| 摘要 |
A crane structure is mounted on a platform and has a tower assembly with spaced apart columns spanned at their upper extremities by an upper structure. A gantry includes a central section, fixedly secured on the upper structure, and first and second outer gantry sections. The outer sections are pivotally connected to the central section, and are movable between horizontal operating positions and generally vertical transport positions. The gantry sections have at least two vertically spaced series of tracks thereon. In the upper tracks a counterweight is mounted on casters or rollers, and a lift trolley is similarly disposed on the lower tracks. A sheave and winch assembly interconnects the counterweight and the lift trolley through a cable arrangement, whereby corresponding movements of the counterweight and the lift trolley are effected through operation of the winch. The lift trolley is adapted to travel substantially the full lengths of the gantry sections when the sections are in operating positions. An operator's cab is mounted on an arm pivotally secured to one of the columns.
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