| 摘要 |
An improved derrick structure comprising a column for supporting the derrick structure, a bracket horizontally rotatably mounted on the column, a boom vertically pivoted on the bracket so that the boom is divided into a first boom portion and a second boom portion, a winch drivable to hoist a hook for engaging an article intended to be transported by the derrick structure, a first dolly drivable to move the hook along the first boom portion, a counterweight drivable to move along the second boom portion to effectively balance the loading of the article hoisted by the derrick structure, and a controlling device for activating an electrical control circuit to control the driving of the winch, the dolly and the counterweight.
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