Actuating system for transportable articulated booms having raisable platforms

In a vehicle, an operator controlled elevatable platform and a lift boom consisting of an upper boom and a lower boom having a mounting providing operatively selectable movement on a vertical axis, said platform being disposed at the projected end of said upper boom, means for elevating the lower boom by arcuate displacement in a vertical plane about the pivoted end thereof, and actuator means disposed between said upper and lower booms at the articulated connection therebetween and comprising a fluid motor actuator, including a cylinder having an intermediate trunnion mounting disposed at the geometric center of one of said booms, and a four bar linkage force-transmitting connection comprising a base link a driver link, a driven link and a follower link, between said fluid motor actuator and said boom and effective at full contraction of said booms relatively to each other wherein said upper boom is in surmounted parallel relation to the lower boom and wherein said fluid motor actuator is fully retracted into its associated boom, the respective bars of said four bar linkage being arranged in which the active forces on each bar of said bar linkages are limited to tension and compression and at least one of said bars is disposed wholly within the associated boom when said fluid motor actuator is fully retracted, said four bar linkage having three pivot connections with said upper and lower booms respectively and so disposed that a line connecting said trunnion mounting and the connection of said fluid motor actuator with said four bar linkage is geometrically offset relatively to the pivoted end of said upper boom and disposed to impart lift force to said upper boom commencing from full retraction of said upper and lower booms.