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Information Models for Design Tolerancing: From Conceptual to the Detailed Design



Sudarsan Rachuri, Utpal Roy


Tolerance design is the process of deriving a description of geometric tolerance specifications for a product from a given set of desired properties of the product. Existing approaches to tolerance analysis and synthesis entail detailed knowledge of geometry of assemblies and are mostly applicable during advanced stages of design, leading to a less than optimal design. During the design process of assemblies, both assembly structure and associated tolerance information evolve continuously and significant gains can be achieved by effectively using this information to influence the design of an assembly. Any pro-active approach to the assembly or tolerance analysis in the early design stages will involve making decisions with incomplete information models. In order to carry out early tolerance synthesis and analysis in the conceptual product design stage, we need to devise techniques for representing function-behavior-assembly models that will allow analysis and synthesis of tolerances, even with the incomplete data set. A 'function' (what the system is for) is associated with the transformation of an input physical entity into an output physical entity by the system. The problem or customer's need, initially described by functional requirements on an assembly and associated constraints on the functional requirements defines the concept of an assembly. This specification of functional requirements and constraints define a functional model for the assembly. Many researchers have studied functional representation (function based taxonomy and ontology), function to form mapping, and behavior representation (behavior means how the system/product works). In a recent paper, we presented a strong need for comprehensive unction-assembly-behavior (FAB) integrated model. In this report, we discuss extension of the ideas presented in our recent paper and explain the integration of function, assembly, and behavior representation into a comprehensive information model (FAB models). To do this, we need to develop appropriate assembly models and tolerance models that would enable the designer to incrementally understand the build-up or propagation of tolerances (i.e., constraints) and optimize the layout, features, or assembly realizations. This will ensure ease of tolerance delivery. In an earlier paper, NISTIR-6223, a multi-level approach called Design for Tolerance [DFT] process was proposed which enables tolerancing to be addressed at successive stages of design in an incremental fashion We also address the effective use of the FAB and DFT model for design tolerancing, starting from conceptual stage of the design and continuously evolving throughout the entire design process to the final detailed design. These models can eventually lead to tolerance and assembly standards.
NIST Interagency/Internal Report (NISTIR) - 6524
Report Number


assembly, behavior models, design tolerancing, function, object information architecture, tolerance and synthesis


Rachuri, S. and Roy, U. (2000), Information Models for Design Tolerancing: From Conceptual to the Detailed Design, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed April 24, 2024)
Created July 31, 2000, Updated October 12, 2021