On-line statistical process control

Statistical process control (SPC) has evolved to mean the use of statistical methods to improve process productivity and product quality. Included are all the statistical techniques involved with the design of experiments, the analysis of data, and on-line quality control methods, as well as the managerial aspects involved in effectively carrying out these improvement programs. The area of SPC addressed in this study is that of on-line quality control. An examination is made of the interface between process control and on-line control. Examples are used to introduce the on-line quality control problem. Statistical quality control charts have also been used extensively to monitor quality variables and to respond to ″out-of-control″ situations. CUSUM (cumulative sum) charts are also being actively used. More recently, process control approaches based on discrete stochastic control theory have been used in a number of these situations. An overview of these latter two approaches is given, it is shown where they overlap, and recommendations are provided for their use.