| 摘要 |
A window blind includes a housing, slats, and a bottom rail. A shaft is journalled in the housing. A pair of pull ropes extends through the housing and the slats, and connects the shaft to the bottom rail. A drive cord is coupled to the shaft. An operating device includes a pulling unit, a braking unit, and a positioning unit. The pulling unit permits extension of the drive cord therethrough, has the drive cord secured thereto, and is operable so as to rotate the shaft for raising the bottom rail. The braking unit provides a braking force that is transmitted to the shaft so as to retain the bottom rail at a desired vertical distance relative to the housing. The positioning unit permits extension of the drive cord therethrough and is operable so as to release the braking force for lowering the bottom rail.
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