Abstract
In this article, modified multiple dependent (or deferred) state sampling control charts for the attribute and the variable quality characteristics are presented. The proposed control charts are designed using the symmetry property of the normal distribution. The control chart coefficients are estimated through simulation at different levels of the parameters using the normal distribution. The proposed control chart scheme is evaluated by calculating the in-control average run lengths and out-of-control average run lengths. Tables are constructed for the selection of parameters for different control limit coefficients under several shift levels for the attribute data as well as the variable data. Examples are included for the practical application of the proposed control chart schemes. The proposed control chart scheme is also compared with the existing control charts. It has been observed that the proposed schemes are better in quick detection of the out-of-control processes.
Highlights
Process monitoring is an important tool of quality improvement or maintaining the current quality level
Walter introduced the technique of control charts during the 1920s, which is a graphical display with control limits generated from samples collected from the production process to indicate whether the process is in-control or out-of-control to prevent the scrapping of items
The performance of the proposed chart is assessed by computing the values of average run length (ARL), so the in-control ARL0 denoted by r0 is obtained as the average number of samples when the false alarm indicates for the specified values of the multiple dependent (or deferred) state (MDS) sample parameter i
Summary
Process monitoring is an important tool of quality improvement or maintaining the current quality level. The process is considered as in-decision if some plotting statistic is between the outer and inner control limits In this situation, the existing MDS sampling guide the practitioner to collect information from previous in-control subgroups. In the proposed MDS, the decision about in-control state is taken on the basis of previous in-control subgroups and allowing that a maximum of one subgroup may lie in between the outer and inner control limits. The probability that the process is declared as in-control under the modified MDS sampling is given as follows [16]: m [ P( LCL2 ≤ D ≤ UCL2 )] +.
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