A graph-based path planning algorithm for the control of tower cranes

This paper presents a new path planning procedure for transportation tasks of three degrees of freedom tower cranes assuming a known, regularly updated and quadratic obstacle map derived by imaging sensors. Key objectives are the identification of either short, energy-efficient or low exciting load sway paths and the capability to be combined with an anti-sway controller and its trajectory generation module. An exact cell decomposition is carried out for the workspace of the tower crane introducing cells in the shape of circle parts. The height of each cell is determined considering the payload dimensions to ensure collision free paths. Moreover, a graph is derived by assigning a node to each cell and connecting the neighbors with circle arcs in tangential direction and lines in radial direction. The path finding is carried out utilizing an extended version of the novel graph searching algorithm L*. The extension follows from the fact that the height costs depend on the investigated path and thus need to be considered during the search. A simulation example of a realistic scenario is provided in order to discuss the generated paths.