Door shutter mechanism

Two nut stacking mechanism, each comprising:

• a rotatable screw with external thread of length L and pitch P1;
• at least one traveling nut mounted on said screw, said traveling nut having internal thread of pitch P1 and external thread of pitch P2 and coaxial with said internal thread, P1>P2;
• an arrester adapted to engage said traveling nut so as to prevent rotation thereof within an axial length L1 of said screw, while allowing said traveling nut to slide along said screw;
• a threaded member with internal thread of pitch P2 adapted to engage the external thread of said traveling nut within an axial length L2 of said screw, said length L2 being adjacent to said length L1, so that, by means of continuous rotation of said screw in one direction, said traveling nut can slide along said screw within said length L1 at rate P1 per 1 turn of the screw under the action of said arrester and said thread with pitch P1, can transit smoothly and reversibly from L1 to L2, and can slide with rotation along said screw within said length L2 at a rate P2 per 1 turn of the traveling nut under the action of said thread with pitch P1 and said thread with pitch P2;
• said two nut stacking mechanisms, are disposed parallel to each other at two opposite sides of said access aperture with their threaded members at a third side of said access aperture, referred as “stacking side”, with their nuts in symmetric disposition, and their screws adapted for synchronous rotation,
• a plurality of N shutter members extending between said stacking mechanisms perpendicularly to the screws thereof, each connected to a pair of said connection elements,
• said shutter members being distributed over said access aperture in the first position of the stacking mechanisms, whereby said access aperture is closed, and
• said shutter members being stacked at said stacking side in the second position of the stacking mechanisms, whereby said access aperture is opened.