A stacking mechanism for shutter members of a shutter mechanism, comprising: a rotatable screw with external thread of length L and pitch P1; a plurality of N traveling nuts mounted on the screw, having internal thread of pitch P1 and external thread of pitch P2,P1>P2; an arrester preventing rotation...http://www.google.com/patents/US7370684?utm_source=gb-gplus-sharePatent US7370684 - Door shutter mechanism
