The Geometric Accuracy Analysis Of Precision Assembly Based On The Sensitivity Calculation

The geometries of machined surface have an great effect on the assembly accuracy of the micro.structured precision machinery products,while this ongoing error research focuses on the diamension and postion error according to Tolerancing Standards within Tolerance Principle,without considering the geometric effect on accuracy of precision machinery products assembly.Therefore,in this paper,the study is conducted in the process of multi.stage assembly to learn how assembly accuracy of precision products caused by geometric error of matching surface including shape distribution formed and transmitted,establishing a multi.process assembly precision model based on geometric error of matching surface to show how the geometric errors of assmebly components are transmitted,Accumulated and formed into the final assembly precision mechanism in the assmebly process,aiming to find out the main error factors affecting system assembly accuracy by quantitative analysis in order to control these key factors in application.This research mainly includes four parts as below:In the beginning,an analysis of assembly error sources is done to verfiy: geometric error(shape and position)is the main error source affecting system assembly accuracy.The position and orientation of the extracted features are collected by defining the coordinate system.On this basis,use small displacement screw(SDT)and the homogeneous transformation matrix to represent the geometrical errors and pose changes of the components,referring to Homogeneous coordinate space transformation theory,to finalize a transformation matrix in order to get SDT vector for the geometric error of components features.This paper reveals the mechanism of how the geometrical errors of components are transferred and accumulated in the process of precision assembly,and also calculates the mismatch error of two-part assembly applying Surface Fitting.On this basis,with the Coordinate transformation theory,the error transfer model of multi-process assembly is established,and the general formula of multi-process error transfer model is derived.Based on the error transfer model of multi-process assembly process and the direct matrix differential method,the sensitivity analysis and calculation of geometrical error of components are carried out to establish a sensitivity matrix of geometric errors and get the sensitivity coefficient of corresponding geometric error,in order to confirm the quantitative impact degree of the key features geometry error of each component on the system assembly precisionFinally,based on the theory of graph theory and directed graph,an error graph construction method of precision assembly process is proposed,that is,to visualize all the features of each component,its geometric error,matching error,assembly constraint relation and error transfer relation between all features,and other error sensitivity information collected during precision assembly in a error graph to apply in assembly accuracy analysis.