Partitioning and Guided Search: A Generalized Approach to Problem Solving in Preliminary Design

We report on using problem partitioning and constraint-guided search as a generalized approach to problem-solving in preliminary design. Specifically, a generic design template has been created as a tool to structure information to facilitate problem-solving in three different domains. The approach has been tested through the implementation of knowledge-based systems for the preliminary design of mechanical springs, composite sublaminates and expert systems. Information in each implementation has been partitioned as hierarchical levels of abstraction related through constraints. Function identifies the top level design goals to reduce the search involved for feasible solutions. Goal-directed search, driven by the design application and top-down refinement, reduces the number of possible alternatives. The commonalities extant in the domains have been represented as design goals at three levels of abstraction in the design template. Similar frame-based knowledge representations with inheritance hierarchies and mixed reasoning have been developed for the KEE™-based implementations in each domain. Distinctions among the domains have been modelled as low level slots in the frame hierarchy. Parametric studies in the domains of mechanical springs, composite sublaminates and expert systems indicate that the minimum number of decision levels required to characterize the preliminary design process in these domains is three; fewer levels would be insufficient to fundamentally characterize the designs. Further, it is observed hierarchical structuring of design information facilitates capturing the interactions among design variables at different levels of abstraction. By using the template representation and reasoning in other divisible domains, the effectiveness of our approach can be further investigated.

Quantitative Inference in a Mechanical Design “Compiler”

This paper introduces the theory underlying a computer program that takes as input a schematic of a mechanical or hydraulic power transmission system, plus specifications and a utility function, and returns catalog numbers from predefined catalogs for the optimal selection of components implementing the design. Unlike programs for designing single components or systems, this program provides the designer with a high level “language“ in which to compose new designs. It then performs much of the detailed design process. The process of “compilation”, or transformation from a high to a low level description, is based on a formalization of quantitative inferences about hierarchically organized sets of artifacts and operating conditions. This allows design compilation without the exhaustive enumeration of alternatives. The paper introduces the formalism, illustrating its use with examples. It then outlines some differences from previous work, and summarizes early tests and conclusions.

FDDL: A Feature Based Design Description Language

This paper presents the development of a new high-level design language called Feature based Design Description Language — FDDL. The traditional and computer-aided design and manufacturing procedures were analyzed and the important gaps between CAD and CAM have been identified. These include the lack of uniform representation of parts and products, and lack of effective links between CAD and CAM. The FDDL is proposed and designed in association with a feature representation scheme as a means of integrating design and manufacturing tasks planning. Its syntax, semantics and vocabulary have been defined taking into consideration ease of use, compatibility with engineering terminology and ease of computer implementation. The FDDL system consists of a number of lexical analyzers, a parser and three code generators. Once the products or parts modeled using FDDL or the feature based modeler are processed by the FDDL system, syntax error free input files are created for use by manufacturing task planning systems. The FDDL has been applied to a feature based cellular manufacturing planning system, an expert automated CMM inspection task planner, and a mechanical assembly sequence planner.

The Nature of Constraints and Their Effect on Quality and Satisficing

A taxonomy of constraints is presented based on design considerations, source, context, strength, and use. The taxonomy is developed from observations of two sets of real-time protocol data of mechanical designers, along with the work of other researchers. The taxonomy begins to explain the nature of constraints. A hypothesis of how introduced constraints affect design quality is also presented. Finally, a more specific definition of satisficing is developed based on an experiment demonstrating constraint satisfaction.

A Transformational Approach to Mechanical Design Using a Bond Graph Grammar

During the design process, a designer transforms an abstract functional description for a device into a physical description that satisfies the functional requirements. In this sense, design is a transformation from the functional domain to the physical domain; however, this transformation process is not well characterized nor understood for mechanical systems. The difficulty arises, at least in part, because mechanical designs are often composed of highly-integrated, tightly-coupled components where the interactions among the components are essential to the behavior and economic execution of the design. This assertion runs counter to design methodologies in other engineering fields, such as software design and circuit design, that result in designs in which each component fulfills a single function with minimal interaction. Because of the geometry, weight, and cost of mechanical components, converting a single behavioral requirement into a single component is often both impractical and infeasible. Each component may contribute to several required behaviors, and a single required system behavior may involve many components. In fact, most mechanical components perform not only the desired behavior, but also many additional, unintended behaviors. In good mechanical designs, these additional behaviors often are exploited. The long term goal of our research is to create a transformational strategy in which the design specifications for a mechanical system can be transformed into a description of a collection of mechanical components. To realize this goal requires formal representations for the behavioral and the physical specifications of mechanical systems as well as formal representations for the behaviors and the physical characteristics of mechanical components. Because the interactions of components are important in our synthesis strategy, the representation of the behaviors of mechanical components must be linked to the representation of their physical characteristics; that is, we are concerned with modeling the relationship between form and function of components. Finally, we need a strategy that enables us to transform an abstract description of the desired behavior of a device into a description that corresponds to a collection of available physical components. In this paper, we present a graph-based language to describe both the behavioral specifications of a design as well as the behavior of the available physical components. We also briefly discuss a graph-based grammar for the representation of the physical characteristics of the components that enables us to guide the translation from specifications to components [Pinilla 89]. The transformation strategy is discussed in a companion paper [Hoover 89].

Rules of Constructing Primitives for Integration of Design and Manufacture

This paper analyzes the difficulties of basic primitives of geometric modeling systems currently in effect, which is met in the application of numerical control manufacture. On the bases of the analysis, the paper proposes the primitive designing rules for the integrated CAD / CAM systems. The paper is divided into four parts. The first part analyzes the defects of often-used primitives. The second part discusses requirements of primitive in the integration of design and manufacture, and proposes the basic rules and unified method of designing primitives. The third part introduces rules and basic principles of constructing primitives offered by the writer. The last part provides an example to show the advantages of the modeling rules.

Observations From an Empirical Study of the Workspaced Activity of Design Teams

Small group design sessions were studied empirically to better understand collaborative work. Shared workspace activity — the listing, drawing and gesturing of the group — was studied in order to guide the design, development, and introduction of tools to support group work. An understanding of workspace activity needs to include the role of gestures, the use of the workspace to develop ideas, and the use of the workspace to help mediate interaction. The following observations of group workspace activity are reported: • gestures, and the relationship of gestures to the workspace, convey important information • the process of storing information can be problematic • the process of expressing ideas conveys information beyond the resulting artifacts created • listing, drawing, and gesturing activities fluently intermix • orientation, amount of simultaneous access, and proximity to the workspace structure the use of the workspace These observations are illustrated with examples from the video data.

Comparing Fuzzy and Probability Calculus for Representing Imprecision in Preliminary Engineering Design

A technique to perform design calculations on imprecise representations of parameters using the calculus of fuzzy sets has been previously developed [17]. An analogous approach to representing and manipulating uncertainty in choosing among alternatives (imprecision) using probability calculus is presented and compared with the fuzzy calculus technique. We find that the fuzzy calculus is well suited to representing and manipulating the imprecision aspect of uncertainty, and probability is best used to represent stochastic uncertainty.

A Methodology for Incorporating Multiple Goals in Automated Abstract Design

This paper deals principally with two important issues of design automation, the use of abstract design problem solving to guide detail design in top down refinement models, and the incorporation of multiple requirements in design. An iterative, incremental methodology involving generation and selection of abstract decompositions and of abstract operators defining design moves is described. Multiple requirements are handled by organizing relevant evaluation, generation and choice knowledge around individual requirements and providing each requirement with the capability to determine when it has a contribution to make, what that contribution should be, and how it interacts with other requirements. The methodology has been implemented as part of the MOSAIC project and is illustrated by examples of the automated preliminary design of mechanical structures.

Extending the Iterative Redesign Model to Configuration Design: Sheet Metal Brackets As an Example

An iterative redesign model has been proven effective at the parametric level of design; that is, at the point in the design process where the attributes of the design are known and their numerical values are varied to produce an acceptable design. In this paper an extended iterative redesign model is proposed for use at the configuration level of design; that is, at the point in the design process where the attributes themselves, not their values, are being determined. The proposed model is demonstrated in a working computer system for the automated configuration design of a limited set of sheet metal brackets for simple structural joints.