The Inversion And Optimization Of Geometric Errors Of Multi-axis Machine Tool Based On Robust Design

As the basal and principal equipment of advanced manufacturing technology, thedesign and manufacture and the utilization of CNC machine tools restrict thedevelopment of manufacturing and high technology. The most important indicator tomeasure the machining feature of CNC machine tools is machining precision. Thispaper do deeply researched on accuracy optimal allocation of4-axis precisionhorizontal machining center on the basis of multi-body system theory modeling, andsensitivity analysis is also conducted to the accuracy reliability of machine tool basedon reliability design theory.Firstly, based on the characteristics and basic research method of multi-bodysystem theory, abstract the4-axis precision horizontal machining center into topologicalstructure of multi-body system, and describe the relationship between each body oftopology structure through lower body array. Then establish the generalized coordinatesystem in the multi-body system, homogeneous characteristic matrix is used to describethe variations in relative positions and orientations between each sub-coordinate systemin the generalized coordinate system, the characteristic matrix of different movementbetween any two adjacent bodies in the multi-body system both under an ideal conditionand in the presence of errors can be deduced. On the basis of this, according to thekinematics equations of multi-body system under an ideal condition and in reality terms,the volumetric error model of4-axis horizontal machining center can be obtained.Secondly, on the basis of the volumetric error model, the sizes of the assemblycomponents which have the greatest impact on the geometric errors can be classifiedby their machining features, according to the most suitable costs-tolerance model ofeach feature size, the manufacturing cost of assembly components associated withgeometric errors can be set up, combine with the quality loss cost caused by geometricerrors, the optimization model which takes the minimum cost as the objective functionis established. Then based on the relationship between geometric errors and accuracyparameters of assembly components, the accuracy optimization model which takes theaccuracy parameters of assembly components as variables and the maximum of theEuclidean norm of all variables as the objective function can be established. Synthesizetwo models above, and Isight is introduced to optimize the multi-objective functionintegrated with Matlab. Finally, in consideration of the manufacturing accuracy ofmachine tool, the geometric errors are optimized allocation and accuracy grades of mainfeeding components of mechanical assemblies are specified, and the cost is reducedeffectively.At last, according to the volumetric error model, along with reliability design theory, the first-order second-moment reliability method is introduced to compute themean value and variance of spatial error of machine tool, then the accuracy reliabilityof machine tool can be obtained. Based on the mean values and variances of geometricerrors, we can know the sensitivity of accuracy reliability of machine tool to eachgeometric error, then the geometric errors which are sensitive to the accuracy reliabilityof machine tool can be determined, and the critical error sources which have an effecton the accuracy reliability of machine tool can be identified. In designing process ofmachine tool, to control the critical error sources reasonably is an effective way toimprove the machining precision of machine tool while controlling costs.