Deadlock-free and collision-free coordination of two robot manipulators

The authors describe a method for coordinating the trajectories of two robot manipulators so as to avoid collisions between them. It is assumed that the robots' environment is known and that the robots' paths can thus be planned in advance but that there may be significant variations in the execution time of some of the path segments. The goal is to allow the motions of each manipulator to be planned nearly independently and to allow the execution of the path segments to be asynchronous. The coordination is achieved by introducing explicit coordination commands into the path. The key problems in coordinating trajectories are to avoid collisions between the two robots and to avoid deadlock, that is, situations where each manipulator is waiting for the other to proceed.