| 摘要 |
The specification discloses a crane including a base having a boom pivotally supported at one end from the base. The opposite end of the boom is adapted for receiving the load to be carried by the crane. A mast and upper tension member system are affixed to the top surface of the boom, supporting the load receiving end of the boom so that the boom structure is relieved of bending moments. Hydraulic cylinders are connected between the base and the boom for elevating and lowering the boom. In one embodiment the upper tension member system includes a spring and dampener which serves to cushion dynamic overloads during operation of the crane. In another embodiment a counterweight is hingedly attached to the end of the boom supported from the base. The weight of the counterweight is borne by a cable which joins into the upper tension member system. In yet another embodiment the tension member system supporting the load receiving end of the boom includes diagonally arrayed cables which serve to counteract loads imposed on the boom by operation in out of level conditions such as attendant to rough terrain or marine applications. When the counterweight is aligned with the boom, it may be selectively moved from an extended to a retracted position along a path substantially parallel to the longitudinal axis of the boom. The crane is adapted with structure for maintaining the hingeable counterweight horizontal as the boom is rotated on the base.
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