Assembly Error Modeling And Analysis Of Mechanical Product Meta Action Unit

Precision is an important index to measure the quality of mechanical products.The level of precision often determines the grade of products.In the design stage of mechanical products,the prediction of assembly errors can not only verify the rationality of tolerance design of parts,but also provide guidance for error compensation and tolerance optimization.In this paper,an assembly error modeling,analysis and prediction method based on meta action unit is proposed.This paper mainly includes the following contents:(1)Based on the analysis of common geometric elements(plane,cylinder,axis)in typical meta action unit assembly,the error variation characteristics of common geometric elements are analyzed and modeled based on SDT.For geometric elements under the action of multiple tolerances,constraint inequalities are used to express the error components of geometric elements.According to the qualified rate,the actual distribution range of geometric element error components is calculated from the statistical point of view.The effectiveness and accuracy of the proposed method are verified by an example.(2)In the assembly process,the error is generally transferred by the way of face to face matching.In this paper,the error transfer attributes of common mating surfaces are analyzed,and the error transfer attributes of mating surfaces are solved by error pose transformation matrix.For the special fitting surface: in the combined fitting surface,the small plane and narrow plane are respectively equivalent points and lines to form the equivalent plane,and then the error transmission property of the combined fitting surface is solved;in the parallel fitting surface,the concepts of constraint strength and fit priority are introduced,and the entity interference is judged by using the special points,and the error transmission attribute of the parallel fitting surface is solved and the tolerance design is optimized.An example is given to illustrate the process of solution and optimization.(3)According to the structure model of meta action unit,the assembly directed graph is drawn,and the main error transfer path in the element is found by taking the output part and support part of meta action as the starting point,and the final main error transmission path is combined according to the type of mating surface.By using the homogeneous transformation matrix method,the assembly accuracy of the meta action unit is predicted and the reliability of the prediction result is analyzed.The feasibility and effectiveness of this method are proved by taking the moving element action unit of worktable as an example.