Research On Optimization Of Sampling Strategy For Measurement Points Of Freeform Surface

The freeform surface measurement technology is used in advanced manufacturing industries such as aviation,aerospace,ships,and molds.It is one of the key development technologies in our country's manufacturing industry.In freeform surface measurement,the quality of sampling strategy of the measurement points directly affects the measurement error and efficiency.Traditional freeform surface sampling strategies have the disadvantages of poor adaptability and poor controllability of sampling accuracy.To improve the sampling accuracy and controllability of freeform surface measurement,in this paper,a new sampling algorithm is proposed based on traditional freeform surface sampling algorithms of measurement points.Improve the differential evolution algorithm and use the improved differential evolution algorithm to optimize the key sampling parameters of the sampling algorithm.The results of sampling and reconstruction simulation and measurement experiments of freeform surfaces verify the sampling algorithm's performance.Develop software for sampling measurement points to improve the automation degree of the algorithm sampling operation.The main research contents are as follows:(1)Propose a new algorithm for sampling the measuring points of freeform surfaces-adaptive curvature chord height method.The algorithm enables adaptive adjustment of the sampling threshold of each original measurement point by setting and optimizing the sampling parameters.In this way,the shortcomings of the traditional sampling algorithms of measurement points such as inflexible and the sampling accuracy and stability are difficult to control are solved.Reduce the curve and surface reconstruction errors to improve the sampling accuracy by setting the maximum sampling interval and increasing the sampling midpoint in the curvature mutation areas.(2)Adaptively improve the differential Evolution(DE),improve the adaptiveness of the differential mutation operator in the differential evolution(DE)and apply this adaptive improved differential evolution(IADE)to optimally set the sampling parameters of the adaptive curvature chord height method.The experimental results of sampling parameter optimization show that compared with DE,IADE can significantly improve the optimization speed without reducing the sampling parameter optimization accuracy.Provide a simple and fast parameter optimization method—incremental optimization method to meet the sampling requirements of different scenarios.The experimental results of sampling parameter optimization show that compared with the DE and IADE,the incremental optimization method greatly improves the efficiency of the parameter optimization when slightly decreasing the optimization accuracy.(3)Apply chord height difference method,angular deviation method,curvature sampling method based on the lever balance system,and the adaptive curvature chord height method to the measurement point sampling and reconstruction simulation experiments of variable section non-torsional freeform surface and variable-section torsional freeform surface.The sampling and reconstruction simulation results of the single section free curve,the section free curve group,and the whole free surface show that the newly proposed adaptive curvature chord height method has higher sampling accuracy and better accuracy controllability than the other three classical sampling algorithms.(4)To further verify the effectiveness of the adaptive curvature chord height method,use four algorithms to sample the measurement points of the variable section non-torsional freeform surface.The experimental equipment is a three-coordinate measuring machine(CMM).The experimental results show that the adaptive curvature chord height method can effectively improve the measurement accuracy of freeform surfaces compared with the traditional sampling algorithm in the actual sampling when the number of measurement points remains unchanged.(5)Develop software for sampling measurement points of freeform surfaces.The software realizes the automatic sampling and reconstruction process of four sampling algorithms(chord height difference method,angular deviation method,curvature sampling method based on the lever balance system,and the adaptive curvature chord height method),which standardizes the algorithms sampling process and improves the sampling efficiency.