Actuation mechanism comprising a main rotational driving means and a roller screw mechanism coupled to said driving means , the roller screw mechanism comprising: - a screw comprising an external thread , - a nut arranged around and coaxially with said screw , the nut comprising an internal thread , - a plurality of rollers that are interposed between the screw and the nut and each comprise an external thread in engagement with the external thread and internal thread respectively of said screw and of said nut , one among the screw and the nut being coupled to the main rotational driving means , the other being able to move in translation and in rotation with respect to the rollers , and - an annular guide for circumferentially and axially holding the rollers , said guide being mounted radially between the screw and the nut , and comprising a first annular lug and a second annular lug , wherein the annular guide comprises a cylindrical sleeve extending axially from one of the annular lugs out beyond the nut , the screw extending in a bore of said sleeve , said sleeve being coupled to a secondary rotational driving means , characterized in that the annular guide further comprises a plurality of elongate portions that axially connect the first and second lugs so as to define a plurality of recesses that are separated from one another in the circumferential direction by said elongate portions , each one of said recesses receiving a roller , and in that the main rotational driving means comprises a first motor, and wherein the secondary rotational driving means comprises a second motor that is distinct from the first motor. - a screw comprising an external thread , - a nut arranged around and coaxially with said screw , the nut comprising an internal thread , - a plurality of rollers that are interposed between the screw and the nut and each comprise an external thread in engagement with the external thread and internal thread respectively of said screw and of said nut , one among the screw and the nut being coupled to the main rotational driving means , the other being able to move in translation and in rotation with respect to the rollers , and - an annular guide for circumferentially and axially holding the rollers , said guide being mounted radially between the screw and the nut , and comprising a first annular lug and a second annular lug , wherein the annular guide comprises a cylindrical sleeve extending axially from one of the annular lugs out beyond the nut , the screw extending in a bore of said sleeve , said sleeve being coupled to a secondary rotational driving means , characterized in that the annular guide further comprises a plurality of elongate portions that axially connect the first and second lugs so as to define a plurality of recesses that are separated from one another in the circumferential direction by said elongate portions , each one of said recesses receiving a roller , and in that the main rotational driving means comprises a first motor, and wherein the secondary rotational driving means comprises a second motor that is distinct from the first motor. wherein the annular guide comprises a cylindrical sleeve extending axially from one of the annular lugs out beyond the nut , the screw extending in a bore of said sleeve , said sleeve being coupled to a secondary rotational driving means , characterized in that the annular guide further comprises a plurality of elongate portions that axially connect the first and second lugs so as to define a plurality of recesses that are separated from one another in the circumferential direction by said elongate portions , each one of said recesses receiving a roller , and in that the main rotational driving means comprises a first motor, and wherein the secondary rotational driving means comprises a second motor that is distinct from the first motor. <EOS>