Optimization of precision reliability for thetransmission mechanism of NC machine
                                                                               XU Qi, LUO Luping, XIA Li
                    (Key Laboratory of E&M (Ministry of Education), Zhejiang University of Technology, Hangzhou 310014, China)

Abstract: Aiming at the problems of low precision, poor reliability caused by inadequate error tracing of the transmission mechanism of NC machine, the error modeling ,precision reliability analysis and precision reliabilityof NC machine were researched. The space geometric error model of NC machine was established based on the multibody system theory, through structure tracing of the transmission mechanism, the multilayer mapping error transfer model of transmission mechanism was established. Based on the precision reliability function of the transmission mechanism of NC machine, the precision reliability analysis of mixed uncertain of the transmission mechanism of NC machine was carried out via the first order two order moment method (FOSM). The reliability analysis result which was used as the standard of precision performance judgment, combined with the results of sensitivity analysis, the optimization model of precision distribution was established, which takes the lowest manufacturing cost as the optimization goal and satisfies the requirement of precision as the constraint. The genetic algorithm and Monte Carlo method were used to optimize the precision distribution of the transmission mechanism of NC machine. The results indicate that, after precision distribution optimization, the precision of transmission mechanism of NC machine is optimized from 96.89% to 99.87%, and the manufacturing cost is reduced by 34.74%.

Key words: NC machine; multilayer mapping mode; precision reliability analysis; precision reliability optimization