| With the improvement of advanced manufacturing technology,there are more and more mechanical parts with high precision surface,which requires high precision and wide range contour measurement for these parts.Stylus profilometer is widely used in the field of surface profile measurement because of its large measuring range,high stability and low environmental requirements.But the research shows that the measuring accuracy of the instrument is mainly affected by the geometric errors such as the nonlinear error of the sensor,the radius of the measuring ball and the straightness of the guide rail.In order to improve the measurement accuracy,these errors need to be improved and reduced.This thesis mainly focuses on the compensation for geometric errors of stylus profilometer.The main work is as follows:（1）In view of the nonlinear errors of the existing stylus profilometer,polynomial model is mostly used to compensate for the nonlinear errors by establishing the polynomial function relationship between the indicated value and the true value of the sensor.Due to the limited fitting ability of polynomial,the nonlinear error compensation based on polynomial model has a large residual error as the increase of measurement range.In this thesis,a non-polynomial error model for a stylus sensor is established.Using the standard ball as the standard,combined with Levenberg-Marquardt optimization algorithm,the sensor nonlinear error calibration is completed.Finally,the nonlinear error of the stylus profilometer sensor is compensated for by the calibration parameters.（2）The influence of straightness error of guide rail on contour measurement is studied,a specific scheme of straightness error compensation for X-direction guide is proposed,a polynomial model of straightness error for X-direction guide is established,and the mathematical formula of straightness error calibration and compensation for guide rail is given.（3）The influence of the radius of the probe on the measurement results was studied,and the contact state between the probe and the measured surface was analyzed in the microscopic state.The probe radius compensation method based on near point fitting was proposed,and the compensation method was verified by simulation.The simulation results show that this method has good effect on radius compensation in microscopic state.（4）The geometric error compensation software for the stylus profiler was written,which was embedded in the measurement software in the form of dynamic link library,to realize the real-time compensation of geometric error for the stylus profiler.The geometric error compensation experiment of the stylus profilometer was carried out,and the geometric error compensation algorithm of the stylus profilometer and the linear error compensation algorithm for guide rail were verified.The experimental results show that by using of polynomial nonlinear error compensation model proposed in this paper,the nonlinear error of sensors in the absolute average relative residual reduce to 12.388×10-6 by 3188.2×10-6,nevertheless,absolute mean of relative residuals only reduce to124.49×10-6 using traditional polynomial model.Which shows that the non-polynomial model proposed in this paper has a good suppression effect on the sensor nonlinear error.The comprehensive compensation experiment with guide straightness error and sensor nonlinear error are carried out,absolute mean of relative residuals reduce to1.096×10-6 by 1.281×10-6,which indicates that the comprehensive compensation can effectively improve error compensation effect of the large size workpiece measurement,thus prove the validity of the guide rail straightness error compensation. |
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