| 摘要 |
PROBLEM TO BE SOLVED: To house wiring in a lightweight large cross-sectional mast, and easily perform the wiring from an opening part of a mast side surface. SOLUTION: A mast 4 for connecting upper and lower carriages is composed of front columns 6 and 7, a rear column 8, a lattice material 16, and a plate material 18, and ducts 22 and 23 are arranged in a hollow part of the mast 4 to house the wiring 24 and 25 between the upper and lower carriages.
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