In current tolerancng practice, designers have to manually specify tolerances: either on a drawing or in a CAD system. Different designers will possibly arrive at different tolerance specifications for the same nominal geometry. ,The paper demonstrates that this situation can be avoided in the case of functional tolerancing with a focus on the geometry relevant for functioning. Under this restriction, the specification of too tight or too many tolerances can also be avoided. The paper describes a tool for functional tolerance specification which supports the user in automatically proposing geometric tolerance types where the user only has to give in the tolerance values. Apart from this semi-automatic tolerance type specification, manual specification is still possible.

A computer aided tolerance analysis tool is presented that assists the designer in evaluating worst case quality of assembly after tolerances have been specified. In tolerance analysis calculations, sets of equations are generated. The number of equations can be restricted by using a minimum number of points in which quality of assembly is calculated. The number of points needed depends on the type of surface association. The number of parameters in the set of equations can be reduced by considering the most critical direction for the assembly condition. The latter direction, called virtual plan fragment direction, is determined using a virtual plan fragment table, based on an analogy to the plan fragment table used in degrees of freedom (DOF) analysis. This reduced set of equations is then solved and optimized in order to find the maximum/minimum values for the assembly condition using simulated annealing. This method for tolerance analysis has been implemented in a feature based (re-Idesign support system called FROOM, as part of the functional tolerancing module.

A computer aided tolerancing tool is presented that assists the designer in functional tolerance specification. The theoretical concepts for subsequent tolerance analysis are also provided. The computer aided tolerancing tool is part of a feature based object oriented (re)-design support system, called FROOM. FROOM's assembly modelling capabilities provide basic information for functional tolerance specification. Assembly constraints are satisfied by means of degrees of freedom (DOF) analysis. This method is based on the use of kinematic analogies. The rotations and translations (macro-DOF's) that components are allowed to have, are inferred using this technique. The tolerance representation in FROOM is based on the TTRS method, by Clément et al., which is also based on kinematic analogies. In this method, the small displacements that are allowed in the tolerance zone can be described by a tolerance torsor or transformation matrix. Using the tolerance torsor or transformation matrix, tolerances are described as constraints. The small displacements that are still allowed by means of the torsor are referred to as micro-DOF's. For tolerance analysis, the torsor approach offers a mathematically correct description of tolerance zones, although a lot of equations are generated. These are reduced by applying a kind of degrees of freedom analysis considering both the macro-DOF's and the micro DOF's (tolerances).