dissertation · UPT. Syiah Kuala University Library (Syiah Kuala University) · 2014

Attribute control charts for effective statistical process control

Salah Haridy Gad Haridy

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Abstract

The control chart is fast becoming a necessity rather than a fashion in different\n\n\n\n\n\n\n\nmanufacturing processes and service sectors. No tool can capture the voice of a process better\n\n\n\n\n\n\n\nthan the control chart. It is an effective tool to monitor a process, reduce variation, improve\n\n\n\n\n\n\n\nproductivity and ensure quality. The applications of the control chart have now moved into\n\n\n\n\n\n\n\nengineering, service management, biology, health care and finance.\n\n\n\n\n\n\n\nThe control chart is considered as one of the most powerful monitoring techniques in\n\n\n\n\n\n\n\nStatistical Process Control (SPC). It is basically used to achieve the statistical control of a\n\n\n\n\n\n\n\nprocess and its output. SPC provides the decision maker with the ability to monitor the quality\n\n\n\n\n\n\n\ncharacteristics of the product, evaluate the process performance and take a quick corrective\n\n\n\n\n\n\n\naction when out-of-control statuses and abnormal conditions are going to occur in order to avoid\n\n\n\n\n\n\n\ndamages and serious economic losses.\n\n\n\n\n\n\n\nAttribute control charts play a vital role in monitoring the quality characteristics which\n\n\n\n\n\n\n\ncannot be conveniently measured in a continuous numerical scale. Nowadays, attribute charts\n\n\n\n\n\n\n\nenjoy a wide range of applications in many fields such as manufacturing processes, healthcare\n\n\n\n\n\n\n\nsystems and service industries.\n\n\n\n\n\n\n\nThe main objective of this thesis is to develop new attribute control charts with high\n\n\n\n\n\n\n\ndetection effectiveness. This thesis proposes five new attribute charts, namely, a synthetic & np\n\n\n\n\n\n\n\n(Syn-np) chart, an optimal np & Cumulative Sum (np-CUSUM) chart, a CUSUM chart with\n\n\n\n\n\n\n\ncurtailment (Curt_CUSUM), an optimal Sequential Probability Ratio Test (SPRT) chart for\n\n\n\n\n\n\n\nmonitoring p, and finally a novel attribute chart (AFV chart) for monitoring the mean and\n\n\n\n\n\n\n\nvariance of a variable.\n\n\n\n\n\n\n\nA second goal is to provide an overall effectiveness evaluation and systematic\n\n\n\n\n\n\n\ncomparison among the newly developed charts and different attribute charts in the literature\n\n\n\n\n\n\n\nunder the same false alarm rate for a fair comparison. The results of this evaluation give a clear\n\n\n\n\n\n\n\nconclusion on the overall detection effectiveness of the charts and provide a practical guide to\n\n\n\n\n\n\n\nboth academia and industry. To achieve this goal, several types of commonly used control charts\n\n\n\n\n\n\n\nfor attributes including np chart, synthetic chart, Cumulative Sum (CUSUM) chart, Exponentially Weighted Moving Average (EWMA) chart, and Sequential Probability Ratio Test\n\n\n\n\n\n\n\n(SPRT) chart are studied in this thesis. The results of these evaluation and comparison can be\n\n\n\n\n\n\n\nused as guidelines to facilitate the selection of the attribute control charts for different SPC\n\n\n\n\n\n\n\npractitioners.\n\n\n\n\n\n\n\nIn addition, a general model for the optimal design of the attribute control charts is\n\n\n\n\n\n\n\nproposed. In this model, all the independent and dependent charting parameters are optimized\n\n\n\n\n\n\n\nusing an exhaustive search algorithm in order to achieve the best overall performance. This\n\n\n\n\n\n\n\nsearch algorithm is simple and reliable. The Average Number of Defectives (AND) is adopted as\n\n\n\n\n\n\n\nan objective function to design and compare the charts subject to the same false alarm rate. Since\n\n\n\n\n\n\n\nAND is an overall measure of chart performance, therefore, minimizing AND will ensure that the\n\n\n\n\n\n\n\ncontrol chart has an excellent overall performance across the entire shift range of interest.\n\n\n\n\n\n\n\nThe results of the quantitative comparative study reveal that the new charts developed in\n\n\n\n\n\n\n\nthis thesis have achieved a significant improvement in detection effectiveness. Specifically, the\n\n\n\n\n\n\n\nSyn-np chart stands as the most effective Shewhart-type chart for attributes in current SPC\n\n\n\n\n\n\n\nliterature, the np-CUSUM chart and Curt_CUSUM charts are considered as the fastest CUSUM\n\n\n\n\n\n\n\ncharts for detecting p shifts and the optimal SPRT chart is able to double the overall detection\n\n\n\n\n\n\n\nspeed compared with the basic SPRT chart. Although the design of the Syn-np, np-CUSUM,\n\n\n\n\n\n\n\nCurt_CUSUM and optimal SPRT charts is more complicated and their implementation is slightly\n\n\n\n\n\n\n\nmore difficult than the existing counterpart charts, the application of the new charts developed in\n\n\n\n\n\n\n\nthis research can be justified by the substantial improvement in performance.\n\n\n\n\n\n\n\nFinally, the new AFV chart that employs a simple attribute inspection is found to\n\n\n\n\n\n\n\noutperform the variable X-bar&R and X-bar&S charts from an overall viewpoint, under different\n\n\n\n\n\n\n\ncircumstances. As a limitation, the AFV chart is not able to detect decreasing variance shifts.\n\n\n\n\n\n\n\nMoreover, it is not quite suitable to monitor the processes parameters which change frequently.\n\n\n\n\n\n\n\nThe new charts developed in this thesis may help SPC practitioners elsewhere to make a\n\n\n\n\n\n\n\ncorrect and timely decision in face of critical problems, to substantially reduce damages and\n\n\n\n\n\n\n\nquality cost in the long run, and to pave the way for a new cutting-edge research in attribute\n\n\n\n\n\n\n\nSPC.

Cite this paper

APA 7

Haridy, S. H. G. (2014). Attribute control charts for effective statistical process control. UPT. Syiah Kuala University Library (Syiah Kuala University).

MLA 9

Haridy, Salah Haridy Gad. “Attribute control charts for effective statistical process control.” UPT. Syiah Kuala University Library (Syiah Kuala University), 2014.

Chicago

Haridy, Salah Haridy Gad. 2014. “Attribute control charts for effective statistical process control.” UPT. Syiah Kuala University Library (Syiah Kuala University).

Harvard

Haridy, S.H.G. (2014) ‘Attribute control charts for effective statistical process control’, UPT. Syiah Kuala University Library (Syiah Kuala University).

BibTeX

@phdthesis{haridy2014attribute,
  title = {{Attribute control charts for effective statistical process control}},
  author = {Haridy, Salah Haridy Gad},
  school = {UPT. Syiah Kuala University Library (Syiah Kuala University)},
  year = {2014}
}

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