| 摘要 |
A boom mechanism that is cooperable with a lift vehicle or base structure (108) includes a tower boom (12) and an upper boom (20) liftable in a dependent relationship by a single lifting mechanism (28). The tower boom an d the upper boom are respectively pivotally secured to an upright (16) having a fixed orientation by a tower link (34) or the like. A timing link (26) is secured between the tower boom and the upper boom, and a lifting mechanism i s secured between the upright and the upper boom. As the upper boom is driven by the lifting mechanism, the timing link secured to the tower boom causes the tower boom to pivot about a tower boom nose pivot (18), thereby raising both the upper boom and the tower boom in a dependent relationship. The construction helps to minimize the need for tail and frame counterweight (11 2) by controlling a position of the platform (24) in configurations of both forward and rearward instability. As a consequence, the gross vehicle weight can be considerably reduced.
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