Research On Vehicle Autonomous Guidance System Based On Magnetic Sensor Array

Traffic jam and traffic accident are the two main problems for the road transportation. It is efficient way to improve the road traffic capacity and the transportation safety by developing the intelligent vehicles. In the city environment, due to the complicated road traffic, the performances and realiability of vehicle guidance with the GPS technique, vision technique and wireless technique are usually deteriorated due to the complicated environment, sunlight and climate conditions. Magnetic sensing has been proven to be one promising technology for intelligent vehicle guidance and control. Magnetic sensors are less susceptible to the influence of rain, snow, fog or other environmental conditions than a sensing system based on an optical technique such as image processing. In this dissertation, the vehicle lateral offset measurement, vehicle localization and path following are studied in detail.Magentic sensing system plays the important role for study on magnetic guidance of intelligent vehicle. The application of magnetic sensing technology in intelligent vehicle field is influenced by the reliability and robustness of the magnetic sensing system. In this paper, the overall architure of the vehicle autonomous guidance system is described, and the design criterion on the magnetic sensing modules is presented in detailed. As the main two modules, the magnetic marker module and the magnetic sensor array module are discussed separately. The optimal objective function of the magnet module is constructed and the size of magnet is optimized. The magnetic sensor array with two different spacing between sensors is designed and the numbers of sensors are reduced. The new magnetic sensing system with high sensitivity, high reliability, low-cost and high installment height has been realized and some experiments have been implemented.In the magnetic sensing system of intelligent vehicle, it is very significant for the vehicle guidance to measure the lateral offset with high accuracy. The earth magnetic field and the external magnetic object are main sources of the disturbance, and the effective dual sensor differential method is proposed to get rid of the disturbance. On the basis of the accurate mathematic model of magnet, the sequencing threshold method is proposed to measure the lateral offset of the vehicle. Although this method is simple and robust, the measurement accuracy is not enough for the high accuracy measurement. In order to improve the measurement accuracy, the new sequencing ratio method is presented in detailed. The sequencing ratio method is insensitive to the variations of the vertical position and the longitudinal position. The relationship between the magnetic field ratio and the lateral offset is linear. The linear function relationship is decided by the spacing of the neighbouring sensors, and is easy to realize.The accuate localization is one of the important parts of the autonomous vehicle guidance. The kinematics model, odometry model and measurement model are created in this paper. Owing to the accumulative errors from the dead-reckoning system based on odometry, it is necessary to fuse some absolute positioning information to get rid of the error. Comparing with EKF, UKF directly utilizes the nonlinear system function and nonlinear measurement function, and can obtain high measurement accuracy with 3rd Thalor series. In order to avoid missing magnets or detecting the false magnets, the data association method is introduced to judge the validity of the measurement data from the magnetic sensing system in the measure update phase. Some experiments are implemented and the results showed the robustness and the validity of the method.The path following and the ride comfortability are the two main problems for vehicle path following. In this paper, the front and rear lateral offset and their derivatives are defined as the state variables and the new system state equation is derived. Owing to the two different polarities, the magnet coding method is proposed to provide the upcoming road charateristic information to improve the performance of the path following. In the road section with road curvature variation, the curvature smoothing method based on clothoid curve is proposed to smooth the road curvature. Some simulation experiments are performed and the results prove the validity of the road curvature smoothing method.