Calibration Technology Of Wheel Tread 3D Measurement System Based On Phase Measurement Profilometry

In recent years,with the continuous improvement of load and speed for the railway,the wheel bears an unprecedented load,which seriously influence the safety of railway transportation.How to effectively obtain the wheel tread information and the wheel tread defect information and to prevent the occurrence of accidents in the operation are more and more important.In this case,the high precision Phase Measuring Profilometry is selected to obtain the phase information of the wheel tread.Besides,the calibration is operated both in plane and depth direction respectively.Finally,the 3D information of the wheel is obtained according to that.The specific studies are shown as follows:Firstly,the basic principle of Phase Measurement Profilometry is introduced,and the expression of phase measurement is deduced;at the same time,this thesis introduces the algorithm of package,which lays the foundation for the following work.Secondly,the structure of the measurement system is analyzed,and the calibration method of the measurement system is discussed both in the plane and at the height direction.Thirdly,the Phase Measuring Profilometry for measuring the height direction is simulated,which uses a traditional phase height mapping algorithm and a new phase height mapping algorithm.Firstly,the 5mm high plane is measured,the average height of the traditional phase height mapping algorithm is 4.9995mm,the average relative error is 0.043%,and run time is 35.9082s,but the average height of the new phase height mapping algorithm is 5.1123mm,the average relative error is 0.97%,and run time is 3.2145s.Then,the wheel tread height is measured,and the average absolute error of the wheel tread is 0.0942mm,and running time is 37.3878s by the traditional method,while the average absolute error of the new phase height mapping algorithm is 0.1740mm,and running time is 3.6835s.Finally,the defect depth of the wheel tread is measured,the average defect depth of the traditional phase height mapping algorithm is 1.9872mm,the average relative error is 0.0531%,and running time is 39.2565s,while the average defect depth of the new phase height mapping algorithm is 2.1147mm,the average relative error is 0.0673%,and run time is 3.7094s.The results of the two methods are compared according to the measurements of the plane,the wheel tread and the defect on the wheel tread,we can see that the traditional method and the new method can correctly restore the height information of the object,but the traditional method is more accurate than the new one.According to the running time,we can see the traditional method is far greater than the new method.At the same time,the operation of the traditional measurement method is complex during the progress,while the new method only needs seven system parameters independent of pixel point,which makes the operation simple.When the number of image pixels is large and the requirement of the precision is not high,the new method has more advantages.Finally,the calibration experimental platform for 3D profile measurement of wheel tread is designed and constructed.The traditional method and the new method were used to measure the height of the LMA wheel,the drop from the LMA wheel flange to the tread was 28±0.5mm.According to the traditional method,the drop from the LMA wheel flange to the tread is 28.4973mm,and the running time is 389.9639s,while the drop from the LMA wheel flange to the tread is 29.1846mm using the new method,and running time is 60.8058s.It can be seen that in the actual measurement process,the traditional method and the new method can correctly restore the wheel tread height information.At the same time,the running time of traditional method is longer than the new method.Combined with the calibration on the plane,we can get the 3D point cloud of the wheel tread.At last,the factors affecting the measurement results are also analyzed.