ONLINE MEASURING METHOD AND SYSTEM FOR DIAMETER PARAMETERS OF WHEEL SET WU Kaihua, ZHU Feng, ZHUANG Fei, YAN Kuang School of Automation, Hangzhou Dianzi University, Hangzhou 310018, P.R.China, Email: wukaihuahdu.edu.cn Keywords: Wheel set diameter, online measurement, optoelectronic measurement, automatic measuring system. Abstract The measuring of diameter parameters of wheel set is an important step for the safety of train vehicle running. The wear degree of wheel increases with the speedup of train. The paper introduced an online measuring method of diameter parameters of running wheel set based on optoelectronic detecting technique while the train is running in low-speed within 5-10km/h. The method used precision laser displace-ment sensor, high speed and high resolution CCD and digital image processing technology to realize the non-contact automatic measuring of wheel set parameters. These parameters include the diameter, roundness and diameter difference. The main influence factors for measuring accuracy, including movement, vibration and trigger error were analyzed. The automatic measuring system was designed. The system included wheel detector, laser displacement sensor, semiconductor laser source, CCD, online image acquisition and processing circuits. Theoretic and experimental results showed that the measuring accuracy of diameter parameters was within 1.0mm. The accuracy meets the demand of online diameter measurement. 1 Introduction In order to ensure the safety of a running train, its very important to detect the status of the wheel set automatically and regularly. The wearing degree of the wheel set is one of the main factors that influence the safety and stability of running train. In China, the measurement of wheel set wear is still static and by handwork mostly which limits the accuracy and reliability. The difference between different operators is often too big. The detecting efficiency is also very low. In recent years, the running speed has increased to 160-200km/h. The wear degree and speed are much quicker than before. The static and handwork measuring method cannot meet the development of high-speed train. Researching the automatic and online method is an urgent need of transportation and maintaining departments. The wear parameters of wheel set include geometrical parameters and surface defects. The main geometrical parameters include flange thickness, flange height, wheel diameter, roundness and diameter difference etc. The surface defects include scotching and flaking on wheel tread. These parameters are the main factors that influence the safety and stability of vehicle. The paper mainly introduced the online measuring method and system of diameter parameters. Up to now, most of the maintaining factories were still using special mechanic tools to measure the geometrical parameters by manual work, especially in China. These tools, including special vernier caliper, wheel diameter ruler and rim inside distance ruler, will wear down. The status of these tools will influence the measuring accuracy. The manual work manner had strong labor intensity and low efficiency. The man-made factors produced by different operators perhaps bring different and variable error. The measuring accuracy, reliability and repeatability cannot meet the demand of wheel set maintaining departments. The automatic measuring methods and systems had been researched in recent years1,2,3,4. Yet these methods were only suitable for maintaining factory and the vehicle must be disassembled. Several countries, such as Germany5, Japan, Italy and the United States, have developed online automatic detecting systems based on different principles. These systems are very expensive and have not been widely used. In China, there are also research on this field6, but no practical equipment had been developed. Regular measurement and repair cannot fill the requirements of maintenance. The online measuring of profile parameters is important to the distinguishing and forecast of failures while the train is running in low-speed. The preventive repair will reduce the maintenance cost greatly. The paper introduced a new non-contact online measuring method and system of diameter parameters. 2 Measuring method 2.1 Definition of diameter parameters Train vehicle wheel set is a rolling parts produced by pressing two wheels into an axle. Fig. 1 is the profile of a cargo wheel section. Tread is the contacting part with the rail. The right plane is rim inside plane. The plane wont contact with the rail and has no wear. The part between rim inside plane and tread is called flange. The taping point is a base point on the tread and has 70mm distance to rim inside plane7. The rolling circle is a circle passing through the taping point on the tread . The average diameter of rolling circle equals wheel diameter. The roundness can be derived from diameters at different positions on the rolling circle. The