Lyapunov-based damping controller with nonlinear MPC control of payload position for a knuckle boom crane

A crane control system is proposed where the crane payload follows a desired position trajectory with ultimately bounded pendulum motion. The proposed control system includes a Lyapunov-based damping controller, which stabilizes the dynamics of the payload by increasing the damping of the pendulum motion. The crane with the resulting stabilized dynamics is controlled with a tracking controller based on NMPC (nonlinear model predictive controller). The Lyapunov-based damping controller is designed so that the stabilized closed-loop pendulum dynamics are exponentially stable. This means that the pendulum motion is ultimately bounded in the presence of bounded perturbations. The control variables of the NMPC tracking controller are constrained so that the perturbations to the damping controller are sufficiently bounded. The resulting system tracks the desired payload position with bounded pendulum motion. The control system is validated in simulations and experiments using a scaled laboratory version of a knuckle boom crane.