Abstract: A platform leveling system for an aerial lift truck utilizes a master/slave combination of helical hydraulic rotary actuators to automatically level the work platform in response to movements of the boom. For a two-stage aerial lift comprised of a lower boom and an upper boom, a first rotary actuator is coupled to the base of the lower boom, a second rotary actuator is coupled to the elbow where the upper boom is hinged to the lower boom, and a third rotary actuator is coupled directly to the platform and upper boom. Movement of the lower boom relative to the base causes the first rotary actuator to displace a fixed amount of hydraulic fluid, and movement of the upper boom relative to the lower boom caused the second rotary actuator to disperse a fixed amount of hydraulic fluid.

Abstract: An aerial lift including an improved structure for supporting the bucket or platform and compensating for changing forces on the bucket support structure as the bucket rotates from a side hung position to a forward position. The compensating structure provides for leveling of the bucket when the bucket rotates from the side hung position to the forward position and such that the bucket will be maintained level in both the side hung position and the forward position.

Abstract: An aerial lift includes a bucket mounted at the outer end of an articulated boom assembly having upper and lower booms. A hydraulic cylinder is provided for extending the upper boom relative to the lower boom, and a rotary actuator is provided for varying the rotational position of the bucket relative to the upper boom. An auxiliary cylinder, actuated in response to actuation of the upper boom hydraulic cylinder, provides hydraulic fluid to the rotary actuator so as to maintain the bucket in a substantially level position as the articulated boom assembly is raised and lowered. The load train including a chain and sector-shaped sprocket automatically compensate upper boom angle for changes in the angle of the lower boom relative to horizontal so that the rotary actuator is actuated only in response to actual changes in the angular position of the upper boom relative to horizontal.

Abstract: A mobile lifting apparatus has a chassis with front driving wheels and steerable rear wheels. A vertical mast comprised of a pair of extendible hydraulic cylinders is spacedly mounted on the front of the chassis. One or more jam stay cylinders are mounted on the chassis rearwardly of the vertical mast. A pair of extendable booms are mounted on the vertical mast and jam stay cylinders. The load may be attached to the end of the booms. A hydraulic or other power supply extends and retracts the boom and drives the driving wheels. A counterweight is mounted on the rear of the chassis and the chassis may be extended to increase the capacity and stability of the lifting apparatus.