1. An actuator consisting of a first linear displacement device containing a first linear displacement screw, a first nut and a first primary propulsion device mounted with relative linear displacement between the first linear displacement screw and the first nut, and from a second linear displacement device containing a second screw linear displacement, the second nut and the second primary propulsion device, mounted with the possibility of relative linear displacement between the second linear displacement screw and the second nut, while the actuator is mounted with the possibility of extension with relative linear movement between the first linear displacement screw and the first nut or with relative movement between the second linear displacement screw and the second nut, and the first or second linear displacement device is installed with the possibility of continued movement when jamming one of the linear displacement devices, the first or second. ! 2. The mechanism according to claim 1, in which at least part of one of the linear displacement screws, first or second, is installed inside at least a part of the other linear displacement screw, first or second, when the actuator is in the retracted state . ! 3. The mechanism according to claim 1, in which the first linear displacement device is installed with the possibility of reverse movement. ! 4. The mechanism according to claim 3, in which the second linear displacement device is installed with the possibility of only direct movement or with the possibility of reverse movement with significantly lower mechanical efficiency compared to
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