Positioning device of the thread skein-end of the thread for service trolleys for open-end spinning machines

A device (71) for the control and positioning of the thread (F) for automatic service trolleys for spinning units of open-end spinning machines to effect intervention cycles for start-up, re-attachment of the thread, depositing of the final thread reserve and removal of the bobbins onto the single spinning units, said trolley carrying on board organs or groups of organs destined for single or multiple operations of said cycles, said device (71) comprising a worm screw, with a horizontal axis and parallel to the front of the spinning machine, equipped with a cantilever supporting arm which allows it to be lowered and lifted maintaining the worm screw horizontal and parallel to the front of the spinning machine and in certain positions, and activated in controlled clockwise/anticlockwise rotation driven by a motor, thus determining both the level and the axial coordinate to which the thread is brought, the thread itself being engaged inside the cavity of the threading of the worm screw, which by rotating determines its axial coordinate, characterized in that the device (71) is equipped with an axial movement organ (72) of the whole device (71) so that its worm screw (32) can be axially and alternatingly moved into a withdrawn position so that the beginning of the worm screw on the internal side of the arm (33) coincides with the axial coordinate corresponding to the base of the bobbin (25), or into an extended position so that the free threaded end of the worm screw (32) coincides with the axial coordinate of the winding end of the bobbin (25) on the tip of the tube (28);

• and in that on the free end of the worm screw (32) there is a cylindrical cavity (73) coaxial with the screw in which an extractable and withdrawable cylindrical plug (74) is housed.