On-Line Manipulation Planning for Two Robot Arms in a Dynamic Environment

In a dynamic and partially unpredictable environment, 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 motions are being executed. This paper describes an on-line planner for two cooperating arms whose task is to grab parts on a conveyor belt and transfer them to their respective goals, while avoiding collision with obstacles. Parts arrive on the belt in random order, at any time. This scenario is typical 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 both in a simulated environment and with a real dual-arm system. Its competitiveness has been evaluated against an oracle making (almost) the best decision at any one time. The planner compares extremely well.