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Article
Publication date: 14 December 2021

Arijit Maji and Indrajit Mukherjee

The purpose of this study is to propose an effective unsupervised one-class-classifier (OCC) support vector machine (SVM)-based single multivariate control chart (OCC-SVM…

Abstract

Purpose

The purpose of this study is to propose an effective unsupervised one-class-classifier (OCC) support vector machine (SVM)-based single multivariate control chart (OCC-SVM) to simultaneously monitor “location” and “scale” shifts of a manufacturing process.

Design/methodology/approach

The step-by-step approach to developing, implementing and fine-tuning the intrinsic parameters of the OCC-SVM chart is demonstrated based on simulation and two real-life case examples.

Findings

A comparative study, considering varied known and unknown response distributions, indicates that the OCC-SVM is highly effective in detecting process shifts of samples with individual observations. OCC-SVM chart also shows promising results for samples with a rational subgroup of observations. In addition, the results also indicate that the performance of OCC-SVM is unaffected by the small reference sample size.

Research limitations/implications

The sample responses are considered identically distributed with no significant multivariate autocorrelation between sample observations.

Practical implications

The proposed easy-to-implement chart shows satisfactory performance to detect an out-of-control signal with known or unknown response distributions.

Originality/value

Various multivariate (e.g. parametric or nonparametric) control chart(s) are recommended to monitor the mean (e.g. location) and variance (e.g. scale) of multiple correlated responses in a manufacturing process. However, real-life implementation of a parametric control chart may be complex due to its restrictive response distribution assumptions. There is no evidence of work in the open literature that demonstrates the suitability of an unsupervised OCC-SVM chart to simultaneously monitor “location” and “scale” shifts of multivariate responses. Thus, a new efficient OCC-SVM single chart approach is proposed to address this gap to monitor a multivariate manufacturing process with unknown response distributions.

Details

International Journal of Quality & Reliability Management, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 26 July 2021

Imane Mjimer, ES-Saadia Aoula and EL Hassan Achouyab

This study aims to monitor the overall equipment effectiveness (OEE) indicator that is one of the best indicators used to monitor the performance of the company by the…

Abstract

Purpose

This study aims to monitor the overall equipment effectiveness (OEE) indicator that is one of the best indicators used to monitor the performance of the company by the multivariate control chart.

Design/methodology/approach

To improve continually the performance of a company, many research studies tend to apply Lean six sigma approach. It is one of the best ways used to reduce the variability in the process by using the univariate control chart to know the trend of the variable and make the action before process deviation. Nevertheless, and when the need is to monitor two or more correlated characteristics simultaneously, the univariate control chart will be unable to do it, and the multivariate control chart will be the best way to successfully monitor the correlated characteristics.

Findings

For this study, the authors have applied the multivariate control chart to control the OEE performance rate which is composed by the quality rate, performance rate and availability rate, and the relative work from which the authors have adopted the same methodology (Hadian and Rahimifard, 2019) was done for project monitoring, which is done by following different indicators such as cost, and time; the results of this work shows that by applying this tool, all project staff can meet the project timing with the cost already defined at the beginning of the project. The idea of monitoring the OEE rate comes because the OEE contains the three correlated indicators, we can’t do the monitoring of the OEE just by following one of the three because data change and if today we have the performance and quality rate are stable, and the availability is not, tomorrow we can another indicator impacted and, in this case, the univariate control chart can’t response to our demand. That’s why we have choose the multivariate control chart to prevent the trend of OEE performance rate. Otherwise, and according to production planning work, they try to prevent the downtime by switching to other references, but after applying the OEE monitoring using the multivariate control chart, the company can do the monitoring of his ability to deliver the good product at time to meet customer demand.

Research limitations/implications

The application was done per day, it will be good to apply it per shift in order to have the ability to take the fast reaction in case of process deviation. The other perspective point we can have is to supervise the process according to the control limits found and see if the process still under control after the implementation of the Multivariate control chart at the OEE Rate and if we still be able to meet customer demand in terms of Quantity and Quality of the product by preventing the process deviation using multivariate control chart.

Practical implications

The implication of this work is to provide to the managers the trend of the performance of the workshop by measuring the OEE rate and by following if the process still under control limits, if not the reaction plan shall be established before the process become out of control.

Originality/value

The OEE indicator is one of the effective indicators used to monitor the ability of the company to produce good final product, and the monitoring of this indicator will give the company a visibility of the trend of performance. For this reason, the authors have applied the multivariate control chart to supervise the company performance. This indicator is composed by three different rates: quality, performance and availability rate, and because this tree rates are correlated, the authors have tried to search the best tool which will give them the possibility to monitor the OEE rate. After literature review, the authors found that many works have used the multivariate control chart, especially in the field of project: to monitor the time and cost simultaneously. After that, the authors have applied the same approach to monitor the OEE rate which has the same objective : to monitor the quality, performance and availability rate in the same time.

Details

International Journal of Lean Six Sigma, vol. 13 no. 4
Type: Research Article
ISSN: 2040-4166

Keywords

Article
Publication date: 31 December 2015

Jeffrey E. Jarrett

The purpose of this paper is to suggest better methods for monitoring the diagnostic and treatment services for providers of public health and the management of public…

1970

Abstract

Purpose

The purpose of this paper is to suggest better methods for monitoring the diagnostic and treatment services for providers of public health and the management of public health services. In particular, the authors examine the construction and use of industrial quality control methods as applied to the public providers, in both the prevention and cure for infectious diseases and the quality of public health care providers in such applications including water quality standards, sewage many others. The authors suggest implementing modern multivariate applications of quality control techniques and/or better methods for univariate quality control common in industrial applications in the public health sector to both control and continuously improve public health services. These methods entitled total quality management (TQM) form the foundation to improve these public services.

Design/methodology/approach

The study is designed to indicate the great need for TQM analysis to utilize methods of statistical quality control. All this is done to improve public health services through implementation of quality control and improvement methods as part of the TQM program. Examples of its use indicate that multivariate methods may be the best but other methods are suggested as well.

Findings

Multivariate methods provide the best solutions when quality and reliability tests show indications that the variables observed are inter-correlated and correlated over time. Simpler methods are available when the above factors are not present.

Research limitations/implications

Multivariate methods will provide for better interpretation of results, better decisions and smaller risks of both Type I and Type II errors. Smaller risks lead to better decision making and may reduce costs.

Practical implications

Analysts will improve such things as the control of water quality and all aspects of public health when data are collected through experimentation and/or periodic quality management techniques.

Social implications

Public health will be better monitored and the quality of life will improve for all especially in places where public development is undertaking rapid changes.

Originality/value

The manuscript is original because it uses well known and scientific methods of analyzing data in area where data collection is utilized to improve public health.

Details

International Journal of Quality & Reliability Management, vol. 33 no. 1
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 1 June 1991

Meng‐Koon Chua and Douglas C. Montgomery

Three functions are identified and integrated into one unique control scheme for multivariate quality control. The control scheme will identify any out‐of‐control samples…

Abstract

Three functions are identified and integrated into one unique control scheme for multivariate quality control. The control scheme will identify any out‐of‐control samples, select the subset of variables that are out of control, and diagnose the out‐of‐control variables. New control variable selection algorithm and diagnosis methods are proposed and a framework for the control scheme is developed based on simulation results.

Details

International Journal of Quality & Reliability Management, vol. 8 no. 6
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 2 January 2018

Jeh-Nan Pan, Chung-I Li and Jun-Wei Hsu

The purpose of this paper is to provide a new approach for detecting the small sustained process shifts in multistage systems with correlated multiple quality characteristics.

Abstract

Purpose

The purpose of this paper is to provide a new approach for detecting the small sustained process shifts in multistage systems with correlated multiple quality characteristics.

Design/methodology/approach

The authors propose a new multivariate linear regression model for a multistage manufacturing system with multivariate quality characteristics in which both the auto-correlated process outputs and the correlations occurring between neighboring stages are considered. Then, the multistage multivariate residual control charts are constructed to monitor the overall process quality of multistage systems with multiple quality characteristics. Moreover, an overall run length concept is adopted to evaluate the performances of the authors’ proposed control charts.

Findings

In the numerical example with cascade data, the authors show that the detecting abilities of the proposed multistage residual MEWMA and MCUSUM control charts outperform those of Phase II MEWMA and MCUSUM control charts. It further demonstrates the usefulness of the authors’ proposed control charts in the Phase II monitoring.

Practical implications

The research results of this paper can be applied to any multistage manufacturing or service system with multivariate quality characteristics. This new approach provides quality practitioners a better decision making tool for detecting the small sustained process shifts in multistage systems.

Originality/value

Once the multistage multivariate residual control charts are constructed, one can employ them in monitoring and controlling the process quality of multistage systems with multiple characteristics. This approach can lead to the direction of continuous improvement for any product or service within a company.

Details

International Journal of Quality & Reliability Management, vol. 35 no. 1
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 4 September 2017

Sagar Sikder, Subhash Chandra Panja and Indrajit Mukherjee

The purpose of this paper is to develop a new easy-to-implement distribution-free integrated multivariate statistical process control (MSPC) approach with an ability to…

Abstract

Purpose

The purpose of this paper is to develop a new easy-to-implement distribution-free integrated multivariate statistical process control (MSPC) approach with an ability to recognize out-of-control points, identify the key influential variable for the out-of-control state, and determine necessary changes to achieve the state of statistical control.

Design/methodology/approach

The proposed approach integrates the control chart technique, the Mahalanobis-Taguchi System concept, the Andrews function plot, and nonlinear optimization for multivariate process control. Mahalanobis distance, Taguchi’s orthogonal array, and the main effect plot concept are used to identify the key influential variable responsible for the out-of-control situation. The Andrews function plot and nonlinear optimization help to identify direction and necessary correction to regain the state of statistical control. Finally, two different real life case studies illustrate the suitability of the approach.

Findings

The case studies illustrate the potential of the proposed integrated multivariate process control approach for easy implementation in varied manufacturing and process industries. In addition, the case studies also reveal that the multivariate out-of-control state is primarily contributed by a single influential variable.

Research limitations/implications

The approach is limited to the situation in which a single influential variable contributes to out-of-control situation. The number and type of cases used are also limited and thus generalization may not be debated. Further research is necessary with varied case situations to refine the approach and prove its extensive applicability.

Practical implications

The proposed approach does not require multivariate normality assumption and thus provides greater flexibility for the industry practitioners. The approach is also easy to implement and requires minimal programming effort. A simple application Microsoft Excel is suitable for online implementation of this approach.

Originality/value

The key steps of the MSPC approach are identifying the out-of-control point, diagnosing the out-of-control point, identifying the “influential” variable responsible for the out-of-control state, and determining the necessary direction and the amount of adjustment required to achieve the state of control. Most of the approaches reported in open literature are focused only until identifying influencing variable, with many restrictive assumptions. This paper addresses all key steps in a single integrated distribution-free approach, which is easy to implement in real time.

Details

International Journal of Quality & Reliability Management, vol. 34 no. 8
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 29 April 2014

S.T.A. Niaki and Majid Khedmati

The purpose of this paper is to propose two control charts to monitor multi-attribute processes and then a maximum likelihood estimator for the change point of the…

Abstract

Purpose

The purpose of this paper is to propose two control charts to monitor multi-attribute processes and then a maximum likelihood estimator for the change point of the parameter vector (process fraction non-conforming) of multivariate binomial processes.

Design/methodology/approach

The performance of the proposed estimator is evaluated for both control charts using some simulation experiments. At the end, the applicability of the proposed method is illustrated using a real case.

Findings

The proposed estimator provides accurate and useful estimation of the change point for almost all of the shift magnitudes, regardless of the process dimension. Moreover, based on the results obtained the estimator is robust with regard to different correlation values.

Originality/value

To the best of authors’ knowledge, there are no work available in the literature to estimate the change-point of multivariate binomial processes.

Article
Publication date: 4 October 2011

Florbela Correia, Rui Nêveda and Pedro Oliveira

This article seeks to explain how to monitor the chronic obstructive disease patient and control any complications so that timely treatment can be applied.

Abstract

Purpose

This article seeks to explain how to monitor the chronic obstructive disease patient and control any complications so that timely treatment can be applied.

Design/methodology/approach

Control charts and statistical process control (SPC) theory were used on chronic respiratory patient follow‐up and control. Controlling several variables simultaneously, using univariate charts, can be misleading, more so when there are correlated variables, so multivariate and univariate control charts were studied.

Findings

One‐sided control charts are preferable when the aim is to detect changes in the mean solely in one direction. Thus, one‐sided, univariate and multivariate charts were built, which identified previously undetected out‐of‐control events.

Research limitations/implications

The study's main limitation is its retrospective nature. However, following‐up individual patients can highlight medical therapy effects.

Practical implications

The article concludes that control charts, in particular one‐sided ones, are a valuable tool for monitoring chronic respiratory patients, thus contributing to medical decision making.

Originality/value

The article highlights control chart application to chronic respiratory patient follow‐up, permitting a global view of patient evolution over time.

Details

International Journal of Health Care Quality Assurance, vol. 24 no. 8
Type: Research Article
ISSN: 0952-6862

Keywords

Article
Publication date: 11 January 2022

Daniel Ashagrie Tegegne, Daniel Kitaw Azene and Eshetie Berhan Atanaw

This study aims to design a multivariate control chart that improves the applicability of the traditional Hotelling T2 chart. This new type of multivariate control chart

Abstract

Purpose

This study aims to design a multivariate control chart that improves the applicability of the traditional Hotelling T2 chart. This new type of multivariate control chart displays sufficient information about the states and relationships of the variables in the production process. It is used to make better quality control decisions during the production process.

Design/methodology/approach

Multivariate data are collected at an equal time interval and are represented by nodes of the graph. The edges connecting the nodes represent the sequence of operation. Each node is plotted on the control chart based on their Hotelling T2 statistical distance. The changing behavior of each pair of input and output nodes is studied by the neural network. A case study from the cement industry is conducted to validate the control chart.

Findings

The finding of this paper is that the points and lines in the classic Hotelling T2 chart are effectively substituted by nodes and edges of the graph respectively. Nodes and edges have dimension and color and represent several attributes. As a result, this control chart displays much more information than the traditional Hotelling T2 control chart. The pattern of the plot represents whether the process is normal or not. The effect of the sequence of operation is visible in the control chart. The frequency of the happening of nodes is recognized by the size of nodes. The decision to change the product feature is assisted by finding the shortest path between nodes. Moreover, consecutive nodes have different behaviors, and that behavior change is recognized by neural network.

Originality/value

Modifying the classical Hotelling T2 control chart by integrating with the concept of graph theory and neural network is new of its kind.

Details

International Journal of Quality & Reliability Management, vol. 39 no. 7
Type: Research Article
ISSN: 0265-671X

Keywords

Article
Publication date: 1 June 1998

Orlando O. Atienza, Loon Ching Tang and Beng Wah Ang

We propose a simple controlcharting scheme for simultaneously displaying univariate and multivariate process information. The proposed chart can be used as a diagnostic…

6348

Abstract

We propose a simple controlcharting scheme for simultaneously displaying univariate and multivariate process information. The proposed chart can be used as a diagnostic tool for understanding the nature of out‐of‐control conditions in multivariate statistical process control (SPC). The chart is easy to implement and interpret. Two examples are given for illustration purposes.

Details

International Journal of Quality Science, vol. 3 no. 2
Type: Research Article
ISSN: 1359-8538

Keywords

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