Importance

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Abstract

In a truck mounted overcenter aerial device having an articulating boom assembly, a mechanism for articulating the upper boom relative to the lower boom. A star wheel on the upper boom is acted upon by a pair of linkages powered by hydraulic cylinders mounted on the lower boom. The linkages are pinned at their outer ends to the star wheel so that the upper boom is pivoted in opposite directions when the cylinders are extended and retracted. Each linkage includes pivotally connected links which fold up on the star wheel against stop surfaces as the linkage is extended. The stop surfaces are arranged to control the angular speed of the upper boom and the torque applied to it by the linkages as desired during each angular segment of articulation. The hydraulic control circuit for the cylinders includes counterbalance holding valves which maintain both linkages under tension at all times to avoid any slack or jerkiness when the boom goes overcenter.

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First Claim