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

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.