THEORETICAL UNDERPINNINGS OF FUNCTIONAL MODELING: PRELIMINARY EXPERIMENTAL STUDIES

ABSTRACTA model of how a product should function to satisfy custom-ers is an essential element in clarifying, identifying, and estab-lishing product architectures. Such functional models greatlyenhance the generation of creative form solutions to a chosen ar-chitecture. A wider breadth of solutions is generally possible,implementing new and stable technologies. In turn, using therecent concepts of design repositories, the possibilities exist toarchive, retrieve, compute, reconfigure, and reason with the prod-uct forms. To realize these benefits to the fullest extent possible,functional modeling needs further theoretical development. Aformalism of function classes, vocabulary, topologies, and meth-odology is a first step towards this goal. Recent research effortshave focused on each of these elements, where great strides to-ward repeatable formalisms have been made. Yet, across the en-gineering design field, very little active experimentation has beenpursued to test the veracity of these elements, individually and asa whole. We address this issue here through a preliminary set ofexperiments conducted at three separate universities. Designteams and individuals are asked to create functional models, inthe context of product development, with and without the for-malisms. The outcomes of the modeling effort are analyzed todetermine the repeatability of the process. Early results are quiteencouraging. Very repeatable results are obtained for three prod-uct evolutions, including a toaster, a power screwdriver, and a toydart gun. In addition, weaknesses in current formalisms are un-covered, pointing to new directions for advancing the field andfor carrying out more advanced experimentation.1. INTRODUCTIONFunctional modeling is a key step in the product design process,whether original or redesign. This article reports on our collabo-rative research efforts to develop a theoretical approach to func-tional modeling. By developing a formal theory of functionalmodeling, we intend to push functional modeling into the realmof repeatable, and even computable, engineering analysis. Whilewe have not yet reached our final destination on this journey,substantial progress has been made with our functional modelderivation and common functional language as demonstrated byinter-institutional experimental results. Namely, we show thatour flow tracing methodology to function structure developmentprovides reasonably repeatable results in function structure form,across a variety of persons trained in the approach.Several factors motivate the research into the theoretical un-derpinnings of functional modeling. In particular, use of the func-tional modeling theory described in this article significantly con-tributes to the following six product design areas.• Systematic function structure generation. The most com-mon criticism of functional models (particularly their graphi-cal representation known as a function structure) is that agiven product does not have a unique representation. Evenwithin a systematic function-based design methodology, dif-ferent designers can produce differing function structures,even under the same process choices. A common set of func-Kevin N. OttoCenter for Innovation in Product DevelopmentMassachusetts Institute of TechnologyCambridge, MA 02139knotto@mit.edu