Research On Laser On-line Measurement Method For Geometric Quantity Of Axle Bushings

Axle bushing is one major part in the suspension system of military and civilian vehicles,which has a substantial impact on the performance of the suspension system.In production,the geometric quantity of the bushing needs to be detected to ensure that the bushing meets the requirements of assembly and performance.Laser measurement technology has the advantages of fast measuring speed and high accuracy,which is very suitable for on-line measurement of mechanical workpiece geometry.To research the laser on-line measurement method for the geometric quantity of bushings exhibits great significance to improve the processing quality and geometric accuracy of bushings.In this dissertation,aiming at the requirement of on-line measurement in bushing production,the on-line measurement method on geometrical diameter of axle bushing is studied based on the principle of laser shadow,and the system scheme of laser on-line measurement is put forward.Furthermore,the accurate calculation method and expression formula for bushing diameter measurement are derived,and thus the measurement accuracy and sensitivity of the system are simulated and analyzed.According to the shadow spot characteristics obtained by CCD,the edge detection algorithm to improve the measuring accuracy is designed.The experimental system of laser shadow measurement is set up,and test validation of the diameter calculation method and the edge detection algorithm is carried out.The main research contents are as following:(1)Research on the calculation method of the axle bushing diameter.Based on the laser shadow measurement principle,the system scheme of the on-line diameter measurement is designed.According to the position relationship of each component in the system,the analytical geometry method and the area alternative method to accurately calculate the bushing diameter are proposed,respectively.The approximate solution method of these two methods is derived,which is effectively simplify the diameter calculation within a certain error range.(2)Measurement accuracy and sensitivity analysis of the diameter measurement system.Simulation analysis of the measuring accuracy of the diameter calculating method is conducted from the three perspectives of system structure parameters,workpiece size and CCD structure parameters.The results show that the theoretical measuring accuracy of the analytical geometry method and the area alternative method could reach up to 1μm,and the analytical geometry method is less affected by the parameters.The sensitivity of the system structure parameters is simulated and analyzed using the local sensitivity analysis method.The results show that the system is less sensitive to the two parameters:laser source position and measurement center position,and more sensitive to the parameter of measured workpiece position.(3)Design of shadow edge detection algorithm.Aiming at the degradation of the shadow spot edges acquired by CCD due to the change of laser incidence angle and straight edge diffraction,the variable window sliding filtering algorithm and the midpoint threshold selection algorithm are designed to detect and locate the shadow edges.Simulation and comparison with existing algorithms show that the edge detection algorithm designed in this dissertation can obtain the shadow boundary point coordinates and the length of the shadow quickly and accurately.Moreover,the actual length represented by the shadow pixels captured by CCD is calibrated by using a standard gauge block.(4)Diameter measurement test using laser shadow method.Combining the production environment of the bushing part,the laser shadow diameter measurement test system is designed and built.The measuring tests of three different diameters of cylindrical standard parts are carried out,and the measurement results are subjected to one-sample mean t-test and measurement error analysis.The results show that the test system could accurately measure the diameter of cylindrical standard parts with a confidence level of 95%.For the measured cylindrical standard parts,the measurement error is 0.024～0.050 mm,under the present test system with the given system parameters.The validity of the diameter calculation method and edge detection algorithm is verified,which meets the requirements of online measurement for diameter of bushing in actual production.