Transportation for 4-DOF Tower Cranes: A Periodic Sliding Mode Control Approach

In this paper, a novel periodic sliding mode control method is designed for 4-DOF tower crane systems with unmatched disturbances as well as unknown/time-varying control directions. Specifically, the nonlinear disturbance observer is constructed to solve the unmatched uncertainties. The problems arising from unknown/time-varying control directions are tackled through the period sliding mode technique. Unlike most previous unknown control direction-related studies, the control coefficient is allowed to cross 0 in a continuous way. In addition, to improve the payload swing suppression and elimination performance, nonlinear terms involving payload swing information are elaborately injected into the control design. As far as we know, the designed periodic sliding mode control scheme provides the first control method for crane systems to successfully guarantee positioning as well as anti-swing performance in spite of unmatched disturbances and unknown control directions. The rigorous theoretical analysis is presented through Lyapunov techniques. Several simulations and experimental results are carried out to illustrate the merits of the designed periodic sliding mode control method.