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.
Architectures for the control of mobile robot formations are often described by three levels of abstraction: an
intelligence layer for task planning, a network layer for relaying commands and information throughout the formation,
and finally, at the lowest level of abstraction is a robot model layer where each robot is locally controlled to be
consistent with the current formation task. In this work, the network and robot model layers are considered, and an
output feedback control law for leader-follower based formation control is developed using neural networks (NN) and
limited communication. A NN is introduced to approximate the dynamics of the follower as well as its leader using
online weight tuning while a novel NN observer is designed to estimate the linear and angular velocities of both the
follower robots and its leader. Thus, each robot can achieve its control objective with limited knowledge of its leader's
states and dynamics while simultaneously reducing the communication load required in the network layer. It is shown
using Lyapunov theory that the errors for the entire formation are uniformly ultimately bounded while relaxing the
separation principle. Numerical results are provided to verify the theoretical conjectures, and the reliability of the
scheme is evaluated by introducing processing and communication delays, as well as communication failures.