Global Coordinate Method for Determining Sensitivity in Assembly Tolerance Analysis

Abstract

Tolerance sensitivity indicates the influence of individual component tolerances in an assembly on the variation of a critical assembly feature or dimension. Important applications include assembly tolerance analysis and tolerance allocation. This paper presents a new method for determining tolerance sensitivity using vector loop assembly tolerance models. With a vector loop model, the assembly kinematic constraints or assembly functions can be established automatically as implicit functions. This method evaluates the derivatives of the kinematic constraint equations with respect to both manufactured dimensions and assembly variables. The derivative matrices are then used to calculate the tolerance sensitivity matrix. This is a closed form method which relates the derivatives of the assembly functions to the coordinates of the joints or nodes and the orientations of the vectors and the local joint axes in an assembly. It is accurate, simple and very suitable for design iterations.