Partial feedback linearization control of overhead cranes with varying cable lengths

Overhead cranes are under-actuated mechanical systems with three degrees-of-freedom (trolley displacement, cable length, and cargo swing angle) and only two actuators: one for cargo hoisting and another for trolley driving. An overhead crane transfers the trolley to a desired position, hoists the cargo up and down until the desired cable length is achieved while keeping the cargo swing angle small during the transfer process. The rope should no longer have a swing angle at the load destination. In this research, a nonlinear controller is proposed for an overhead crane system, in which partial feedback linearization technique is used. To show the effectiveness of the proposed controller, we perform both simulation and experimental study. The simulation and experimental results show that the crane system with the proposed controller is asymptotically stable. Furthermore, all state trajectories of the system reach a steady state within a considerably short time even if the inherent structure of the system is changed.