The Study On Prediction And Optimization Of Assembly Accuracy Based On Joint Surface Error Modeling

This dissertation is devoted to the prediction and optimization of the accuracy of the complex assembly.Based on the study of related researches,such as error modeling method and the tolerance optimization design method,the error modeling methods of parts geometric elements under the tolerance coupling function were discussed.The error formation mechanism and transfer characteristics of joint surface were analyzed,and the method of obtaining error transfer path of complex assembly was proposed.The error model of assembly was established,and then the accuracy prediction and tolerance optimization were realized.Furthermore,the framework and the realization method of the accurate design system were given,and the dedicated simulation platform was built.The main contents of this dissertation could be summarized as follow:(1)Error models of part's geometry elements in tolerance coupling conditions were set up.Small displacement torsors method was used to describe the error variation of geometric element.According to tolerance coupling situations of common geometric elements,the corresponding error variation inequality and constraint inequalities were established.On the basis Monte Carlo method was used to simulate the actual processing error,the actual variation interval bandwidth of each geometric element's error component was obtained,it laid the important basis of calculating the joint surface error.Through the response surface method,the explicit function relation between the actual variation interval bandwidth of geometric element's error component and tolerance was established;this provided an important safeguard for improving the efficiency of the later tolerance optimization.(2)Joint surface error modeling methods were proposed and joint surface error transfer properties were analyzed.An assembly error analysis method based on joint surface was proposed,according to the error accumulation and transfer function of joint surface,the error formation mechanism of all kinds of joint surface was analyzed from the perspective of error accumulation,the part constraint functions of different joint surface were analyzed and the error transfer properties of all kinds of joint surface were provided from the perspective of error transfer.The solving methods of error transfer properties of joint surface groups were discussed based on the correlation of adjoining joint surfaces.In light of the mutual influence of error transfer properties between the parallel joint surfaces,the solving method of the actual error transfer properties of parallel joint surfaces based on the assembly position priority was proposed,and then the assembly error modeling process of parallel joint surface group was elaborated,it provided a foundation for assembly error modeling.(3)A solving method of assembly error transfer path based on JSS matrix was proposed.The description requirements of complex assembly relationship were analyzed,and based on polychromatic sets theory,joint surface symbols were used to replace the Boolean value in assembly relation polychromatic sets matrix,then,the joint surface matrix(called JSS matrix)that can express multidimensional information such as the composition of assembly,assembly relationship,the geometry type of joint surface,connection mode,fitting type,and so on was established.The search method of assembly error transfer path was presented on the basis of JSS matrix,and the solution of the main error transfer path of assembly was achieved,this effectively reduced the complexity of the assembly error analysis and provided an important basis for the assembly error modeling which based on joint surface.On this basis,multiple connection JSS matrix method that supports the solution of error transfer path of multi-level complex assembly was investigated.(4)Assembly accuracy prediction and tolerance optimization of assembly were implemented.On the basis of joint surface error model and the main assembly error transfer path,assembly error model was built,and the assembly accuracy prediction was realized.The reliability analysis method of assembly accuracy was proposed,and then according to the accuracy requirements of product,the tolerance optimization of the parts was implemented using the method combining dynamic penalty function method with genetic algorithm,with assembly accuracy reliability as constraint conditions and lowest cost as the goal,thus the processing efficiency was ensured on the premise of meet the precision requirement.(5)The predicted effect of assembly error model was verified and a precision design software system was developed.The predicted accuracy of assembly error model was verified through the high precision NC grinding machine measurement test.An integrated expression method of precision design information was put forward targeting at the expression problems of precision design information in 3D drawings.Aiming at realizing digital precision design,the framework of assembly precision design system was presented,and the specific functional modules were introduced.Based on ACIS&HOOPS platform,a software system with the functions of 3D annotation of precision information,process programming and information management of assembly,assembly precision analysis and so on was developed.Precision information 3D annotation of typical part and assembly process planning of gantry rail grinding machine were completed with the help of the software.