Scott Curland Chase

A Graph Grammar Approach for Structure Synthesis of Mechanisms

This paper presents a general graph grammar methodology for structure synthesis of mechanisms. Much of current mechanism design is based on a systematic method popularized by Freudenstein, Mruthyunjaya, and Tsai (among others). A graph grammar is a more natural expression fbr a method that relies on algebraic abstractions of graph theoretic principles. Our proposed grammar rules add vertices and loops to a start graph to obtain desired structural requirements. A grammar adaptation of an existing linear time algorithm for the detection of isomorphism is presented. Also presented is a specialized grammar for the structure synthesis of Epicyclic Gear Trains. A valid graph grammar for structure synthesis of mechanisms enables both the eventual automation of general atlas construction and atlas construction for customized mechanism classes.

Shapes and Shape Grammars: From Mathematical Model to Computer Implementation

Shape grammars, a well-structured method of generating designs, are suitable for computer implementation. In this paper, a formal representation of shapes as individuals is developed; some binary operations and relations are then defined upon shapes. The formal mechanisms of shape grammars are presented, with some of the computational problems illustrated. Algorithms to solve some of these problems are given. A Prolog implementation of a generic shape grammar system is demonstrated.

A model for user interaction in grammar-based design systems

Grammar-based production systems are considered potentially powerful design tools by their ability to generate sets of designs adhering to user-specified constraints. However, development of such tools has been slow, partly because of the lack of good interaction between user and system. This paper describes modes of user interaction and control possible with grammar-based design systems and presents issues to be examined in the development of models that represent the locus of interactions possible with such systems. The examination of existing grammar-based systems provides empirical evidence to support the validity of such models.

A formal approach for product model information

A formal approach to the representation of engineering and CAD information is developed, called EDM. Its intended use includes defining schemas for integrated engineering databases, a normal form for translating between CAD systems and/or engineering applications, and for archiving. A set of information structures or forms is developed for describing engineering product models. The criteria identified and used to evaluate and justify the structures include: (1) representation of function, as well as the form and physical properties of the product; (2) support for multiple levels of abstraction and for the various phases of the product life cycle; (3) representation of semantics sufficient for all uses and for determining the validity of information used in applications; and (4) extensible semantics, supporting the addition of new functional evaluations, new technologies, and new conceptual generalizations. A small set of class structures and relations is presented. expressed as predicate logic forms, and composed from domains and aggregations. These class structures support: (1) functional descriptions of a product and their accumulation within multiple hierarchies, based on shared physical property descriptions; (2) the definition of physical objects in terms of functional descriptions and their composition into higher level objects; (3) generalizations of objects and functions; (4) constraint structures that specify integrity conditions; and (5) structures able to depict engineering technologies.

SYSTEM ARCHITECTURE FOR COMPUTER INTEGRATION OF DESIGN AND CONSTRUCTION KNOWLEDGE

Abstract A strategy for dealing with the volume and diversity of knowledge involved in design and construction is through integration of a variety of knowledge sources. The representation of design knowledge is a key element is this strategy. The Engineering Data Model (EDM) provides a strong foundation for defining the semantics of a product design. It explicates all relations with the objective of establishing a way to interface modules of knowledge in a uniform manner that does not delimit future extensions. Here, we present EDM as a means of representing design information in a modular way. We present our view of modularity and the integration of knowledge in a computerized design environment. We propose a system architecture for the integration of knowledge and compare it with the PDES/STEP international effort.

A data model for design databases

This paper reviews the premises and current status of work on EDM, a data model for engineering product databases. A new data model is defined, and its application to the modeling of a portion of an intelligent CAD system demonstrated. Application of the data model to CAD database schema definition is discussed, as well as for translation between databases. This work summarizes and extends the previously published work on EDM, presented in (Eastman, Bond and Chase, 1991a) and (Eastman, Bond and Chase, 1991b).

Application and evaluation of an engineering data model

In a companion paper, we introduced an information model called EDM, for representing design and engineering information. EDM defines a small set of structures capable of depicting a wide range of semantics necessary for engineering design. These structures allow the definition of specific product models that are equivalent to database schemas, a fully instantiated structure is equivalent to an engineering or CAD database. EDM was developed in response to several criteria, among them the need to support changing technologies and evaluations and the need to support integrity checking. In this paper, EDM is applied to a small but complex example, a wall in building construction. Geometric, acoustic, and thermal properties are developed for the wall, defined in EDM structures. The example is then considered in terms of the evaluation criteria.

Categorisation of designs according to preference values for shape rules

Shape grammars have been used to explore design spaces through design generation according to sets of shape rules with a recursive process. Although design space exploration is a persistent issue in computational design research, there have been few studies regarding the provision of more preferable and refined outcomes to designers. This paper presents an approach for the categorisation of design outcomes from shape grammar systems to support individual preferences via two customised viewpoints: (i) absolute preference values of shape rules and (ii) relative preference values of shape rules with shape rule classification levels with illustrative examples.

Shape exploration in design: formalising and supporting a transformational process

The process of sketching can support the sort of transformational thinking that is seen as essential for the interpretation and reinterpretation of ideas in innovative design. Such transformational thinking, however, is not yet well supported by computer-aided design systems. In this paper, outcomes of experimental investigations into the mechanics of sketching are described, in particular those employed by practicing architects and industrial designers as they responded to a series of conceptual design tasks. Analyses of the experimental data suggest that the interactions of designers with their sketches can be formalised according to a finite number of generalised shape rules. A set of shape rules, formalising the reinterpretation and transformations of shapes, e.g. through deformation or restructuring, is presented. These rules are suggestive of the manipulations that need to be afforded in computational tools intended to support designers in design exploration. Accordingly, the results of the experimental investigations informed the development of a prototype shape synthesis system, and a discussion is presented in which the future requirements of such systems are explored.

A framework for redesign using FBS models and grammar adaptation

This paper describes a framework for redesign. Stylistic change in the form of rule modification is used to transform grammars to produce designs conforming to new requirements. The mechanism that enables this modification is based on the Function-Behaviour-Structure (FBS) model of design. The framework provides a formal mechanism for redesign and defines a means to generate and link structures with different behaviour and functions within the FBS model of design. Redesign of a wall illustrates this framework.