Motor element, in particular medical handpiece with a collet chuck

In the case of a motor element, in particular of dental technical handpiece or a motor spindle, which at least in its front region has an elongated shank, rotatably mounted in which there is a hollow drive shaft, arranged in whose front end region there is a collet chuck for a tool that is connected in its rear end region by means of a coupling to a rod that extends towards the rear and is pretensioned towards the rear or towards the front by means of the force of a spring and can be displaced towards the front or towards the rear against the force of the spring by means of an actuating mechanism, with the spring being stayed on the draw rod towards the rear and being stayed against an inner first shoulder of the drive shaft towards the front, arranged at the front end region of the spring there is at least one supporting element that is elastically pretensioned radially outwards and springs out behind the shoulder when the draw rod is pushed with the spring from the front into the drive shaft, and the supporting element reaches a position located behind the shoulder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in particular to a medical handpiece.

2. Description of Related Technology

A handpiece of this kind is described in DE 44 06 855 A1. In the case of this previously known handpiece, a collet chuck is arranged in the front end region of a hollow drive shaft and is connected on the rear side to a draw rod, for the compression of the collet chuck, which at the same time is a longitudinal section of the drive shaft. The draw rod is formed by a pressure spring that is arranged between it and the hollow drive shaft in the form of a helical spring that is stayed with its front end at a shoulder of the hollow drive shaft directed towards the rear and acts with its rear end on a shoulder of the draw rod directed towards the front and thus pretensions the draw rod towards the rear. In this connection, the drive shaft in the region of the pressure spring consists of two sleeve-shaped portions that are extended in terms of their cross-sectional size with regard to the other axial sections of the drive shaft and overlap each other and are fixedly connected together. In the case of this known development, a complicated construction emerges that not only results in large cross-sectional dimensions, but also presupposes expensive assembly and disassembly.

GENERAL DESCRIPTION OF THE INVENTION

The underlying object of the invention is to develop a medical handpiece of the kind specified at the beginning in such a way that, whilst guaranteeing a simple construction, assembly and disassembly can be effected with little outlay.

In the case of the handpiece in accordance with the invention, arranged at the front end of the spring there is at least one supporting element that is elastically pretensioned outwards and springs out behind the shoulder when the rod is pushed with the spring from the front into the drive shaft, and the supporting element reaches a position located behind the shoulder. As a result, not only is it possible to achieve a construction that has a small cross-sectional size, but assembly of the rod with the spring is also possible from the front, this resulting in a substantial simplification, because the handpiece does not need to be opened at the rear for the assembly and subsequently be closed again. The construction of small cross section that is striven for is therefore possible, because already a slight engagement behind the shoulder by the supporting element renders possible reliable staying of the spring towards the front, and the handpiece can therefore be realized with a small cross-sectional size.

The supporting element can be formed in a simple and inexpensive manner by means of a spring arm that can be sprung out of a relaxed position, in which it engages behind the shoulder, radially inwards into a position in which it is adapted to the inner cross-sectional size of the drive shaft.

The introduction of the supporting element into the drive shaft can be simplified and configured in a handling-friendly manner thereby if arranged on the rear side on the supporting element and/or on the front edge of the drive shaft there is an oblique or rounded lead-in face which when pushing in the rod with the spring automatically causes the supporting element to spring into the position in which it fits in the receiving hole of the drive shaft.

The shoulder in the drive shaft can be formed by an annular groove. It is not only possible to produce such a development simply and inexpensively, but when pushing in the rod with the spring there is no need to pay heed to any particular rotational position, because the supporting element matches the shoulder face in each rotational position.

A further advantage of the development in accordance with the invention lies in the fact that the rod with the spring can be disassembled by pushing it further from the front towards the rear, for which purpose, if applicable, the handpiece can be opened at the rear so that the rod with the spring can be pushed out towards the rear. If in this connection oblique or rounded lead-in faces are provided for the supporting element at the rear on the supporting element or on the rear edge of the annular groove, these automatically give rise to a springing-in of the supporting element.

The development in accordance with the invention also renders possible in this respect a simple construction that can be produced inexpensively, because the receiving hole in the drive shaft can be formed so that it is hollowly cylindrical substantially over the whole of its length.

Within the scope of the invention it is possible to provide one or more supporting elements that are arranged so that they are distributed over the periphery. In this connection, it is advantageous to form the supporting element or elements on a guide ring or on a guide bushing in which the draw rod can be guided in a sliding manner.

Further developments of the invention, whilst guaranteeing simple developments, improve the advance or backward movement of the rod for the purpose of opening or closing the collet chuck by means of a pressure element, which is manually accessible from outside the handpiece, and return by spring force.

The present invention is not restricted to medical or dental applications but can generally be used with motor elements with a collet chuck for a rotatable tool. Another application would—for example—be a high frequency motor spindle.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a preferred embodiment of the present invention is described be means of a medical handpiece (hereinafter “handpiece”) for a medical or dental laboratory. It has to be emphasized, however, that the solution according to the present invention can also be used in other motor elements, for example in spindle systems.

The handpiece1is on account of its stable and sufficiently large construction suitable for machining casts, artificial parts such as prostheses, or impressions of the human or animal body. In technical terminology the handpiece1is termed a medical technical or dental technical handpiece or working handpiece. The exemplary embodiment is less well suited for treating teeth in the mouth space of a patient because of its construction size. However, the invention realized in the case of the exemplary embodiment is in principle also suitable for such handpieces that are suitable for the treatment of teeth in the mouth space of a patient. The same also applies to the medical field.

The main portions of the handpiece1are a shank2which is used for manual gripping and extends in a straight manner at least in its front region and in the case of the exemplary embodiment extends so that it is straight as a whole, a drive shaft3which extends longitudinally in the shank2and is mounted in the shank2so that it is rotatable in a front and a rear pivot bearing4,5and is axially non-displaceable, a drive motor6which is preferably electric and is arranged in the shank2as a rotary drive for the drive shaft3, and a clamping arrangement7for a tool8, shown by way of indication, which can be plugged with a tool shank8ainto a plug hole9of the clamping arrangement7and can be clamped and can also be disconnected again.

The clamping arrangement7has a tool-holder12which is preferably formed by a so-called collet chuck11which in the case of the exemplary embodiment is mounted in the drive shaft3so that it can be displaced in its longitudinal direction and has a plurality of, for example three, clamping segments11awhich are arranged on the end side and so that they are distributed over the periphery and can be clamped by means of a clamping mechanism against the tool8or the tool shank8aand can also be released again by means of a release mechanism13that is manually accessible from without. The collet chuck11can be longitudinally displaced between a clamping position and a position of release for the clamping and releasing process. In the case of the exemplary embodiment, the clamping segments11aare preferably compressed radially inwards against the tool8or its shank8awhen the collet chuck11moves back. A clamping cone15with an inner cone15ain the drive shaft3and matching outer cone faces15bon the clamping segments11ais used for this purpose. In the position of release of the collet chuck11where it is displaced towards the front, the clamping segments11aare not under any clamping pressure so the tool shank8acan be plugged into or drawn out of the collet chuck11. So that the clamping segments11aare not moved too far radially inwards in the absence of the tool8, arranged at the front ends of the clamping segments11athere are flange pieces11bthat limit the movement of the collet chuck8axially inwards by butting against the drive shaft3.

A longitudinally extending rod16, in the exemplary embodiment in accordance withFIG. 1, a draw rod that is mounted so that it is coaxially displaceable in the drive shaft3and is detachably connected at its front end to the rear end of the collet chuck11, is used to move the collet chuck11to and fro in a longitudinally directed manner. To this end, arranged between the rod16and the collet chuck11there is a coupling17, which is effective axially and in a form-locking manner, having a first coupling element17aon the one portion that is to be coupled and a second coupling element17bon the other portion that is to be coupled, with the first coupling element17abeing moveable between a coupling position where it engages in a form-locking manner behind the other coupling element17bin an undercut17cand a position of release where it has moved out of the undercut17cand being capable of being locked by means of a locking element8bin the coupling position. As a result of the locking it is guaranteed that the movable coupling element17anot only engages behind the other coupling element17bin the coupling position in a form-locking manner, but that it is also locked therein in order to prevent it from moving out As a result, the coupling security is guaranteed so that the coupling17can transmit axial forces from the rod16to the collet chuck11or vice-versa.

The invention is not limited to a tool-holder12in the form of a collet chuck11. Within the scope of the invention a clamping arrangement7can be provided, for example, in the front end region of the tool-holder12and have, for example, a gripping screw with which a tool can be firmly gripped on the tool-holder. That is why the description continues in the following with reference to the component tool-holder12, if a collet chuck11is not required.

Within the scope of the invention, the radially movable first coupling element17acan be arranged on the rod16and the radially rigid second coupling element17bcan be arranged on the tool-holder12. In the case of the exemplary embodiment, the reverse arrangement is provided. The first coupling element17ais arranged on the tool-holder12and the second coupling element17bis arranged on the rod16. Such a tool-holder12has a rear tool-holder section with which it can be plugged into the drive shaft3, formed so that it is hollow in the front-end region, as far as the region of the coupling17. A spring element which pretensions the first coupling element17ainto its coupling position where it engages behind preferably automatically effects the movement of the first coupling element17ainto the undercut17c. In the case of the exemplary embodiment, the first coupling element17ais arranged on a spring arm19, which extends towards the rear from the tool-holder body, and protrudes radially outwards from this spring arm19. The first coupling element17aand the spring arm19are separated from the rest of the body of the tool-holder12by means of radial longitudinal slots21that open out axially at the associated end.

It is advantageous, in order to achieve rotational securement, to form the undercut17c, which in the case of the exemplary embodiment is provided behind the second coupling element17b, namely the counter-coupling element, with recessed faces17dthat delimit the first coupling element17ain both peripheral directions with clearance of motion (FIG. 5). In this respect, rotational securement that is effective in both peripheral directions in a form-locking manner results for the tool-holder12in the drive shaft3. It is, however, also advantageous to form the undercut17cas an annular groove or as a groove that continues in the clamping segments11ain the peripheral direction. In such a case, whilst there is no rotational securement in the region of the coupling17, the advantage that is achieved as a result is that the tool-holder12can be pushed into the coupling17in any selectable rotational position and can be coupled. Rotational securement can then be realized in a different way. In the case of the formation of the tool-holder12as a collet chuck11, rotational securement is provided by the gripping cone of the collet chuck11.

In order to facilitate the assembly and/or disassembly of the tool-holder12, it is advantageous to form the first coupling element17aand/or the second coupling element17bwith front or rear oblique or rounded lead-in faces22a,22bor lead-out faces23a,23brespectively which have such a great incline with regard to the longitudinal central axis and rotational axis10of the drive shaft3that the tool-holder12can be pushed into the coupling17and/or drawn out of the coupling17with an axial force that can be applied in a handling-friendly manner, with the movable coupling element17aspringing out automatically. As a result, a latching arrangement is formed whose latching faces are so large that during the functional operation the axial coupling of the tool-holder12is guaranteed and the coupling17can be over-pressed, for assembly and/or disassembly of the tool-holder12, with axial expenditure of force that can be applied manually.

In the case of the exemplary embodiment, in which a plurality of, preferably three, movable first coupling elements17awith associated second coupling elements17bwith undercuts17care arranged so that they are distributed over the periphery, the movable coupling elements17aare formed with the associated spring arms19in each case as identical segments that are arranged on the end side and are separated from each other by means of preferably three longitudinal slots21that open out on the end side. The width of the longitudinal slots21that is directed in the peripheral direction is so great that the movable coupling elements17acan spring out in each case, with the existing width of the longitudinal slots21thereby being reduced somewhat in each case.

When the tool-holder12is formed as a collet chuck11with a plurality of, preferably three, clamping segments11a, which are arranged so that they are distributed over the periphery, are separated from each other by means of longitudinal slots24and are arranged on spring arms19aformed thereby, in order to reduce the overall length it is advantageous to arrange the longitudinal slots21in relation to each other so that they are staggered with regard to the longitudinal slots24in the peripheral direction, with it being possible for the longitudinal slots21,24to overlap each other, as clearly shown inFIG. 3.

The sleeve-shaped tool-holder12has a hollowly cylindrical plug hole9, a front conical longitudinal section a and a substantially hollowly cylindrical longitudinal section b extending from the latter towards the rear, the longitudinal sections each being formed by the previously described segments. The cross-sectional shape and size of the plug hole9is adapted with little clearance of motion to the cross-sectional shape and size of the tool8or tool shank8arespectively. The wall sections of the preferably hollowly cylindrical plug hole9thus form in the region of the clamping segments11ahollow-cylinder-section-shaped clamping faces and in the region of the coupling segments hollow-cylinder-section-shaped stop faces, with which the coupling segments17erest against the peripheral face of the tool8or shank8arespectively.

The developments in accordance withFIG. 1or2respectively, on the one hand, andFIG. 5, on the other hand, differ as a result of the lateral surface form of the coupling elements17e. In accordance withFIG. 1or2, the coupling elements17eare thicker before the associated undercut17c, with the undercuts17cbeing concavely rounded in the longitudinal cross section. In accordance withFIG. 5, the undercut17cextends from the convex coupling elements17asubstantially cylindrically towards the front.

In the case of the exemplary embodiment, the rod16extends from the coupling17towards the rear longitudinally through the sleeve-shaped drive shaft3, preferably projecting thereby over the rear end of the drive shaft3. Behind the front end region of the rod16, in which a plug hole9ais arranged, the rod16extends with a rod section16athat tapers in cross section and is guided in a longitudinally displaceable manner in its front end region in a guide bushing25in the drive shaft3. Located between the rear end of the guide bushing25and a shoulder face26that is directed towards the front in the rear end region of the rod16there is a pressure spring27in the form of a helical spring on the tapered rod section16apretensioning the rod16towards the rear. When the tool-holder11is disassembled, the thickened front end region16bof the rod16rests with a rear-side shoulder face16cagainst the guide bushing25. The shoulder face26that is arranged on the rear side thereof can be formed by a bushing16dthat is pushed onto the rod section16aand is fixed thereon and with which the rear end region of the rod16is mounted in the sleeve-shaped drive shaft3in an axially displaceable manner. The guide bushing25inFIG. 2differs from the other exemplary embodiments in so far as it is formed by an inner ring projection of the drive shaft3.

In the normal position, the rod16which is pretensioned towards the rear by the spring27is limited in its movement directed towards the rear in that when a tool8is plugged into the collet chuck11the outer cone of the collet chuck11rests against the inner cone of the drive shaft3. In order to release the tool8, the rod16is moved forwards by the actuating mechanism13. This can be effected by means of a pressure element29which is formed, for example, as a preferably cylindrical cross pin31which can be moved forwards towards the rear end of the rod16(portion16aand/or16d) by means of the actuating mechanism13. In the case of the exemplary embodiment, the cross pin31is displaceably mounted in the region of its, for example, tapered ends31ain grooves33which are located with a pitch in the peripheral direction of the handpiece1in an actuating sleeve32which is mounted in an annular groove32aof the handpiece1so that it cannot be displaced axially and so that it is rotatable in the peripheral direction. One of the two grooves33is shown by way of example inFIG. 1as a developed view. The grooves33, which are preferably arranged in an inner bushing32b, made in particular from wear-resistant material, for example steel, extend in the peripheral direction in such an oblique or rounded manner that starting from the clamping position shown inFIG. 1given a relative twist of the actuating sleeve32the pressure element29is displaced towards the front and thereby moves the rod16towards the front and releases the collet chuck11. In this position of release, the ends31aof the pressure element29are located in the end regions B of the grooves33. In this connection, the arrangement can be such that the end region B of the grooves33that is associated with the position of release is not directed obliquely, but in the peripheral direction so that any automatic untwisting of the actuating sleeve32on account of the spring tension and, if applicable, on account of the effect of vibrations is prevented. The incline36running obliquely towards the front with regard to an associated transverse plane35that is directed at right angles to the longitudinal central axis can vary in the region of the length of the grooves33. In the case of the exemplary embodiment, starting from the end region A that is associated with the clamping position, a comparatively greatly inclined course of inclination c is provided, following which there is a course of inclination d that is inclined less greatly, following which there is an end region B of the grooves33that is directed in the peripheral direction. Provided in the end regions B of the grooves33, in which the pressure element ends31aare located in a position that corresponds to the clamping position, there are preferably locating depressions37in which the ends31acan latch and which are directed towards the front in the case of the exemplary embodiment. The pressure element29can be pretensioned towards the front and thus also into the locating depressions37by means of a spring38, for example a helical pressure spring, that is arranged behind the pressure element29. When the actuating sleeve32is rotated into the position of release B, the pressure element29, the rod16and the collet chuck11are moved forwards into the position of release. When the actuating sleeve32is turned back into the clamping position A, the pressure element29is moved back again into the distanced clamping position (free position) in which it frees the rod16, and the collet chuck11is clamped on account of the axial spring force that exists.

In the case of the previously described forward and backward movements of the pressure element29, said element is guided longitudinally, for example by means of sliding sleeves31bthat sit thereon, in longitudinal grooves30aof a bearing peripheral wall30bof a handpiece housing30.

The electric motor6is provided as a rotary drive for the drive shaft3, this being arranged in the handpiece1and being arranged, for example, with a sleeve-shaped stator6aon the inside of the peripheral wall of the existing handpiece housing and sitting with its sleeve-shaped rotor6bon the drive shaft3. An electric current line39, which is shown by way of indication, extends from the rear through a flexible cable bushing41made from elastically deformable material which is connected to a rear housing section of the handpiece housing.

The housing30includes two bearing peripheral walls, namely the rear longer peripheral wall30band a front shorter peripheral wall30cthat overlap in the front region of the housing30and in this region are screwed together by means of an outside thread and an inside thread set therein and adjoin each other at a division joint42. The screw connection that is arranged, for example, behind the division joint42is denoted by43. The rear peripheral wall30bis formed so that it is substantially hollowly cylindrical and the stator6ais arranged in the region thereof. The front handpiece section and the front peripheral wall30ctaper towards the front end of the handpiece1.

The front pivot bearing4is arranged in the front peripheral wall30cand is formed by a rolling bearing4awhich on the outside sits in a bearing bore44that is open towards the rear in the front peripheral wall30cand on the inside sits on the hollow drive shaft3, being delimited on the rear side by an annular collar45on the drive shaft3.

The rear pivot bearing5is also formed by a rolling bearing which on the outside sits in a bearing bore46that is open towards the front in the rear end region of the rear peripheral wall30band on the inside sits on the drive shaft3. The inner ring of the rear rolling bearing5ais delimited on its front side by the rotor6bor an intermediate sleeve47that rests therein. The rotor6bis delimited at its front end by an annular collar48on the drive shaft3which could also be formed by the annular collar45. Located on the rear side of the rear rolling bearing5athere is a threaded nut49which is screwed from the rear onto a threaded section of the drive shaft3and presses the inner ring and also the further ring portions that are arranged on the front side of the latter on the drive shaft3against the annular collar48and axially fixes them.

In this connection, the drive shaft3with the rotor6band the rod16with the pressure spring27form a constructional unit51that can be preassembled, seeFIG. 6.

In the case of the present exemplary embodiment, this constructional unit51includes two constructional units51a,51b, with the constructional unit51ahaving the drive shaft3, the rotor6b, whilst the second constructional unit51bhas the rod16, the bushing16d, the pressure spring27and the guide bushing25.

One or more shoulder faces52that are directed towards the rear and against which the guide bushing25is limited in the direction towards the front and positioned are provided in the drive shaft3behind the thickened end region16bfor the axial positioning of this constructional unit51b. The pressure spring27is stayed on the rear side on the bushing16dand it pretensions the guide bushing25towards the front, pretensioning the rod16towards the rear on account of the axial staying of the guide bushing25on the at least one shoulder face52. In the assembled state, in this case the rod16or the bushing16dis stayed on the rear side on the pressure element29. This staying can, however, also be effected by delimiting the collet chuck, the clamping segments11aor the flange pieces11bon the rear side by means of the drive shaft3.

In the case of the present exemplary embodiment, the inner constructional unit51bcan be plugged from the front into the hollow drive shaft3and be assembled. This is achieved in that the guide bushing25has at its front end one or more spring arms25awhich are arranged so that they are distributed over the periphery and the front ends of which in the relaxed state take up a radial measure with regard to the longitudinal central axis10that is greater than the radial measure of the receiving hole53, which is cylindrical preferably over the whole of its length, in the drive shaft. The shoulder face52is formed by an annular groove in the receiving hole53.

In order to install the inner constructional unit51bin the drive shaft3, the constructional unit51bis plugged from the front into the receiving hole53until the spring arm or arms25a, which thereby spring therein, spring out behind the at least one shoulder face52and position the constructional unit51atowards the front at the at least one shoulder face52.

In the disassembled state, on account of the spring tension of the pressure spring27the guide bushing25rests against the shoulder face16cthat is arranged in front of it. In the assembled state, on the other hand, between the shoulder face16cand the guide bushing25there is axial clearance of motion even in the clamped state of the clamping segments11a, that is, in the state in which they have been displaced towards the rear, so the clamping effect of the clamping segments11athat is directed radially inwards is not impaired.

In order to disassemble the constructional unit51b, after the tool-holder9or the clamping segments11ahas/have been removed, the rod16is pushed out towards the rear, with the spring arms25aspringing in without being damaged.

In the case of the exemplary embodiment in accordance withFIG. 9, in which the same or comparable portions are provided with the same reference numerals, the handpiece3has a tool-holder12which is formed by a push-out collet chuck11that is actuated in that for a clamping process the rod16is not drawn back, but is pushed forward and exerts a forwardly directed pressure on the collet chuck. In the case of this development as well, a group of clamping elements formed, for example, by clamping segments11awith cooperating cone faces are arranged in the tool-holder12so that they are distributed around the plug hole9and can be moved for a clamping process towards the plug hole9, although the cone faces, here the inner cone15ain the drive shaft3and the outer cone faces15bon the clamping segments11a, are formed so that they converge towards the front and in such a way that they match each other. These cone portions are preferably arranged in the front region of the collet chuck11.

In the case of this development, no coupling between the collet chuck11and the rod16is required, since a drawing action does not take place when clamping. The pressure of the rod16, pressing, for example, obtusely from the rear against the collet chuck11, in which case no coupling is required, suffices for the clamping function. The collet chuck11is held as well in a form-locking manner so that it is undetachable between the inner cone15aand the rod16. In the case of this development as well, the clamping segments11aare arranged on spring arms19awhich are formed by longitudinal slots24that are arranged so that they are distributed over the periphery and open out towards the front. In this connection, longitudinal slots21which open out towards the rear can also be provided here, subdividing the collet-chuck body into segments at the rear.

In order to facilitate the assembly of the collet chuck11, the drive shaft3, which is formed in a sleeve-shaped manner in this region, is transversely divided behind the inner cone15a, and the drive-shaft portions3a,3bare connected together by means of a releasable connection61, in particular a screw connection.

In the case of this modified development, the rod16is pretensioned by the pressure spring27towards the front into its clamping position. The collet chuck11is released by a drawing movement of the rod16towards the rear that can be generated by the release mechanism13moving it towards the rear in opposition to the force of the pressure spring27.

For this, for example, the grooves33can have an opposite pitch so the pressure element29is moved towards the rear for the release and draws the rod16towards the rear, for example in that the rod16engages behind the pressure element29and thereby passes through to engage in a hole and engages behind a head portion16eso that the spring27pushes the clamping elements towards the front through the rod16and clamps them. In this respect, the push-out collet chuck11is effective in an opposite way to that of the draw-in collet chuck11in accordance withFIG. 1.

The clamping effect of this tool-holder12can be improved in that in accordance with the exemplary embodiment in accordance withFIG. 10two groups of clamping elements are provided that are arranged axially one after the other and in each case around the plug hole9and can be moved towards the plug hole9. This can be achieved by means of common application of pressure to the groups, that is, in particular in a simple way if arranged in each group there are clamping segments of which the clamping segments11aof the front group have outer cone faces15bconverging towards the front and those of the rear group have outer cone faces15bconverging towards the rear, with the rod16having at its front end a common pressure element which is formed in particular by an inner cone15cand cooperates with the rear outer cone faces15b. In this connection, the pressure of the rod16acts simultaneously on all the clamping elements.

AsFIGS. 11 and 12, show in particular, in the case of this tool-holder12held at both axial ends there is a respective group of, for example, three clamping segments11a, in each case held on a spring arm19aand thus capable of moving radially inwards against the spring-arm force. The clamping segments11aand the spring arms19aare formed by longitudinal slots24in the sleeve body that open out in each case on the end side and therefore guarantee the radial spring path. The longitudinal slots24and the clamping segments11aare preferably arranged so that they are staggered in relation to each other in the peripheral direction. As a result, it is possible to arrange the slots24so that they overlap axially, in particular in the central region of the sleeve body and thus in the region between the groups of the clamping segments11aor clamping elements.

As already mentioned earlier, the construction according to the present invention generally results in improvements in case a tool holder for a rotatable tool is coupled to a rod. Thus, in addition to the described medical application, the present invention can also be used in other motor driven elements, for example in a motor spindle.