Simultaneous task allocation and motion scheduling for complex tasks executed by multiple robots

Abstract

The coordination of multiple robots operating simultaneously in the same workspace requires the integration of task allocation and motion scheduling. We focus on tasks in which the robot's actions are not confined to small volumes, but can also occupy a large time-varying portion of the workspace, such as in welding along a line. The optimization of such tasks presents a considerable challenge mainly due to the fact that different variants of task execution exist, for instance, there can be multiple starting points of lines or closed curves, differentfilling patterns of areas, etc. We propose a generic and computationally efficient optimization method which is based on constraint programming. It takes into account the kinematics of the robots and guarantees that the motions of the robots are collision-free while minimizing the overall makespan. We evaluate our approach on several use-cases of varying complexity: cutting, additive manufacturing, spot welding, inserting and tightening bolts, performed by a dual-arm robot. In terms of the makespan, the result is superior to task execution by one robot arm as well as by two arms not working simultaneously.