splined section 21 and the threaded section 22 of the toolholder shaft therefore constitute a single piece.

[0011] However, this architecture does not make it possible to integrate conventional automatic tool holder changers, for example of the HSK type.

[0012] This is because in spindles of conventional architecture, i.e. without an integrated feed movement, the HSK mounting system of the tool holder mounted at the front of the drive shaft of the tool holder is conventionally actuated by an actuating device to release the tool holder. This device can thus automatically place the tool holder to be clamped on the HSK mounting system mounted on the spindle in the released state to allow the tool holder to be exchanged. The actuating device conventionally consists of a control rod which is axially slidable on the tool holder shaft of conventional spindles, the mounting system of the tool holder being movable via the control rod between a clamped position and a released position. During this, a clamping force generating device, in particular a spring device, is connected to the control rod in order to generate a clamping force of the mounting system of the tool holder. The actuating device also consists of an actuating module arranged at the rear of the spindle tool holder shaft, by means of which the mounting system can be moved by the control rod to the released position against the clamping force of the spring device. This actuating module can be hydraulically, pneumatically or electrically actuated.

[0013] However, in an integrated-feed spindle architecture, as presented with reference to Figure 1, due to the presence of the threads 22 on the tool holder shaft 2, it is as mentioned above not possible to implement an HSK mounting system for automatically changing the tool holder, especially with regard to the working module arrangement. Thus, according to the architecture of Figure 1, changing the tool holder 3 involves bringing the tool holder shaft 2 into the right-most position in the figure, corresponding to the maximum travel of the tool, at which point the tool holder is changed manually.

[0014] There are currently no known systems capable of addressing the problem of automatically changing tool holders with integral-feed architectures, particularly in HSK-type, integral-feed spindles, where the problem arises of generating the actions required to clamp / release the tool holder mounting system. [Means for solving the problem]

[0015] The object of the present invention is to solve this problem.

[0016] To this end, the invention provides a toolholder shaft having a forward end on which a toolholder can be mounted via a mounting system between the toolholder and a forward end of the toolholder shaft, a first drive actuator for driving the shaft connected to a coupling member slidably connected to a first portion of the shaft for rotationally driving the shaft, and a second drive actuator connected to a nut helically connected to a second portion of the shaft for axially moving the shaft, the first and second portions extending continuously along a common length of the shaft between the forward end of the shaft and an opposite end of the shaft, the spindle includes a control rod for a tool holder mounting system connected to the second portion of the shaft by a fixed connection; the spindle includes a locking means movably mounted between the first and second portions of the shaft via the switching means between a first position in which the second portion of the shaft is fixedly coupled to the first portion of the shaft and a second position in which the second portion of the shaft is slidably coupled to the first portion of the shaft; The second portion is adapted to move axially relative to the first portion to permit axial movement of the control rod under the action of a second drive actuator to pass the mounting system through a position to release the tool holder.

[0017] Advantageously, the first and second shaft portions are connected together by a bushing coaxial with the first and second shaft portions, the bushing being fixedly connected to the first shaft portion and slidably connected to the second shaft portion.

[0018] Advantageously, the locking means comprises a plurality of rotatably mounted locking cams having control surfaces oriented generally radially outwardly and locking surfaces which in a first position are arrangeable to engage mutually opposing stop surfaces of the first and second shaft portions respectively and which in a second position are arrangeable to disengage from the respective stop surfaces under the action of the switch means on the control surfaces.

[0019] Advantageously, the locking surface of the cam is resiliently biased to the first position.

[0020] According to one embodiment, the locking cam is mounted for rotation about an axis perpendicular to the axis of the toolholder shaft.

[0021] According to another embodiment, the locking cam is mounted for rotation about an axis parallel to the axis of the toolholder shaft.

[0022] Advantageously, the switch means comprises an actuating rod extending in a plane perpendicular to the axis of the drive shaft, which can be actuated to switch the locking cams to their second position when the toolholder shaft has advanced to a predetermined position for changing the toolholder and the actuating rod is facing a respective control face of the locking cams.

[0023] Advantageously, the actuating rod may be hydraulically, pneumatically or electrically actuated.

[0024] According to one embodiment variant, the switch means may consist of a coupling member slidably connected to a first part of the toolholder shaft and fixed in the axial direction, which coupling member comes into sliding contact with a control surface of the locking cam by virtue of the toolholder shaft being advanced into a predetermined position for changing the toolholder, in order to switch the locking cam to the second position upon reaching the predetermined position for changing the toolholder.

[0025] Advantageously, the mounting system is an HSK type mounting system.

[0026] Moreover, the structure and advantages of the invention will become more clearly apparent upon reading the following description, given with reference to non-limiting examples and the accompanying drawings, in which: [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic cross-sectional view of a spindle having what is known as an integrated-feed architecture, as described in the preamble. [Diagram 2] FIG. 1 is a schematic cross-sectional view of the junction zone between a first and second portion of a toolholder shaft in an integrated-feed spindle according to a first embodiment of the invention, with the locking means of the invention in a first position, known as the axial locked position, where no axial movement of the second portion relative to the first portion is permitted, this first position being the normal mode of spindle operation (machining, positioning etc.). [Diagram 3]2, now with the locking means of the present invention set in a second position known as the axial unlocked position, allowing axial movement of the second portion relative to the first portion of the toolholder shaft, this second position being a mode corresponding to automatic toolholder changing of the spindle. [Figure 4] FIG. 4 is a schematic cross-sectional view of the spindle of the present invention, illustrating an intermediate phase with respect to the situation shown in FIGS. 2 and 3, where the toolholder shaft is brought into position for the exchange of the toolholder. [Diagram 5] Corresponding to FIG. 3, axial feed movement of the second part relative to the first part is shown, which is permitted by switching the locking means into the second position. [Figure 6] 11 is a schematic cross-sectional view of a spindle according to the present invention, showing a modified embodiment of switching the locking means from the shaft lock position to the shaft unlock position. FIG. [Figure 7] Corresponding to the view of FIG. 6, the locking means has been switched to the axial unlocked position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] In the following text, the same reference numbers are used to describe the same parts in the various figures. Furthermore, the same reference numbers used in Figure 1 represent the same parts in Figure 2. See below.

[0029] Starting from the known integrated-feed spindle architecture, as described with reference to Figure 1, an interface zone is essentially formed between a first splined portion 21 of the toolholder shaft 2 and a second threaded portion 22 of the toolholder shaft 2, as described in more detail with reference to Figure 2 et seq., whereby the threaded portion 22 of the shaft is fixedly connected to the splined portion 21 of the shaft during normal operation phases of the spindle and is also slidably connected to this same part during toolholder changing phases.

[0030] Its use therefore takes advantage of the spindle capacity, i.e. to provide an axial feed movement of the threaded portion 22 of the shaft via a second motor connected to a nut that is screw-connected to the threaded portion 22, and to provide the action required to release the mounting system 4 of the tool holder 3, if the threaded portion 22 of the shaft is slidably connected to the splined portion and an axial movement of the threaded portion with respect to the splined portion is permitted. Thus, in this configuration, by using an actuator already present in the spindle, a second motor, other dedicated high-power actuating means, as in the case of conventional actuating devices for clamping and releasing the tool holder mounting system, is avoided in this particular case.

[0031] A fixed connection between two parts means in the context of the present invention any connection that does not allow any degree of freedom of one part with respect to the other part. It may be for example a screw connection, an adhesive connection, a solder connection etc.

[0032] In the following description, the terms "front" and "rear" refer to elements or locations oriented to the right and left, respectively, in the drawings.

[0033] With reference to Figure 2, the joining zone of the threaded portion 22 and the splined portion 21, which follow each other from rear to front along the toolholder shaft 2 of the spindle, is shown more specifically in cross section. As already described with reference to Figure 1, the splined portion 21 of the toolholder shaft 2 is slidably connected to a sleeve 11. A part of the sleeve 11 is axially fixed and rotatably drivable by a first motor, which is described in Figure 1 but is not shown here.

[0034] A control rod 24 in the mounting system of a toolholder (not shown in FIG. 2) mounted at the front end of the toolholder shaft 2 is fixedly connected to the threaded section 22 of the shaft 2. In other words, the threaded section 22 of the toolholder shaft and the control rod 24 form one part from a kinematic point of view.

[0035] The control rod 24 has a rear end embedded in a front end 220 of the threaded section 22, said front end 220 being delimited by a front end stop surface 221 and a rear end stop surface 222 and extending radially with respect to the axis 20 of the toolholder shaft 2. The control rod 24 extends from this front end 220 of the threaded section 22 and passes through an axial hollow 211 of the splined section 21 of the toolholder shaft 2. In this axial hollow 211 the control rod 24 is allowed to slide as long as its front end is connected to the toolholder mounting system. The toolholder mounting system is moved by the control rod 24 between the clamped and released positions of the toolholder. A return device 25, in this case a return spring 25, is associated with the control rod 24 to generate a clamping force of the toolholder mounting system.

[0036] A tip 220 of the threaded portion 22 of the shaft 2 extends into a recess in the splined portion 21 of the shaft 2 adjacent to a rear stop surface 210 of the splined portion 21 which extends radially with respect to the axis 20 of the toolholder shaft 2. In other words, the radial stop surfaces 221 and 210 of the front and rear of the threaded portion 22 and the splined portion 21, respectively, face each other and extend at a substantially constant distance from each other in the configuration of FIG.

[0037] Furthermore, the threaded portion 22 and the splined portion 21 of the toolholder shaft 2 are connected together by a bushing 26 which is coaxial with the two portions and which is fixedly connected to the splined portion 21 of the shaft for the one hand and slidably connected to the threaded portion 22 of the shaft for the other hand. The bushing 26 prevents any relative rotational movement between the threaded portion 22 and the splined portion 21 of the shaft.

[0038] The bushing 26 is disposed behind the distal end portion 220 of the threaded portion 22 of the toolholder shaft.

[0039] For example, the bushing is screwed to the splined portion 21 of the shaft. In other words, the splined portion 21 of the shaft 2 and the bushing 26 form one part from a dynamics point of view. The part of the threaded portion 22 of the shaft extending behind the tip 220 provides, for example, a female spline that engages with a male spline 260 provided on the bushing 26, so that the threaded portion 22 of the shaft can slide axially with respect to the splined portion 21 of the shaft.

[0040] In particular, in the configuration of FIG. 2, the ability of this threaded portion 22 to slide axially relative to the splined portion 21 is not permitted.

[0041] The reason is as follows: in the joining zone between the threaded portion 22 and the splined portion 21 of the toolholder shaft 2, a locking means 40 is provided, which is movably mounted between the threaded portion 22 and the splined portion 21 of the shaft between a first position, known as the axially locked position, corresponding to the example of Fig. 2, in which the threaded portion 22 of the shaft is fixedly connected to the splined portion 21 of the shaft, and a second position, known as the axially unlocked position, corresponding to the example of Fig. 3, in which the threaded portion 22 of the shaft is slidably connected to the splined portion 21 of the shaft, allowing an axial movement of the threaded portion 22 with respect to the splined portion 21.

[0042] These locking means advantageously consist of a plurality of locking cams mounted for rotation about respective axes of rotation 44. Each locking cam 40 has a control surface 41 oriented generally radially outwards and extending behind the cam with respect to the respective axis of rotation 44, and a locking surface 42 opposite the control surface with respect to the axis of rotation. This locking surface 42 can be positioned to engage with the mutually opposed stop surfaces 221 and 210 of the threaded and splined portions 22 and 21 of the shaft, respectively, corresponding to an axially locked position as illustrated in FIG. 2, and to disengage from the respective stop surfaces, corresponding to an axially unlocked position as illustrated in FIG. 3. The passage of the cam 40 from the axially locked position to the axially unlocked position is effected under the action of a switch means acting on the control surface 41 of the cam for rotation about the axis of rotation 44.

[0043] 2, the switch means consist of actuator rods 50 extending in a plane perpendicular to the axis 20 of the shaft 2. They are arranged, for example, on the outer periphery of the sleeve 11 and are adapted to pass through corresponding holes 110 formed in the sleeve 11.

[0044] Advantageously, the locking surface 42 of the cam 40 is resiliently biased into engagement, via a spring 43, with mutually opposing stop surfaces 221 and 210, respectively, on the threaded and splined portions 22 and 21 of the shaft, so that the latter ensure the locked position of the cam 40 in the normal mode of operation of the spindle.

[0045] According to the exemplary embodiment shown in the figures, the locking cams 40 are mounted for rotation about an axis 44 perpendicular to the toolholder shaft axis 20. They are contained in a plane substantially parallel to the toolholder shaft axis 20. They are received, for example, in an axial groove formed in the splined portion 22 of the toolholder shaft 2.

[0046] In a variant, the locking cams 40 may be included in a plane substantially perpendicular to the axis 20 of the toolholder shaft 2. In other words, according to this variant, they may be mounted to rotate about an axis parallel to the axis 20 of the toolholder shaft 2.

[0047] In the configuration of FIG. 2, the threaded portion 22 is fixedly connected to the splined portion 21 of the toolholder shaft 2. In particular, on the one hand, the splined portion 21 cannot rotate with respect to the threaded portion 22 due to the bush 26. On the other hand, the threaded portion 22 and the splined portion 21 cannot exhibit any relative axial movement between each other, since the locking surface 42 of the cam 40 is biased and abuts against the mutually facing front and rear stop surfaces of the threaded portion 22 and the splined portion 21, respectively. In other words, the bush 26 prevents any relative rotational movement between the threaded portion 22 and the splined portion 21 of the shaft 2, and the cam 40 in the axial locking position shown in FIG. 2 prevents any relative axial movement between the threaded portion 22 and the splined portion 21 of the shaft 2. Furthermore, the rear stop surface 222 of the tip portion 220 of the threaded portion 22 abuts against the bush 26.

[0048] This operating configuration corresponds to the normal mode of spindle (machining, positioning, etc.) operation.

[0049] To ensure good contact stiffness despite vibrations generated during normal modes of spindle operation, there are at least two locking cams 40, preferably at least three cams 40, and more preferably at least four locking cams 40.

[0050] Next, another mode of operation corresponding to the exchange of the tool holder will be described. To this end, first the tool holder shaft 2 is positioned in a predetermined position for the exchange of the tool holder. This may for example be the forward most position of the shaft 2.

[0051] 4, in this position for changing the tool holder, the control surface 41 of the locking cam 40 is disposed adjacent to a corresponding hole 110 formed in the wall of the sleeve 11 and therefore adjacent to the actuator rod 50. The actuator rod 50 is therefore ready to be actuated to switch the locking cam 40 from a first position, known as the locked position, shown in FIG. 2, to a second position, known as the unlocked position, shown in FIG.

[0052] The actuator rod 50 may be hydraulically, pneumatically or electrically actuated. In any case, the power required to actuate the locking cams now to pass the actuator rod 50 from its first position to its second position is relatively low, at least sufficient to counter the return force of the spring 43.

[0053] Thus, as shown in Figure 3, when the toolholder shaft is brought into position for insertion over the toolholder, the actuator rod 50 is actuated towards the locking cam to urge the cam's control surface 41 such that the locking cam is rotated to the unlocked position, in which the cam's locking surface 42 is switched out of engagement with the mutually opposed stop surfaces 221 and 210 of the threaded and splined portions 22 and 21 of the shaft, respectively.

[0054] In this position, the threaded portion 22 of the toolholder shaft 2 is therefore axially unlocked with respect to the splined portion 21 and, being slidably connected to the bush 26, is allowed to slide axially with respect to the latter. Under the effect of the actuation of a second motor (not shown here) which is normally used for the axial movement of the toolholder shaft 2 and drives a nut fixed to rotate the threaded portion 22, as explained with reference to Fig. 1, the threaded portion 22 is driven for a feed movement with respect to the splined portion 21, part of which is axially locked with respect to the threaded portion 22. According to this exemplary embodiment, the axial stop of the splined portion 21 is achieved by abutment with an actuator rod 50 which is moved downwards through a hole 110 in the sleeve 11.

[0055] The actuation of the threaded portion 22 thus results in a feed movement of the threaded portion 22 relative to the splined portion 21 along a given feed movement C, which allows the control rod 24 to move the toolholder mounting system into a release position against the clamping force of the spring device 25. This release position of the toolholder mounting system is shown in FIG. 5 and is the position in which the front radial stop surface 221 of the front end 220 of the threaded portion 22 abuts against the rear radial stop surface 210 of the splined portion 21. The given feed movement is, for example, of the order of a few millimeters and corresponds to the distance between the front radial stop surface 221 of the front end 220 of the threaded portion 22 and the rear radial stop surface 210 of the splined portion 21, when the rear radial stop surface 222 of the front end 220 of the threaded portion 22 abuts against the bush 26.

[0056] When slidably connected to the splined portion 21, the feed movement of the threaded portion 22 can therefore advantageously provide the action required to release the tool holder.

[0057] Figures 6 and 7 show an embodiment variant of the switch means used to rotate the locking cam 40 from the axial locking position to the axial unlocking position. According to this embodiment variant, the actuator rod 50 is no longer required for that purpose. With reference to Figure 6, the locking cam 40 is arranged in the axial locking position, in which the threaded part 22 and the splined part 21 of the toolholder shaft 2 are fixedly connected. With further reference to Figure 6, the toolholder shaft 2 is brought into a predetermined position for changing the toolholder. The locking cam 40 is arranged in such a way that during the feed movement of the shaft 2 to the predetermined position for changing the toolholder, the sleeve 11 abuts against the control surface 41 of the locking cam 40 under the effect of the movement of the shaft 2. Thus, when the predetermined position for changing the toolholder is reached, the sleeve 11 presses the cam 40 against the return force of the spring 43 in order to switch the cam into the unlocked position.

[0058] In the position for changing the toolholder shown in Fig. 7, the locking surface 42 of the cam 40 is switched out of engagement with the mutually facing stop surfaces 221 and 210 of the threaded and splined portions 22 and 21 of the shaft, respectively. The threaded portion 22 of the toolholder shaft 2 is therefore axially unlocked with respect to the splined portion 21 and is allowed to slide axially with respect to the latter by being slidably connected to the bush 26. In this position, the bush 26 abuts against the sleeve 11 via the outer peripheral radial stop surface 261 of the bush 26. The abutment of the stop surface 261 (not shown) of the bush 26 against the sleeve 11 allows the axial locking of the splined portion 21 of the toolholder shaft with respect to the threaded portion 22. However, the axial locking of the splined portion 21 with respect to the threaded portion 22 may be ensured by any other suitable stop surface.

[0059] Then, in the same manner as described above with reference to Figure 5, driving the unlocked threaded portion 22 axially relative to the splined portion 21 is used to effect a feed movement of the control rod 24 along the given feed movement, which is necessary for the movement of the toolholder mounting system to the release position. [Explanation of symbols]

[0060] 2 Tool holder shift 3 Tool holder 4 Mounting System 10 First drive actuator 11 Coupling parts 21 First part of shaft 22 Second part of shaft 24 Control Rod 30 Second drive actuator 31 Nut 40 Locking means 50 Switching Means

Claims

1. a toolholder shaft having a front end on which the toolholder can be mounted via a mounting system (4) between the toolholder (3) and a front end of the toolholder shaft (2); a first drive actuator (10) for driving the shaft connected to a coupling member (11) slidably connected to a first portion (21) of the shaft for rotationally driving the shaft; and a second drive actuator (30) connected to a nut (31) helically connected to a second portion (22) of the shaft for axially moving the shaft, the first and second portions extending continuously along a common length of the shaft between the front end of the shaft and an opposite end of the shaft, The spindle comprises a control rod (24) for a tool holder mounting system connected to the second portion (22) of the shaft by a fixed connection; the spindle includes a locking means movably mounted between the first and second portions of the shaft via the switching means between a first pivotal position in which the second portion of the shaft is fixedly coupled to the first portion of the shaft (21) and a second pivotal position in which the second portion of the shaft is slidably coupled to the first portion of the shaft; allowing axial movement of the second portion (22) relative to the first portion (21) to allow axial movement of the control rod (24) under the action of a second drive actuator (30) to pass the mounting system (4) into a position releasing the tool holder; The locking means comprises a plurality of rotatably mounted locking cams (40) having outwardly oriented control surfaces (41) and locking surfaces which are positionable to engage mutually opposing stop surfaces (210, 221) of the first and second shaft portions (21, 22) respectively in a first pivot position and which are positionable to disengage from the respective stop surfaces under the action of a switching means on the control surfaces (41) in a second pivot position.

1. A machine tool spindle comprising:

2. 2. A machine tool spindle according to claim 1, characterized in that the first (21) and second (22) shaft portions are connected together by a bushing (26) coaxial with the first and second shaft portions, the bushing (26) being fixedly connected to the first (21) shaft portion and slidably connected to the second (22) shaft portion.

3. A spindle for a machine tool as described in claim 1 or 2, characterized in that the locking surface of the locking cam (40) is elastically biased to the first rotation position.

4. 4. A machine tool spindle according to claim 1, wherein the locking cam (40) is mounted for rotation about an axis (44) perpendicular to the axis (20) of the toolholder shaft (2).

5. 4. A machine tool spindle according to claim 1, wherein the locking cam (40) is mounted for rotation about an axis parallel to the axis (20) of the toolholder shaft (2).

6. 6. A spindle for a machine tool according to claim 1, characterized in that the switching means comprises an actuating rod (50) extending in a plane perpendicular to the axis (20) of the drive shaft (2), and which can be actuated to switch the locking cams (40) to their second pivot position when the toolholder shaft (2) advances to a predetermined position for changing the toolholder and the actuating rod (50) faces a respective control surface (41) of the locking cams (40).

7. 7. A machine tool spindle according to claim 6, characterized in that the actuating rod (50) is hydraulically, pneumatically or electrically actuated.

8. 6. A machine tool spindle according to claim 1, characterized in that the switching means consists of a coupling member (11) slidably connected to the first part (21) of the tool holder shaft and fixed in the axial direction, said coupling member being in sliding contact with a control surface (41) of the locking cam (40) by virtue of the tool holder shaft being advanced to a predetermined position for changing the tool holder, in order to switch the locking cam to the second pivot position when the predetermined position for changing the tool holder is reached.

9. 9. A machine tool spindle according to claim 1, characterized in that the mounting system is an HSK type mounting system.

Images