embodiment of the present invention in which the reference numbers of the parts similar to those of fig7 are increased by 100 this device differs from the previous one essentially in that a differential connection is provided between the shaft 207a and the flange 207 and because the limit switch is replaced with detectors that by way of example are positioned along the path of the rolling shutter the differential connection between the shaft 207a and the flange 207 is established by means of a toothed wheel 237 mounted at the opposite extremity of the shaft 207a that is provided with the toothed wheel 219 the toothed wheel 232a engages with a pinion 238 that meshes with inside teeth 232a of the stationary part 232 the axis of rotation 239 of the pinion 238 rests upon the flange 207 in such a manner that the toothed wheel 237 may cause the flange 207 to rotate by using the pinion 238 as a planet gear it is understood that several pinions 238 may be distributed along the periphery of the toothed wheel 237 the mechanism operates as follows while the toothed wheel 219 is immobilized by the endless screw 221 the toothed wheel 237 blocks the rotation of the flange 207 should the connection between the endless screw 221 and the toothed wheel 219 be disengaged the toothed wheel 237 may be turned by the pinion 238 and it no longer prevents the movement of the flange 207 the differential connection established between the toothed wheel 219 and the flange 207 allows the use of the ratio of the number of teeth of the elements 237 238 and 232a in order to constitute.