Patent ID: 6752194
Filing Date: 2004-06-22
Classification: E06B

Abstract:
A window blind comprising:an elongated top housing; first and second horizontal shafts journalled within said top housing; a plurality of horizontal slats suspended one above another from said top housing; a bottom rail disposed below said slats; a pair of pull ropes extending through said top housing and said slats, each of said pull ropes having an upper end connected to said first horizontal shaft and a lower end connected to said bottom rail; a pair of ladder cords connected to said slats, each of said ladder cords having an upper end connected to said second horizontal shaft and a lower end connected to said bottom rail; and an operating device including a hollow frame mounted on said top housing and having an inner wall surface, a drive bobbin disposed rotatably in said frame and coaxial with said first horizontal shaft, a drive cord having an upper end that is connected to said drive bobbin, and a lower end that extends out of said frame and through said top housing, a spiral spring wound on said drive bobbin, and having opposite ends connected to said drive bobbin and said frame, respectively, said spiral spring providing a biasing force for biasing said drive bobbin to rotate in a first direction for winding said drive cord on said drive bobbin, a clutch unit including a driven hub disposed rotatably in said frame and sleeved securely on said first horizontal shaft, and a coupling spring unit sleeved fittingly on said drive bobbin and said driven hub, said coupling spring unit being in friction engagement with said inner wall surface of said frame, a braking unit disposed in said frame, and including a braking member and a releasing cord, said braking member providing a braking force that acts on said driven hub when said driven hub tends to rotate in the first direction due to the weight of said bottom rail transmitted to said first horizontal shaft through said pull ropes, said releasing cord having an upper end that is connected to said braking member, and a lower end that extends out of said frame and through said top housing, said releasing cord being operable so as to enable said braking member to release said driven hub from the braking force, a rotary tilt control unit including a tubular connector coupled to said second horizontal shaft, said tubular connector being axially rotatable relative to said frame such that axial rotation of said tubular connector results in corresponding axial rotation of said second horizontal shaft to adjust tilting angles of said slats, said tubular connector extending out of said top housing, and permitting extension of said lower ends of said drive and releasing cords therethrough, a positioning unit coupled to said tilt control unit, said positioning unit permitting extension of said lower ends of said drive and releasing cords therethrough, and being connected to said lower end of said releasing cord, and a pulling unit permitting extension of said lower end of said drive cord thereinto, said pulling unit being connected to said lower end of said drive cord; wherein rotation of said drive bobbin in a second direction opposite to the first direction due to pulling action applied on said pulling unit enables said coupling spring unit to contract in radial inward directions in order to transmit rotation of said drive bobbin to said driven hub against biasing action of said spiral spring so that said driven hub rotates with said drive bobbin in the second direction, thereby resulting in corresponding rotation of said first horizontal shaft in the second direction for winding said pull ropes thereon and for raising said bottom rail toward said top housing; wherein rotation of said drive bobbin in the first direction due to restoring action of said spiral spring when said pulling unit is released from the pulling action enables said coupling spring unit to expand in radial outward directions so that said driven hub does not rotate with said drive bobbin; and wherein the braking force provided by said braking member is released upon operating said releasing cord so as to lower said bottom rail, and is sufficient so as to support the weight of said bottom rail and the weight of said slats that acts on said bottom rail in order to retain said bottom rail at a desired vertical distance relative to said top housing.