Nonlinear Control of a Gantry Crane

Abstract

This paper treats the nonlinear control of a laboratory model of a gantry crane, where a trolley can be moved on a rail and the load is fixed at the end of a rope of variable length. The system is differentially flat, and the coordinates of the load, which also are the variables to be controlled, are a flat output. This fact allows us to determine a feedforward control law in a straightforward manner. Because of friction, the results achievable by a pure feedforward law are, as expected, not satisfying. This does not apply to the “pendulum subsystem”, with the position of the trolley and the length of the rope as input, since it is almost free of friction. Therefore, a feedforward control for the “pendulum subsystem” is designed such that it shows an excellent tracking behavior. Finally, cascaded control is used for the guidance of the overall system.