Statistical Quality Control, 7th Edition

12 Engineering Process Control and SPC

CHAPTER OUTLINE

12.1   PROCESS MONITORING AND PROCESS REGULATION

12.2   PROCESS CONTROL BY FEEDBACK ADJUSTMENT

12.2.1   A Simple Adjustment Scheme: Integral Control

12.2.2   The Adjustment Chart

12.2.3   Variations of the Adjustment Chart

14.2.4   Other Types of Feedback Controllers

12.3   COMBINING SPC AND EPC

CHAPTER OVERVIEW AND LEARNINC OBJECTIVES

Throughout this book we have stressed the importance of process control and variability reduction as essential ingredients of modern business strategy. There are two statistically based approaches for addressing this problem. The first of these is statistical process monitoring by control charts, or statistical process control (SPC). The focus of SPC is on identifying assignable causes so that they can be removed, thereby leading to permanent process improvement or reduction in variability. The second approach is based on adjusting the process using information about its current level or deviation from a desired target. This approach is often called feedback adjustment, and it is a form of engineering process control or EPC. Feedback adjustment regulates the process to account for sources of variability that cannot be removed by the SPC approach.

This chapter introduces simple methods of feedback adjustment and shows how these techniques can be easily implemented in processes where there is a manipulatable variable that affects the process output. We also show how simple SPC schemes can be combined ...