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Representations and Methodologies for Assembly Modeling



Kevin W. Lyons, Venkat Rajan, Raj Sreerangam


Most products are assemblies of components. The number of components can range from a few tens to a few millions. Design of electro-mechanical assemblies involves the description of the constraints between a group of parts that allows them to behave in the desired fashion. This includes the description of the relatie motion between components, fit requirements, and joint strength requirements. While some of these cosntraints are generated during the conceptual design stage, additional details are developed during the preliminary and detailed design stages. Any such information generated during a previous level of the design needs to be captured and propagated to the next lower level of design. In this research, a thorough study is conducted of representations and methodologies available for assembly modeling during the various stages of design. The objective is to evaluate, and, if necessary, extend the current STEP representations dealing with assemblies. The study indicates that the current notion of assembly modeling is limited both in the existing research literature and commercial CAD implementations. Therefore, a set of three representations are developed to support the conceptual, preliminary and detailed design phases. Constraint propagation and verification methodologies are also developed to link information between the representations. The relevance of the representations and methodologies to downstream activities such as assembly analysis and planning are discussed. The impact of the proposed representations on the STEP standard is also discussed. A prototype Assembly Modeling System (AMS) has been developed in which the constraint verification methodology has been implemented. Case studies demonstrating the operation of this system are also described.
NIST Interagency/Internal Report (NISTIR) - 6059
Report Number


assembly modeling, constraints, design methods and models, representations


Lyons, K. , Rajan, V. and Sreerangam, R. (1997), Representations and Methodologies for Assembly Modeling, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed July 13, 2024)


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Created October 31, 1997, Updated October 12, 2021