Error Compensation Technique For On-machine Measurement System Based On Complex Surfaces

On-machine measurement system combines with parts processing and measuring function,and can avoid secondary positioning error and measurement limitations of large parts.So it is widely used in precision measurement of large complex workpiece.Aiming at the technical problem of complex surface of STL model existed in the on-machine measurement system,the key technology of measuring points planning,radius error compensation and pre-travel error compensation are deeply researched in this paper.The research contents are as follows:(1)Based on the data redundancy of STL model and the independence of triangular faces,the triangular mesh model is topologically reconstructed and optimized.The midpoint offset parabola method is used to calculate cutting points,which makes the calculated cutting points more close to the original model.Then NURBS algorithm is used to obtain the intercept curve,and the high string method is used to realize the adaptive planning of measuring points.Finally the sine triangular mesh model is used to demonstrate the effectiveness of measuring points planning method.(2)Based on the characteristics of the anisotropy of the probe,the pre-travel error compensation is realized by RBF neural network algorithm.With the help of MATLAB neural network tool,pre-travel error model is established,and the measuring data obtained though the standard ball calibration method are as original data to train and test RBF neural network.(3)When the measurement points are in the vertices of the triangular meshes,a normal estimation method is put forward based on the angle,centroids distance and perimeter,and validated by triangular mesh models of three quadric surfaces,experimental results demonstrate that the improved algorithm can effectively improve the accuracy of the normal vector estimation.And when the measurement points locate in the interiors of triangles,barycenter coordinates method is proposed to compute the normal vector,and verified by two different grid density of sine-like surfaces.(4)Based on C language,MFC and OpenGL,a set of software of on-machine measurement system is developed.The feasibility and validity of the error compensation of the on-machine measurement system are verified by processing and on-machine testing of the sine model.