The industrial manufacturers are pleased to set up robotic manipulators instead of human workers to execute painting tasks which greatly reduces the risk of workers’ being poisoned and is more conductive to maintain stable quality because of the manipulator’s high repetitive accuracy. When the industrial manipulator is employed to paint on big parts, the operating mode is also changed. The manipulator is mounted on a mobile platform, which is usually a NC-machine, to extend its workspace for painting on big parts. And the manipulator starts operation just as the mobile platform arrives at a proper position and stops.
However it is difficult for a human worker to figure out a proper stop position in which the manipulator can reach all goal points with a regular process velocity due to the special mechanical structure of serial revolute joints and the compound free-form surfaces, which is the most significant barrier to develop robotic big-parts painting.
In this paper, we put forward a novel idea based on analysis of the base’s workable location space (BWLS) of the manipulator to solve the stop position optimizing problem in order to get a bigger continuous operating area for the manipulator once stops and improve painting quality. Compared to previous study on the reachability of the end-effector fixing the base of the manipulator, we explore the BWLS while the center wrist point of the manipulator is determined. Through formulating an analytical expression, we can describe the BWLS more precisely and the intersection curves between these workable spaces can be also obtained when the wrist moves to the target points. With considering these boundary surfaces derived from the physical limits of the manipulator, the planning results will be more efficient and reliable.
The optimization results are verified by computer simulation. A 3D model of the manipulator with a mobile platform has been constructed. The painting trajectory for a target plane surface is firstly performed and the corresponding optimized stop position is then provided. Thus the method is proved to be effective and less time cost which could significantly reduce the planning time in comparison with manual operation.