| 摘要 |
<p>In connection with a pair of articulated booms there is a leveling system consisting of a sprocket wheel at the base of the lower boom and a co-acting sprocket wheel at the free end of the upper boom with chains and rods interconnecting the two sprockets and constituting part of the leveling system maintaining the basket connected to the free end of the upper boom in a level condition. The angular position of the sprocket wheel on the upper boom is calibrated so as to be in a direct relationship to the perpendicularity of the upper boom relative to the horizon, which in turn is related to chain movement at the upper boom. A control valve associated with the upper boom is actuated by a cam on the chain so the valve is operated at whatever preselected critical angle of perpendicularity of the upper boom is desired. The control valve, in turn, has fluid connections with power actuator means associated with each of the upper and lower booms to preclude further movement of either the upper or lower boom which would increase the perpendicularity of the upper boom beyond its critical predetermined amount. Fluid connections are provided to the power actuator means associated with the upper and lower booms to permit either or both of the booms to be actuated in a direction decreasing the perpendicularity of the upper boom from its critical position whether the control valve has been operated or not.</p> |
