An Application of Fuzzy Structural Modeling to Relation Diagram Method in Quality Control

Fuzzy sets theory is relatively little known to the sphere of quality control(QC)/quality management (QM). In the clerical, sales and research and development departments, however, objective numerical data are sometimes hard to gather, and the need to handle subjective data arises quite often.The Relation Diagram Method, one of “the Seven Management Tools for QC”, is employed to solve a complex problem, such as out-of-contol caused by human factors in production process, by means of arrangement of cause and effect relationships of a problem. In applying the Relation Diagram Method to complex relationships among many elements of causes and/or results in the problem to be solved, it is often desirable and sometimes essential to create hierarchies. However, the process of rearranging elements in a hierarchy is not dealt with in the existing Relation Diagram Method.In order to deal with such a relationship practically and systematically, the author proposes to create a hierarchy and rearrange the elements in a relation diagram by applying the Fuzzy Structural Modeling, which is developed on the basis of the fuzzy sets theory.In order to demonstrate how the proposed method works, a practical example is given in which the structure of the relation diagram has been successfully identified and the usefulness of applying the Fuzzy Structural Modeling to relation diagrams is confirmed.