Gain-scheduled positioning control for varying rope length in travelling cranes

In this paper we report a design method for controlling a travelling crane mounted on a flexible structure. In order to control the position of the crane cart, the sway of the crane rope and the vibration of the flexible structure, a robust servosystem is designed using the normalized coprime factor H^∞ robust stabilization approach. We consider varying the length of the crane rope in positioning control and schedule the H^∞ compensator in accordance with varying the natural frequency of the crane rope. By numerical calculation the settling performance of the gain-scheduled H^∞ compensator is compared with that of a switching H^∞ compensator. We verify the efficiency of the gain-scheduled H^∞ compensator.