A Comparative Study of Joint Monitoring Schemes for APC Processes

Abstract

To monitor processes under automatic process control (APC), several joint monitoring schemes have recently been proposed, such as the U statistics, U 0 and U ∞ , that originate from the uniformly most powerful test. It is known that the U 0 chart is sensitive to large shift detection whereas the U ∞ chart is sensitive to small shift detection. To take advantage of both charts, this paper examines a combined use of the two U charts. A comparative study indicates that the combined procedure improves over a single U chart and performs better than other joint monitoring schemes, including Hotelling's T 2 chart for APC processes.

Bayesian monitoring to detect a shift in process mean

“…• refining control chart methods to be more efficient, to interact with more types of information, and to produce better diagnostics, as in Batson et al 2 , Chakhunashvili and Bergman 3 , Cheng and Thaga 4 , Guh 5 , Nichols and Padgett 6 , Perry et al 7,8 , Trip and Wieringa 9 , Wu et al 10 , and Ye et al 11 ; • developing methods for integrating statistical process control with engineering process control, as in Del Castillo 12 , Jiang et al 13 , Nembhard and Chen 14 , Runger et al 15 , and Yang and Sheu 16 ; • developing monitoring methods for non-stationary and/or auto-correlated data, as in Nembhard and Changpetch 17 , Nembhard and Valverde-Ventura 18 , Noorossana and Vaghefi 19 , Shepherd et al 20 , and Triantafyllopoulos 21 ; • synthesizing theory and practice, as in Barone et al 22 , Nikolaidis et al 23 , and Stoumbos and Reynolds 24 ;…”

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“…However, there is usually little effort in Six Sigma training devoted to EPC, even for individuals who will practice Six Sigma in the chemical and process industries. Recent papers in the Journal devoted to EPC and SPC include Jaing et al 3 , Runger et al 4 , and Yang and Sheu 5 .Forecasting and time series methods are not usually sufficiently addressed in many Six Sigma training programs. Forecasting is perhaps the most important analytic tool in many business operations, because forecasts provide the information upon which many management decisions are made.…”

“…However, there is usually little effort in Six Sigma training devoted to EPC, even for individuals who will practice Six Sigma in the chemical and process industries. Recent papers in the Journal devoted to EPC and SPC include Jaing et al 3 , Runger et al 4 , and Yang and Sheu 5 .…”