Multi Robotic Conflict Resolution by Cooperative Velocity and Direction Control

Collision avoidance is one of the essential pillars of a wheeled robotic system. A wheeled mobile robot (called mobile robot for conciseness henceforth) requires for effective functioning an integrated system of modules for (i) map building, (ii) localization, (iii) exploration, (iv) planning and (v) collision avoidance. Often (i) and (ii) are entailed to be done simultaneously by robots resulting in a vast array of literature under the category SLAM, simultaneous localization and mapping. In this chapter we focus on the aspect of collision avoidance specifically between multiple robots, the remaining themes being too vast to even get a brief mention here. We present a cooperative conflict resolution strategy between multiple robots through a purely velocity control mechanism (where robots do not change their directions) or by a direction control method. The conflict here is in the sense of multiple robots competing for the same space over an overlapping time window. Conflicts occur as robots navigate from one location to another while performing a certain task. Both the control mechanisms attack the conflict resolution problem at three levels, namely (i) individual, (ii) mutual and (iii) tertiary levels. At the individual level a single robot strives to avoid its current conflict without anticipating the conflicting robot to cooperate. At the mutual level a pair of robots experiencing a conflict mutually cooperates to resolve it. We also denote this as mutually cooperative phase or simply cooperative phase succinctly. At tertiary level a set of robots cooperate to avoid one or more conflicts amidst them. At the tertiary level a robot may not be experiencing a conflict but is still called upon to resolve a conflict experienced by other robots by modifying its velocity and (or) direction. This is also called as propagation phase in the chapter since conflicts are propagated to robots not involved in those. Conflicts are resolved by searching the velocity space in case of velocity control or orientation space in case of direction control and choosing those velocities or orientations that resolve those conflicts. At the individual level the search is restricted to the individual robot’s velocity or direction space; at the mutual level the search happens in the velocity or direction space of the robot pair experiencing the conflict and at tertiary levels the search occurs in the joint space of multiple robots. The term cooperative is not a misnomer for it helps in achieving the following capabilities: