1. Field of the Invention
The invention relates to a motor element, in particular to a dental medical handpiece.
2. Description of the Related Technology
A handpiece of this kind is described in DE 44 06 855 A1. In the case of this previously known handpiece, a tool-holder that is formed as a collet chuck is pushed into a drive shaft that is formed so that it is hollowly cylindrical at least on the front side, with a coupling for the axial connection of the tool-holder to the drive shaft being formed by a screw coupling. Consequently, the tool-holder is connected to the drive shaft by screwing in and can be disconnected again by unscrewing, in order to clean it for example. This outlay on assembly and disassembly is comparatively great. Moreover, it is mechanically difficult to fix the tool-holder in the screwed-in state in order to avoid unintentional untwisting. It is to be taken into consideration in this connection that during the functional operation of the handpiece when switching the drive shaft on and off torques result that can loosen a screw securing arrangement based on screw-fastening so that the function of the collet chuck can be impeded and impaired without this defect being directly noticeable. A further disadvantage lies in the fact that screw-fastening is comparatively difficult, because the collet chuck is arranged so that it is largely sunk in the drive shaft and it is difficult therefore to reduce a torque for screw-fastening at the front end of the collet chuck.
The underlying object of the invention is therefore to improve the coupling of the tool-holder or the locking and/or unlocking of the coupling in the case of a handpiece in accordance with the invention.