| 摘要 |
The arm (2) of the crane (1) or derrick can pivot about the vertical axis of the support pillar (3). The arm has a hollow box section with sidewalls (4) and horizontal plates (5). The steel cable (6) runs from the winch, which is moutned above the pillar, through the arm to a pulley at its outer end. Loads are lifted by a motor (8) which rotates the cable drum. The drum and motor are mounted in a support which has side plates (9) and a base plate (10). The front lip (11) of the base plate is located in a U-shaped hook (12) on the arm, while its rear end is attached to the arm by a spring loaded bolt (18) and nuts (15, 16). If the tension on the cable exceeds a predetermined level, the rear end (14) of the base plate lifts up and operates a microswitch (18, 19, 20) and cuts off the supply to the motor.
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