| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a boom expanding/contracting structure with which expansion is made by using one cylinder in such a boom segment sequence as one after another first from the foremost electrically insulated boom. SOLUTION: One end of a wire for elongation 31 is coupled with the base end of the first boom 11, and this is set on a fourth sheave 21b and stretched, while the other end is coupled with the base end of the third boom 13. One end of a wire for shrinkage 32 is coupled with the tip of the first boom 11, and this is set over around the first, second, third sheaves 12a, 12b, 21a and stretched, while the other end is coupled with the base end of the third boom. Disengagement of the second locking device 42 is made in the condition that the second boom 12 is fixed in the accommodating position by the first locking device 41, and the third boom is expanded or contracted till the full elongation relative to the second boom, followed by disengagement of the first locking device 41 in the condition that the third boom 13 is secured to the position with full elongation relative to the second boom 12 by the second locking device 42, and the second boom 12 is elongated.</p> |
