Research On Free-form Surface Sampling Strategy Based On CMM

With the development of manufacturing industry in the direction of high precision and high performance,people have higher and higher requirements for the processing quality and processing efficiency of free-form surface parts,and how to improve the inspection efficiency and inspection accuracy of coordinate measuring machine(CMM)for free-form surface parts is of great significance to the processing and manufacturing of parts.In the actual inspection process,people tend to get more accurate inspection accuracy by arranging a large number of measurement points on the part,which can greatly reduce the inspection efficiency.In this paper,several aspects of CMM sampling parameter selection,free-form surface measurement point arrangement and path planning are studied as follows.(1)Studied the effect of probe diameter and retreat distance on the CMM inspection results to obtain the appropriate sampling parameters selection method.First,an overview of the measured probe diameter and retraction distance is presented.Then,a free-form surface part is used as the experimental object to generate free-form surface measurement points using the equal-step method.Finally,CMM inspection experiments are conducted to analyze the test data and obtain a suitable sampling parameter selection method.(2)For the problem of measurement points arrangement,the free-from surface Gaussian curvature property and the isoparametric line curvature property are studied,and the free-from surface Gaussian curvature variation grid method and the isoparametric line curvature variation grid method are proposed,so that most of the measurement points are located in the region where the curvature degree of the free-surface varies greatly.The measurement points are arranged for two free-form surfaces and CMM inspection experiments are conducted to verify the validity of the method.(3)Considering that only theoretical free-form surfaces are arranged,the obtained set of measurement points are not necessarily the points where the actual free-form surface parts have large errors.Therefore,the clustering-Voronoi diagram based combined with kriging method is proposed.The method obtains the actual machining quality information of some free-form surfaces by first obtaining the information,then using a genetic simulated annealing clustering algorithm,Voronoi diagram for boundary delineation,and Kriging method for prediction to obtain the set of points with large errors.and finally experimental validation is performed by CMM to verify the effectiveness of the method.(4)In order to improve the inspection efficiency and reliability,the problem of large-scale measurement point path planning for free-form surfaces is studied.First,the composition of the inspection path is analyzed and the objective function is determined.Secondly,an improved genetic algorithm is proposed for path planning of large-scale measurement points to address the problem that the traditional intelligent algorithm is ineffective in solving the path planning problem of large-scale measurement points.Finally,the effectiveness of the improved algorithm is verified by analyzing the data through simulation experiments with MATLAB software and physical inspection experiments with CMM.