The invention relates to a lift-driving apparatus for grab screens, having two outer lifting-rope drums (17, 18) and a central controlling-rope drum (19) which is arranged coaxially with the latter and can be driven either synchronously with the lifting-rope drums or can be rotated in both directions of rotation relative to the lifting-rope drums, as desired. To obtain a very simply constructed and reliable apparatus which permits relative rotation of the controlling-rope drum (19) even during the rotary drive of the lifting-rope drums (17, 18), two separate drives (42, 45), on the one hand for the lifting-rope drums and on the other hand for the controlling-rope drum, are provided. Of these, the control drive (45) is fixed rigidly to one of the lifting-rope drums (18) and is thus rotatable therewith, said drive being designed so as to be self-locking when inoperative and being non-positively drive-connected to the controlling-rope drum (19) via a backgear (50 to 53). IMAGE
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