the endoscopic instrument which is represented in the drawings comprises a housing 2 , at the distal side of which a tubular hollow shank 4 is arranged . the hollow shank 4 is designed in a straight and rigid , longitudinally extended manner and at the proximal side is connected to an inner housing 6 which is arranged in the longitudinal extension of the hollow shaft 4 and is arranged in the housing 2 . a receiver 8 for a tool 10 is arranged at the distal end of the hollow shank 4 . the tool 10 comprises a shank 12 , at whose distal end a spherical machining head 14 is arranged for removing material . the tool 10 by way of the shank 12 is rotatably mounted in the receiver 8 about a rotation axis which is formed by the shank 12 . the receiver 8 is fastened on the hollow shank 4 by way of bearing pins 16 , wherein the bearing pins 16 form an axis , about which the receiver 8 with the tool 10 mounted therein can be bent from an initial position , in which the receiver 8 with the tool is arranged in the direct longitudinal extension of the hollow shank 4 , into a direction transverse to the longitudinal extension of the hollow shank 4 . the receiver 8 is coupled in movement to a push - pull element guided through the hollow shank 4 to the housing 2 , for the control of the bending of the receiver 8 with the tool 10 which is mounted therein . this push - pull element and also the other components for the control of the bending of the receiver 8 are generally known from the state of the art , for example from de 42 41 767 c1 and corresponding u . s . patent , u . s . pat . no . 4 , 475 , 485 a , the entire contents of which are incorporated herein by reference , and are not represented in the drawings for the purpose of a better overview . a window 18 is formed on the distal end of the hollow shank 4 , on a peripheral region of the hollow shank 4 which is directed in the direction of the bending of the receiver 8 . a channel 20 , into which an endoscope is introduced , extends through the hollow shank 4 and the inner housing 6 , departing from this window 18 , wherein the eyepiece 24 of the endoscope projects out of the instrument at the proximal end of this . the shank 12 of the tool is actively connected to a motor shaft 28 of a motor 30 via a belt drive 26 , for producing the rotation movement of the tool 10 . with regard to the motor 30 it is the case of an electric motor . the belt drive 26 corresponds essentially to a belt drive which is known from de 42 41 767 c1 and corresponding u . s . patent , u . s . pat . no . 4 , 475 , 485 a , with an endless belt 32 which wraps a belt disc which is arranged at the distal end of the hollow shank 4 and which is not represented in the drawings for the purpose of a better overview , and a belt pulley 34 which is arranged in the inner housing 6 arranged at the proximal side of the hollow shank 4 . the belt pulley 34 is connected in a rotationally fixed manner to a drive shaft 36 mounted in a rotatable manner about its middle axis in the inner housing 6 . the drive shaft 36 is aligned normally to the longitudinal extension of the hollow shank 4 , wherein the end of the drive shaft 36 which is away from the belt pulley 34 projects out of the inner housing 6 . the drive shaft 36 at this end is releasably connected to the motor shaft 28 of the motor 30 via a coupling 38 . the motor 30 is arranged in a housing attachment 40 extending transversely to the longitudinal extension of the housing 2 . the coupling 38 which is designed as a jaw coupling comprises a first coupling half 42 which is connected in a rotationally fixed manner to the drive shaft 36 , and a second coupling half 44 which is connected in a rotationally fixed manner to the motor shaft 28 . as is particularly evident from fig7 - 11 , the coupling halves 42 and 44 in each case comprise a circular - disc - like main body 46 , from which three projections or jaws 48 extend in the direction of the respective other of the coupling halves 42 and 44 . the three jaws 48 of each of the two coupling halves 42 and 44 are arranged adjacent to the outer periphery of the main body 46 and are uniformly distributed over the periphery of the main body 46 , wherein intermediate spaces 50 which are thus formed between adjacent jaws 48 serve for receiving the jaws 48 of the respective other coupling half 42 and 44 respectively , in the coupled condition of the coupling 38 , and in this manner create a positive connection between the coupling halves 42 and 44 . for this purpose , the dimensions of the intermediate spaces 50 with respect to the outer periphery of the main body 46 correspond to the respective dimensions of the jaws 48 . a cylindrical recess which departing from a face side 52 of the jaws 48 which is away from the main body 46 extends parallel to the longitudinal extension of the motor shaft 28 and the drive shaft 36 respectively , in the direction of the main body 46 , is formed on each of the jaws 48 of the two coupling halves 42 and 44 . a permanent magnet 54 is arranged in each of these recesses in each case , wherein a face side of the permanent magnets 54 which is away from the main body 46 is essentially aligned to the face side 52 of the jaw 48 . with regard to the permanent magnets 54 , it is the case of rod magnets . these are inserted in each case into the recesses formed on the jaws 48 of the two coupling halves 42 and 44 , such that the end of the permanent magnets 54 which is aligned to the face side 52 of the jaw 48 contains the north pole of the permanent magnets 54 , whereas the other end of the permanent magnets 54 which is adjacent the base of the recess forms their south pole . however , here it is to be noted once again that the permanent magnets 54 could also be inserted into the recesses of the jaws 48 of the two coupling halves 42 and 44 in the reverse manner , so that the end of the permanent magnets 54 which is aligned to the face side 52 of the jaws 48 in each case contains their south pole . what is decisive however , is merely the fact that all permanent magnets 54 of both coupling halves 42 and 44 are arranged such that in each case the same pole points in the direction of the respective other coupling half 42 and 44 respectively . the significance of the permanent magnets 54 which are inserted in the jaws 48 of the coupling halves 42 and 44 and of their alignment is evident from fig7 - 11 . the coupling half 44 which is arranged on the motor shaft 28 , when attaching the motor 30 on the endoscope is connected to the coupling half 42 arranged on the drive shaft of the belt pulley 34 by way of an insert ( plug - in ) connection . hereby , as is represented in fig7 and 10 , it can be the case that the angular position of the coupling halves is not such that the jaws 48 of the coupling half 44 can engage into the intermediate spaces 50 between the jaws 48 of the coupling half 42 , since the jaws 48 of the coupling half 44 completely or partly overlap the jaws 48 of the coupling half 42 . in this case , magnetic repulsion forces which also include a force component in the rotation direction of the coupling halves 42 and 44 transverse to the approach direction of the coupling halves 42 and 44 , arise between the permanent magnets 54 of the coupling halves 42 and 44 which are arranged in the jaws 48 , when the coupling half 44 approaches the coupling half 42 . the coupling halves 42 and 44 are rotated relative to one another by way of these force components , in a manner such that the jaws 48 of the coupling half 44 lie opposite the intermediate spaces 50 of the coupling half 42 , as is represented in fig8 and 11 . then , as is evident from fig9 , the jaws 48 of the coupling half 44 engage into the intermediate spaces 50 of the coupling half 42 due to the further approach of the coupling half 44 onto the coupling half 42 , by which means the coupling halves 42 and 44 are connected to one another with a positive fit . while specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention , it will be understood that the invention may be embodied otherwise without departing from such principles .
a releasable coupling for the transmission of a rotation movement . this coupling includes a first and a second coupling half which include engagement structures which correspond to one another and which can positively engage with one another . at least one permanent magnet is arranged on at least one coupling half in a manner such that with the approach of the coupling halves to one another , these with respect to a rotation axis are rotated into a defined angular position relative to one another , by way of the magnetic force which is produced by the permanent magnet .