AERIAL LIFT PLATFORM LEVELING APPARATUS AND SYSTEM

摘要

Apparatus and system for leveling the work platform or basket of an aerial lift. A vertical seeking pendulum is mounted on the boom of the lift independent of the platform. Changes in the relative angle between the pendulum and boom are transposed into control signals by means of an epicyclic gear train. The control signals operate an actuator for pivoting the platform in a direction to maintain a level orientation. Platform movement relative to the boom generates a feedback signal which is carried through the epicyclic gear train to cancel the control signal. In one embodiment the pendulum is damped by means of a pair of balls guided in a circular raceway so as to follow the pendulum independent of the boom position. In another embodiment pendulum movement is damped by means of a viscous liquid constrained within a housing so as to surround the pendulum independent of boom position. The system includes a control circuit incorporating a reversible pump selectively operable in one mode to direct fluid to the leveling actuator and through a two-way valve into an hydraulic actuator for raising and lowering the boom, and in another mode to direct fluid to the leveling actuator for moving the platform to its stowed position. An emergency supply circuit directs return fluid from the boom actuator to the leveling actuator as the boom is lowered should the primary hydraulic power source by inoperable for any reason.