Time-Varying Formation Tracking for Nonholonomic Mobile Robots With Asymmetric Input Constraints

This article provides a solution to time-varying formation (TVF) tracking control problems of nonholonomic mobile robots (NMRs) with asymmetric input constraints. Different from existing works, the configuration of the formation for NMRs is time-varying, which requires formation tracking errors to keep convergent even if the configuration of the desired formation changes over time. A novel sliding mode controller is proposed to handle this problem, and the closed-loop stabilities of NMRs under given control protocols are proven by Lyapunov theory. As special cases of TVF, the above control methods can be directly applied to flexible formation and fixed formation studied in existing works. It should be pointed out that if the desired formation is fixed, the angular velocity of the tracking target is not necessary when designing the corresponding control algorithm. In addition, there is no singularity in the methods provided in this article. By collaborative selection of parameters in these control protocols, the adjustment ranges of linear and angular velocities associated with the leader or virtual leader are almost the same as that of followers. Numerical simulations and hardware-in-the-loop (HiL) simulations further verify the theoretical results.