Quality In Process Control Charts

IV Preface The aim of the present thesis is to make aware the reader of the need of good methods and competent people to achieve and improve quality in the field of process control charts. As clearly pointed out on chapter 1, need of good methods entails that not all the methods for quality are quality methods: this means that only Logic and Scientific Approach can provide the right route to discriminate between sound and misleading methods. Actually not only good methods, but also good applications are needed: chapter 2 shows an example of wrong application in the field of control charts. Process control charts are presented in detail in chapter 3, where the term "classical" is used to indicate the theory developed by W. A. Shewhart in the second half of 1920s. An example of the recent developments in the field of process control charts, namely a bayesian adaptive control chart for nonconformities, is presented and analysed on chapter 4. A theory which is going to gain ground in the field of control charts, is the so-called fuzzy sets theory, whose fundamentals are reported on chapter 5; an example of application of this theory, namely the construction of control charts for linguistic variables, is presented and analysed on chapter 6. The matter of the use of control charts for linguistic variables, is analysed also on chapter 7, where a tool for the evaluation and check-on-line of service quality, namely the Qualitometro in its versions I and II, is presented. The scientific analysis of all these methods, will bear out the importance of good methods to achieve quality and the need of understanding the soundness of a method before applying it to take decisions which may have heavy effects on companies' reputation and credibility.