Flatness-based nonlinear control of a three-dimensional gantry crane

The paper deals with a flatness-based control concept for a three-dimensional gantry crane. It is well known from literature that the payload position serves as a flat output if the payload is assumed to be a point mass. The validity of this assumption is investigated in more detail for the laboratory gantry crane under consideration. The overall control concept consists of a flatness-based feedforward controller with friction compensation and a trajectory error controller. In contrast to similar works in the literature the trajectory error controller has a special cascaded structure with subordinate velocity controllers and an outer linear quadratic regulator (LQR). The motivation of this structure is that it simplifies the model for the LQR design and makes it more intuitive to tune the controller parameters. Measurement results of the laboratory crane demonstrate the good performance of the proposed control concept.