Rachuri Sudarsan

Function-to-form mapping: model, representation and applications in design synthesis

Design of a new artifact begins with incomplete knowledge about the final product and the design evolves as it progresses from the conceptual design stage to a more detailed design. In this paper, an effort has been made to give a structural framework, through a set of generic definitions, to product specification, functional representation, artifact representation, artifact behavior and tolerance representation. A design synthesis process has been proposed for evolution of a product from the product specification. The proposed design synthesis method is a mapping from the functional requirements to artifacts, with multi-stage constrained optimization during stages of design evolution. Provisions have been kept to augment and/or modify the product specification and domain knowledge during stages of development to guide the design process. The effectiveness of the proposed design process has been illustrated with a simple design example based on a sample artifact library. An overall design scheme has been presented.

Design for tolerance of electro-mechanical assemblies: An integrated approach

Tolerancing decisions can profoundly impact the quality and cost of electro-mechanical assemblies. Existing approaches to tolerance analysis and synthesis in design entail detailed knowledge of geometry of the assemblies and are mostly applicable during advanced stages of design, leading to a less than optimal design process. During the design process of assemblies, both the assembly structure and associated tolerance information evolve continuously. Therefore, significant gains can be achieved by effectively using this information to influence the design of the assembly. Motivated by this, we identify and explore two goals for future research that we believe can enhance the scope of tolerancing for the entire design process. The first goal is to advance tolerancing decisions to the earliest possible stages of design. This issue raises the need for effective representation of tolerancing information during different stages of design and for effective assembly modeling. The second goal addresses the appropriate, synergistic use of available methods and best practices for tolerance analysis and synthesis, at successive stages of design. Pursuit of these goals leads to the definition of a multilevel approach that enables tolerancing to be addressed at successive stages of design in an incremental fashion. The resulting design process, which we call the design for tolerance process, integrates three important domains: (1) design activities at successive stages of design; (2) assembly models that evolve continuously through the design process; (3) methods and best practices for tolerance analysis and synthesis. We demonstrate major steps of our proposed approach through a simple, yet illustrative, example.

THE OPEN ASSEMBLY MODEL FOR THE EXCHANGE OF ASSEMBLY AND TOLERANCE INFORMATION: OVERVIEW AND EXAMPLE

In early design phases an effective information exchange among CAD (Computer Aided Design) tools depends on a standardized representation for the product data in all PLM (Product Lifecycle Management) tools. The NIST Core Product Model (CPM) and its extension are proposed to provide the required base-level product model that is open, non-proprietary, generic, extensible, independent of any one product development process and capable of capturing the full engineering context commonly shared in product development [1,2]. The Open Assembly Model (OAM) Model extends CPM to provide a standard representation and exchange protocol for assembly. The assembly information model emphasizes the nature and information requirements for part features and assembly relationships. The model includes both assembly as a concept and assembly as a data structure. For the latter it uses the model data structures of ISO 10303, informally known as the Standard for the Exchange of Product model data (STEP)[3]. The objective of the paper is to show how the OAM can be used to realize seamless integration of product information, with an emphasis on assembly, throughout all phases of a product design. A gearbox design example is used to illustrate the process.Copyright

TOWARDS MODELING THE EVOLUTION OF PRODUCT FAMILIES

A strategy successfully used by manufacturing companies is to develop product families so as to offer a variety of products with reduced development costs. This paper introduces our initial research on the representation of the evolution of product families and of the rationale of the changes involved. The information model representing product families is an extension of the NIST Core Product Model and consists of three submodels: Product Family, Family Evolution, and Evolution Rationale. In addition, a Unified Modeling Language (UML)-based representation and a prototype implementation of the conceptual model are introduced.Copyright

Sustainable Manufacturing: Metrics, Standards, and Infrastructure - Workshop summary

This report summarizes the presentations, discussions, and recommendations of the National Institute of Standards and Technology (NIST) Workshop “Sustainable Manufacturing: Metrics, Standards, and Infrastructure” held at NIST, Gaithersburg, Maryland, USA, October 13 through October 15, 2009. The primary objective of this Workshop was to bring together experts and various stakeholders to identify and discuss measurement and standards enablers that positively affect the social, economic, environmental, and technological aspects of designing sustainable production processes and products. The Workshop was well attended and consisted of thirty presentations organized under five sessions: 1) Government Initiatives; 2) Industry Perspectives; 3) University Research; 4) Non-Government Organizations (NGOs) research; and 5) Solution Providers Views. Two breakout sessions and an industry panel provided a set of recommendations for addressing critical issues in sustainable manufacturing.

A scheme for mapping tolerance specifications to generalized deviation space for use in tolerance synthesis and analysis

Tolerances impose restrictions on the possible deviations of features from their nominal sizes/shapes. These variations of size/shape could be thought of as deviations of a set of generalized coordinates defined at some convenient point on a feature. Any tolerance specification for a feature imposes some kind of restrictions or constraints on its deviation parameters. These constraints, in general, define a bounded region in the deviation space. In this paper, a method has been presented for converting tolerance specifications as per maximum material condition (MMC)/least material condition (LMC)/regardless of feature size (RFS) material conditions for standard mating features (planar, cylindrical, and spherical) into a set of inequalities in a deviation space. Both virtual condition boundaries Virtual condition boundary: A constant boundary generated by the collective effects of a size features specified MMC or LMC material condition and the geometric tolerance for that material condition. (VCB) and tolerance zones are utilized for these mappings. The mapping procedures have been illustrated with an example. Note to Practitioners-This paper deals with methods to convert tolerance specification as per ASME Y14.5M into a set of generalized deviation of features and vice-versa. These are intermediate relationships that are required for use in deviation-based tolerance synthesis methods. In this work, different examples have been presented to show how different tolerance specifications (such as positional tolerance at maximum material condition (MMC), least material condition (LMC), etc.) applied to different features could be treated on a generalized basis for tolerancing of manufactured parts.

SYNTHESIS OF GEOMETRIC TOLERANCES OF A GEARBOX USING A DEVIATION- BASED TOLERANCE SYNTHESIS SCHEME

In this paper a step-by-step procedure for carrying out synthesis of geometric tolerances of a planetary gearbox using a deviation-based tolerance synthesis (TS) scheme has been presented. The TS scheme uses an optimization for minimizing total cost of manufacturing, subject to constraints for assemblability of parts and constraints for functional requirements. The TS work is carried out in several stages. First the gearbox with its nominal dimensions is converted into a model that could serve as input to the synthesis module. Cost functions and constraints equations are then generated using deviation parameters of features. The optimization is carried out using these equations in standard non-linear minimization tools (Matlab) and the optimal deviation parameters are subsequently mapped into suitable tolerance specifications or tolerance zones as per ANSI Y14.5 tolerancing standards.Copyright

Design for tolerance of electro-mechanical assemblies

Tolerancing decisions during the design of electromechanical products profoundly affect cost and quality. Existing approaches to tolerance analysis and synthesis entail detailed knowledge of geometry of the assemblies and are mostly applicable during advanced stages of design, leading to a less than optimal design process. During design, both the assembly structure and associated tolerance information evolve continuously and significant gains can be achieved by effectively using this information to influence the design. We explore two goals of research to expand the scope of tolerancing to the entire design process. The first goal is to advance tolerancing decisions to the earliest possible stages of design. This issue raises the need for effective representation of tolerancing information during early stages. The second goal addresses the appropriate use of industry best practices and efficient computational approaches. Pursuit of these goals leads to the definition of a multilevel approach that enables tolerancing to be addressed at successive stages of design in an incremental, continuous ongoing fashion. The resulting design process, which we call the design-for-tolerance process, integrates three important domains: (1) design activities at successive stages of design; (2) assembly models that evolve continuously through the design process; and (3) methods and best practices for tolerance analysis and synthesis. We demonstrate major steps of our proposed approach through a simple, yet illustrative, example.

Formal Representation of Product Design Specifications for Validating Product Design

As collaborative efforts in electro-mechanical design have scaled to large, distributed groups working for years on a single product, an increasingly large gulf has developed between the original stated goals of the project and the final design solution. It has thus become necessary to validate the final design solution against a set of requirements to ensure that these goals have, in fact, been met. This process has become tedious for complex products with hundreds of design aspects and requirements. By formalizing the representation of requirements and the design solution, tools can be developed to a large extent automatically perform this validation. In this paper, we propose a formal approach for relating product requirements to the design solution. First, we present a formal model for representing product requirements. Then, we introduce the Core Product Model (CPM) and the Open Assembly Model (OAM) for representing the design solution. Finally, we link these models formally and provide an example with an actual consumer device.

A Scheme for Transformation of Tolerance Specifications to Generalized Deviation Space for Use in Tolerance Synthesis and Analysis

Traditionally tolerances for manufactured parts are specified using symbolic schemes as per ASME or ISO standards. To use these tolerance specifications in computerized tolerance synthesis and analysis, we need information models to represent the tolerances. Tolerance specifications could be modeled as a class with its attributes and methods [ROY01]. Tolerances impose restrictions on the possible deviation of features from its nominal size/shape. These variations of shape/size of a feature could be modeled as deviation of a set of generalized coordinates defined at some convenient point on the feature [BAL98]. In this paper, we present a method for converting tolerance specifications as per MMC (Maximum Material Condition) / LMC (Least Material Condition) / RFS (Regardless of Feature Size) material conditions for standard mating features (planar, cylindrical, and spherical) into a set of inequalities in a deviation space for representation of deviation of a feature from it’s nominal shape. We have used the virtual condition boundaries (VCB) as well as tolerance zones (as the case may be) for these mappings. For the planar feature, these relations are linear and the bounded space is diamond shaped. For the other cases, the mapping is a set of nonlinear inequalities. The mapping transforms the tolerance specifications into a generalized coordinate frame as a set of inequalities. These are useful in tolerance synthesis, and analysis as well as in assemblability analysis in the generalized coordinate system (deviation space). In this paper, we also illustrate the mapping procedures with an example.Copyright