An increased coupling-based control method for underactuated crane systems: theoretical design and experimental implementation

A novel increased coupling-based nonlinear control strategy is proposed for underactuated overhead crane systems, which guarantees both fast trolley positioning and sufficient payload swing elimination performance. The developed controller is applicable to both regulation control and trajectory tracking control. To artificially increase the trolley-translation/payload-swing internal coupling, a payload position-like composite variable is introduced and a corresponding elegant error signal is then constructed, based on which a novel control law is designed to transform the overhead crane system into an interconnected system consisting of two subsystems with respect to (w.r.t.) the constructed error signal and the payload swing angle, respectively. Both subsystems are proven to be input-to-state stable (ISS); by invoking the small gain theorem, we show that the overall interconnected system is also ISS. LaSalle's invariance theorem further proves that the system states asymptotically converge to the desired equilibrium point. Experimental results are included to demonstrate the feasibility and effectiveness of the proposed method and also its superior control performance over some existing schemes.