Adaptable Virtual Structure Formation Tracking Control Design for Nonholonomic Tracked Mobile Robots, With Experiments

This paper presents an adaptable virtual structured-based formation tracking control design for nonholonomic mobile robots to follow time-varying formation configurations. The formation configuration considered here is based on curvilinear relative longitudinal and lateral separations instead of the commonly used rectilinear relative separations. And the tracked mobile robots assumed here are equipped with low-level velocities control systems with non-trivial dynamical effects. The key contributions of this work are twofold. First, we proposed a curvilinear-based real-time formation reference generator to generate formation reference poses and velocities correspond to the time-varying formation configuration. Second, we develop a nonlinear tracking controller for each robot to follow its real-time generated formation reference pose with guaranteed stability. One of the key challenges that the nonlinear tracking controller handles is the tracking of the formation reference pose that may not satisfy the nonholonomic kinematic constraints where on the other hand, the considered mobile robots are nonholonomic. One positive feature of this control design is that it does not require any detailed model of the robots´ low-level velocities control systems to implement the control design on the physical mobile robots. The formation tracking control performance of the design was validated in both simulations and experimentation where the experimental trials were conducted in some off-road environments. Comparison runs were also conducted to show the advantages of the proposed control scheme.