A Combined np(x) - (X)over-bar Control Chart to Monitor the Process Mean in a Two-Stage Sampling

作者：Sampaio Elvis S; Ho Linda Lee^*; de Medeiros Pledson G

来源：Quality and Reliability Engineering International, 2014, 30(7): 1003-1013.

DOI：10.1002/qre.1528

• quality control
• monitoring the process mean
• control chart
• control chart (X)over-bar
• np(x) control chart
• combined control chart

This paper proposes a new combined np(x) - (X) over bar control chart for monitoring the mean of a process. A sample of size n is split into two sub-samples of sizes n(1) and n(2) = n-n(1), determined by an optimization search. The units of the first sub-sample are evaluated by attributes and plotted on an np(x) 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) over bar 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) over bar and np(x) control charts. The proposed procedure exhibits superior performance to the (X) over bar control chart for a variety of sample sizes, n, and shifts, delta, of the target mean. The average time to signal (ATS) for the combined control chart was lower than that calculated for a single (X) over bar or np(x) control chart, indicating that the combined control chart is an efficient tool for monitoring the process mean.

• 出版日期2014-11