In a constantly changing and partially unpredictable envi ronment, robot-motion planning must be on-line. The planner receives a continuous flow of information about occurring events and generates new plans while previously planned mo tions are being executed. This article describes an on-line planner for two cooperating arms whose task is to grab parts of various types on a conveyor belt and transfer them to their respective goals, while avoiding collisions with obstacles. Parts arrive on the belt in random order, at any time. Both goals and obstacles may be dynamically changed. This scenario is typi cal of manufacturing cells serving machine tools, assembling products, or packaging objects. The proposed approach breaks the overall planning problem into subproblems, each involving a low-dimensional configuration or configuration x time space, and orchestrates very fast primitives solving these subproblems. The resulting planner has been implemented and extensively tested in a simulated environment, as well as with a real dual- arm system. Its competitiveness has been evaluated against an oracle making (almost) the best decision at any one time; the results show that the planner compares extremely well.
International Journal of Robotic Research - IJRR , vol. 16, no. 2, pp. 144-167