Actuator for covering canvas of top-bodies

An actuation system (10) for a covering tarpaulin of an open top-bodies (12) is described, comprising centerings (16) slidable with their own feet (17) on the top of the side panels (S) of the top-body to support and open out/pack the covering tarpaulin, and a ring of rope to move the centerings above the panel so as to open out/pack the covering tarpaulin. In order to correct the variations in tension of the rope there are means for modifying the path of the rope in response to a variation of the tension thereof, so as to compensate for the loosening or the tightening of the rope and to keep the tension at a desired value.