Optimization-Based Multipoint Trajectory Planning Along Straight Lines for Tower Cranes

On common construction sites, it is often the case that tower cranes must move heavy payloads along straight lines either due to obstacles or it is the direct route to a target location. In order to enable this motion for autonomous tower cranes, the goal of this work is an offline trajectory planning algorithm for the tower crane's payload to follow multiple straight connection lines of waypoints and compute smooth transitions at the intersection of the connection lines. The considered tower crane is a rigid tower crane with five degrees of freedom. An optimal control problem (OCP) is formulated in order to compute the trajectory for the transition between two waypoints minimizing the transition time and weighted path error. The smooth transitions between the connection lines are obtained by solving the OCP for the next connection line utilizing the current position as initial condition. The simulation results investigate the time gain in comparison to a trajectory that precisely positions the payload at each waypoint. The experimental validation with a real large-scale tower crane verifies that the crane is able to time-efficiently pass through an obstacle course.