| In recent years, Chinese automobile manufacturing industry and road-transport industryexperienced a rapid development, the amount of automobiles increased rapidly, bringingtraffic safety, environmental protection and other social problems which cause urgentrequirement of people to the automobile detection/diagnosis technology and equipment. Theautomobile braking performance plays a vital role for the safety of vehicle operation, andalso has certain influence on vehicle fuel economy and transport-efficiency. Therefore,automobile braking performance as an important detect factor of automobile safety andeconomic benefit has significant meaning.At present, the anti-force roller brake tester and the plate brake tester which werewidely used in safety testing of the public security system, performance testing oftransportation system and maintenance testing of repairing factory are limited by theirstructure and the measurement principle, can only detect vehicles with a very low speed. Itmeans that the braking performance of the vehicle with ABS braking system can’t be wellevaluated, besides the detection parameters are not directly tested parameters such asbraking distance, the test results can not reflect the actual braking performance of thevehicle. Road vehicle braking performance test technology, commonly known as road testmethod is a special method, which is judged by braking efficiency (i.e., braking distance andtime) braking direction stability (i.e. braking deflection and sideslip). This method can trulyreflected condition of a vehicle and is applicable for all vehicles, but the device should beinstall and remove for each individual testing, so it cannot meet the automatic andhigh-speed requirements of testing line. In addition, the national standard GB21861-2008regulates taking the road test as a final result on the circumstances which the owner of thevehicle have doubts on the results or vehicles can’t be online testing, also reflects theimportance of road test method. But current testing equipment impeded the development ofdetection technology, as the result, using advanced computer technology and automaticdetection equipment to replace the traditional detection method is being imperative.Both plate-testing and road-testing methods are still in the stage of human subjectivejudgment when evaluate the stability of the vehicles, so they can not show lateral displacement of vehicle quantitatively. Therefore, this paper is to develop a device to solvethis puzzle, and the device should also has the ability to effectively evaluate the car withABS. Based on these two considerations, this paper choose the road test method to study,developed a detection system based on stereo vision which meet national standards "the safeoperation of motor vehicles technical conditions", proposed measurement methods to realizethe automatic test of the brake performance using binocular stereo vision. This paper basedon the theory of stereo vision, using the extraction and matching of target feature, cameracalibration and other vision technology as the foundation, studied the kinematic model of acar braking process, and also found the suitable algorithm for visual detection system whichdesigned in this paper. To test the accuracy and reliability of automobile brakingperformance in visual detection system proposed by this paper, a visual-inspection brakingperformance verification device is built to simulate the braking process for real. Afteranalysis the data of the system, this paper points out theory allowance of the verificationdevice which exists in its precision verification aspects. Finally, experiment was conductedon the real vehicle, achieving some creative research results. The main research contents andachievements of this paper are as follows:1) Researching image processing algorithms for visual inspection system. Accurateextraction, detection and identification of feature points are the prerequisite for all the visualwork. The study of image processing algorithm for a specific target has been relativelymature, but there is no interoperability between the various algorithms. A key work of thispaper is the measuring tasks of circles, ellipses and rectangles these three characteristics ofthe detection, working out the suitable algorithm for the braking performance of thedetection system. Analyzed the defects of algorithm commonly used from imagepretreatment, line feature extraction, corner detection and stereo matching aspects. On thebasis of these algorithms and to achieving the goal of this article, the author improved thealgorithm by adding a condition and then using stand-alone test to verify the correct of thealgorithm.2) Researching on calibration method for visual inspection system. Camera calibrationis the prerequisite for visual measurement. Get the whole image of the car body requires thatthe double camera was placed in horizontal mode and high precision test requires that thecamera was calibrated by choosing three-dimensional calibration checkerboard grid.Considering the outdoor image acquisition will bring image distortion, a new calibrationmethod of camera parameters based on radial distortion was designed, and then choosecameras with high-resolution to get the camera parameters. Before the calibration algorithm, it is necessary to detect and extract the X-type corners consists of four black andwhite checkerboard corner by the improved Harris corner detection algorithm. The fourfactors that affect the accuracy of the system are: the wiring distance between the center ofthe camera, the distance from camera to the ground, the distance from camera to thecalibration target and the downward sloping angle of camera3) Experimental Researching on precision verification. This paper developed a set ofverification device to proof the precision of automobile braking system, using the transversemovable car, a longitudinal movable car respectively moving with constant speed,acceleration and deceleration in the lateral guide rail and the longitudinal railway, simulatingactual vehicle braking process, by analysis the data after image processing, verifying theaccuracy of the system.4) Designing visual detection system of vehicle braking performance. Combined withthe measurement index, this paper introduced the computer binocular vision inspectiontheory systematically to study the theory and parameters of automobile braking performance.Analyzed the relationship of the lateral path offset value, braking distance, brakingdeceleration in depth, this paper proposed the method using a certain point of a car insteadof the car vehicle for detection. Combining the design target with performance evaluationtarget of visual detection system, this paper finished the reasonable design of brakingperformance test system based on of computer vision. Focusing on the parameters of camerain choosing hardware, then making the hardware as the basis of software development，theycan show the operation of the new method on the road test.5) Experimental verification of vehicle braking performance detection system based onstereo vision. Researching the system designed in this paper with using vehicles. Install theportable braking analyzer in testing the car and pasted four rectangular signs on the roof ofthe car, and then carry out braking test in the track of road test. After image processing, thebraking distance, braking deceleration and vehicle offset distance will be showed on thesoftware of the road test, and the final evaluation results will also be given out. Comparisonof the experimental results proved that this method and theory is correct. Numerousexperiments of other vehicles verified the validity and applicability of the method. The testresults show that the proposed method can realize automatic and non-contact detection ofbraking performance parameters and has high accuracyResearches and developments by this paper of automotive testing are an innovativework and also an example of combining stereo vision detection technology with actual.Visual detection algorithm developed in the paper contributed to the vision detection technology, and added new technology in the automotive road test of vehicle brakingperformance. The method solves the bottleneck problem of the braking performance testmethods, and actively promoted the development of automobile detection industry. |
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