Patent ID: 7281563

Claim:
A venetian blind comprising: a headrail; a bottom rail; a covering unit disposed between said headrail and said bottom rail and including a plurality of slats, and at least two lifting cords each extending through said slats, each of said lifting cords having a lower end fastened to said bottom rail, and an upper end; and a cord-winding device including a casing fixed on said headrail, a plurality of annular spring-surrounding members disposed rotatably within said casing, said upper ends of said lifting cords being fastened respectively to two of said spring-surrounding members, each of said lifting cords having a portion wound on a corresponding one of said spring-surrounding members, a plurality of co-rotatable gears sleeved respectively and fixedly on said spring-surrounding members, each of said gears meshing with at least one of the rest of said gears so as to allow for synchronous rotation of said gears, and at least one spiral spring disposed within one of said spring-surrounding members and having two ends fastened respectively to said casing and said one of said spring-surrounding members, said spiral spring imparting a spring force to substantially balance the total weight of said bottom rail and said covering unit so as to maintain said bottom rail at any position with respect to said headrail, wherein said cord-winding device further includes a plurality of guiding roller units, each of which includes at least one guiding roller, said guiding roller being disposed rotatably on said casing, said lifting cords extending respectively around two corresponding ones of said guiding rollers, and wherein said guiding roller of each of said guiding roller units has an annular outer surface that is formed with a helical groove, within which a corresponding one of said lifting cords extends.