Research On The Detection Method Of Wheel And Axle Alignment Parameters Of Truck

With the rapid development of China’s highway transportation industry,trucks are increasingly widely used in daily life.Their emergence has greatly enhanced the highway transportation capacity and improved the logistics turnover efficiency.The National Road Traffic Safety Law stipulates that the highway allows the passage of trucks that meet the standards,which further promotes the development of trucks.Due to the characteristics of truck driving for a long time and a long distance,higher requirements are put forward for driving stability and safety.Inaccurate wheel and axle positioning parameters are one of the more common faults of truck driving,which seriously threatens the driving safety of vehicles.Wheel and axle alignment parameter detection is to determine the vehicle status by measuring the wheel and axle alignment parameter values to determine whether the wheel and axle need to be adjusted or repaired.Compared with small passenger cars,the application of wheel and axle positioning technology in trucks has not been paid enough attention.Therefore,it is very urgent and necessary to propose a set of detection methods for truck wheel and axle positioning parametersThis paper first introduces the common reference datum and positioning method of trucks,and selects the standard four-wheel positioning method for the research of the detection scheme of truck wheel and axle positioning parameters in this paper,that is,positioning other parameters based on the coincident thrust line and vehicle geometric centerline,and then proposes the overall measurement scheme of truck wheel and axle positioning parameters,The measuring principle of each positioning parameter is studied and deduced in detail.Because the values of wheel and axle positioning parameters are very small and the accuracy requirements are high,the method of visual measurement is used in this study.By selecting special markers,the image processing process is simplified and the measurement accuracy is improved.In the image processing part,based on Halcon image processing software,the measurement method of plane geometric features is studied,and the image processing algorithm flow is designed.The black rectangular outer frame and white inner panel are selected as special markers to receive laser lines.Since the ultimate goal of image processing is to separate the laser line from the complex background image and calculate its angle and intersection position information in the O _w-X _w-Y_w coordinate system,in the aspect of preprocessing,the image is the first focused on the processing range by gray level transformation,horizontal mirror and segmentation,and then the median filter is selected to remove the image noise,and the image is sharpened and enhanced by using Laplacian operator and emphasize operator.Blob analysis algorithm is mainly used to segment and process the area in the image to achieve accurate positioning of the inner panel of the marker.When measuring geometric features,the measurement reference coordinate system is established based on the XLD contour of the region boundary and the pixel equivalent calibration is carried out.By extracting the XLD contour of the laser line and combining with the pixel equivalent,the measurement of the angle of the laser line and the intersection coordinates of the horizontal and vertical laser lines is completed.Before taking the image,calibrate the camera with Zhang Zhengyou calibration method,and test the calibration effect and verify the calibration accuracy from multiple aspects such as the re-projection error,the stability of the internal parameters obtained by calibration,and the linear correlation between the checkerboard corners after correction of distortion.In order to compare the advantages between the least squares method and the weighted least squares method,the simulation test is designed and compared at the end of the paper.Finally,the weighted least squares method is selected as the fitting method of the geometric centerline of the frame;Since the _wY axis in the ground O _w-X _w-Y_wcoordinate system is used as the reference for the measurement of the positioning parameters in this paper,rather than the geometric centerline of the vehicle,it is necessary to establish the conversion relationship between the _wY axis and the geometric centerline of the vehicle,and use this relationship to correct the required positioning parameters.Except camber and kingpin angle,all the positioning parameters with the _wY axis as the detection reference have been corrected,The corresponding correction formula is derived;Finally,the positioning parameter data corresponding to the specific truck model is obtained through the real vehicle test,which proves the feasibility and rationality of the detection method in this paper;Based on real vehicle test,the system error of the detection scheme in the test process is also analyzed,which is mainly caused by the"deviation"between the rim clamp and the wheel,and the corresponding compensation scheme is expressed.This method can effectively eliminate the system error caused by the deviation of the mounting position of the clamp from the ideal position,which is beneficial to improve the measurement accuracy.