Fault Tolerant Control of Nonholonomic Mobile Robot Formations
In this chapter, a fault tolerant kinematic/torque control law is developed using backstepping for leader-follower based formation control in order to accommodate the dynamics of the robots and the formation in contrast with kinematic-based formation controllers. First, nominal control laws are derived for the leader and follower robots under the assumption of normal operation (no faults), and the stability of the individual robots and the formation is verified using Lyapunov methods. Subsequently, in the presence of state faults such as actuator fault, flat-tire etc., which could be incipient or abrupt in nature, an online fault detection and accommodation (FDA) scheme is derived to mitigate the effects of a fault by modifying the nominal controller. In other words, an additional term is introduced to the existing control law to minimize the effects of the fault, and this additional term is a function of the unknown fault dynamics which are recovered using the online learning capabilities of a neural network. Further, mathematical stability results are derived using Lyapunov theory, and both the FDA scheme and the formation errors are guaranteed to render asymptotic stability in the presence of faults. Numerical results are provided to verify the theoretical conjectures.