Clamping device

The invention relates to a device for clamping a hollow shaft tool (1) or tool holder provided with a conical hollow shaft (3) in a machine spindle (2) provided with a taper bore (4), especially for use in a machine tool. The device comprises a clamping sleeve (7), axially displaceable inside the machine spindle (2), a tow-rod (8) for displacing the clamping sleeve (7) and being movable between a release position and a clamping position, and a plurality of pincer elements (19) associated with the clamping sleeve (7). The pincer elements are radially displaced by the displacement of the clamping sleeve (7) and have clamping faces (21, 24) to be placed on a conical inner surface (22) of the conical hollow shaft (3) and an opposite surface (26) on the work spindle (1). The aim of the invention is to provide a clamping device of the aforementioned kind wherein the hollow shaft tool is reliably retained in the machine spindle even when the tow-bar is already released. For this purpose, the clamping sleeve (7) can be axially displaced relative to the tow-bar (8) and is axially biased by a compression spring (14) against the motion of release of the tow-bar (8).

The invention relates to a clamping device for clamping a hollow shaft tool or tool holder provided with a conical hollow shaft in a machine spindle provided with a taper bore, especially for use in a machine tool.

A clamping device of this type is known from DE 101 59 611 C1. Here, a clamping bushing is disposed within a machine spindle that is provided with a taper bore so that it can be displaced by means of a tow-bar, wherein several pincer elements are spaced apart from one another in the circumferential direction and adjoin the outside of said clamping bushing. The front ends of these pincer elements have oblique first clamping faces that are designed to adjoin corresponding oblique clamping faces of the hollow shaft tool; the rear ends of the pincer elements have oblique second clamping faces that are designed to adjoin a corresponding opposite surface of the machine spindle. When the clamping bushing is axially displaced, the pincer elements are displaced radially outward or inward in a parallel position relative to the central axis of the machine spindle such that the hollow shaft tool is respectively clamped in position or released. In order to ensure that the hollow shaft tool is also reliably retained and secured from falling out when the pincer elements are released, an additional clamping sleeve with radially resilient clamping segments for frictionally engaged fixing of the holding pincers is disposed within the machine spindle in this known clamping device. However, such an additional clamping sleeve increases the fabrication and installation costs.

The invention is based on the problem of developing a clamping device of the initially described type that makes it possible also to reliably retain the hollow shaft tool in the machine spindle when the tow-bar is already released without requiring an additional clamping sleeve.

This problem is solved by the clamping device with the characteristics of the present invention.

In the clamping device according to the invention, the clamping sleeve can be axially displaced relative to the tow-bar and is axially biased by a compression spring against the motion of release of the tow-bar. When the tow-bar is displaced into the release position, the clamping sleeve is prevented from participating in the entire axial movement of the tow-bar since the compression spring holds the clamping sleeve in a position in which the pincer elements, actuated by the clamping sleeve are still engaged with the conical inner surface of the conical hollow shaft with a small region of their clamping faces. In this position, the hollow shaft tool is still retained within the machine spindle although the tow-bar is already located in the release position. Consequently, the actuating mechanism for releasing the clamping device can already be activated before an automatic tool changing apparatus engages on the hollow shaft tool. This makes it possible to reduce the tool change-over time. In the clamping device according to the invention, the pincer elements carry out an axial and radial stroke relative to the machine spindle rather than a pivoting movement. This makes it possible to realize a retention area instead of merely a retention point. Such a retention area makes it possible to slow the acceleration of the tool during its expulsion.

In a practical embodiment of the invention, the clamping bushing is displaceably guided on an ejection sleeve that is rigidly connected to the tow-bar. This ejection sleeve may be connected to the tow-bar by means of screws or other suitable means.

The clamping sleeve preferably can be displaced relative to the ejection sleeve between an annular shoulder on the ejection sleeve and a rear annular collar of a reducer mounted on the rear end of the ejection sleeve.

In one advantageous embodiment, the compression spring is braced between the front face of the clamping sleeve and a biasing nut on the front end of the ejection sleeve. The spring force consequently can be varied by adjusting the biasing nut, and the tool withdrawing force can be externally adapted to user requirements.

FIGS. 1–3respectively show longitudinal sections through a clamping device for clamping a hollow shaft tool1in the machine spindle2of a machine tool in a clamping position, a retention position and a tool-changing position. The hollow shaft tool1has a conical hollow shaft3that engages with a corresponding taper bore4on the front end of the hollow, cylindrical machine spindle2.

The clamping device comprises an ejection sleeve6that is arranged within the machine spindle2concentric to its central axis5, with a clamping sleeve7being guided on said ejection sleeve in an axially displaceable fashion. The ejection sleeve6is mounted on the front end of a tow-bar8that is biased rearward (toward the right inFIG. 1) by means of a not-shown spring arrangement and can be displaced opposite to the spring arrangement by means of a not-shown actuating device in the direction of the hollow shaft tool1. On its front end that faces the hollow shaft tool1, the tow-bar8is provided with threads9, onto which the ejection sleeve6is screwed. The ejection sleeve7[sic;6] is axially secured on the tow-bar8with an additional counter screw10. The clamping sleeve7is guided on the ejection sleeve6such that it can be axially displaced between a front annular shoulder11and a rear collar12of a reducer13that is mounted on the rear end of the ejection sleeve6. In the embodiment shown, the reducer13is screwed, for example, into the rear side of the ejection sleeve6with the aid of the corresponding threads. The compression spring14biases the clamping sleeve7rearward relative to the ejection sleeve6. The compression spring14is braced between the front face15of the clamping sleeve7and a biasing nut16that is screwed onto the external threads17on the radially widened front end of the ejection sleeve6. The bias can be varied by adjusting the biasing nut16. Axial bores18for a corresponding tool are arranged on the face of the ejection sleeve6in order to steady the ejection sleeve6during the adjustment of the biasing nut13.

The outside of the clamping sleeve6[sic;7] is adjoined by several pincer elements19that are equidistantly separated in the circumferential direction and extend parallel to the central axis5of the machine spindle2. The front ends of the pincer elements19that point toward the conical hollow shaft3have a radial thickening20with a first clamping face21that is respectively formed by a conical surface segment. In the clamping position shown inFIG. 1, this clamping face21adjoins a conical inner surface22inside the conical hollow shaft3. The conical inner surface22has an angle of inclination relative to the longitudinal axis of the conical hollow shaft3that corresponds to the relative angle of inclination of the first clamping face21of the pincer elements19. The rear ends of the pincer elements19also have a thickening23with a second clamping face24that is inclined opposite to the first clamping face21and serves to support the pincer elements19on a conical opposite surface26that is arranged within an annular groove25of the machine spindle2. The second clamping face24of the pincer elements19is also formed by a conical surface segment and has an angle of inclination that corresponds to the inclination of the opposite surface26.

On the outside of its front end that faces the conical hollow shaft3, the clamping sleeve7has first conical clamping surface areas27that are respectively adjoined by a corresponding inner surface28on the front end of the pincer elements19. Second conical clamping surface areas29are also provided on the outside of the rear end of the clamping sleeve7. The second conical clamping surface areas are respectively adjoined by a corresponding inner surface30on the rear end of the pincer elements19. The clamping surface areas27and29of the clamping sleeve7and the corresponding inner surfaces28and30of the pincer elements19are adapted to one another in such a way that an axial displacement of the clamping sleeve7causes the pincer elements19to be displaced radially outwardly or inwardly in a parallel position relative to the central axis5of the machine spindle2.

A spacer which is arranged within the machine spindle2adjacent to the rear ends of the pincer elements19and is not described in further detail, serves to separate the pincer elements19by a predetermined distance in the circumferential direction. On the end that faces the pincer elements19, the spacer comprises a radially outer holder31, which is realized in the form of a bushing and comprises several axially protruding extensions32with beveled faces33that are equidistantly separated in the circumferential direction. The holder31can be displaced on a bushing34and is mounted such that it is acted upon in the direction of the pincer elements19by a compression spring35. On its rear end, the bushing34has an annular shoulder36and adjoins an annular surface38inside the machine spindle2with its rear face37. A sleeve39is arranged within the bushing34concentric to its longitudinal axis and adjoins the annular shoulder36with its rear face. On its front end, this sleeve comprises several ring segments40with beveled contact surfaces41that are separated from one another in the circumferential direction and protrude between the extensions32of the holder31.

According toFIG. 2, the extensions32of the holder31engage in a groove42on the rear end of the pincer elements19and their beveled faces33adjoin a correspondingly beveled opposite surface43in the base of the groove42. The beveled contact surfaces41of the sleeve39adjoin a bevel44on the rear end of the pincer elements19. This bevel44is inclined opposite to the beveled opposite surface43.

The function of the above-described clamping device is discussed below:

In the clamping position shown inFIG. 1, the ejection sleeve6is pressed into the retracted position shown by the tow-bar8and a—not-shown—spring arrangement in the form of a disk spring assembly. In this position, the clamping sleeve7adjoins the front annular shoulder11of the ejection sleeve6, and the compression spring14is in the compressed state. The pincer elements19are pressed radially outward in this position by the clamping sleeve7such that the clamping faces21and24are respectively engaged with the conical inner surface22on the conical hollow shaft3and the opposite surface26in the machine spindle2. The hollow shaft tool1is thereby retained under tension in the machine spindle2.

In order to release the clamping device, the ejection sleeve6is displaced from the clamping position shown inFIG. 1in the direction of the hollow shaft tool1until it reaches the position shown inFIG. 2, with the aid of the tow-bar8that is actuated, e.g., by means of a hydraulic piston or another suitable actuating mechanism. The forward movement of the ejection sleeve6also causes the clamping sleeve7to be displaced in the direction of the hollow shaft tool1. During this process, the pincer elements adjoining the outside of the clamping sleeve7are moved radially inward. However, the clamping sleeve7that is displaceably guided on the ejection sleeve6does not participate in the entire axial movement of the ejection sleeve6because it is held in the retaining position shown inFIG. 2by the compression spring14. In this retaining position, the pincer elements19adjoining the outside of the clamping sleeve7are displaced radially inward to such a degree that only small areas of their clamping faces21are still engaged with the conical inner surface22and the inside of the conical hollow shaft3. In this position, the hollow shaft tool1is still retained within the machine spindle2although the ejection sleeve6and the tow-bar2as well as their actuating mechanism are already in the release position.

When the hollow shaft tool1is pulled out of the machine spindle2in this position, e.g., by an automatic tool changing apparatus, the pincer elements19are additionally displaced radially inward such that the clamping sleeve6[sic;7] is transferred from the retaining position shown inFIG. 2into a tool changing position that is shown inFIG. 3against the force of the compression spring14. In this position, the pincer elements19adjoining the outside of the clamping sleeve7are displaced radially inward to such an extent that the clamping faces21are disengaged from the conical inner surface22inside the conical hollow shaft3and the hollow shaft tool1can be easily withdrawn.

The actuating mechanism for releasing the clamping device consequently can already be activated before an automatic tool changing apparatus engages with the hollow shaft tool1. This makes it possible to reduce the tool change-over time.