A Computation Method for the Consequences of Geometric Errors in Mechanisms

The work presented here goes along the research for the principles that, starting from functional requirements, allow to compute the nature and value of tolerances on each part of a mechanism. In comparison with A.Clement’s or J.Turner’s works, our contribution is included in the formal description of the elements of tridimensional tolerance chains. This approach is built upon two elements, a modelization of geometric errors and a method of computation for their propagation inside of a mechanism. The modelization of geometric variations proposed here is founded upon the association of small displacement torsors to the different types of deviations that can be met in a mechanism. From then on, determining the parts’ small displacements under the effect of deviations and of gaps of the parts in a mechanism, becomes a computation of the composition of the modelized geometric errors. This computation of each part’s position yields two results. First, the formal determination of the part’s position in the mechanism in relation with the chains of influent geometric variations influenced by the parts’ surfaces. Then, the description of a combina- tory of a mechanism’s configurations. The application of this method shows the results obtained as well as the possibilities of extension towards a tolerancing aiding tool.