Research On Path Planning And Tracking Control Of Four-wheel Steering Automatic Parallel Parking System

The development of science and technology has always promoted the development of the automobile industry.With the improvement of people’s consumption level,the number of cars is increasing year by year,which leads to the frequent occurrence of traffic accidents,the parking space has become increasingly tight."Difficult parking" has become a common phenomenon in the society.At the same time,the narrow parking space also increases the difficulty of parking and is prone to parking accidents.In order to reduce the parking space as much as possible,increase the available parking spaces,enhance the comfort and safety of the parking process,and improve the parking success rate.After analyzing the background and development status of the automatic parking system,this paper draws up the research content of this paper and launches the research.Firstly,a two-degree-of-freedom dynamics and kinematics model of a four-wheel steering vehicle is established based on the front wheel steering system.Aiming at the problem of front-rear rotation angle distribution of 4WS vehicles,the mathematical expressions of the proportional coefficients of front-rear rotation angles of 4WS vehicles under ideal conditions are obtained through the dynamic model.According to the kinematics model,combined with the vehicle structural parameters and the geometric relationship between the vehicle and the parking space,the parallel parking process is analyzed,and the minimum turning radius of the centroid point,the minimum parking space size,various parking parameters and the parallelism are calculated.The feasible range of parking starting points for parking obstacle avoidance constraints,curvature constraints,and pose constraints provides conditions for subsequent 4WS automatic parking system path planning.Secondly,this paper uses a fifth degree polynomial to plan the path of parallel parking,establishes a polynomial equation system according to the parking position constraints,attitude constraints,obstacle avoidance constraints,curvature constraints and other conditions,and selects three points(lower limit point,middle point,and upper limit point)are used as the starting point for parking,and the path planning simulation calculation is performed in MATLAB/Simulink to obtain three trajectory curves that meet various constraints.Using the control method based on non-time reference,design three different path tracking controllers of ordinary sliding mode,terminal sliding mode and exponential approach law sliding mode,build the controller model in MATLAB/Simulink,select the lower limit point in the feasible parking area the trajectory obtained as the starting point is used as the reference trajectory for path tracking.In combination with the control method of proportional distribution of front and rear wheel angles,three different path tracking controllers are simulated and verified under the condition of constant vehicle speed effect.The results show that the three control methods can track the reference path when the vehicle speed is constant,but compared with the three,the exponential approach law sliding mode control method has the best tracking effect.At the same time,it is verified that the exponential approach law sliding mode controller can also track the reference path under the condition of speed fluctuation.Finally,combined with a non-time reference exponential approach rate sliding mode controller,three different parking starting conditions are selected,and Simulink and CarSim are used to perform parallel parking joint simulation verification.Through the position deviation of the center of mass point of the target vehicle,the analysis of the heading angle deviation verifies the feasibility of the controller.