Fuzzy QFD

Abstract

Fuzziness concept, i.e. vagueness, is an essential part of the human mind and philosophy, like nature and the environment, which are guided by some mathematical rules but also by vagueness. A simplified approach to fuzzy mathematics applied to QFD is proposed in this chapter. The aim is to give the reader some basic tools to be used if the team wants to manage fuzziness in QFD projects. The reader can consider, for example, how much fuzziness exists when she/he fills in a questionnaire or puts a symbol of correlation inside a QFD matrix. In other words, interviewees, QFD team people and specialists from the departments involved in a QFD project, all are humans and so, they can sometimes change their opinion or are unable to express what they really feel. Starting from “fuzzy sets” and operations with fuzzy sets, we will focus on the so called “fuzzy numbers”, that are particular fuzzy sets. Then, the mathematical operations between fuzzy numbers, like addition, subtraction, product and division are presented with examples. At a later stage we will return to the traditional, or “crisp”, mathematics and workflow, which the previous chapters are founded on. We will review, from a fuzzy point of view, some QFD process phases, like fuzzy questionnaire design, fuzzy Preplan matrix and fuzzy QFD matrices. We will learn how to calculate the final ranking of sentences, examined in the QFD matrices, and how to set a ranking order through “defuzzification” of fuzzy numbers.