Research On Precision Assignment Technology Of CNC Machine Tool Based On Meta-action Theory

Accuracy is an important index to evaluate the quality of machine tools.The guarantee of machine tool precision depends on the accuracy of machine tool precision design to a great extent.Most of the traditional precision design methods take the key parts of the machine tool as the design object and use similar product analogy or experiential design method to determine the design precision value of each part.The accuracy obtained in this way is often of strong subjectivity and cannot be a good guide for the precision design of machine tools.Therefore,supported by the project of National Natural Science Foundation of China,this paper applies the Meta-Action theory to the accuracy distribution of CNC machine tools,and deeply studies the accuracy distribution technology of CNC machine tools based on "function-movement-motion(FMA)decomposition".The main research work is as follows:(1)The accuracy waterfall assignment method of CNC machine tool based on FMA decomposition was studied.The relevant concepts,definitions and decomposition steps of Meta-action theory and FMA decomposition theory are introduced.According to the characteristics of precision distribution of CNC machine tools,the FMA decomposition tree suitable for precision distribution of CNC machine tools is obtained.Then,based on the waterfall model,the accuracy distribution of CNC machine tool was divided into "Complete Machine-Function layer(CM-F)","function-Motion layer(F-M)" and "Motion-Action layer(M-A)".Finally,the precision distribution principle of each layer is analyzed,and the precision waterfall distribution model of CNC machine tool is established,which lays a solid foundation for subsequent precision distribution.(2)The accuracy distribution method of F-M layer of CNC machine tool based on motion error model was proposed.According to the tree-shaped structure of F-M layer,the relationship between the sub-function and the moving layer is established by using the theory of multi-body system.Then,the ideal kinematics and actual kinematics models were established by using the screw theory,and the motion error model was established according to the actual pose matrix and ideal pose matrix obtained by the kinematics model.Based on the motion error model,the accuracy distribution model of F-M layer was established with the minimum cost and quality loss as the design criterion,and the NSGA-II algorithm was used to solve the model.Finally,the rationality and effectiveness of the accuracy distribution of F-M layer are verified by taking the milling function of CNC machine tool as an example.(3)A precision assignment method for M-A layer of CNC machine tools based on error transfer model was proposed.According to the characteristics of M-A layer chain structure,the motion of the element chain is analyzed,and the motion transfer relationship between the elements is obtained.Then the relation between motion transfer error and motion error of meta-motion unit is analyzed from the structural error of meta-motion unit,and the error transfer model is established.Secondly,A precision assignment model of M-A layer was established by combining sensitivity index and error transfer model,and the model was solved by using multi-island genetic algorithm.Finally,the rationality and effectiveness of the accuracy distribution of M-A layer is verified by taking the rotary motion unit of CNC turntable as an example.