Study On Testing System Of Automobile Wheelbase Difference Based On Stereo Vision

In the course of automatic detection technology, universal attention to hardware technology, ignore some testing item of difficulty and invested more than and social not obvious, that these tests are lack of appropriate detection equipment, which has affected the speed of automobile detection, hinder the Intelligent development and automation of Detection technology. Ignore the detection of the wheelbase difference. The wheelbase difference has a significant influence on automotive performance. When the difference exceeds a certain limit, vehicles stability changed for the worse; when braking or running at high speed, it will enable the auto will occur to turn to radical sliding or overturn; when straight line travel, it will Increases the body's road width, impact on road safety, increase tire wear, brought economic losses and potentially dangerous.Since 2001, it is enacted national standards about the automobile wheelbase difference. According to"National Standards multiple performance requirement and detecting methods for commercial vehicle"GB18565-2001, the equipment requirements for vehicle goes: vehicle equipment should be complete, intact and effective and fastening parts should be well-connected. The body should be modified, (from 1.5m high with measurement), wheelbase defect between the right and the left should be less than 1.5/1000 of the wheelbase. In 2004, about national wheelbase difference are more stringent, promulgated the transportation industry standards, According to"Operating vehicle technology classification and assessment requirements"JT/T198-2004: The body should be modified, (from 1.5m high with measurement), wheelbase defect between the right and the left should be less than 1.2/1000 of the wheelbase. Then, also promulgated"National the motor vehicle running safety technical conditions"GB7258-2004, Automobile in straight line travel process, the center of front axle and rear axle of Automobile Should be consistent with the direction of the road. In 2005, "Specifications for multiple-function detecting test station of vehicle transport" GB/T 17993-2005: 0 ~ 20000mm (wheelbase defect);error allowed 1mm. This shows that the request of wheelbase difference detection accuracy is more and more high. This requires more advanced and more accurate detection methods.Based on above background, this subject study on testing system of the wheelbase difference based on stereo vision, by using the binocular stereo vision, realization do not stop the dynamic measurement, and meet requirements for measurement accuracy.The Key technologies, such as the Image processing technology, camera calibration, as well as Corner extraction and stereo matching and 3D reconstruction and camera calibration, are studied and discussed thoroughly. This paper shows detection algorithm of this subject, and detection of the automobile body. Experiments show that, this testing system has better detection accuracy and repeatability.The main research works are as following:1. Study the background and meanings of the paper, analyzed detection technology of the wheelbase difference internal and overseas, proposed testing method of the wheelbase difference based on stereo vision, and describes the key features of the paper.2. Produced ranging principle of stereo vision, and composition and contents of stereo vision, illustrates the detection principle of the wheelbase difference. Uses camera installation program of axial mode, proposed the project design of the wheelbase difference based on stereo vision.3. Using pattern recognition key technologies, obtains the wheel hub image. Analysis by image processing applies to this thesis research in the key technologies of detection methods: Median filter and image segmentation method of OTSU algorithm, area fill select Scan line seed fill algorithm, used mathematical morphology to remove the boundary, and opens operation processing of mathematical morphology to obtain the wheel image, by least square method to circular feature extraction, obtains pixel coordinates of wheel center. Study on stereo vision algorithm, uses Harris algorithm to extraction of target corner, and stereo vision matching technology, uses outside polar line geometric constraint, it is better to eliminate the undesirable match under various conditions, obtains the very high correct match rate, meets the precision of a measurement system requirements.4. Study calibration system of the wheelbase difference based on stereo vision. First of all, analysis camera parameters are required, and described the world coordinate system, camera coordinate system, the definition of the image coordinate system and the transforming relationship between them, as well as the camera imaging model, research on camera calibration algorithm, uses calibration method based on a step radial direction distortion, and description of the algorithm in detail. Finally realizes the rapid and accurate calibration of the parameters inside and outside and structural parameters of the sensor. And experimented with the target, verify the calibration of this algorithm. Through calibration experiments of different baseline distance, Description Effect of baseline distance calibration accuracy. 5. Study on 3D reconstruction models of several typical track width vehicles when Oblique straight line driving. First introduced 3D reconstruction algorithm of point and the straight line, then completion of the experiment with tires of different tread vehicle, 3D reconstruction of wheel center At different angles when Oblique straight line driving, and drawn the absolute error curve. It is verified Accuracy of 3D reconstruction algorithm of this paper.6. The experimental study of the wheelbase difference based on stereo vision. Reasonable design system programs of hardware and software. Uses vehicle body to a experimental study on the design of this system, and correction and compensate the Error when Automobile curve travel. The experiment results show that, this detection system can meet the test line of real-time detection requirement; test results were consistent with error range.The main contents of the study and the results are as follows:1. Based on stereo vision in automobile wheelbase difference non-contact 3D measurement method.Research and design for a variety of typical track automobile wheelbase difference detection system,the system can realize the accrate measurement of left and right axle distance difference.2. Based on the wheel hub image matching algorithm, the digital image processing algorithm and the actual testing project combining,complete detection system hardware and software development,relize automobile wheelbase difference measurement.3. Based on wheel hub of 3D image reconstruction algorithm,which allows the extraction of the hub center coordinate more accurately,thereby improving the wheelbase difference calculation precision.The research and the development work made by this paper is a typical example of application which makes a number of research results in the technology and algorithms. At the same time, this paper leads the technology of stereoscopic vision into the detection of wheelbase difference, realizes the automation process of vehicle detection.