Review of research in feature-based design

Research in feature-based design is reviewed. Feature-based design is regarded as a key factor towards CAD/CAPP integration from a process planning point of view. From a design point of view, feature-based design offers possibilities for supporting the design process better than current CAD systems do. The evolution of feature definitions is briefly discussed. Features and their role in the design process and as representatives of design-objects and design-object knowledge are discussed. The main research issues related to feature-based design are outlined. These are: feature representation, features and tolerances, feature validation, multiple viewpoints towards features, features and standardization, and features and languages. An overview of some academic feature-based design systems is provided. Future research issues in feature-based design are outlined. The conclusion is that feature-based design is still in its infancy, and that more research is needed for a better support of the design process and better integration with manufacturing, although major advances have already been made

Estimating the cost of functional requirements for tolerance allocation on mechanical assemblies

When allocating tolerances to geometric features of machine parts, a target variation must be specified for some functional requirements on the assembly. Such decision, however, is usually made from experience without consideration of its effect on manufacturing cost. To allow such an assessment, the paper describes a method for estimating the cost of a requirement as a function of its variation. The estimation can be done before solving a tolerance allocation problem, at the time the variation on the requirement is chosen as an optimization constraint. A simple expression for the cost of requirements of various types is obtained using the extended reciprocal-power function for the cost of part tolerances, and the optimal scaling method for tolerance allocation. As a result, the costs of both requirement variations and part tolerances can be treated in the same way; this allows a hierarchical approach to tolerance allocation, which can simplify the problem when dealing with complex dimension chains. Furthermore, simple calculations based on the proposed method suggest general cost reduction criteria in the design of assemblies

Overview of database projects

The use of entity and object oriented data modeling techniques for managing Computer Aided Design (CAD) is explored

Considerations for a design and operations knowledge support system for Space Station Freedom

Engineering and operations of modern engineered systems depend critically upon detailed design and operations knowledge that is accurate and authoritative. A design and operations knowledge support system (DOKSS) is a modern computer-based information system providing knowledge about the creation, evolution, and growth of an engineered system. The purpose of a DOKSS is to provide convenient and effective access to this multifaceted information. The complexity of Space Station Freedom's (SSF's) systems, elements, interfaces, and organizations makes convenient access to design knowledge especially important, when compared to simpler systems. The life cycle length, being 30 or more years, adds a new dimension to space operations, maintenance, and evolution. Provided here is a review and discussion of design knowledge support systems to be delivered and operated as a critical part of the engineered system. A concept of a DOKSS for Space Station Freedom (SSF) is presented. This is followed by a detailed discussion of a DOKSS for the Lyndon B. Johnson Space Center and Work Package-2 portions of SSF

SUPPORTING FUNCTIONALITY-BASED DESIGN IN COMPUTER-AIDED DESIGN SYSTEMS

Designs are conceptualized in terms of the functions they need to accomplish. The need for a new product design arises as a result of the identification of a new functionality to be accomplished by the product. That is, design is functionality driven. However, existing CAD tools are not equipped to capture functionality or reason in such a fashion to support design for product functionality. This research proposes a new design formalism to enable functionality-driven design of mechanically engineered products. This procedure provides a methodology that allows a designer to model product functionality and to carry out conceptual design with the aid of a computer. It also serves as a bridging tool between the conceptual design phase and detailed design phase of a product. Thus, the primary objective of this research is to develop a methodology that will support the following activities in CAD systems: functionality modeling, functionality data structuring, and form conceptualization.The functionality modeling methodology developed in this work includes the use of operands, operators, and coupling bonds to describe product functionality in CAD systems. The Universal Modeling Language (an object-oriented programming technique) is used to model product functionality in computer systems. The tools developed in this research provide a means of modeling and propagating product functionality information to downstream design activities. The propagation of functionality as a constraint is achieved using Extensible Markup Language (XML) data files. These tools also provide a mechanism for verifying and enforcing constraints on solid CAD models. The functionality definition interface is implemented with a customized Microsoft Visio graphics engine.The tools developed in this research provide a means of modeling and propagating product functionality information to downstream design activities. It also provides a mechanism for verifying and enforcing constraints on solid CAD models. The functionality definition interface is implemented with a customized Microsoft Visio graphics engine

A FRAMEWORK FOR FUNCTION SPECIFICATIONS-TO-CONCEPTUAL FORM TRANSLATION TOOL IN FUNCTION-ORIENTED MECHANICAL DESIGN SYSTEMS

Design is functionality driven. All products and parts have some intended reason behind their existence. Although computer aided systems have made considerable advances in capturing and representing geometrical shape, not much progress has been made in capturing and modeling product functionality and its physical realization. This research proposes a methodology to assist designers during the first stages of design. This methodology provides a framework to help the designer translate functional specifications into conceptual forms. This research develops a translation tool to model functionality and to carry out conceptual design with the aid of the computer. This tool serves as a bridge between the conceptual design phase and the detailed design phase of a product. The translation tool developed in this research supports the conceptual design phase by providing a functional data model, a function server model, and a conceptual product model. The functional model includes the use of operands and relations to define and capture product functionality. The function server model represents the physical realization of the specified functions. The conceptual product model organizes and documents the product information in both the functional and the physical domains. The knowledge base for the function servers is stored in a function driven database. This database allows the designer to view design possibilities that may never have occurred to them.Models provided in this work have been implemented as a relational database system by using MySQL. A web-based graphic user interface is developed with PHP to provide an interactive environment for modeling and for searching the function driven database. Propagation of functional and physical information to downstream design activities has been enabled by the use of the XML data format. The models and concepts developed in this research are validated through a case study of a realistic mechanical device