| 摘要 |
A pleated fabric is connected between an upper fixed sill and a movable sill. The movable sill is between the upper fixed sill and a lower fixed sill. Two string loops are resiliently secured to the sills and slidably frictionally engaged with the movable sill symmetrical relative to the sills and to a central axis parallel to the direction of movement of the movable sill. The tension in the strings is adjustably set by a single tension spring and a turnbuckle connected between and to the loops. The friction engagement of the strings to the movable sill is set to a friction load having a value which provides smooth operation and tends to keep the movable sill in place at whatever location the sill is moved to regardless the blind orientation relative to gravity.
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