Patent ID: 7451799

Claim:
Improved self-locking device for blinds ( 21 ) and shutters of the type that include: a drive shaft ( 1 ) operateable in both rotational directions, a rolling drum ( 23 ) for a blind ( 21 ) rotating together with the drive shaft ( 1 ), a first freewheel mechanism ( 2 ) in which the drive shaft ( 1 ) revolves and whose outer bush ( 3 ) is joined to a drive cylinder ( 4 ) which has a freeing sector ( 5 ), a second freewheel mechanism ( 15 ) in which a locking shaft ( 16 ) revolves and whose outer bush ( 3 ) is joined to a transmission pinion ( 14 ), a cogged wheel ( 17 ) joined to the locking shaft ( 16 ) that has a number of protuberances ( 18 ) on its periphery, suitably spaced so that extensions ( 19 ) to slats ( 20 ) on the blind ( 21 ) fit into them, a transmission crown ( 6 ) rotating freely on the drive shaft ( 1 ) with a locking sector ( 26 ) on one of its faces and with a housing to receive the freeing sector ( 5 ) on the drive cylinder ( 4 ) with a certain clearance, a braking mechanism consisting of a brake spring ( 9 ) formed by various turns of elastic wire distributed axially on the same diameter with its ends bent radially to form stops ( 10 ), the brake spring ( 9 ) being firmly housed inside a brake cylinder ( 7 ) joined to a casing ( 11 ) of the device, the locking sector ( 26 ) acting on the stops ( 10 ) in a first direction and the freeing sector acting on the stops ( 10 ) in a second direction, said second direction being opposite of the first direction, to increase the apparent diameter of the brake spring ( 9 ), and the locking sector ( 26 ) acting on the stops ( 10 ) in the second direction and the freeing sector acting on the stops in the first direction to decrease the apparent diameter of the brake spring, a transmission mechanism that joins the transmission crown ( 6 ) to the transmission pinion ( 14 ), characterised in that it comprises: a number of teeth ( 27 ) on the periphery of the brake cylinder ( 7 ), multiple articulated ratchets ( 28 ) on the transmission crown ( 6 ) each equipped with a respective guide ( 29 ) which pass through a respective opening ( 30 ) in the transmission crown ( 6 ) itself, with a respective end ( 31 ) of each ratchet ( 28 ) being able to be housed in the teeth ( 27 ) on the brake cylinder ( 7 ), wings ( 32 ) on the drive cylinder ( 4 ) with a respective hole ( 33 ) to receive and guide the respective guide ( 29 ) on the respective ratchet ( 28 ), a slot ( 34 ) in the freeing sector ( 5 ) on the drive cylinder ( 4 ) which closely grips one of the stops ( 10 ) on the brake spring ( 9 ).