Immune sliding mode control for formation tracking and obstacle avoidance of uncertain wheeled mobile robots

This paper proposes an immune fuzzy sliding mode kinematic controller integrated with a proportional derivative dynamic controller for trajectory tracking by a nonholonomic differential-drive wheeled mobile robot subject to uncertainties and disturbances as well as its extension to the leader-follower formation control by multiple robots using the separation-bearing strategy. To deal with the drawbacks of a traditional first-order sliding mode control, such as the chattering phenomenon and the requirement of a priori knowledge of the bounds of uncertainties and disturbances, inspired by a regulation mechanism of the humoral immune response, it is derived a fuzzy system to establish the control reaction effect for an artificial immune system design to adjust online the gains of the control robustness portion adaptively. Furthermore, this paper proposes an obstacle avoidance strategy based on a reactive approach, being a variable avoidance radius also considered, to navigate in execution time the leader robot around static obstacles during the trajectory tracking. Simulation and experimental results demonstrate the effectiveness of the proposed controller with obstacle avoidance, and the Lyapunov theory proves the stability of the closed-loop control system.