Control is a continuous endeavor to keep measures of quality as close as possible to their
target values for indefinite periods of time"[1]. Process monitoring and process
adjustments are two different techniques to achieve this goal, and they are part of
statistical process control (SPC) and engineering process control (EPC) respectively.
Shewhart charts, cumulative sum (CUSUM) charts and exponentially weighted moving
average (EWMA) charts are frequently employed in SPC to find the special causes which
should be further removed or eliminated. Unfortunately, sometimes the special causes are
known but cannot be economically removed, so compensation must be made to prevent a
process from wandering off the target, calling for feedback control and feedforward
control in EPC. SPC has historical foundation in parts industry and EPC has originated in
process industry. SPC and EPC were applied by people with different technical
backgrounds for different control objectives. Box and Kramer [2] discussed the interface
between SPC and EPC, and how they can be integrated efficiently