Formation Control for Non-Holonomic Mobile Robots: A Hybrid Approach

Abstract

In this chapter it has been addressed the problem of the autonomous navigation for a group of non-holonomic mobile robots. In a first stage we considered the classic leader-based formation control problem. In spite of the stability property of this controller, we have detected large transitory errors in some circumstances, being these errors unacceptable for many applications, such as transporting large objects in a cooperative way. Based on these observations and in order to present a formal solution, we have developed a hybrid approach for the formation problem. The continuous formation controller has been complemented with an orientation controller for each follower, allowing a considerable reduction of formation errors during leader manoeuvres. The resulting hybrid control system presents a switched architecture characterized by the presence of a supervisor which generates a switching signal indicating the active controller at any moment. Besides, it has been included a formal stability proof for the whole switched system based on the theory of multiple Lyapunov functions. At the end of this chapter, we exposed simulations results that allow comparing both main strategies. Next, we have included experimental results for a two-robots formation navigating on different settings: without obstacles, and avoiding isolated obstacles by considering a reactive algorithm on the leader robot. Through these experimental results it can be concluded the good performance of the hybrid approach. Future works on this area will be related to the improvement of the obstacle avoidance capability and to increase the perception abilities of the follower robots (adding new sensors).