Design for Product Variety: Key to Product Line Structuring

This study develops a method to capture the broadest customer preference in a product line while minimizing the life-cycle cost of providing variety. The paper begins with an overview of product variety and its importance in overhead costs: supply chain, equipment and tooling, service, and recycling. After defining the product structure graph as a representation of variety, the paper introduces an approximate measure for the customer importance and life-cycle cost of product variety The cost measure utilizes the concept of late point identification which urges standardization early in the manufacturing process and differentiation at the end of the process. The variety importance-cost map allows engineers to identify cost drivers in the design of the product or the manufacturing system and seek improvements. The refrigerator door example illustrates the concept. On-going work seeks to validate and enhance the method with several companies from different industries.

Managing Risk by Reordering Tasks in Engineering Design

This paper describes a model of how reordering tasks in the engineering design and development process affects resource usage in a risky environment. All development projects are risky; their outcome and level of success is unpredictable. Many projects are canceled at some time during the development process, or never produce a working product or produce a product that fails in the marketplace. Doing engineering development is expensive; it requires high-cost labor as well as other potentially expensive resources. To some extent the magnitude of the risk is estimable; it is possible to predict now much resources (time, labor or other costs) any particular development task will consume as well as some estimate of whether or not an insurmountable technical problem is likely to be discovered. Also, development tasks are not independent; there are constraints on their ordering due to needed technical knowledge. The model presented in this paper uses those estimates to suggest an ordering of the tasks in an attempt to minimize the expected resource consumption for those projects that run a risk of cancellation.

A New Model-Based Tool for Fault Detection and Isolation in Machine- and Rotordynamics

Reliability and safety aspects are becoming much more important due to higher quality requirements, complicated and/or connected processes. The fault monitoring systems to be commonly used in machine- and rotordynamics are based on signal analysis methods. Furthermore, various kinds of fault detection and isolation (FDI)-schemes are already applied to a lot of technical applications of detecting and isolating sensor and actuator failures (Isermann, 1994; van Schrick, 1994) and also to fault detection in power plants (in general) or in manufacturing machines. An implicit assumption is that process or machine changes due to faults lead to changes in calculated parameters, which are unique and unambiguous. In the case of applying methods of signal analysis this means spectrums etc. the vibration behaviour will be monitored very well but have to be interpreted. On the other hand signal parameters usually only describe the system by analyzing output signals without use of known and unknown inner parameters and/or inputs. These parameters are available, and normally this knowledge is used by the operating staff interpreting the resulting signal parameters. In this way a decision-making problem appears so that questions about the physical character of faults, about the existence of special faults and also about the location of failures/faults has to be answered. In this way the experience and knowledge of the interpreting persons are very important. In this contribution the problems of the decision-making process are tried to defuse: • The available knowledge about the unfaulty system parameters is used to built up beside a nominal system model an unambiguous fault-specific ratio. Inner states of the structure are estimated by an PI-observer. • The developed robust PI-observer (Söffker et al., 1993a; Söffker et al., 1995a) estimates inner states and unknown inputs. In (Söffker et al., 1993b) this new method is applied to the crack detection of a rotor, but not proved. In this paper the proof is given and a generalization is described. The advantages in contrast to usual signal based vibration monitoring systems and also modern FDI-schemes are shown.

Firmware Design Capture

One of Allen-Bradley’s goals is leveraging — taking better advantage of existing resources. We are developing a methodology and supporting tools that help engineers share and reuse (i.e., leverage) their firmware design and development work. Writing reusable firmware source code is especially difficult due to the tight constraints in most embedded systems — code must usually be written for product specific hardware needs and resources. Reuse of engineering work at the design level is a more effective approach. With this in mind, we have been working with Allen-Bradley Power Products engineers and managers to pilot a Firmware Design Capture (FDC) system. In a FDC system, engineers work in their own paper or electronic workbooks compiling descriptions of their domains’ technologies and algorithms in loosely structured electronic document sets called technology books. Product-specific information is placed in complementary document sets called product books. Engineers can access this growing body of ‘Strategic Design Information’ that they and others have created; freely drawing from, commenting on, or adding to it. Key characteristics of this FDC system are: • A focus on collecting reusable and accessible design information • Incremental, small-grained development of documents during design activity • Electronic format of documents, for ease of refinement and access • Unobtrusive tools and methods, determined through frequent user feedback We expect this methodology to help engineers improve schedule predictability and reduce the firmware development life cycle, better retain vital technologies and product data, and increase product quality. Feedback from our initial work supports these expectations.

A New Shaft Coupling Design for a High-Speed Rotor Wheel

A high-speed rotor wheel for a wind-tunnel experiment has been designed. The rotor wheel was similar to one in an axial turbine, except that slender bars replaced the blades. The main parameters of the rotor wheel were an outer diameter of 10“, a maximum rotational speed of 24,000 RPM and a maximum transferred torque of 64 lb-ft. Due to the working environment, the rotor had to be designed with high safety margins. The coupling of the rotor wheel with the shaft was found to be the most critical issue, because of the high stress concentration factors associated with the conventional coupling methods. The efforts to reduce the stress concentrations resulted in an advanced coupling design which is the main subject of the present paper. This new design was a special key coupling in which six dowel pins were used for keys. The key slots, now pin-grooves, were placed in bosses on the inner surface of the hub. The hub of the rotor wheel was relatively long, which allowed for applying the coupling near the end faces of the hub, that is, away from the highly loaded centerplane. The long hub resulted in low radial expansion in the coupling region. Therefore, solid contact between the shaft and the hub could be maintained for all working conditions. To develop and verify the design ideas, stress and deformation analyses were carried out using quasi-two-dimensional finite element models. An overall safety factor of 3.7 resulted. The rotor has been built and successfully accelerated over the design speed in a spin test pit.

A Method for Assessing the “Local” Accuracy of Weight Functions for Plates With Embedded Cracks

In this paper a procedure is developed to assess the “local” accuracy of weight functions for finding stress intensity factors of centrally cracked finite plates given by Tsai and Ma (1989). It is found that the weight functions can be used to calculate stress intensity factors for practical cases, with “local” accuracy being within 6 %. In addition, weight functions generated from two finite element analyses are found to be accurate and may be used to assess new algorithms for finding weight functions.

A Spectral Optimization Algorithm for Multi-Objective Prototype Selection

In design synthesis, engineering prototypes make an ideal representation medium for preliminary designs. Unlike parametric design wherein a pre-specified design is parametrically varied, design synthesis demands artistic creativity and engineering experience to transform the previously known components, relationships and designs into a new form. The process compels the designer to ascertain which prototypes will, in some sense, best satisfy the design task. The challenge in this assignment lies in selecting the “right” design prototype. This selection process typically entails an objective evaluation of different designs that perform the same functions or have similar intended behavior and comparing trade-offs between alternate designs. This paper introduces a multi-objective spectral optimization algorithm for the selection of design prototypes based upon their functional representations. The optimization algorithm returns an index of rank, scoring the functional similarity of the proposed design to the goal design. Two illustrative examples apply the algorithm to the selection of a heat fin and beam.

Consistency Management in Feature-Based Parametric Design

One of the main problems to be solved in design-by-features is to preserve the semantic correctness of feature-based models. Currently, feature-based parametric design (FbPD) is being used as one of the most powerful approaches for solving this problem. In this paper, a fundamental principle of this approach is introduced. Three aspects stated, are: FbPD deals with functional design primitives, it solves the automatic generation of model variations, and it offers the basis for the development of a mechanism to check the semantic correctness of feature-based models. Several concepts for the definition of semantic constraints are presented. They instigate the classification of semantic constraints in four different categories, based on the constraint evaluation-time, purpose, behaviour, and representation. Sinfonia, a system for feature-based parametric design, is presented as a testbed environment for design-by-features applications. One of its modules, the Consistency Handler, uses the constraint concepts introduced in order to preserve the semantic consistency of the models. Several examples illustrate the different types of constraints. In addition, an algorithm applied for the process of a consistent feature modification is presented.

A Design Process Model That Unifies General Design Theory and Empirical Findings

This paper proposes a new design process model that unifies theoretical results of General Design Theory (GDT) and empirical findings obtained from design experiments. It first reviews the design process models that were developed within theoretical work on GDT. Then, we describe experimental work on design based on protocol analysis, which resulted in a cognitive design process model from which further a computable design process model was derived. While these experimental results are supposed to support the theoretical conclusions obtained from GDT, we could also find out incompatibilities. We then propose a new design process model, called the refinement design process model, that can unify both theoretical results of GDT and experimental finding obtained from design experiments. The refinement model has better agreements with experimental findings and suggests various issues as a guiding principle to develop a future, advanced CAD system that helps a designer to focus on functional information. We propose and illustrate the concepts of such an advanced CAD system equipped with intensive design knowledge, called a computational framework for knowledge intensive engineering.

Elementary Education and Engineering Design: Concrete Experiences in Mathematics and Science

The education community has focused attention recently on a number of initiatives to evolve, and perhaps revolutionize, approaches for teaching science, mathematics, and engineering. In this paper, we present a new engineering and design technology program, initiated in 1992 and referred to as DTEACh, that focuses on the elementary grades. Two components comprise this new program: (1) open-ended design and exploration lessons that use hands-on models to teach integrated mathematics and science principles, and (2) a two-part teacher preparation program to provide teachers with the necessary engineering, mathematics, and science fundamentals for DTEACh. In this paper, we focus on a description of the teacher preparation program, including discussions of a novel teaching model, the subject matter for engineering and design fundamentals, and evaluation of the program. Results of the evaluation that teachers are more confident and equipped to facilitate the instruction of mathematics, science, and engineering principles.