Implementation and experimental evaluation of flexible formation tracking controllers for car-like mobile robots with velocity and steering controllers in the loops

This paper presents an implementation and an experimental validation of a virtual structure and a leader-follower flexible formation tracking controllers for car-like non-holonomic mobile robots with velocity and steering controllers in the loops. The formations are flexible in the sense that their formation configurations are defined based on curvilinear longitudinal and lateral relative separations instead of the commonly used rectilinear relative separations. The two formation controllers leverage on our recently developed cascaded nonlinear trajectory tracking controller [19] to attain stable flexible formation control in the presence of low-level dynamical control latencies in the loops without needing any dynamical model of the robots' low-level control systems when implementing the controllers. The performances of the two controllers have been validated in both simulation and partial experimentations with satisfactory results. For the virtual structure formation controller, it was experimented in an on-road environment up to the speed of 4.1m/sec, and the leader-follower formation controller was tested in both on-road and off-road environments up to the speed of 4.5m/sec. The results provide the foundation to develop formation navigation systems for the considered nonholonomic mobile robots to navigate in a team in both on-road and off-road environments.