Two-Stage Control for Container Cranes.

For fast loading/unloading of the containers from a container ship, the quick suppression of the residual sway of the container at the end of trolley traveling is crucial. Due to the unmodeled dynamics of the plant and to disturbances like wind, a residual sway always exists. In this paper, a two-stage control for container cranes is investigated. The first stage control is a modified time-optimal control with feedback for the purpose of fast trolley traveling. The second stage control is a nonlinear control for the quick suppression of the residual sway while lowering the container at the target trolley position. The secondary control combines the partial feedback linearization to account for the unknown nonlinearities as much as possible and the variable structure control to account for the unmodeled dynamics and disturbances. The nonlinear control is investigated from the perspective of controlling an underactuated mechanical system. Simulations and experimental results are provided.