Research On Vision Measurement Method For Automotive Wheel Alignment Parameters With Small Size And Large Baseline

In recent years, with the development of the automotive industry and roadtransportation，vehicles have got access to people’s work and life. Though cars play the roleof walk for people, it also leads to many problems including traffic safety. Many reasons canlead to change of automotive wheel alignment parameters like road bumps and trafficaccidents. If the wheel alignment parameters are incorrect, the car will tend to produce avariety of failures, including vehicle skidding, the steering wheel shaking, steering hard,front wheel shimmy, abnormal tire wear, fuel consumption increasing and so on. Hence, weneed to detect wheel alignment parameters regularly, and conduct adjustments and repairstimely, to make it always within the normal range.This article extends the visual measurement technology to the field of intelligent vehicledetection. For the requirements of wheel alignment parameters detection at automotivetesting line, a binocular vision measurement system with the feature of small size and largebaseline is constructed. The characteristic law of the binocular vision system is analyzed.The structure program with two symmetrically placed plane mirror systems and twobinocular vision systems is designed. The optimal system size result is received through thesimulation method of particle swarm optimization. In order to unify the measurement resultsof feature points that are in different visual systems with different locations and directions tounder the same world coordinate, and relize measurement in the vehicle size, a T-type modelof the three-dimensional calibration system including mechanical moving part and thedisplacement angle measurement part is established. Finite element analysis of the keycomponents of the calibration system is executed. The T-type calibration system ismanufactured. A coordinate transformation model of the feature points which are rotated andmoved is established. The world coordinates of feature points on a three-dimensionalcalibration board in a large view field are calculated. The conversion relationships betweenthe spatial coordinates of feature points on the calibration board at each location are obtained.Calibration tests of the binocular vision system are conducted. We come to the conclusionsthat the measurement error decreases when baseline is increasing. And it increases whenmeasurement distance is increasing. Besides, the measurement error is minimum in a direction perpendicular to both the baseline and the measured distance. Calibration tests forcoaxial position and the angular position of the global calibration are executed. Fromanalysis results we can know that the global calibration system can ensure measurementaccuracy. Finally, the wheel alignment parameters set by testing equipment are actuallymeasured. And the stability of the measurement results is evaluated.This paper combines visual measurement technology with global calibration method ofthree degrees of freedom. And global calibration for measurement systems in differentpositions is relized. Meanwhile, the binocular vision method with small size and largebaseline is applied to wheel alignment parameters measurement. A small detection system ofwheel alignment parameters is provided for automotive test line.