Leader-Following Formation Control of Nonholonomic Mobile Robots With Velocity Observers

In many existing formation control approaches for nonholonomic mobile robots, the leader velocity is required to be measured and transmitted to the follower for controller design. Though some existing approaches can remove such a requirement, they have their respective shortcomings. For example, some are discontinuous, while others only ensure local closed-loop stability. In this article, we develop novel continuous formation controllers for mobile robots without measurement of the leader velocity such that communication between the mobile robots is not required. To address the unavailability issue of the leader velocity, observers based on adaptive control technique are proposed to obtain estimation of the leader velocity from information of the follower's onboard sensors. The effect of the velocity estimation error on the closed-loop stability is considered in the stability analysis based on Lyapunov stability theory, and it is shown that global stability of the combined observer-controller closed-loop system is ensured by the developed approaches. The effectiveness and performance of the developed approaches is illustrated using experimental results.