A flexible virtual structure formation keeping control design for nonholonomic mobile robots with low-level control systems, with experiments

This paper presents a flexible virtual structure formation keeping control design for nonholonomic mobile robots that are driven by low-level velocities control systems that possess non-trivial dynamical effects. The formation is flexible in the sense that the formation configuration is defined based on a set of curvilinear relative separations instead of commonly used rectilinear relative separations. The main contribution of this work is the use of a novel concept of formation reference generation to compute accurate formation reference pose in real-time based on curvilinear relative separation coordinates along the virtual formation leader trajectory. Another contribution of this work is the application of a recently developed trajectory tracking control scheme, which enables the considered mobile robots to track their formation reference poses stably when executing the formation maneuvers. This formation control scheme allows a virtual formation leader to guide the formation of mobile robots flexibly in an environment to carry out its formation navigation tasks. The formation control performance was validated in both simulations and experimentations. Field trials were conducted in some off-road environments at speeds up to 4m/sec to validate the control design. The scheme was implemented on a full-sized nonholonomic tracked vehicle, following a virtual leader in formation. The obtained simulations and experimental results confirm the effectiveness of the proposed formation control scheme.