A Study On Turnouts Profile Measurement Using Two-Dimension Laser Sensor

Switch is one of the most important equipments of railway track connection,the profile greatly changes due to wear and tear which influences the operation safety of the train, so the rail profile measurement is particularly important. Nowadays, Laser measurement technology is gradually applied to the railway industry, while the applications on switch profile measurement is very little,due to the large size and complicated structure of the switch. In this paper, the two-dimensional laser sensor used in the measurement of switch outline shape was studied, the main works as follows:Firstly, the current situation of switch testing and laser measurement was analyzed by accessing to information. The laser measurement technology, switch parameters and evaluation method were studied, and the research program of the total system was determined.Secondly, the communication protocols and library functions of the two-dimensional laser sensor were studied, and the dynamic link library was called based on VC++platform, and then the corresponding program was written to implement the transmission and preservation of the measured data.Thirdly, under the situation that only the sensor rotation angle was fixed, times of measurement data were transfered to the same coordinate by coordinate transformation, curve fitting was respectively by means of least square method, by comparing the slope, the public areas were found out and the translation amount was gained, so as to realize the registration of multiple measurement curve, and the error of the curves splicing method was analyzed. The results show that:this method is able to implement the whole profile stitching,but there is a certain error. The error is large by comparing the slope of the fitted curve to get the amount of translation.And it is found that stitching at the areas with smaller slope, the errors of the translation amount are greater. The rotation angle error is the main cause of uneven distribution of rotating part of the error. It can be seen, only determine the rotation angel of the sensor but not determine the translation amount, the results of the splicing are difficult to meet the precision requirement, so it needs to determine both the rotation angle and the translation amount of the sensor.Fourthly, by determining the rotation angle and translation amount, through coordinate tranformation of the times of measuring data in MATLAB to realize data splicing. At the same time the corresponding positive solution model and inverse solution model were established, and the error caused by parameter was simulated. The results show that:(1)when the sensor rotating reference point is located in the position of 215mm along the light, the error of the x coordinate and y coordinate are minimal.(2) under the circumstances of (1), the error is smaller when measuring away from the edge of the area in X direction and Y direction.(3)Sensor rotation angle error Δθ also affects the error, and the smaller is the Δθ,the smaller is the error, so the appropriate angle encoder can be selected according to the requirement of the measure precision.