System for extending or retracting two members and cam-locking the members in the extended position

System for unfolding or folding up a first and a second element into an unfolded or a folded position, wherein said first and second elements are linked in rotation one with respect to the other about an axis of articulation and wherein said system is for locking or unlocking said first and second elements at least in the unfolded position, said system including:

• a cam (4), rotatably connected to the first element (2) and having a contact surface (4A) in the shape of logarithmic spiral having an origin;
• a flat bearing face (8) provided on the second element (3) and against which said contact surface (4A) of the cam can press;
• a shaft (5), rotatably connecting said cam to said first element on which the cam can turn about a first axis (10) containing the origin of the spiral, and wherein said shaft is mounted so that it can also rotate with respect to said first element about a second axis (11) which is offset parallel to said first axis (10) of rotation of the cam;
• elastic means (6) tending to make said cam turn in a first direction such that said contact surface (4A) of the cam moves towards said beating face;
• a finger (7), integral in terms of rotation with said shaft and capable of driving said cam in a second direction, opposite the first direction;
• and
• drive means (9) for driving the said shaft in rotation, wherein said drive means (9) are motorized and also drive said rotation of the first and second elements one with respect to the other about said axis of articulation, and wherein said drive means comprise:
• a motor (9A), having an axis of rotation (17) which is parallel to the first and second axes of rotation (10, 11) of the cam, said axis of rotation (17) corresponding to said axis of articulation;
• a transmission (18) linking said motor to said shaft;
• and
• a radial link (19), integral in terms of rotation with said motor and able to drive said second element in rotation about said axis of articulation.