| 摘要 |
PROBLEM TO BE SOLVED: To provide an elastic member formed so as to maximize restoration force in the beginning time when it is pulled out and to minimize the restoration force when it is completely pulled out. SOLUTION: The elastic member 1 wound around a pivoted rotatable free shaft is set on a frame body of a head box 9 of a blind mounted on a window frame, at the same time, a take-up shaft for taking up the elastic member 1 is provided, the depth/thickness/area of the elastic member are reduced with the approaches of them to the center shaft, the restoration force rewinding the elastic member is gradually changed, a rising and falling string 6 of the blind 7 is wound around the take-up shaft and a pulley 5 provided thereto, and when the blind 7 is located on an open position (the highest position), the elasticity of the elastic member l (restoration force) becomes the highest strength, the elasticity (restoration force) becomes the weakest strength when the blind 7 is located on the lowest position in a shielding state, the rising and falling string 6 wound around the pulley 5 is taken up or rewound to raise and lower the blind, and a blind rising and falling device is so constituted that it has a strong tendency to return by the restoration force of the elastic member at a predetermined position of the blind to become a rising tendency and that the restoration force of the elastic member 1 is weak from the predetermined position of the blind to become a falling tendency by self-weight of the blind.
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