Saturated PD with sliding mode control method for 4-DOF tower crane systems

A new saturated PD with sliding mode control method (or saturated PD-SMC in short) was designed by this paper for 4-DOF tower crane systems. The design was based on uncertain dynamics, external disturbances, and control input constraints. By means of jib/trolly-position/velocity and payload swing-feedback with limited control inputs, the designed control method, which is model free, can achieve accurate positioning and rapid swing suppression and elimination. Besides, by adopting the advantages of simple structure, the designed control method can be easily realized in the applications of the PD control, compared with existing control methods. This method also has strong robustness of the SMC method regarding to model uncertainties and external disturbances. As a result, this design avoids the requirements of accurate model knowledge concerned with the SMC method, as well as rapid payload swing reduction of the swing suppression control. Rigorous Lyapunov-based analysis is employed in order to ensure the stability of the controlled system. According to the information this paper has, this is by far the first model-free control method without any linearization operations for tower crane systems with uncertain dynamics, external disturbances, and control input constraints. The superior control performance and strong robustness of the designed control method was validated by a number of experimental results.