Identifying the Time of a Change in High yield Processes

Quality control charts have proven to be very effective in detecting out-of-control signals. When a signal is detected a search begins to identify and eliminate the source(s) of the signal. A critical issue that keeps the mind of process engineer busy at this point is the time that the process first changed. Knowing when the process first changed can assist process engineer to focus efforts effectively to eliminate the source(s) of the signal. The time when a change in the process takes place is referred to as the change point. This paper provides an estimator of a time of a step change in the process nonconformity level in high yield processes where the number of items till the occurrence of the first nonconforming item can be modeled by a geometric distribution. The performance of the proposed model is investigated through several numerical examples. The results indicate that the proposed estimator provides an accurate estimate for the time of the change in the process nonconformity level.

Keywords:

Change Point , Maximum Likelihood Estimator , Geometric Control Chart , Statistical Process Control , High Yield Processes