The actuator has a rope drum (1) comprising a drive axle (2) and rotatably mounted in a sleeve (3). The rope drum comprises a drum cladding with a groove (5) for retaining of a rope. The groove runs over a circumference of the rope drum in a helical manner. The sleeve is dimensioned such that the sleeve prevents sliding of the rope from the groove. A slot (4) exhibits a slit width for feedthrough of the rope, where the slit width is smaller than 1/8 of a circumference of the rope drum. The slot is extended parallel to the drive axle.