A Combined Process Control Procedure by Monitoring and Repeated Adjustment

  • Published : 2000.12.01


Statistical process control (SPC) and engineering process control (EPC) are based on different strategies for processes quality improvement. SPC reduces process variability by detecting and eliminating special causes of process variation. while EPC reduces process variability by adjusting compensatory variables to keep the quality variable close to target. Recently there has been needs for a process control proceduce which combines the tow strategies. This paper considers a combined scheme which simultaneously applies SPC and EPC techniques to reduce the variation of a process. The process model under consideration is an integrated moving average(IMA) process with a step shift. The EPC part of the scheme adjusts the process back to target at every fixed monitoring intervals, which is referred to a repeated adjustment scheme. The SPC part of the scheme uses an exponentially weighted moving average(EWMA) of observed deviation from target to detect special causes. A Markov chain model is developed to relate the scheme's expected cost per unit time to the design parameters of he combined control scheme. The expected cost per unit time is composed of off-target cost, adjustment cost, monitoring cost, and false alarm cost.


  1. Technometrics v.36 no.4 Selection of Sampling Interval and Action Limit for Discrete Feedback Adjustment Box, G.E.P.;Luceno, A.
  2. ASQ Statistics Division Newsletter v.18 no.1 A Perspective on Models and the Quality Sciences Some Challenges and Future Directions Montgomery, D.C.
  3. Quality Engineering v.4 Bounded Adjustment Charts Box, G.E.P.
  4. The Statistician v.44 Discrete Proportional-Integral Control with Constrained Adjustment Box, G.E.P.;Luceno, A.
  5. Technometrics v.38 Monitoring Processes That Wander Using Integrated Moving Average Models Vander Wiel, S.A.
  6. Technometrics v.21 no.1 Sampling Interval and Feedback Control Abraham, B.;Box, G.E.P.
  7. Journal of Quality Technology v.30 no.3 Integrated Process Controlfor Startup Operations Nembhard, H.B.;Mastrangelo, C.M.
  8. Journal of Quality Technology v.30 Combining SPC and EPC in a Hybrid Industry Janakiram, M.;Keats, J.B.
  9. Journal of Quality Technology v.26 Integrating Statistical Process Control and Engineering Process Control Montgomery, D.C.;Keats, J.B.;Runger, G.C.;Messina, W.S.
  10. Journal of Quality Technology v.29 no.3 Discrete Proportional-Integral Adjustment and Statistical Process Control Box, G.E.P.;Luceno, A.
  11. Technometrics v.36 no.4 Statistics Process Control and Feedback Adjustment-A Discussion Box, G.E.P.;Kramer, T.
  12. Technometrics v.34 no.3 Algorithmic Statistical Process Control : Concepts and an Application Vander Wiel, S.A.;Tucker, W.T.;Faltin, F.W.;Doganaksoy, N.
  13. Proceedings of the International Statistical Institute Further Contributions to Adaptive Quality Control : Simultaneous Estimation of Dynamics : Non-Zero Costs Box, G.E.P.;Jenkins, G.M.
  14. Quality Engineering v.4 Feedback Control by Manual Adjustment Box, G.E.P.
  15. Total Quality Management v.4 Process Adjustment and Quality Control Box, G.E.P.
  16. Statistical Control by Monitoring and Feedback Adjustment Box, G.E.P.;Luceno, A.