A Novel EPT Autonomous Motion Control Framework for an Off-axle Hitching Tractor-trailer System with Drawbar

A tractor-trailer system is an underactuated system that is subject to nonholonomic constraints and exhibits extremely nonlinear behaviors. Its trajectory planning and control issues remain widely researched. In this paper, on the basis of establishing a precise kinematic model, a novel method is proposed to realize autonomous motion control of an off-axle hitching tractor-trailer system with a drawbar. The proposed method is roughly divided into three steps: EXTRACTING (E) a virtual subsystem, trajectory PLANNING (P) for the original full system, and trajectory TRACKING (T) by feedback control techniques, thus the “EPT method”. In the E step, two alternative strategies are considered to construct a virtual subsystem by extracting a part of an original towed aircraft system. Then, in the P step, a two-layer optimal control-based method is developed to generate a reference trajectory. A trajectory for the virtual subsystem is generated in the first layer, where the Reeds-Shepp curve with artificial expertise in selecting intermediate nodes is introduced to provide initial guesses. The results obtained in the first layer are utilized to initialize partial state and control variables in the trajectory planning for the original full system in the second layer. Finally, in the T step, a receding horizon controller is designed to drive the carrier aircraft to track the reference trajectory under various external disturbances. Numerical simulations demonstrate that the EPT method is applicable and highly efficient. The proposed method is also applicable for generalized tractor-trailer systems and other chain-link systems.