Skew control of a container crane

This article describes the mathematical model of the 3-dimensional motions of a container crane used in the dockside of a container terminal. The container is suspended by four cables via a spreader. When the container is accelerated or affected by wind, the container will oscillate around horizontal axis (sway) or vertical axis (skew). And an accurate position control of the container is difficult to realize because of uncertain weight, inertial sway, and winds. This paper proposes a simple PID control of the skew motion based on the analysis of 3-dimensional dynamics of the container. This system uses four cylinders to increase and decrease forces in the individual cables so that the container can be affected by yaw torque to reduce the skew error. The simulation results show the effectiveness of the PID controller in controlling the skew motion in the presence of winds.