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Title: Variable sampling interval np chart with estimated parameter Authors:  Shu Wu - Wuhan University of Technology (China) [presenting]
Abstract: In recent years, the variable sampling interval(VSI) X-bar chart has been investigated by many researchers, because the VSI control charts have important application and useful in service industries. The VSI control charts sample at a higher rate when there is evidence of a change in the process, and are thus able to detect process changes faster than traditional control charts. But the properties of the attribute control charts like VSI np chart with estimated parameter is not investigated yet. The performances of the VSI np chart are evaluated and compared in terms of its average time to signal(ATS), in the case where the process parameter is known and is estimated, the results demonstrate that the performances of VSI np chart are quite different when the number of samples used during Phase I is small. The number of Phase I samples are computed to provide a new optimal constants to have approximately the same in-control average time to signal. An optimization technique to find the suitable chart parameter of VSI np chart is also developed.