Research On Path Planning And Tracking Control Of Parallel Parking

The automatic parking system can effectively avoid accidents during the parking process,and has gradually become a research hotspot for major domestic and foreign automobile manufacturers,scientific research institutions,and universities.Some car manufactures have launched their own automatic parking system.This paper focuses on the core problems of automatic parking systems: path planning and path tracking.It conducts path planning for parallel parking scenarios,and designs a path tracking controller with obstacle avoidance function.Through software simulation,Hardware-in-the-loop and a smart toy cars verify the validity of the model and provide a useful reference for the laboratory to develop and build low-cost automatic parking systems or driver assistance systems.First of all,this paper analyzes the motion process of parallel parking.Based on a passenger car,a kinematic model of the vehicle was established.Based on the geometric relationship between the body and the rear center reference point,the motion law of the vehicle outline was derived.According to the vehicle parameters,the required minimum parking space size and the theoretical feasible parking starting area are determined.The advantages and disadvantages of various parallel parking path curves are compared and analyzed.The superimposed curve of constant velocity offset and sine function with simple structure,continuous curvature and easy to track was selected as the parallel parking path in this paper.Combining the environmental constraints and the kinematics constraints of parallel parking scenes,the starting areas that meet the parking conditions are divided,and different parking paths are designed for different areas.In view of the small size of parking space,an attitude adjustment path was planned.Considering the problem that vehicles encounter obstacles during parking,the applicable scenarios of two obstacle avoidance methods are analyzed.Then,the vehicle speed controller was designed based on the PID control algorithm.In order to reduce the impact of vehicle speed on the path tracking effect,and to ensure that the vehicle meets the conditions of vehicle minimum turning radius constraints and vehicle corner speed constraints during path tracking,a path tracking controller was designed based on the soft constraint quadratic programming model predictive control theory.A path tracking simulation was performed in Simulink.The simulation results showed that the actual driving path of the vehicle was in good agreement with the expected path,and the control effect was good.Aiming at the obstacle avoidance control of pedestrians,animals and other dynamic obstacles during the path tracking process,an obstacle avoidance controller was designed based on the ultrasonic radar signals.Finally,combined with veDYNA vehicle dynamics model,PreScan parking scene model and Simulink vehicle motion control model,the joint simulation verification of the parallel parking system control strategy was completed.A real-time system test platform was built using NI-PXI equipment,which verified the consistency and real-time performance of the control model after it was compiled into embedded code.A smart toy car test platform was built,the control model code was loaded into the Raspberry Pi,and a Ford Fiesta ST Rally car model was controlled for a parallel parking test,which verified the effectiveness and stability of the control model.