| Tolerance specification is an integral part of design since it affects functionality, assemblability, and cost. Traditional methods analyze the functionality of a product using a tolerance stack-up approach in one dimension along a given functional dimension, or the assemblability of a product using a generate-and-test approach. Based on the concept of adjustability, this thesis proposes a novel assemblability analysis method using tolerances and clearances. Tolerances work against the assemblability because small deviations of part shapes can make it impossible to fit or to assemble some combinations of manufactured parts. However, the assemblability not only depends on tolerances but also clearances because clearances can be used for adjusting part poses for successful assembly of the parts.;The contributions of this thesis are as follows: the concept of adjustability was investigated in the assemblability analysis, algorithms for both Monte Carlo and analytic solutions were developed and implemented, practical aspects of assembly problems can be easily incorporated into the proposed framework, a tolerance based cost evaluation for assembly sequences brings the field of assembly planning closer to reality, and CAD tools for assemblability analysis can be built based on the proposed algorithms to help the designers to evaluate product designs during the design stage.;Tolerances are modeled by ellipsoids in a deviation space of translation and rotation parameters. With normal distribution assumption, ellipsoids statistically approximate tolerances. Clearances are modeled by ellipsoids and ranges. Ellipsoids approximate nominal clearances, whereas ranges approximate the statistical variations of clearances. Two methods, Monte Carlo and analytic, are proposed for calculating the propagation and accumulation of tolerances and clearances. Practical aspects of the problem like fixturing, assembly sequence, and functionality are considered in the assemblability analysis. In addition, two related problems were investigated: cost evaluation and tolerance synthesis. |
