Research On Autonomous Obstacle Crossing Planning And Control Of Eight-wheel Four-swing Arm Unmanned Ground Vehicle

The application of unmanned technology to the field of special unmanned ground vehicles can improve the efficiency of field transportation,rescue and combat missions,and improve the autonomous control capability of vehicles,which is of great significance to seize combat opportunities and reduce casualties.Special unmanned ground vehicles working in unstructured environments in the wild usually need to deal with more complex road conditions and more rugged road environments.Based on the eight-wheel four-swing arm all-terrain unmanned ground vehicle(8W4AUGV)developed by Sunward Intelligent Equipment Co.,Ltd.,this paper aims at the typical obstacle in the field complex environment—vertical obstacle,and provides the motion planning for the 8W4 AUGV in the process of autonomous obstacle crossing.Researches related to tracking control are carried out,the main contents are as follows:(1)By analyzing the steering mechanism and plane steering mechanism of 8W4 AUGV,the kinematics and dynamics model of8W4 AUGV during skid steering is established,and the constraint relationship between the state quantity and the control quantity during the8W4 AUGV plane steering motion is determined;Mechanism and obstacle crossing mechanism,using the Denavit-Hartenberg parameter method of robotics to establish the coordinate system of the swing arm,the kinematic model of the 8W4 AUGV swing arm and the trajectory curve of the swing arm movement are obtained.The experimental results show that the constructed mathematical model has high accuracy and can meet the algorithm requirements of subsequent obstacle crossing planning and tracking control.(2)The world coordinate system and the coordinate system of the key parts of the car body are established for the process of crossing the vertical obstacles.By analyzing the geometric constraints between the various parts of the car body and the vertical obstacles at the key node of the obstacle crossing,the optimization problem with constraints is constructed and solved.The optimal motion parameters of the swing arm during obstacle crossing.Through the mechanical analysis of the "dangerous points" in the obstacle crossing process,the feasibility of the obstacle crossing planning parameters is verified,and the obstacle crossing performance of the8W4 AUGV is obtained.The simulation analysis shows that the optimal obstacle crossing motion planning algorithm can ensure that the obstacle crossing process is efficient and the energy consumption is the least,and the maximum vertical obstacle height that can be crossed can reach 1.05 m.(3)The model predictive control algorithm(MPC)was applied to the trajectory tracking control of 8W4 AUGV,and the model reference control algorithm(MRAC)was applied to the swing angle tracking control of the swing arm over obstacles.Through Jacobian derivation,the error model of8W4 AUGV is obtained.After discretization,the cost function and constraint equation of the model are established,and the problem is transformed into a standard quadratic programming problem.The optimal control solution of trajectory tracking is obtained by solving the quadprog function in MATLAB.By establishing the dynamic model of the hydraulic cylinder and taking the simplified model as the reference model,the closed-loop control of the swing angle of the swing arm is realized.The simulation results show that the MPC algorithm has high tracking control accuracy and anti-delay characteristics.The lateral error at large curvature turns is less than 0.4m,far less than the 8W4AUGV’s wheelbase of 1.54 m,which can meet the needs of obstacle crossing control.(4)According to the above motion planning algorithm and control algorithm,based on the ROS robot operating system,the algorithm is deployed to the computing platform.Using 8W4 AUGV as the experimental platform,the tracking effect of the MPC algorithm in the plane line tracking experiment and the actual effect of the optimal motion planning algorithm in the obstacle crossing experiment are verified.The experimental results show that 8W4 AUGV can quickly and accurately cross vertical obstacles of a specific height with the best solution,and the obstacle-crossing efficiency is improved by 300% compared with manual operation,which has certain engineering practical value.