Safety-Critical Control for Nonholonomic Tractor-Trailer Systems Using Control Barrier Functions and Differential Flatness

This paper presents a safety-critical control method for nonholonomic tractor-trailer systems subject to safety constraints and physical constraints. Safety is a fundamental issue in autonomous mobile robot design. To ensure the safety of the tractor-trailer system while achieving the control objectives, hard constraints are integrated into Control Barrier Functions (CBFs) to generate a safe set for the tractor-trailer system to avoid obstacles. Furthermore, CBFs are naturally harmonized with Control Lyapunov Functions (CLFs) to design a desired safe trajectory for the system. We optimize the decay rates of the CBFs and CLFs to mitigate the conflict between CBFs and CLFs and improve the obstacle avoidance performance. The concept of differential flatness is used to design and simplify the controller, which enables the system to track the desired safe trajectory. Finally, the effectiveness of the method is demonstrated through numerical simulations.