Palm, Andrew C. (1990, ASQC) James River Corporation Towel & Tissue, Norwalk, CT
As both statistical process control (SPC) and automatic process control (APC) have become more widespread, interactions between advocates for these two approaches to process improvement have ranged from helpful cooperation to a complete lack of appreciation of the strengths of the other's viewpoint. Unfortunately, some attempts to explain Shewhart charts to control engineers have wrongly emphasized the use of these charts as a part of feedback control of a process average. Even worse, some people have suggested that Shawhart charts are old-fashioned and that more recently invented types of charts are generally superior to them. On the other hand, some have marketed Shawhart charts as simple cure-alls, completely neglecting the need for an art of application of this prof6und tool.
In this paper, the author looks at the nature of SPC and APC in their true roles in process improvement. After a discussion of some misconceptions concerning Shawhart charts, there is an explanation of a basic feedback control element, the PID loop, and what it is supposed to do. A simple example is then used to show how SPC and APC look at a process and how both together may be used to improve it. In a discussion of the use of computers in SPC and APC some points are made on the potential problems with using computerized control charts. Finally, the complementary aspects and the common ground of the two approaches are summarized.
Statistical process control (SPC),Statistics