Formation Control of Multiple Nonholonomic Mobile Robots

Abstract

Tracking control problem of multiple mobile robots is considered. Our system is composed of a reference and follower robots of unicycle type. The robots are assumed to satisfy pure rolling and non-slipping conditions, which lead to nonholonomic velocity constraints. The purpose is to control the followers so that the reference is tracked with arbitrary desired clearance and also to avoid an inter-robot collision. To accomplish this goal, we first introduce a virtual robot (VR) tracking control to establish and maintain the formation when no collision is detected. VR is an ideal robot fixed with each follower and helps in simplifying the control, as the tracking errors become zero in final stage. During the process, if a possibility of collision is detected, a collision avoidance technique (l-ψ or l-l control) will be applied to the lower priority robot. The result of this control gives a monotonic convergence in an internal shape of distance variables, which enables us to predict the movement of the robots during this control and leads to the collision-free movement. These processes are repeated until the desired motion is accomplished. Simulation results prove effciency of our control techniques.