A Flexible Leader-Follower Formation Tracking Control Design for Nonholonomic Tracked Mobile Robots with Low-Level Velocities Control Systems

Abstract

This paper proposed a flexible leader-follower formation tracking control design for nonholonomic tracked mobile robots. The mobile robots considered here are driven by low-level velocities control systems that possess non-trivial dynamical effects. The formation is flexible in the sense that its configuration is defined by a set of curvilinear-based longitudinal and lateral relative separations instead of commonly used rectilinear relative separations. The contributions of this work are twofold. First, we proposed a novel curvilinear-based real-time formation reference generator to generate nonholonomic compatible formation reference pose for each robot to execute based on the most updated leader's motion information. Second, we integrate our recently developed nested-loop nonlinear trajectory tracking control scheme with the reference generator to achieve stable curvilinear-based formation maneuvers for the considered mobile robots without require any detailed model of the robots' low-level control systems. The control design allows the formation's leader to guide the formation of ground mobile robots stably without any pre-planned formation trajectory. The formation tracking control design was validated in both simulations and physical experimentation. Field trials were conducted in some off-road environments at different formation speeds up to 4m/sec to validate the control design. The formation controller was implemented on a sport utility vehicle (SUV) which acted as a leader, and a nonholonomic full-sized tracked vehicle, which acted as a follower vehicle. The obtained simulation and experimental results confirm the effectiveness of the proposed formation control scheme.