A combined npx X control chart to monitor the process mean in a two-stage sampling

• Autor(a) principal: Sampaio, Elvis S.
• Data de Publicação: 2013
• Outros Autores: Ho, Linda Lee, Medeiros, Pledson G. de
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFRN
• Texto Completo: https://repositorio.ufrn.br/handle/123456789/52057
• topic: Quality control; Monitoring the process mean; Control chart; Control chart X¯; Npx control chart; Combined control chart

This paper proposes a new combined npx X control chart for monitoring the mean of a process. A sample of size n is split into two sub-samples of sizes n1 and n2 =n-n1, determined by an optimization search. The units of the first sub-sample are evaluated by attributes and plotted on an npx control chart. If this chart signals an out-of-control condition, then values of the quality characteristic of interest are collected from the units of the second sub-sample, and the sample mean is calculated and plotted on an X control chart. If both control charts signal, then the process is halted for adjustment. The possibility that all n items will not be inspected may lead to a reduction in both the cost and time spent on examining the sampled items. The performance of the proposed procedure is compared to that of two separate X and npx control charts. The proposed procedure exhibits superior performance to the X control chart for a variety of sample sizes, n, and shifts, d, of the target mean. The average time to signal (ATS) for the combined control chart was lower than that calculated for a single X or npx control chart, indicating that the combined control chart is an efficient tool for monitoring the process mean.