| 摘要 |
PROBLEM TO BE SOLVED: To prevent the generation of excessive tension in a jib hoisting rope by simple structure. SOLUTION: A load detector is provided in a connection device connecting a boom 2 and a jib 3 to detect the connection force (tensile force S) between the boom 2 and jib 3. Since this tensile force S has a specified correlation with the tension T of a jib hoisting rope 13, when rope tension T increases, tensile force S also increases. Then, when tensile force S reaches a specified predetermined value S0 (corresponding to the allowable limit value T0 of rope tension T), a control signal 1 is output to the solenoid of a solenoid valve to stop the hoisting drive of a jib hoisting winch 12 and the lowering drive of a boom hoisting winch 4. Through these operations, the generation of excessive force in the jib hoisting rope 13 is prevented.
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