| 摘要 |
PROBLEM TO BE SOLVED: To ensure that a GPS receiving device mounted at the boom end of a crane for detecting the hanging position of the crane end can receive satellite waves by always orienting in a certain vertical direction a satellite wave receiving antenna mounted at the boom end, even if the boom of the crane is raised and lowered. SOLUTION: An antenna 3 is vertically pivotably journaled to the end of the boom 1 and a weight 5 is connected to the antenna 3 so that the antenna points in the vertical direction.
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