The variable sampling interval run sum (...) control chart

Traditional control charts for process monitoring are based on taking samples from the process at fixed length sampling intervals. More recently, research works focused on the use of variable sampling intervals (VSIs), where the lengths of the sampling intervals are varied according to the process q...

Full description

Saved in:
Bibliographic Details
Published in:Computers & industrial engineering 2015-12, Vol.90, p.25-38
Main Authors: Chew, XY, Khoo, Michael BC, Teh, SY, Castagliola, P
Format: Article
Language:English
Subjects:
ATS
Control charts
Intervals
Markov analysis
Mathematical models
Optimization
Optimization techniques
Process controls
Sampling
Scoring
Steady state
Studies
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Traditional control charts for process monitoring are based on taking samples from the process at fixed length sampling intervals. More recently, research works focused on the use of variable sampling intervals (VSIs), where the lengths of the sampling intervals are varied according to the process quality. A short sampling interval is considered when the process quality indicates a possible out-of-control situation while a long sampling interval is considered, otherwise. In this paper, the VSI run sum (RS) X chart is proposed with its optimal scores and parameters determined using an optimization technique to minimize the out-of-control average time to signal (ATS) or the adjusted average time to signal (AATS). A Markov-chain method is used to evaluate both the ATS and AATS of the proposed chart, for the zero and steady state cases, respectively. Results show that the VSI RS X chart is considerably more efficient than the basic RS X chart. The VSI RS X chart performs generally well compared with other competing charts, such as the standard X, synthetic X, exponentially weighted moving average (EWMA) X, VSI X and VSI EWMA X charts. The sensitivity of the VSI RS X chart can be enhanced further by adding more scoring regions or a head-start feature. An illustrative example is presented to explain the implementation of the proposed VSI RS X chart.
ISSN:0360-8352
1879-0550
DOI:10.1016/j.cie.2015.08.015