Knowledge-Based Engineering (KBE) Design Methodology at the Undergraduate and Graduate Levels*
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Int. J. Engng Ed. Vol. 16, No. 1, pp. 21±38, 2000 0949-149X/91 $3.00+0.00 Printed in Great Britain. # 2000 TEMPUS Publications. Knowledge-Based Engineering (KBE) Design Methodology at the Undergraduate and Graduate Levels* D. E. CALKINS University of Washington, Mechanical Engineering Department, Box 3526000, Seattle, WA 98195, USA NATHANIEL EGGING and CHRISTIAN SCHOLZ Sandia National Laboratories, MS 9105 P.O. Box 969, Livermore, CA 94550, USA. E-mail: [email protected] An emerging design technology known as knowledge-based engineering (KBE) is the next step beyond CAD for product representation. KBE allows a true generative virtual prototype to be developed that represents both the geometric and the non-geometric characteristics of a product. Both an undergraduate and graduate level design course based on this technology is described. A new version of the design process is presented for the development of a virtual prototype. Examples of products (systems) that were modeled include a hand held vacuum and a parametric human which are presented and described. BACKGROUND design tool and environment that can help make decisions early in the design synthesis (conceptual THE DEVELOPMENT of complex systems design) process. This integrated design tool will requires a sequence of engineering and manage- enable a diverse and multi-disciplinary team of ment decisions which must satisfy many competing engineers, designers and stylists to achieve consen- requirements. Design is recognized as the primary sus of design intent under complex design require- contributor to the final product form, cost, relia- ments and increased design constraints. The bility and market acceptance. The high-level en- design tool should allow the design team to gineering design and analysis process (conceptual examine more configurations at greater levels of design phase) is particularly important since the detail. The problem then is to develop an archi- majority of the life-cycle costs and overall quality tecture for a design tool that meets all of these of the system are determined during this phase. requirements. The major opportunities for cost savings occur in the earliest phases of a product design. Approxi- mately seventy per cent of the life-cycle costs are SYSTEMS DESIGN frozen by the end of the conceptual design phase, Fig. 1. The key to shortening the design cycle is Design process to shorten the conceptual design phase, which A process is defined as an ordered set of steps will also reduce the amount of engineering in the that are performed to accomplish a task, i.e. the redesign stage. design of a product. The steps in a process that are The engineering trade-off process during intended to define how each step is to be accom- conceptual design is undertaken using good esti- plished. Design methodologies accomplish that mations and informal heuristics. Current tradi- task. While many models have been proposed for tional CAD tool support is extremely limited for the design process, the one used attempts to the conceptual design phase. There is need to incorporate current technology and tools available rapidly conduct design analyses involving multiple for design, Fig. 2. The process shown consists of disciplines communicating together (trading off six steps starting with `Problem Definition' and such things as performance, cost, reliability, etc.). ending with `Prototyping.' Finally, it is necessary to be able to manage a large amount of domain-specific knowledge. The solu- tion is to commit more resources at the conceptual Design process stages design stage to reduce the cycle time by eliminating The design of a product traditionally proceeds redesign. through a series of well defined stages or phases All of these factors argue for an integrated including: . conceptual design (concept exploration and * Accepted 10 October 1999. development); 21 22 D. Calkins, et al. Fig. 1. Conceptual design effect on life cycle cost. preliminary design; and part assembly procedures, are also specified. detail design (production design). Key factors in detail design are: The distinction between these stages is related to . standards the level of design detail that is examined with . standard components regard to the system and its components. tolerances Concept, or conceptual design, deals with devel- . materials opment of a system at its very highest level, usually . manufacturing processes. with a very coarse representation with only the major subsystems represented. Design types Preliminary design proceeds to the next level of Types of design include: representation and is also known as embodiment . parametric design design. routine design Detail design includes analysis and results in a . selection or component design design description at a level suitable for manufac- . prototype-oriented design. ture. The arrangement, form, dimensions, toler- ance and surface properties of individual parts are Routine design, which comprises 80% of the specified. Materials and manufacturing processes, engineering activity, is based on minor variations Fig. 2. Design process. Knowledge-Based Engineering (KBE) Design Methodology 23 of pre-existing practice or procedure. Knowledge- system. A true virtual prototype contains this full based engineering (KBE) is the tool that is used for range of design knowledge. routine design where the product (system) is com- plex and has many assemblies, subassemblies, etc. ENABLING TECHNOLOGIES FOR DESIGN Current design tools Many design tools have been developed to aid Types of knowledge the design engineering in the process of design. `Knowledge', as applied to KBE, can be divided These include 2-D CAD, 3-D CAD including into four types [1]: wireframe, surface and solid modeling CAD, 2-D . facts, NURBS-based systems and parametric modeling, . procedures, all of which are geometry based. CAD systems . judgments, have been key in the development of drafting . control. automation, but are not able to deal with know- ledge such as rules, engineering practices or manu- Formalized knowledge found in handbooks facturing processes. Parametric modeling CAD such as material specifications, engineering data, systems are based on the geometrical relationships ASTM standards, and equipment specifications is between parts. Parts can be transformed by vary- considered factual knowledge. Algorithmic and ing dimensions, thereby making changes easier and operative knowledge are the two forms of pro- faster in the traditional design process. However, cedural knowledge. Numeric and non-numeric they do not easily manage the non-geometrical procedures for solving a problem or accomplishing knowledge about a product design. some end are all elements of algorithmic proce- Product design knowledge must also include dural knowledge (APK). Facts are transformed by non-geometrical knowledge about the system APK through engineering and analysis algorithms. performance to truly reflect the design intent. Operative procedural knowledge (OPK) is used to This aspect of the design process analysis has create, delete, and transport facts. Examples of been traditionally addressed by applying proce- OPK programs are finite-element analysis, optimi- dural languages such as FORTRAN, Pascal or zation, and database management systems [1]. C. The procedural languages are powerful tools Rules of thumb and common best-practices are for engineering analysis applications, but have no examples of judgment knowledge. Heuristics, inherent geometric capability. Another limitation observations, experience, and plausible reasoning of current CAD/CAE techniques is that they are are also included in judgment knowledge. Logic not appropriate at the concept or early stage and the formal principles of reasoning are funda- design level of complex systems. mental to judgment knowledge application. Control knowledge is metaknowledge or know- ledge about knowledge. The other types of know- VIRTUAL (DIGITAL) PROTOTYPE MODEL ledge are managed by control knowledge. Pattern directed actions, anticipation of unexpected devel- What is needed is a way to represent the product opments, and dealing with uncertainties are all design process to obtain a true virtual prototype features of control knowledge [1]. which would allow the early development and evaluation of a product. The virtual prototype Knowledge-based engineering (KBE) would replace traditional physical prototypes and The technology that allows the development of a allow the design engineer to examine `what-if' true virtual prototype of a product is known as scenarios while iteratively updating their designs. knowledge-based engineering, or KBE. KBE is the A true virtual prototype would not only represent methodology for capturing and structuring know- the shape and form, i.e. the geometry, it would also ledge about a design and its design process. KBE represent non-geometric attributes such as weight, may be used to define engineering methods and material, performance and manufacturing pro- procedures [2]. In KBE, the product structure tree cesses. Designers want a design representation (topology) is dynamic, so that KBE offers true that will be an exact representation of a physical engineering automation including application prototype with both geometrical and non-geome- development, geometric modeling, application trical attributes. deployment and tools integration. Knowledge- Product representation has moved from the 2-D based engineering is a programming tool used to orthographic drawing representation of the shape develop a virtual