Orientation control of a crane´s spreader: Application on mobile harbor

In this paper, the orientation control (trim, list, and skew control) of the load (container) in the crane located in the mobile harbor (MH) is investigated based on the derived mathematical model of the four-rope crane. A container hooked to a spreader is suspended in air by four ropes. When the container is accelerated by the trolley or is disturbed by winds, it rotates (trim, list, and skew) as well as sways in the vertical plane. When this happens, the accurate positioning of the container becomes difficult because of the rotation even with the swaying under control. This paper proposes a feedback control technique for the orientation control of the container based on the dynamics of the spreader including the container. The adopted control system uses four actuators that vary the lengths of the four ropes, respectively. Experiments are performed with a 1/20 scale MH, in which four snag devices are used, instead of the ball screws as a conventional crane in practice, to vary the rope lengths.