F. van Slooten

A computer aided tolerancing tool I: tolerance specification

current tolerancing 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 tolerancing tool II: tolerance analysis

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-)design support system called FROOM, as part of the functional tolerancing module.

A Tolerancing Tool Based on Kinematic Analogies

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. FROOMs 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--DOFs) that components are allowed to have, are inferred using this technique. The tolerance representation in FROOM is based on the TTRS method, by Clment 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-DOFs. 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-DOFs and the micro DOFs (tolerances).

Conceptual graphs in constraint based re-design

This paper elaborates on the use of conceptual graphs for the representation of different types of objects and constraints in a re– design support system. Conceptual graphs, or conceptual structures, have been proposed for use in natural language processing and for representing mental models. However, recently they have also been proposed for use in the field of CAD/CAM. Conceptual graphs are graphs with two different kinds of nodes: concepts and conceptual relations. ReAesign support involves the modelling of assemblies and components, which on their turn are composed of features and geometric elements. The assemblies, components, features and geometric elements are represented by the concepts in the conceptual graph. The constraints between these entities are represented as conceptual relations. Constraints, such as geometric, kinematic, and manufacturing constraints are represented using conceptual graphs. Thus, conceptual graphs provide for an elegant way of representing hods functioning and manufacturing constraints. Constraints are satisfied using a ‘mukibrid’ constraint satisfaction approach, employing geometxy related domain knowledge for the geometry related constraints and an algebraichmmeric approach for the remaining constraint equations. The combination of the constraint satisfaction mechanism and the conceptual graphs allows for a unified way of handling assembly, comprnent and feature related information, Conceptual graphs are not only used in representing assemblies, components, features, and constraints, but also in supporting a mixed topiown and bottom-up design style,

Conceptual Graphs in CAD

This paper elaborates on the use of conceptual graphs in a prototype of a computer based support system for re-design. Re-design support involves the modelling of assemblies and components. The requirements of the components to be modelled are a compromise between the functioning of the assembly and the manufacturability of the individual components. Conceptual graphs provide for an elegant way of representing both functioning and manufacturing aspects. In the prototype system, conceptual graphs are used for representing and defining assemblies, components and features as well as the relations between these entities. Constraints, such as kinematic, tolerance and manufacturing constraints are also represented using conceptual graphs.

Collaborative Product Development in CAD and CAPP

This paper addresses collaborative product development, focusing on computer support of collaboration between users of CAD systems alone, between users of CAPP systems alone and between users of both CAD and CAPP systems. Computer support of collaborative product development may enhance informal information exchange. Apart from formal information exchange between CAD and CAPP systems, informal information exchange is necessary in achieving the goals of Concurrent Engineering. Collaboration can be started in a number of ways; as a result of one or more conflicts in constraints belonging to several users or voluntarily on the initiative of a user. Both these ways of starting collaboration should be supported. A prototype implementation restricted to a re-design support oriented CAD system supporting both conflict based and voluntary communication is presented. The re-design support system currently supports several constraint types. The present implementation uses parameter constraints in the support of conflict based communication. A parameter constraint solver based on the use of simulated annealing is employed.