Process control by quality charting

The efficiency of automated process control depends on the used statistical process control technique intended for testing uniformity and stability, representing two major process characteristics. Stability characterizes the statistical process behavior, whereas uniformity reflects the ability of the process to yield the products with the same (or similar) properties. Control charts, representing one of the main tools in statistical process control, deal with the first characteristic, whereas uniformity is evaluated by means of process capability study. In contrast to the continuous procedure of charting the study implies only the periodical auditing on the full set of special collected data and therefore provides a poor basis for on-line process control and improvement. This paper represents an attempt to adjust the charting technique for simultaneous analysis of process quality behavior and, thereby optimize automated process control by feedback adjustment intended to keep product properties at their target values