Decentralized Control of Two Cooperative Car-Like Robots Performing a Transportation Task

Abstract This paper describes an approach to the coordination of two car-like robots that must cooperate in accomplishing a transportation task, namely carrying a long beam that neither one can carry alone. The robots are not allowed any form of explicit exchange of information, and can therefore only "communicate" through the task that they perform together. We propose for this problem a decentralized controller that relies on a two-stage strategy. At the higher level, each robot computes, based on the information available to it, a desirable motion for the beam. The lower-level controller must then generate controls to be fed to the robot's actuators (its steering and propulsion motors), so that the beam's actual motion approximates as well as possible the desired one. This article presents our mathematical formalism and the derivation of the corresponding control laws. We present the results of simulation runs of this decentralized, two-level control strategy, as well as the experimental testbed built for studying such coordination tasks.