| 摘要 |
PROBLEM TO BE SOLVED: To surely execute an inspection work without requiring a troublesome procedure by detecting that one of boom state detecting elements reaches at least two preset states by another boom detecting means, and automatically judging that the boom detecting means is abnormal when the detection value is out of a prescribed range. SOLUTION: A slewing base has a limit switch (another boom state detecting means) in a first derricking angle position. When an expansion boom is moved toward the preliminarily determined first derricking angle position during a work, the dog of the boom is engaged with the limit switch, and a control device 12 judges whether the detection value of a derricking angle detecting device 10 is within a prescribed range or not. When it is out of the range, the abnormality of the derricking angle detecting device 10 is alarmed by a buzzer or the like. A limit switch is also provided in a second derricking angle position. When the same boom operation is performed, a control device 12 functions in the same manner. Further, the slewing angle detection and length detection of the boom are also performed in the same structure.
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