Articulated aerial device with hydraulic upper boom compensation

摘要

An aerial lift unit is truck mounted. The lift includes a lower boom pivoted to the truck and an upper boom pivotally connected to the outer end of the first boom. A lower boom cylinder unit is connected to pivot and thereby raise and lower the lower boom. A second tandem cylinder unit consists of first and second cylinders with the head end interconnected and having cylinder rods extending coaxially outwardly from the opposite rod ends. The one cylinder rod is connected to the lower boom and the second piston rod is connected to the base of a V-shaped coupling member having one arm pivotally connected to the lower boom and a second arm is pivotally connected to the upper boom. The second cylinder positions the upper boom in a preset orientation with respect to the lower boom. The first cylinder is connected in a hydraulic supply circuit with the lower boom cylinder and with the hydraulic fluid flow serially through the lift cylinder and second cylinder. The hydraulic fluid flow in one direction raises the lift unit and in the opposite direction lowers the lift unit, with automatic compensation of the upper boom position relative to the lower boom in all positions of the latter.