Design of fuzzy process control charts for linguistic and imprecise data

Even the first control chart was proposed during the 1920's by Shewhart, today they are still subject to new application areas that deserve further attention. If the quality-related characteristics cannot be represented in numerical form, such as characteristics for appearance, softness, color, etc., then control charts for attributes are used. Except for the special cases, fuzzy control charts are used for attributes control charts such as p or c charts. The theory of classical control charts requires all the data to be exactly known. The major contribution of fuzzy set theory is its capability of representing vague data. Fuzzy logic offers a systematic base in dealing with situations, which are ambiguous or not well defined. Fuzzy control charts based on the fuzzy transformation methods are reviewed and a design for the control charts in the case of vague data using fuzzy sets as real valued interpretations of uncertainty and vagueness is proposed.