| 摘要 |
PROBLEM TO BE SOLVED: To expand a working area of a boom device having a working bench arranged in the tip part of a freely derricking boom via a derricking arm freely turning horizontally. SOLUTION: A vertical post 6 always maintaining a vertical position is arranged at the tip of the freely derricking boom 4, and the working bench is installed to the vertical post 6 via the arm 8, which can be freely turned horizontally or risen, and a working bench post 9. By means of a control unit controlling operation of the boom device, a relative position between the boom 4 and the working bench 10 is calculated from a turning angle of the arm 8 to the boom 4, a boom hoisting angleθ1, and an arm derricking angleθ2. An interference preventing device is constructed so that the boom 4 derricking operation and the arm 8 derricking operation allowing the working bench 10 to enter a predetermined interference restriction area A are restricted when the working bench 10 is positioned above the boom 4.
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