Model-Free Saturated PD-SMC Method for 4-DOF Tower Crane Systems

In this article, we design a novel saturated proportional-derivative (PD) with sliding-mode control (SMC) method or saturated PD-SMC in short for 4-DOF tower crane systems under uncertain dynamics, external disturbances, as well as saturated control input constraints. The designed control method is model free, which can achieve accurate positioning and rapid swing suppression and elimination using only jib/trolly position/velocity and payload swing feedback with limited control inputs. Different from the existing control methods, the designed control method takes the advantages of simple structure and being easily realized in practical applications of the PD control, strong robustness of the SMC method with respect to model uncertainties and external disturbances, avoiding the requirements of accurate model knowledge associated with the SMC method, as well as rapid payload swing reduction of the swing suppression control. The stability of the controlled system is ensured by rigorous Lyapunov-based analysis. To the best of our knowledge, this is the first model-free control method without any linearization operations for tower crane systems with uncertain dynamics, external disturbances, and saturated control input constraints. Several experimental results are given to validate the superior control performance and strong robustness of the designed control method.