| 摘要 |
The danger of a jib falling off a boom due to an erroneous operation during movement of the jib between a stowage position and an extended position is eliminated. The jib is provided with a pivot pin insertion state detector, pivot pin retraction blocking element, a coupling pin insertion state detector, first and second cables, wherein movement of a coupling pin to a retracted position is restricted by a coupling pin retraction blocking element via the first cable when the pivot pin insertion state detector has detected that the pivot pin is retracted, and movement of the pivot pin to the retracted is restricted by the pivot pin retraction blocking element via the second cable when the coupling pin insertion state detector has detected that the coupling pin is retracted, so that simultaneous removal of both of the pivot pin and the coupling pin is prevented. |
