WO2009033679A1

WO2009033679A1 - Machine tool

Info

Publication number: WO2009033679A1
Application number: PCT/EP2008/007475
Authority: WO
Inventors: Dirk Prust; Rudolf Haninger
Original assignee: Chiron-Werke Gmbh & Co. Kg
Priority date: 2007-09-16
Filing date: 2008-09-11
Publication date: 2009-03-19
Also published as: DE102007044114A1; DE102007044114B4

Abstract

A machine tool is provided with at least one preferably vertically aligned work spindle (22) that has a tool receiving socket (35) for tool holders (34) carrying tools (23) and has a clamping system (42) comprising a plurality of collet segments (46) that are displaceable between a radially outer clamping position, in which, by means of their lower heads (47), they clamp in a rotationally rigid manner in the work spindle (22) a tool holder (34) inserted in the tool receiving socket (35), and a radially inner initial position, in which the tool holder (34) can be inserted in and removed from the tool receiving socket (35). At least some of the lower heads (47) of the collet segments (46), when in their initial position, have such a radial spacing in relation to each other that they take hold of a tool holder (34) inserted in the tool receiving socket (35), these lower heads (47) being arranged so as to be movable radially inwards (Fig. 5).

Description

MACHINE TOOL

The present invention relates to a machine tool comprising at least one preferably vertically aligned work spindle that has a tool receiving socket for tool holders carrying tools and has a clamping system comprising a plurality of collet segments that are displaceable between a radially outer clamping position, in which, by means of their lower heads, they clamp in a rotationally rigid manner in the work spindle a tool holder inserted in the tool receiving socket, and a radially inner initial position, in which the tool holder can be inserted in and removed from the tool receiving socket. Such a clamping system is known from EP 0 471 197 Al.

The known clamping system serves, for example, to draw a so-termed HSK tool holder having a tapered hollow shank into a tool receiving socket of a work spindle and to clamp it there in a rotationally rigid manner. The clamping system comprises a clamping arbor, around which a plurality of collet segments are arranged. Provided on each of the upper and lower heads of each collet segment is a retaining shoulder extending obliquely outwards and, respectively, upwards and downwards. Assigned to these retaining shoulders that face axially towards each other, i.e. in the direction of the longitudinal axis of the work spindle, there is a bearing surface on the tool holder and a further bearing surface on the inside of the work spindle.

Further provided on the lower and upper heads of the collet segments and on the clamping arbor and on a retaining bushing of the clamping system are slide bevels, by means of which, upon an axial clamping stroke of the clamping arbor, the collet segments are displaced outwards into their clamping position, parallelwise in relation to each other and parallelwise in relation to the longitudinal axis of the work spindle. Through this clamping stroke, the retaining shoulders exert a pressure upon the bearing surfaces, as a result of which the tool holder is drawn into the tool receiving socket and clamped to the work spindle in a rotationally rigid manner.

In the case of a disengaging stroke extending contrary to the clamping stroke, the collet segments are moved back radially inwards into their initial position, in which the lower heads have such a radial spacing in relation to each other, transversely in relation to the longitudinal axis, that the tool holder comes clear of the clamping system. For this purpose, it may be necessary for the clamping arbor to strike with its end face upon the base of the tapered hollow shank.

The collet segments have a compression spring acting upon them at their upper heads and are thereby held spring-loaded into their position parallelwise in relation to the longitudinal axis of the work spindle. Machine tools in which these or comparable clamping systems are used are known extensively from the prior art.

Thus, DE 41 17 701 Al describes a machine tool in which a multiplicity of tool changers are provided in a distributed manner around the work spindle, each of which tool changers carries a gripper, in which a tool holder, carrying a tool, is inserted. In this way, there are present in this coupled-motion magazine as many tools as there are tool changers.

For the purpose of inserting a tool in the tool receiving socket, the tool changer is moved out, such that the gripper moves with the tool holder beneath the work spindle, whereupon the tool holder is inserted in the tool receiving socket. Provided in the work spindle is a clamping system of the type mentioned at the outset, which takes hold of the inserted tool holder and clamps it in the tool receiving socket.

After the tool holder has been connected to the work spindle in a rotationally rigid manner, the latter is accelerated up to its operating rotational speed. The gripper in this case remains on the tool holder, corresponding measures being provided in order that the tool holder comes clear of the gripper during operation.

When a new tool is to be inserted, the work spindle is braked until it reaches a coupling rotational speed at which the clamping system is disengaged and the tool holder is ejected from the tool receiving socket and received again by the gripper. The gripper then swivels the tool holder back into its magazine position while, in a push-pull action, another tool holder is inserted in the tool receiving socket by the corresponding tool changers and is clamped there by means of the clamping system.

Known from DE 102 25 143 Al is a machine tool having two tool changers that change tools between a machine magazine and the tool receiving socket in the work spindle in a push-pull action. The machine magazine is stationary, whereas the two tool changers are arranged on the spindle head carrying the work spindle. The spindle head moves into a change position, where the one tool changer removes the previously used tool from the tool receiving socket while the other tool changer has already removed from the tool magazine or machine magazine, where the tools are stored, a tool that is to be inserted.

In the case of this machine tool, therefore, the gripper does not remain on the tool that is in use. When a tool is to be removed, the work spindle is firstly braked until it comes to a standstill, before the gripper can take hold of the tool, which is thereupon ejected, in order that it can be deposited in the tool magazine.

In the case of this and other prior art machine tools, it is also possible to change the tools by a pick-up method, for which no tool changers are required. In this case, the work spindle moves directly to the tool magazine, where it firstly deposits the tool to be removed before picking up a new tool, if necessary after corresponding shifting of the tool magazine.

In the case of these machine tools, it is disadvantageous that the work spindle must always first come to a standstill, or at least be braked to a slow coupling rotational speed, before the release operation for the clamped-in tool can begin. This is because, in disengaging the clamping system, there is the risk of the tool holder falling out of the tool receiving socket, for which reason the clamping system is disengaged only when the gripper has again taken hold of the tool. These procedural steps are time- intensive, however, increasing the time required for changing a tool.

Likewise, when a tool is being clamped-in, before the gripper is moved away, it is necessary in this case to wait until the clamping system has securely clamped-in the tool holder, which likewise costs time.

Overall, in the case of the machine tools described thus far, the tool changing time is perceived as being too long, since the tool changing time constitutes a significant element of the chip-to-chip time, which is a measure of the machining speed of the machine tool. This is because, the longer it takes to change a tool, the longer it also takes for the inserted tool to engage again with the workpiece. However, in mass production, in particular, it is desirable to work with chip-to-chip times that are as short as possible.

In order to shorten the tool changing time, DE 101 59 661 Cl proposes a clamping system of the type being discussed here, in which a clamping sleeve having radially resilient clamping portions is provided in addition to the collet segments, which clamping sleeve holds, by frictionally engaged bearing contact, a tool holder that has been inserted in the tool receiving socket, before the clamping system takes hold of the tool holder and clamps it in fully.

DE 299 22 642 Ul discloses a clamping system of the type mentioned at the outset, in which retaining lugs that are resilient in the radial direction are provided in addition to the collet segments. Retaining shoulders, which come into bearing contact with bearing surfaces in the tool holder, are provided both on the actively actuated collet segments and on the retaining lugs. The retaining shoulders of the resilient retaining lugs are located axially lower than the retaining shoulders of the clamping system, such that the retaining lugs take hold of the inserted tool holder earlier than does the clamping system itself.

The tool holder is thus taken hold of by the clamping system immediately after insertion in the tool receiving socket, such that the gripper can move away from the tool holder, or the work spindle can move away from the tool magazine, while at the same time the clamping system draws in and clamps the tool holder.

In both cases, the tool holder is thereby held by spring force, for which reason, in the case of coupling with a rotating work spindle, a relative movement is effected, at least initially, between the tool holder and the resilient holders, which very rapidly results in a high degree of wear, owing to the rapid tool changing. According to knowledge of the present applicant, therefore, in the case of these clamping systems a tool change can be effected only with a stationary work spindle.

Additional to this is the fact that, in both cases, the holding force is determined by the spring force, or clamping force, of the intrinsically yielding retaining lugs or clamping portions, such that, in the case of a tool holder held only by same, the work spindle cannot perform any rapid or jerky movements, since otherwise there is the risk of the tool holders, which, although held, are not yet clamped-in, being thrown out from the work spindle.

In the case of machine tools equipped with such clamping systems, likewise, the tool changing time is not satisfactorily short.

DE 10 2004 029 Al therefore proposes to provide the clamping system with a second set of collet segments, which likewise take hold of the tool holder at the bearing surface. The movement of these second collet segments is controlled by a very much shorter holding stroke of the clamping arbor that precedes the clamping stroke. As soon as the holding stroke has been executed, the tool holder is held captively and the gripper can now already be removed, or the work spindle can be moved away from the tool magazine. Further, after the holding stroke has been completed, the work spindle can already be accelerated again and moved rapidly into the working space of the machine tool.

The same applies to the disengaging stroke, which, although it disengages the tool holder from the first, usual collet segments, and thereby from the tool receiving socket, nevertheless does not disengage it from the second collet segments. During the disengaging stroke, the work spindle can at the same time approach an empty storage space in a tool magazine or a gripper can take hold of a tool. The tool holder becomes free only as a result of a release stroke following the disengaging stroke, such that the work spindle can leave the spindle space or the gripper can remove the tool from the tool receiving socket.

Consequently, in tool changing, time advantages are obtained in comparison with the clamping system described above.

This design, however, like the other solutions from the prior art, is structurally complex.

In view of the above, the present invention is based on the object of further shortening, in a structurally simple manner, the time interval required for a tool change in the case of the known machine tool, without the operational reliability being impaired.

In the case of the machine tool mentioned at the outset, this object is achieved, according to the invention, in that at least some of the lower heads of the collet segments, when in their initial position, have such a radial spacing in relation to each other that they take hold of a tool holder inserted in the tool receiving socket, and in that these lower heads are arranged so as to be movable radially inwards.

In this way, the object underlying the invention is achieved in full.

This is because the inventors of the present application have identified that at least some of the existing collet segments can be used in the same manner as the resilient retaining lugs provided in addition in the case of DE 299 22 642 Ul. For this purpose, the lower heads of at least some collet segments, when in their initial position, are arranged radially further outwards than is the case in the prior art. In this way, these lower heads hold a tool holder that has been inserted in the tool receiving socket, without yet clamping it. However, the tool holder cannot fall out of the tool receiving socket. In order that the tool holder can be inserted in and removed from the tool receiving socket when the heads are in this initial position, the heads are so mounted that they can be moved radially inwards, such that they do not impede the insertion and removal of the tool holders. As soon as the tool holder has been inserted, however, these lower heads resume their initial position.

This solution is structurally more simple than the solutions from the prior art, since it is only necessary, for example, for some of the lower heads to be made resilient and positioned radially further outwards. On the other hand, some of the lower heads can be mounted in an articulated manner on the corresponding collet segments, and either biased by spring force into the initial position or moved actively.

It is preferable, however, if at least some of the collet segments are mounted so as to be tiltable when in their initial position, it being further preferable if the collet segments are realized to be rigid.

These measures are advantageous in respect of design and safety. Since the collet segments themselves are tiltable, it is not necessary for the lower heads to be realized or mounted separately. It is thus possible to use the available collet segments, which, according to the invention, are now mounted so as to be tiltable, such that the lower heads can avoid a tool holder during insertion or removal.

A further advantage is to be found in that the collet segments can all be realized to be rigid, such that the collet segments, whose lower heads hold the tool holder when in the initial position, can likewise be used for clamping when in the clamping posi- tion. All collet segments are thereby available for clamping, some or all collet segments also being used for holding when in the initial position.

In other words, the available circumferential space in the clamping system is used fully by collet segments, which are used for clamping and holding. In the prior art, by contrast, up to 50% of the collet segments are replaced by retaining lugs or other collet segments that are used for holding only, but not for clamping.

Therefore, with the clamping system according to the invention, more rapid tool changing becomes possible with a simple design structure, since the work spindle can be moved rapidly and its rotational speed increased after the insertion of a tool holder.

In the applicant's premises, in the case of a machine tool having tool changing by a pick-up method, it was possible in this way to reduce the chip-to-chip time from 2.4 to 1.9 seconds. Even in the case of machine tools having tool changers, 0.2 to 0.5 seconds can be saved in the chip-to-chip time.

This time advantage results, on the one hand, from the fact that the tool holder is immediately held securely, without loss of time, after insertion in the tool receiving socket, this holding being so secure that the work spindle can already execute rapid and even jerky movements at the same time as the actual clamping operation. A further, additional advantage is that the clamping system need not suffer impairment in clamping, but rather, the maximum possible number of collet segments is also available for clamping.

In removing the tool holder from the tool receiving socket, a corresponding force must be expended in order to move the lower heads inwards, unless this movement is actively controlled. This force is applied by the work spindle itself, which deposits the tool holder in a magazine or gripper, where it is held positively. The magazine and the gripper in this case can absorb the very large forces that can be exerted by the work spindle while moving.

The lower heads can therefore be biased into their initial position via strong springs, ensuring secure holding.

It is preferable in connection therewith if the collet segments have acting upon them, at their upper heads, an axially acting compression spring.

It is advantageous in this case that the compression spring, which is present in any case and holds the collet segments in axial alignment, is also used as a restoring spring for the initial position. This compression spring exerts large compression forces, such that an inserted tool is held securely.

It is further preferable if the clamping system comprises a clamping arbor that displaces the collet segments radially by means of its axial stroke.

In this manner, known per se, the clamping arbor can actuate the clamping device both in clamping and in disengaging by means of its axial stroke, this being advantageous particularly in respect of structure.

Such clamping systems having an axially moved clamping arbor are adequately known from the prior art, and are used, in particular, for HSK tool holders; see, for example, DE 100 31 027 Al. The improvement, according to the invention, of only the clamping system renders possible rapid tool changing without alteration of the HSK tool holder or other modifications of the work spindle.

In general, it is preferable if the clamping arbor has, on its upper portion, a support around which the collet segments are mounted in a tiltable manner, the support further preferably comprising a portionally radial thickening of the upper portion of the clamping arbor. These measures are structurally advantageous, the tilting capability of the collet segments being achieved in that at the top of the clamping arbor there is provided a support around which the collet segments can tilt. The inventors of the present application have determined in tests that, with an otherwise unaltered structure in the case of a usual clamping system, even a slight thickening of a portion of the clamping arbor in its upper region, by a few tenths of a millimetre, is sufficient to provide both for the tilting capability according to the invention and for the lower heads being located radially further outwards. The compression spring, which is provided in any case, biases the collet segments into the new initial position, but allows the collet segments to be tilted inwards in the region of the lower heads.

Overall, it is preferable if the collet segments have, on their lower heads, downwardly facing slide surfaces that extend obliquely downwards and radially inwards and, in their initial position, have such a radial spacing in relation to each other that, as a tool holder is inserted in the tool receiving socket, they come at least partially into bearing contact with this tool holder, as a result of which the lower heads are moved radially inwards.

This measure, likewise, is structurally advantageous. Slide surfaces, via which the heads are already caused to swivel radially inwards by the insertion movement of the tool holder, are to be provided only on the lower heads.

It is also preferable in this case if the collet segments have, on their lower heads, upwardly facing retaining shoulders that extend obliquely downwards and radially outwards and, in their initial position, have such a radial spacing in relation to each other that, after insertion of a tool holder in the tool receiving socket, they come at least partially into bearing contact with bearing surfaces provided on this tool holder, as a result of which the tool holder is held in the tool receiving socket. The retaining shoulders, which are provided in any case, thus also serve to hold the tool holder before clamping and, in the case of removal with corresponding tensile force, they also cause the collet segments to be tilted.

In view of the above, the present invention also relates to a clamping system having the features according to the invention.

In general, it is preferable if the tool holder has a tapered hollow shank, the outer contour of which is matched by the tool receiving socket.

This measure is generally known. With such HSK tool holders, the invention can be used in the case of all standard machine tools.

Particular advantages are obtained, however, if the machine tools have a vertical-axis work spindle, since here in the case of rapid and jerky movement of the work spindle particularly large forces act upon the tool holder, which is now nevertheless held securely by the clamping system according to the invention.

Further advantages become evident from the description and the appended drawing.

It is understood that the features mentioned above and those yet to be explained in the following are applicable, not only in the respectively specified combinations, but also in other combinations or individually, without departure from the scope of the present invention.

An embodiment of the invention is represented in the drawing, and explained more fully in the following description. In the drawing:

Fig. 1 shows a schematic side view of a basic sketch of a machine tool in which the invention is applied; Fig. 2 shows a schematic front view of a basic sketch of another embodiment of a machine tool in which the invention is applied;

Fig. 3 shows in a schematic, partially sectional representation, the working spindle of a machine tool from Fig. 1 or Fig. 2, in the region of the tool receiving socket, with a tool holder having been inserted but not yet clamped-in, the invention not being employed here;

Fig. 4 shows a representation as in Fig. 3, but with a clamping device according to the invention and in a larger section;

Fig. 5 shows a representation as in Fig. 4, but in a smaller section and with greater enlargement;

Fig. 6 shows a representation as in Fig. 4, but with a clamped-in tool holder; and

Fig. 7 shows a representation as in Fig. 5, but with a clamped-in tool holder.

In Fig. 1, 10 denotes a machine tool shown in a schematic representation that is not true to scale or exact in detail.

The machine tool 10 has, on its machine base 11, a first carriage 12 that is movable, in the direction of a first axis 14, on guide rails 15. A second carriage 16 is arranged on the first carriage 12 so as to be movable via guide rails 17 in the direction of a second axis 18.

A spindle head 19 is mounted on the second carriage 16 so as to be movable in the direction of a third axis 21. Rotatably mounted in the spindle head 19 is a work spindle 22, which carries a tool 23 at its lower end. Further provided on the machine base 11 is a workpiece table 24, which carries a schematically indicated workpiece 25 that is machined at various spots by means of the tool 23 through movement of the spindle head 19, and thereby of the work spindle 22, in the three axes 14, 18, 21.

Further mounted on the first carriage 12 is a machine magazine 26, in the form of a chain magazine 27, which is movable in the direction of an arrow 28.

In its spindle position 29, represented by a broken line, the chain magazine 27 enables a tool change to be effected on the tool spindle 22.

This tool change can be effected by a pick-up method, wherein the tool spindle 22 firstly deposits the used tool 23 in an empty space in the chain magazine 27, the chain magazine 27 then brings a new tool 23 into the spindle position 29, and the new tool is then received by the tool spindle 22.

In the case of the embodiment of Fig. 1, however, two tool changers are provided, of which one is represented schematically at 31 on the spindle head 19.

For the purpose of removing a tool 23 from the work spindle 22, a tool changer 31 is brought beneath the work spindle 22, which has been braked to a standstill. The tool changer 31, by means of its gripper, not represented in Fig. 1, takes hold of the tool 23, which is then ejected by a clamping system, likewise not represented in Fig. 1. The tool changer now brings the tool 23 into its magazine position in the chain magazine 27, the other tool changer 31 having at the same time already removed a tool 23 from the chain magazine 27 and now inserting it in the work spindle 22 by a push-pull action. After the tool has been clamped in the work spindle 22, the gripper releases the tool 23 and the work spindle 22 is accelerated up to its operating rotational speed. It must also be mentioned that the tool changer 31 does not take hold of the tools 23 directly, but that the tools 23 are clamped, in a manner known per se, in a tool holder, for which a Standard tool receiving socket is provided in the work spindle 22 and which grippers, provided on the tool changers 31, can take hold of in a manner known per se.

To this extent, this design is comparable to the alternative embodiment of the new machine tool now described in connection with Fig. 2.

In the case of the machine tool shown in Fig. 2, like components are denoted by the same references as in Fig. 1. The machine tool 10 has a plurality of tool changers 31, which are arranged in a distributed manner around the spindle head 19, and of which only two are represented in Fig. 2. Each tool changer 31 comprises a parallelogram guide 32, at the lower end of which there is respectively arranged a gripper 33 carrying a tool 23 that is clamped in a schematically represented tool holder 34.

The work spindle, at its lower end, has a tool receiving socket 35, which is realized as an internal taper and in which the tool holders 34 can be inserted with their geometrically matching hollow cone 36. For this purpose, a sleeve, which is indicated at 37 and which carries the individual tool changers 31, is moved upwards in Fig. 2.

Whereas, in the case of the machine tool from Fig. 1, the work spindle 22 is in each case braked to a standstill before a gripper can take hold of the tool holder to enable the clamping system to eject the tool holder, in the case of the machine tool from Fig. 2 the grippers 33 remain on the tool holder 34 both in the magazine position at a distance from the tool receiving socket 35 and in the working position. After the hollow cone 36 has been clamped in the tool receiving socket 35, the sleeve 37 is lowered by a small amount, as a result of which the tool holder 34 comes clear of the gripper 33 and can rotate freely in relation to the latter. Since, in the case of the machine tool from Fig. 2, the grippers 33 remain permanently on the tool holders 34, the tool holders 34 can be inserted and removed while the work spindle 22 continues to rotate at a coupling rotational speed, resulting in a time advantage in tool changing.

The two machine tools described thus far are adequately known from the prior art mentioned at the outset.

Fig. 3, in a schematic sectional representation, shows the work spindle 22 in the region of the tool receiving socket 35, a tool holder 34 having been inserted with its tapered hollow cone 36 in the tool receiving socket 35, but not yet clamped.

Provided in the work spindle 22 is a schematically indicated clamping system 42 comprising a clamping arbor 44, which is moved by a pull rod 43 and can execute an axial stroke, as indicated by a double arrow 45.

The clamping system 42, in known manner, comprises collet segments 46, which are distributed around the circumference of the clamping arbor 44, and of which two are represented in Fig. 3.

The collet segments 46 act together with the clamping arbor 44 in such a way that they are moved by the axial stroke 45 from their radially inner position, shown in Fig. 3, in which they fully release the hollow shank 36, into their radially outer position, the clamping position, in which they take hold of the hollow shank 36 by means of their lower heads 47 and connect it to the work spindle 22 in a rotationally rigid manner.

For this purpose, the clamping arbor 44 is provided with a conical surface 48, which serves as an opposing bevel for slide bevels 49 on the collet segments 46 such that, upon the clamping arbor 44 being drawn upwards in Fig. 3, the collet segments 46 are moved radially outwards. Provided oppositely to the slide bevels 49 on the collet segments 46 are retaining shoulders 51, which act together with an inwardly projecting bearing surface 52 extending circumferentially in the hollow shank 36 when the collet segments 46 are moved radially outwards.

In the operating state shown in Fig. 3, the hollow shank 36 has been introduced into the tool receiving socket 35 to such an extent that the clamping arbor 44 engages in a cavity 53 provided in the hollow shank 36. The cavity 53 has a cavity base 54 with which, in Fig. 3, the clamping arbor 44 is in bearing contact by means of its end face 55. In this operating situation, the tool holder 34 is held exclusively by the gripper 33 or, alternatively, in a tool place in a tool magazine.

In the operating position shown in Fig. 3, in which the clamping device 42 has not yet executed its clamping operation, i.e. the collet segments 46 are still radially inwards, the tool holder 34, at its annular shoulder 56, has a small spacing from an opposing surface 57 provided on the end of the work spindle 22, which spacing is indicated at 58. This spacing is, for example, 0.5 mm.

In the operating position shown in Fig. 3, the work spindle 22 can be stationary or rotate at a low coupling rotational speed. The clamping arbor 44 now executes a clamping stroke upwards in the direction of the arrow 45, upon which the end face 55 of the clamping arbor 44 is raised from the cavity base 54. As a result of this clamping stroke, the slide bevel 49 slides outwards on the conical surface 48, such that the collet segments 46 are displaced radially outwards and, through their retaining shoulders 51, come into bearing contact with the bearing surface 52. Through upper retaining shoulders, not shown in Fig. 3, the collet segments 46 thereby come into bearing contact with bearing surfaces in the work spindle 22 that are not shown in Fig. 3, such that the tool holder is drawn into the tool receiving socket 35, as is known from the prior art discussed at the outset. The hollow cone 36 is thereby drawn into the tool receiving socket 35 to such an extent that the annular shoulders 56 come into bearing contact with the opposing surface 57. The tool holder 34 is now securely clamped in the tool receiving socket 35, exact positioning of the tool holder 34 in the work spindle 22 being ensured by the planar bearing contact between the annular shoulder 56 and the opposing surface 57, such that high-precision workpiece machining operations can be performed with the tool carried by the tool holder 34. The gripper 33 is now, for example, removed from the tool holder 34 or, alternatively, is lowered to such an extent that the tool holder 34 can rotate freely therein, such that the gripper 33 can remain on the tool holder 34. If the tool change is effected by a pick-up method, the work spindle can now be taken away, out of the spindle position 29.

When use of the inserted tool 23 has been completed, the work spindle 22 is braked down to a standstill or to coupling rotational speed. As soon as the tool is clear of the workpiece and the work spindle, in the case of the machine tool from Fig. 1, has been brought, if necessary, into the spindle position 29, the tool holder 34 is again taken hold of by a holder in the machine magazine 26 or by the gripper 33, unless the gripper has remained on the tool holder 34 in any case, as is the situation in the case of the machine tool from Fig. 2. The clamping arbor 44 then executes a disengaging stroke, by which the action of the clamping stroke is undone.

The clamping arbor 44 is thereby moved downwards in the direction of the arrow 45 in Fig. 3, such that the collet segments 46 come clear of the bearing surface 52 at their retaining shoulders 51. The tool holder 34 is now held entirely by the gripper 33 or the machine magazine 26, and can be moved out of the tool receiving socket 35 in that either the gripper 33 or the work spindle 22 is moved.

Although the known tool change is very reliable, it nevertheless requires an appreciable amount of time, since the tool holder can only be released when the latter is fully clamped in, i.e. when the clamping arbor has fully executed its clamping stroke. According to the invention there is now used, in the case of both machine tools, a clamping system 42 that takes hold of the tool holder 34 as soon as it is inserted with its hollow cone 36 in the tool receiving socket 35. This is effected by a type of latching system, the functioning of which does not require the clamping arbor 44 to execute a stroke.

For this purpose, at least the lower heads 47 of the collet segments 46, in their radially inner position, which is shown in Fig. 3 and which is designated here as the initial position or initial setting, are placed so far radially outwards, compared with known clamping systems, that the retaining shoulders 51 are already partially opposite the bearing surfaces 52.

The collet segments 46 are mounted so as to be tiltable against the force of a restoring spring, such that the heads 47 can shift radially inwards upon the insertion of a tool holder 34 and can tilt back into their initial position when they have sunk into the cavity 53. Owing to their initial position being located radially further outwards, in comparison with Fig. 3, the retaining shoulders 51 thereby already come partially into bearing contact with the bearing surfaces 52, such that the tool holder 34 is securely held by the collet segments 46, which are present in any case, immediately after introduction into the tool receiving socket 35.

After the tool holder 34 has been inserted in the tool receiving socket 35, the work spindle 22 can now be accelerated up to operating rotational speed and/or moved rapidly in the working space of the machine tool. Further, a gripper 33 can be removed from the tool holder 34 immediately after insertion of the latter.

These advantages are also obtained, inversely, in the removal of the tool holder 34, since the clamping arbor 44 can be moved into its release position of Fig. 3 without there being the risk of the tool holder 34 falling out of the tool receiving socket 35. This release operation, likewise, can thus be effected at the same time as the moving and/or braking-down of the work spindle 22, without the necessity of the tool holder 34 having first been received by a gripper 33 or a machine magazine 26.

These advantages are thus obtained both in the case of machine tools having one or more tool changers 31 and, in particular, in the case of machine tools that change tools by the pick-up method described above. Particular advantages are obtained in the case of a machine tool having a vertically aligned work spindle 23, since in this case particularly large forces act upon the tool holder 34 as the work spindles 23 are moved, such that, in the case of known clamping systems, no rapid movements are possible before the tool holders have been fully clamped, which results in long chip- to-chip times in those cases.

The new design of the clamping system 42 is now explained with reference to Figures 4 to 7, which, in schematic sectional representations and two different enlargements, show the work spindle 22 in the region of the tool receiving socket 35, the same references as in Fig. 3 being used for the same assemblies and components.

The collet segments 46 each have an upper head 61 on which there is provided a retaining shoulder 62 that acts together with a bearing surface 63 on the work spindle 22. When the collet segments 46 are moved radially outwards, they clamp the tool holder 34 to the work spindle 22 via the retaining shoulders 51, 62 and bearing surfaces 52, 63.

The upper heads 61 each have an end face 64, bearing on which is a bushing 65 that is pressed downwards, in the direction of the longitudinal axis L in Fig. 4, by the force of a compression spring 66. In its upper portion 67, which is between the heads 47 and 61, the clamping arbor 44 is provided with a support or bearing for the collet segments 46, which support is realized, in this embodiment, as a thickened region 68 that projects by a few tenths of a millimetre over the otherwise cylindrical outer surface of the clamping arbor 44. As a result, the collet segments are aligned substantially parallelwise in relation to the longitudinal axis L, but the lower heads 47 are located radially further outwards than in Fig. 3, such that the retaining shoulders 51 are already partially opposite the bearing surfaces 52 when in the initial position of Fig. 4, such that the tool holder 34 is securely held in the tool receiving socket 34, but is not yet clamped.

Indicated at 69, in contrast to Fig. 3, is the spacing that the lower heads 47 now have in relation to the clamping arbor 44.

Upon a tool holder 34 being inserted in the tool receiving socket 35, the lower heads 47, via downward facing slide surfaces 71 that extend obliquely downwards and radially inwards and have a corresponding spacing in relation to each other in their initial position, come at least partially into bearing contact with an upper edge 72 of a tool holder 34, as a result of which the lower heads 47 are moved radially inwards.

When the lower heads 47 have sunk into the cavity 53, they tilt back into their initial position. Fig. 5, in a manner similar to Fig. 3, shows the state of Fig. 4 in an enlarged, sectional state. On the inside, the clamping arbor 44 is cross-hatched, since the structure there is not of interest.

When the state of Fig. 4 has been reached, the work spindle 22 can consequently be accelerated up to its operating rotational speed and moved without there being the risk of the tool holder 34 falling back out of the tool receiving socket 35, since it is held securely by the collet segments 46, which are again in the initial position and are held in this position by pressure of the compression spring.

During the acceleration and moving of the work spindle 22, the clamping arbor 44 executes its clamping stroke upwards in the direction of the arrow 45, which stroke is shown at 45 in Fig. 3. Figs. 6 and 7 show the collet segments 46 in their clamping position, in which they are pressed radially outwards by the clamping arbor 44. In this clamping position, the tool holder 34 is drawn firmly into the tool receiving socket 35 by the surfaces 51, 52 and 62, 63 that are in bearing contact, and it is connected to the work spindle 22 in a rotationally rigid manner. The clamping collets are aligned parallelwise in relation to the longitudinal axis L, the support, i.e. the thickened region 68, do not interfere with this function.

When the clamping arbor 44 is pressed back inwards for the purpose of releasing, the collet segments 46 are displaced back inwards, for which purpose it may be necessary for the clamping arbor to press the hollow cone downwards in order that the surfaces 51, 52 and 62, 63 come clear of each other again, the surfaces 51, 52 still partially overlapping, however, as shown in Figs. 4 and 5. An annular gap - 58 in Fig. 3 - can be seen between the annular shoulder 56 and the opposing surface 57, the tool holder 34 has thus already moved somewhat downwards out of the tool receiving socket.

As the tool holder 34 is removed from the tool receiving socket 35, its bearing surface 52 presses upon the upwardly facing retaining shoulders 51 of the lower heads 47, which retaining shoulders extend obliquely downwards and radially outwards, as a result of which these heads move radially inwards against the force of the compression spring 66 and release the tool holder 34.

Claims

1. A machine tool comprising at least one preferably vertically aligned work spindle (22) that has a tool receiving socket (35) for tool holders (34) carrying tools (23) and has a clamping system (42) comprising a plurality of collet segments (46) that are displaceable between a radially outer clamping position, in which, by means of their lower heads (47), they clamp in a ro- tationally rigid manner in the work spindle (22) a tool holder (34) inserted in the tool receiving socket (35), and a radially inner initial position, in which the tool holder (34) can be inserted in and removed from the tool receiving socket (35),

characterized in that at least some of the lower heads (47) of the collet segments (46), when in their initial position, have such a radial spacing in relation to each other that they take hold of a tool holder (34) inserted in the tool receiving socket (35), and these lower heads (47) are arranged so as to be movable radially inwards.

2. The machine tool according to claim 1, characterized in that at least some of the collet segments (46) are mounted so as to be tiltable when in their initial position.

3. The machine tool according to either of claims 1 or 2, characterized in that the collet segments (46) are realized to be rigid.

4. The machine tool according to any one of claims 1 to 3, characterized in that the clamping system (42) comprises a clamping arbor (44) that displaces the collet segments radially (46) by means of its axial stroke (45).

5. The machine tool according to any one of claims 1 to 4, characterized in that the tool holder (34) has a tapered hollow shank (36), the outer contour of which is matched by the tool receiving socket (35).

6. The machine tool according to any one of claims 1 to 5, characterized in that the collet segments (46) have, on their lower heads (47), downwardly facing slide surfaces (71) that extend obliquely downwards and radially inwards and, in their initial position, have such a radial spacing in relation to each other that, as a tool holder (34) is inserted in the tool receiving socket (35), they come at least partially into bearing contact with this tool holder, as a result of which the lower heads (47) are moved radially inwards.

7. The machine tool according to any one of claims 4 to 6, characterized in that the clamping arbor (44) has, on its upper portion (67), a support around which the collet segments (44) are mounted in a tiltable manner.

8. The machine tool according to claim 7, characterized in that the support comprises a portionally radial thickening (68) of the upper portion (67) of the clamping arbor (44).

9. The machine tool according to any one of claims 1 to 8, characterized in that the collet segments (46) have acting upon them, at their upper heads (61), an axially acting compression spring (66).

10. The machine tool according to any one of claims 1 to 9, characterized in that the collet segments (46) have, on their lower heads (47), upwardly facing retaining shoulders (51) that extend obliquely downwards and radially outwards and, in their initial position, have such a radial spacing in relation to each other that, after insertion of a tool holder (34) in the tool receiving socket (35), they come at least partially into bearing contact with bearing surfaces (52) provided on this tool holder, as a result of which the tool holder (34) is held in the tool receiving socket (35).

11. A clamping system for a tool holder (34), comprising a plurality of collet segments (46) that are displaceable between a radially outer clamping position and a radially inner initial position,

characterized in that lower heads (47) of the collet segments (46) are arranged so as to be movable radially inwards from the initial position.

12. The clamping system according to claim 11 for a machine tool according to any one of claims 1 to 10, having the features from one or more of claims 2, 3, 4, 6, 7, 8, 9 or 10.