Nonlinear and observer-based PD position and sway control of convey-crane systems

Convey-cranes suffer by undesirable swings when different payloads are carried and therefore a main task of a controller applied on these systems is to sufficiently suppress and eliminate the sway performance. To this end, an energy based nonlinear proportional-derivative (PD) controller for overhead cranes is proposed with its stability examined by using classical Lyapunov techniques and LaSalle's invariance theorem. Despite the constant gains of the conventional PD position controller, in this paper, a D-term varying gain is proposed that takes into account the influence of the payload swing angle and its derivative. Moreover, since in the present case all the system states are needed to be fed-back, a suitable dynamic observer is included to estimate the unmeasurable states, namely the position derivative and the swing angle. The simulation results conducted for two different payload weights verify the superior performance of the system and its robustness, while comparisons made with the conventional PD controllers indicate significant response enhancements in the sway performance.