Research On Automatic Parking Control Strategy Based On Ultrasonic

Automatic Parking System is a car electronic security system which automatically stops the vehicle into parking space through detecting the surrounding environment.Automatic parking as an important part of advanced auxiliary driving system can liberate the driver’s hands,improve the driving safety and comfort and bring numerous convenience to the life,so it has a broad market prospect and huge economic benefits.This article through researching on the working principle of automatic parking,the control strategy of Automatic Parking System based on ultrasonic is presented respectively from the parking space detection,path planning and path tracking.First of all,by using the distance range principle of ultrasonic sensor,the reasonable installation height interval of the sensor is obtained through the multi-group bench experiment,and the sensor distance rang error is measured and analyzed.According to the principle of ultrasonic detection of parking space for the environment conditions of parallel parking,the influence of ultrasonic beam angle on the detection of parking space is analyzed.For the detection error produced,a correction compensation method is proposed,which can effectively reduce the detection error.And the accuracy of the method is verified through experiments.Then the motion characteristics of the vehicle under low-speed running conditions are analyzed.The vehicle coordinate equation and kinematics model under low-speed parking conditions is established,and analyzing the parking motion trajectory.Based on this,combined with the situation of ultrasonic sensor distance ranging,a two-section circular arc parallel parking path planning strategy was proposed.The minimum turning radius of the vehicle was effectively used,and the parking constraints and collisions were judged.A collision-free safe and reliable parking path is planned.And through the MATLAB simulation tool to establish the vehicle movement model,the path planning of different parking environment and starting point is simulated to verify the feasibility of the strategy.Finally,with regard to the planned parking path,in order to address the problem of deviating from the target path caused by improper velocity control because of the time factor and the problem of parking-steering tracking errors.A non-time-based model-free adaptive control path tracking strategy is proposed to eliminate the time domain constraints brought by the acceleration and deceleration of vehicles,so as to track the parking path more efficiently.The vehicle non-time dynamic model is established.The model defines the non-time variable that increase over time as the control reference variable.The desired front wheel angle value to be tracked is generated according to the target path.In addition,adopting the Model-free Adaptive Control strategy that without specific object model information accurately control forward wheel steering to track the desired front wheel angle value,equivalent to realize the tracking of the orientation angle of the car.Thereby realizing the tracking of the parking path and improve the accuracy of path tracking.The MATLAB tool was used to verify the effectiveness of the strategy.Under different speed conditions and compared with PID control simulation,the results show that target forward rotation angle generated by a non-time reference is accurate,MFAC method is higher than PID control in the steering control precision and faster response.The effectiveness of the control strategy is verified and the target path can be tracked.The ultrasonic automatic parking control strategy proposed in this paper has great research potential and lays a foundation for the development of Automatic Parking System.