| 摘要 |
PROBLEM TO BE SOLVED: To provide an elevating device for a shield member, which can reduce an elevation load which is exerted on an elevation cord when the shield member descents, and which is small-sized and inexpensive. SOLUTION: An elevation cord 7 suspended from a wind-up pulley 3 is connected at its lower end to the lower end of a shield member 6 which is suspended from a head box 1 so as to reduce the suspended weight of the shield member 5 as the latter descends, and the elevation cord 7 can be wound up by the wind-up pulley 3 by an elevating load obtained by a spring, overcoming the suspended weight. In this arrangement, the spring is an urging spring which can be accumulated with a force when the shield member 5 ascends. Further, load converting devices 9, 14, 15 which allow a gradient of variation in the suspended load to approximate to a gradient of variation in the elevation load caused by the descent of the shield member 5 are interposed between the urging spring 16 and the elevation cord 7.
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