Observer design and flatness-based feedforward control with model predictive trajectory planning of a crane rotator

This paper addresses the control of a crane rotator. A crane rotator can be considered as a mechanical nonlinear robot system. The crane rotator allows to control the skew angle of a spreader. Spreaders are used to grip containers in harbors. A complete concept for skew angle control is presented in this paper. Rotating the manipulator causes a torsional oscillation since the manipulator is suspended on ropes. The control concept deals with the nonlinear dynamics. It comprises a nonlinear Luenberger observer design, a feedforward control and a tracking controller. The last two components are designed in a two-degrees of freedom structure. The feedforward controller is based on the differential flatness theory. To generate a continuous reference signal for the controller, a model predictive trajectory planner is added to the concept. Simulations and measurement results show the success of the overall structure implemented on the harbor crane LIEBHERR LHM 420.