| 摘要 |
A retractable covering for an architectural opening is reversibly driven through an input assembly, a transmission and an output assembly by a reciprocal operating cord that can be pulled down by an operator and will automatically retract while the covering is held in a predetermined position. While the input assembly is always driven in a first direction, a transmission is shifted between two operative positions through movement of a shift arm depending upon the positioning of the shift arm by the operating cord. The shift arm is pivotal about an axis parallel with a roller for the covering and when the operating cord is pulled straight downwardly, the covering is moved in an upwardly or retracting direction while if the operating cord is pulled downwardly and toward the operator, i.e. away from the architectural opening, the covering is driven in a downwardly or extending direction.
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