Research On Automobile’s Wheel Speed Detection System Based On Image Processing Technology

Automobile’s wheel speed is an important parameter to many control systems such as ABS, VDC and ESP, etc. Accurate wheel speed information is the premise to these systems which can work efficiently and stably. So, how to get accurate and reliable wheel speed has great significance. In automobile performance tests, however, the traditional wheel speed is obtained by the wheel speed sensors. To install the wheel speed sensors, many types of installation tools should be equipped according to different models. This method has hefty workload, low efficiency, poor portability and commonality. Therefore, developing a wheel speed detection system is particularly important which has the features of high reliability, strong commonality and easy to install.A new wheel speed detection system based on image processing technology is proposed. According to analysis the characteristic of the system in detail, a whole scheme is designed. High-speed CCD cameras are used to shoot vehicle wheels which have a characteristic line respectively and transmit the images to computer in real-time. The upper computer is used to preprocess images and extract the characteristic line by image processing technology. The wheel speed is calculated through working out the characteristic line’s angle of two consecutive frames using the curve-fitting method.Firstly, the whole process algorithms are analyzed. In the image preprocessing section, algorithms about image gray, compression, enhancement, difference and filtering are analyzed deeply. Then, the different algorithms’ feature and execution time are compared with the performance of different algorithms. According to the characteristics of the images, an improved image difference algorithm and an image enhancement algorithm are proposed. In the feature line extraction section, edge-detection and corrosion expansion algorithms are mainly analyzed. The wavelet edge detection algorithm is chosen to extract the characteristic line through comparing detection results about six kinds of edge detection algorithm. By image processing, the images only have clear outline of the characteristic lines. In the wheel speed calculating section, least square method is used to calculate the wheel speed which converts the image information to the speed information.Secondly, the hardware platform is built and the design of software is completed. The principles of selecting the hardware equipment are introduced in details, including CCD camera, lens, light source and characteristic line, etc. Then, the software of each function module are completed which realized the image acquiring, processing and wheel speed calculating. Meanwhile, the wheel speed’s display, preservation, import, and others function are realized.Finally, the real automobile experiment is carried out and the experimental deviation is analyzed. Experimental results show that the system not only solves the defects and deficiencies in conditional wheel speed detection system, but also be able to acquire accurate wheel speed in real time which meets the demand of automobile performance test.