Jami J. Shah

Metrics for measuring ideation effectiveness

Abstract Systematic methods for idea generation in engineering design have come about from a variety of sources. Do these methods really aid ideation? Some empirical studies have been conducted by researchers to answer this question. These studies include highly controlled lab experiments by cognitive psychologists, as well as experiments in simulated design environments carried out by engineering design theorists. A key factor in design and analysis of empirical studies is characterization and measurement of ideation effectiveness. This paper describes four objective measures of ideation effectiveness. The theoretical basis of each is discussed and procedures for application of each are outlined and illustrated with case studies.

Assessment of features technology

Abstract Features encapsulate the engineering significance of portions of the geometry of a part or assembly, and, as such, are important in product design, product definition, and reasoning, for a variety of applications. Feature-based systems have demonstrated some potential in creating attractive design environments and in automating the geometric reasoning required in applications such as process planning and manufacturability evaluation. The paper reviews the major concepts and approaches that are in use in feature-based modelling. Several methodologies are prevalent for creating feature models and databases. These fall broadly into the categories of interactive definition, automatic recognition/extraction, and design by features. Within each, there are several subcategories, which are discussed and compared in the paper. Also presented are several schemes popular for representing features. They include augmented graphs, syntactic strings in grammars, and objects in object-oriented programming. Feature interactions and validation issues are outlined. Attempts at developing feature taxonomies are also summarized.

Evaluation of Idea Generation Methods for Conceptual Design: Effectiveness Metrics and Design of Experiments

A wide range of formal methods have been devised and used for idea generation in conceptual design. Experimental evidence is needed to support claims regarding the effectiveness of these methods in promoting idea generation in engineering design. Towards that goal this paper presents a set of effectiveness metrics experimental methods, data collection and analysis techniques. Statistically based Design of Experiments (DOE) principles were used in developing the guidelines. Four classes of operating variables were considered to characterize the design problem and the environment. The effectiveness metrics proposed are based on outcome and consists of the quantity, quality, novelty, and variety of ideas generated. Two experimental approaches have been developed. In the Direct Method, the influence of the type of design problem and various parameters related to the procedure of an idea generation method is measured by using the method in its entirety. In the Indirect Method, each idea generation method is decomposed into key components and its overall effectiveness is predicted by experimentally studying the effectiveness of its components and their mutual interactions.

Automatic recognition of interacting machining features based on minimal condition subgraph

Abstract This paper presents a methodology for efficiently recognizing both isolated and interacting features in a uniform way. The conventional, graph-based recognition method is combined with hint-based feature recognition to recognize and extract alternative interpretations of interacting features. First all isolated (non-intersecting) features are recognized based on a Manufacturing Face Adjacency Graph. Interacting features are then recognized based on the features minimal condition subgraph (MCSG) that is used as a feature hint. Unlike Previous hint-based recognition methods, the MCSGs of all features are defined, generated and completed in a uniform way, independent of the feature type. Hints are defined by an Extended Attributed Adjacency Graph, generated by graph decomposition and completed by adding virtual links, corresponding to entities lost by interactions. An efficient algorithm for generating virtual links is developed. A new classification of feature interactions is also presented.

Expert form feature modelling shell

Abstract Contemporary geometric modellers are unsuitable for mechanical design because of mismatch in abstraction level. The databases of these modellers cannot be used to drive automated applications such as engineering analysis or process planning because of missing product information. The paper outlines an integrated system for design and applications; the system reasons in terms of form features. Object-oriented programming techniques support user definition of form features (volumetric shapes) that may be positioned and manipulated in a logical manner. A solid modeller interface generates equivalent solid representations in parallel with feature representations. Mechanisms for parameter inheritance and validity checking (cognition) are also discussed. The system is modular, which will allow it to be integrated with tolerance and material modellers that are currently under development. Artificial intelligence techniques have been applied to solid modelling, resulting in this powerful feature technology for creating flexible and integrated CAD systems for the next generation of engineering tools.

Assembly modeling as an extension of feature-based design

The advantages and limitations of procedural and declarative approaches for product modeling are discussed. Concepts are developed for modeling all levels of product relations with a uniform set of structures and relationships. It is shown that five basic structures,Part-of, Structuring relation, Degrees of freedom, Motion limits, andFit can be used to define relationships between assemblies, parts, features, feature volume primitives, and evaluated boundaries. Generic relations which facilitate constraint specification between target and reference entities are also presented. Methods for the derivation of the location of an assembly unit from high level constraint specifications, such as mating conditions, and techniques for determining the degrees of freedom, motion limits, and assemblability are required. This can be done by uni-directional parameter derivation in the procedural approach, or by symbolic geometric reasoning or numerical equation solution in the declarative approach. The former is less expensive, easy to implement, avoids conflicts, but leads to combinatorial explosion. The latter is general, flexible, decouples constraint specification from validation, but is expensive, and may require conflict resolution.

Mechanical Engineering Design Complexity Metrics: Size, Coupling, and Solvability

Developing objective measures for evaluating and measuring the complexity of design would facilitate (1) empirical studies that require the use of equivalent but different design problems, (2) the development of design curriculums, and (3) the comparison of computer aided design automation tools. This paper surveys and evaluates different approaches to defining complexity in design for the design problem, process, and product. Three fundamental aspects to complexity are identified, size, coupling, and solvability, and expanded with respect to the three elements of design, problem, process, and product. Alternative methods for measuring these characteristics of the design are based on computational, information, and traditional design views of complexity. A method of measuring size as it relates to complexity is proposed for measuring the information content of design. A second method is proposed for decomposing a graph-based representation of design that provides a measure of the interconnectedness as it relates to complexity. Finally, two methods are proposed for determining the solvability complexity of design based on the effort involved and the degree of freedom of design. These measures are developed specifically for parametric and geometric problems as found in the embodiment design, but these principles may be applied beyond this.

A Comparative Study Of Tolerance Analysis Methods

This paper reviews four major methods for tolerance analysis and compares them. The methods discussed are (1) 1D tolerance charts, (2) variational analysis based on Monte Carlo simulation, (3) vector loop (or kinematic) based analysis, and (4) ASU T-Maps© based tolerance analysis. Tolerance charts deal with tolerance analysis in one direction at a time and ignore possible contributions from the other directions. Manual charting is tedious and error-prone, hence attempts have been made for automation. Monte Carlo simulation based tolerance analysis is based on parametric solid modeling; its inherent drawback is that simulation results highly depend on the user-defined modeling scheme, and its inability to obey all Y14.5 rules. The vector loop method uses kinematic joints to model assembly constraints. It is also not fully consistent with Y14.5 standard. ASU T-Maps based tolerance analysis method can model geometric tolerances and their interaction in truly 3-dimensional context. It is completely consistent with Y14.5 standard but its use by designers may be quite challenging. T-Maps based tolerance analysis is still under development. Despite the shortcomings of each of these tolerance analysis methods, each may be used to provide reasonable results under certain circumstances. No guidelines exist for such a purpose. Through a comprehensive comparison of these methods, this paper will develop some guidelines for selecting the best method to use for a given tolerance accumulation problem.Copyright

Challenges in feature-based manufacturing research

ion Figure 8. A piece of stock, a bracket to be machined from the stock, and the delta volume Countersink-hole Process: Twistdrlling Reamed-hole Counter-sink Free-hole Process: Twistdrlling

Conceptual development of form features and feature modelers

Feature definition, definition methods, properties, and representation are classified and formalized. Fundamental issues related to the definition and semantics of form features are explored. The concept of a form feature is progressively developed by consideration of dimensionality, contiguity, closure, finiteness, uniqueness, and representation. Issues related to feature-feature interactions are identified and the types of interactions classified. The consequences of viewpoint dependence of features and feature transformations are also discussed, specifically with regard to the possibility of feature standardization and data exchange.