A Study On Path Planning And Tracking Control Method For Automatic Parking System

As a kind of convenient and efficient transport, car has become more and moreimportant in people’s life and work. The limited city space is getting croweded withthe increasing number of car, and the parking space assigned to each car is becomingnarrow gradually. Parking a car into the parking lot is becoming more and more difi-cult to the drivers. The difficulty of parking makes automotive consumers request adevice that can help them parking the car easily and safely. The requirement forparking assistant device gets more and more car manufacturers, research institutionsand universities to study and design the automatic parking system. Some car manu-factures abroad have release their own parking assistant systems by now, but we don’thave parking assistant system with independent intellectual property yet. So, this pa-per fucuse on the study of the parallel parking control strategy which is the coretechnology of the automatic parallel parking system. The purpose of this paper is tomake the car parking operation easier and improve the security of the parking process.This paper designs the automatic parking system control stategy with the methodthat combines parking path planning and parking path tracking. The work in this paperare as follows:(1) Parking lot detection method and experimental verification. Understandingthe distance measurement principles of ultrasonic radar, ultrasonic radar and wheelspeedmeter was used to get the information of parking lot. Using the digital radarranging changes analysis and the trip distance, the length of parking lot was got. Thewidth of pakring lot was got from the radar signal. Experiment was used to test andverify the parking lot detection method mentioned above.(2) Parking path planning. Parking path planning based on the B-spline theorywas proposed. Parking mode will be chosed between single-step and two-step modeaccording to the parking lot space. Path constraints were analyzed for two way park-ing respectivly. Parking path optimization functions with multi-nonliear constrintswere established respectively. Based on B-spline theory, the parking paths were de-signed, and the paths met all nonlinear constrained, it would be easy for car to track.(3) Path tracking control method. To reduce requirement on speed controlling tothe driver, non-time based parking path tracking control strategy was proposed. Dueto the maximum steering rate, the car minimum turing radius, the traveling speed and other factors, the car might be deviate from the target path, and the car will not beable to get into the parking lot. The path tracking method combined with point track-ing was proposed to solve the problem mentioned above, and the point tracking con-trol law was designed. Co-simulation by Carsim with Simulink was used to verify thefeasibility of the path tracking method combined with point tracking.(4) Vehicle location method and validation. The vehicle location including initialvehicle position analysis and movement pose culculation. In order to improve the uti-lization of on-street parking spaces and make the parking system more user-friendly,selectable parking criterias will be provided to the driver by parking system accordingto the parking information. Parking system will establish the parking coordinate sys-tem according to the parking criteria that the drive chosed, and then calculate theparking start position. Tire speedometer was used to get the vehicle position andheading angle during parking process, and the location method was tested throughexperiment.(5) Parking system function verification. Parking system was built. The parkingsystem units are sensing systems, steering actuators, human-computer interactionsystems, data acquisition and communications equipment. Parking system controllermodel was built in Simulink, switch controller module between the various controlstates using StateFlow, and rapid control prototyping technology was used to test andverify the parking system function in parking experiments.The innovations in this study are as follows:(1) B-spline theory was proposed to design parking path for automatic parkingsystem. The parking path meets multi-nonlinear constraints, such as high-ordersmoothness, shape modify easily and parking safely and so on. Single-step parkingpath or two-step parking path ware designed according to the parking space.(2) Non-time based parking path tracking control law was proposed to make thepath tracking control method gets rid of the influence of the car speed, and the speedcontrol during parking process becomes easy to the driver.(3) Fixed point tracking control method was proposed to adjust the car’s pose。Car pose adjustment method through fixed point tracking control is useful to raise theparking success rate and helpful to park car strandard.(4) Parking controller modle was bulided use Simulink/StateFlow. Parking pathmethod and path tracking method was tested use simulation, and automatic parkingsystem control logic was verified use a new rapid control prototype method.