Pusher-Watcher: An Approach to Fault-Tolerant Tightly-Coupled Robot Coordination

We present a distributed planar object manipulation algorithm inspired by human behavior. The system, which we call pusher-watcher, enables the cooperative manipulation of large objects by teams of autonomous mobile robots. The robots are not equipped with gripping devices, but instead move objects by pushing against them. The pusher robots have no global positioning information, and cannot see over the object; thus a watcher robot has the responsibility for leading the team (and object) to the goal, which only it can perceive. The system is entirely distributed, with each robot under local control. Through the use of MURDOCH, an auction-based resource-centric general purpose task-allocation framework, roles in the team are automatically assigned in an efficient manner. Further, robot failures are easily tolerated and, when possible, automatically recovered. We present results and analysis from a battery of experiments with pusher-watcher implemented on a group of Pioneer 2 mobile robots.