Research On Ultrasonic Detection Of Parking Slot And Steering Control Algorithm For Automatic Parallel Parking

Automatic parking is an autonomous car maneuvering from a traffic lane into a parking place to perform parallel parking, perpendicular or angle parking. The automatic parking aims to enhance the comfort and safety of driving in constrained environments where much attention and experience is required to steer the car. In order to quicken the realization of the automatic parking system, this paper focuses on the ultrasonic detection of parking slot and steering control algorithm in the parallel parking situation. And then, all of the results will be proved by experiments.In automatic parking system, the detection and location of an empty space are completed by two ultrasonic sensors, which are fixed on lateral sides of the vehicle. So, the design of ultrasonic detecting system consists of two parts, hardware part and software part. The system uses a DSP as control unit, an optocoupler chip to strengthen the ultrasonic waves in the transmitting circle, and the receiving circle makes use of integrated chips to simplify the whole configuration such as integrated filter, programmable gain amplifier and amplitude detection. On the other hand, software system completes timing and measuring distance. Then the controller estimates the length and location of the parking slot by comparing varieties of detecting distance. It is proved by experiments that this system will be accurate especially in detecting from 0.6 to 1.8 meters. Further more experiments are done to get a general method for ultrasonic detection, which is also proved.The steering control algorithm is the core of automatic parking system. This paper uses the veDYNA as the dynamic simulating vehicle model, which can simulate the actual situation well. In case of steady speed while parallel parking, a theory, that the steering control process is determined by four time variables, is given in this paper. That means if the steering wheel is operated in that method, the parking will be successfully. After that, it optimizes the steering control algorithm for different situations by the Genetic Algorithm. The optimization process is that: firstly, it combines the MATLAB and VC programs. Secondly, it sends the timing variables to the veDYNA as the GA's determining variables, and the vehicle's final position coordinates and yaw angle are used as the GA's evaluating function. Thirdly, the program is calculated iteratively in order to get the best consequence. After the optimization, a steering control algorithm is given to direct the parking operation. Then, the steering control algorithm is sent to the veDYNA model again. After the simulation, the vehicle's parking path is obtained. Fourthly, by adjusting the position of the vehicles besides the parking slot and keeping sufficient clearance in the DYNAanimation software, the minimal parking slot and starting position called point O are got. At the end, the paper compares the length of the parking space requested by this system with others, and the former's advantages are proved.The steering control of automatic parking system bases on an electric motor. In the experiment, a DC motor is chose as the executor of the steering. It is fixed on the steering wheel and linked with steering shaft by a retarder in order to reduce the motor's speed and increase torque. The motor is adjusted by a method called PWM, and the control system consists of a DSP controller, a piece of relative driving PCB and a signal sensor. With the feedback of signal sensor, the DSP compares the motor's current speed with request, and then it can adjust the ratio of the PWM, by doing this, the rotational speed will be controlled. With the help of a CAN card, the DSP can communicate with a computer, which programs according to the steering control algorithm for parallel parking. Finally, the parking maneuver, which takes the actual situation of environment into account to ensure collision-free motion within the available space, is achieved by means of coordinated control of the steering angle and speed.Automatic parking system is regarded as the next hot product of automobile industry. It can alleviate driver's physical and cerebral load and reduce traffic accidents. This paper focuses on convenient steering control algorithm and hardware of the automatic parking system, with the purpose of generalizing this system quickly.