Partially saturated nonlinear control for gantry cranes with hardware experiments

Gantry cranes are typically underactuated nonlinear dynamic systems with highly coupled system states. We propose in this paper a partially saturated nonlinear controller for gantry crane systems by converting the crane model into an objective (i.e., desired closed-loop) system. The presented scheme guarantees "soft" cart start by introducing a smooth saturated function into the controller. In particular, we first establish an objective system with desired signal convergence and stability performance. Then, on the basis of the objective dynamics' structure, we derive a partially saturated control law straightforwardly by solving one partial differential equation, without necessity of performing partial feedback linearization operations to the original crane model. The convergence and stability performance of the objective system is assured with Lyapunov-based methods. In order to verify the practical control performance of the proposed method, we implement both numerical simulation and hardware experiments to illustrate that the new method achieves increased performance with respect to existing methods, with lessened control efforts.