Research On Modeling And Motion Control Strategy For Active Articulated Tractor-Trailer Robots

Since articulated tractor-trailer robot has the advantages of large cargo capacity,flexible mobility,low freight cost and low energy consumption,etc.,it has been widely used in various freight scenarios.However,the traditional articulated tractor-trailer robot has poor maneuverability,especially in the face of narrow road conditions.The posture of the trailer is difficult to accurately control,and the flexibility and obstacle avoidance ability of the whole vehicle are greatly limited.To solve these defects,a novel structure of active articulated tractor-trailer robot is proposed in this paper,with its modeling and motion control strategy being studied.Firstly,the system modeling of the active articulated tractor-trailer robot is carried out,which lays a foundation for the subsequent research of motion control strategy.By analyzing the mechanical structure characteristics of this mobile platform,the generalized coordinates of this system are established and the kinematics model can be derived;Then,the Euler-Lagrange equation are adopted to establish the dynamics model under the premise of considering the nonholonomic constraints.Secondly,for the strongly coupled and nonlinear active articulated tractor-trailer robot system,a trajectory tracking control method based on reference path is proposed.Based on the reference path,the generalized coordinate reference information of the system can be obtained firstly through planning;Then,a kinematics controller based on model predictive control(MPC)is designed to track the reference trajectory at the kinematics level;In addition,a dynamic controller based on sliding mode control(SMC)is designed,which can achieve robust trajectory tracking control by controlling torque inputs.Thirdly,an obstacle avoidance control strategy with integrated planning and tracking is proposed for multi-obstacle unstructured environment.To begin with,a hierarchical obstacle avoidance trajectory planning method is established,that is,utilizing artificial potential field(APF)method to plan the obstacle avoidance trajectory for tractor,and adopting geometric relation to determine the obstacle avoidance trajectory for trailer;Then,a double closed-loop obstacle avoidance trajectory tracking control strategy is designed.At the kinematics level,linear quadratic regulator(LQR)is adopted to track the posture signal with high precision,and at the dynamics level,the global terminal sliding mode control(GTSMC)method is used to track the velocity signal with high robustness.Lastly,aiming at the reversing dynamics of the active articulated tractor-trailer robot,a perpendicular reverse parking method based on safety constraints is proposed.Considering the constraints of hitch angle and collision avoidance in the reversing process,a trajectory planner based on model prediction is constructed firstly;Then,based on the planned safe trajectory,the nonsingular terminal sliding mode(NTSMC)tracking control strategy is proposed,with the control laws based on dynamics model being deduced.Through the safe trajectory planning and trajectory tracking,the control of safe perpendicular reverse parking is finally realized.In this paper,the modeling and motion control strategy of the active articulated tractor-trailer robot are studied,and the validity of the theoretical results is verified by Matlab/Simulink platform.The research results of this paper lay a foundation for the application and promotion of the active articulated tractor-trailer robot,and also provide a theoretical reference for the research of articulated vehicles.