Fault Tolerant Formation Control of Nonholonomic Mobile Robots using Online Approximators

For unmanned systems, it is desirable to have some sort of fault tolerant ability in order to accomplish the mission. Therefore, in this paper, the fault tolerant control of a formation of nonholonomic mobile robots in the presence unknown faults is undertaken. Initially, a kinematic/torque leader-follower formation control law is developed for the robots under the assumption of normal operation, and the stability of the formation is verified using Lyapunov theory. Subsequently, the control law for the formation is modified by incorporating an additional term, and this new control law compensates the effects of the faults. Moreover, the faults could be incipient or abrupt in nature. The additional term used in the modified control law is a function of the unknown fault dynamics which are recovered using the online learning capabilities of online approximators. Additionally, asymptotic convergence of the FDA scheme and the formation errors in the presence of faults is shown using Lyapunov theory. Finally, numerical results are provided to verify the theoretical conjectures.