Robust control of container cranes: theory and experimental validation

Fast and swing-free transfer of a suspended load is not easy to obtain in the presence of model uncertainties (e.g. unknown load mass) and disturbances. In this paper, we exploit the positive features that characterize the second-order sliding-mode approach to design a simple control system which, unlike other approaches, guarantees the suppression of the load swing during transport and precise final positioning by relying on a weak amount of information about the crane and load parameters. The trolley position, the rope length and the swing angle are the only measured quantities and, for feedback, the controller also uses estimates of the trolley and rope velocities provided by real-time sliding-mode differentiators. The features of the observer-controller scheme and the relevant implementation issues are discussed, and some results from experiments carried out on a laboratory-sized overhead crane model are provided