| 摘要 |
PROBLEM TO BE SOLVED: To increase reliability of control by increasing detection accuracy while maintaining non-contact characteristics, and achieving reduction of cost and ease of assembly by reducing the number of components.SOLUTION: One elongating and contracting cylinder 11 is arranged in an elongating and contracting boom that can elongate and contract in a plurality of steps, and by repeating the elongating and contracting operations, the elongating and contracting boom is caused to elongate and contract by one step. A boom elongating and contracting mechanism includes: cylinder position detection means 20 for detecting that a cylinder position which is a position of a specific place of the elongating and contracting cylinder is positioned opposed to a target stop position of the elongating and contracting boom inner face when the elongating and contracting cylinder performs an elongating and contracting operation; and control means 30 for controlling the operation of the elongating and contracting cylinder in response to the detection signal. The cylinder position detection means includes: a magnetic sensor 21 provided at the cylinder position; a permanent magnet 23 provided at the target stop position; and a plurality of magnetic materials 24 arranged along the direction of the elongating and contracting operation of the elongating and contracting cylinder so as to set a desired magnetic field limit area within the range where a magnetic field of the permanent magnet extends. |
