• Journal of Korean Society for Quality Management
• /
• v.31 no.3
• /
• pp.126-135
• /
• 2003

A basic assumption in standard applications of control charts is that the observations are statistically independent. However, this assumption is often violated from processes in many industries. The presence of autocorrelation has a serious impact on the performance of control charts, causing a dramatic increase in the frequency of false alarms. This paper considers a process in which the observations can be modeled as a first order autoregressive(AR(1)) process, and develops (equation omitted) charts with the variable sample size(VSS) scheme for monitoring the mean of this process.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.10B
• /
• pp.936-944
• /
• 2006

In order to enhance their own customer satisfaction index that is one of the top level managerial performance indices, Internet communication service providers endeavor onto establishing a total quality management system. Specifically, it is under discussion that some critical Internet communication network quality characteristics closely related to customer satisfaction index should be controlled aiming to this managerial goal. This paper presents an application scheme of I-MR control charts for monitoring Internet communication network quality characteristics. This statistical quality control scheme generates a signal to practitioners when it detects the network quality characteristics out-of control. It is designed based on; 1) individual measurements; and 2) moving ranges between two consecutive individual measurements collected with a constant time interval. Empirical analyses are illustrated to estimate the expected quality improvement ratios that can be realized with the application scheme proposed in this paper. Assuming that the assignable causes can be revealed and eradicated, regarding two Internet communication services A, B, seven network quality characteristics for each service, eleven distinct measuring spots for each network quality characteristic, the expected quality improvement ratios are calculated with which the effect of the application scheme is evaluated. Results show the ranges of the expected quality improvement ratios; 1) Service A, (1) mean (0.31%-11.44%), (2) standard deviation (9.82%-71.10%): 2) Service B, (1) mean (0.29%-17.64%), (2) standard deviation (8.05%-60.59%). Hence, It is anticipated that the I-MR control charts based application scheme can be effective not only to improving the mean and dispersion of the network quality characteristics concerned but also to maintaining the network quality characteristics in-control consequently.

• Journal of the military operations research society of Korea
• /
• v.22 no.2
• /
• pp.126-138
• /
• 1996

The statistical control chart has been proven to be the effective tool most widely used in the manufacturing industry for monitoring and controlling the manufacturing processes. However, the Shewhart chart sometimes gives us false information when the distribution of quality characteristics is skewed. Therefore, it cannot serve as the universal quality control chart if there exist odd events in the manufacturing process. The objective of this study is thus to develop the new technique for constructing the limits of quality control chart based on a sample median and range when the distribution of the underlying population is skewed. This new control chart can effectively solve and manage the processes which have the non-normally distributed quality characteristics frequently occurring in the practical situation.

• Journal of Korean Society for Quality Management
• /
• v.43 no.4
• /
• pp.471-488
• /
• 2015

Purpose: Double sampling $T^2$ chart is a useful tool for detecting a relatively small shift in process mean when the process is controlled by multiple variables. This paper finds the optimal design of the double sampling $T^2$ chart in both economical and statistical sense under Weibull failure model. Methods: The expected cost function is mathematically derived using recursive equation approach. The optimal designs are found using a genetic algorithm for numerical examples and compared to those of single sampling $T^2$ chart. Sensitivity analysis is performed to see the parameter effects. Results: The proposed design outperforms the optimal design of the single sampling $T^2$ chart in terms of the expected cost per unit time and Type-I error rate for all the numerical examples considered. Conclusion: Double sampling $T^2$ chart can be designed to satisfy both economic and statistical requirements under Weibull failure model and the resulting design is better than the single sampling counterpart.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 1995.04a
• /
• pp.827-844
• /
• 1995

Total Quality Management (TQM) is the aggregated management philosophy for quality including production, operation, human resource, leadership, marketing, and etc. TQM is the advanced concept and philosophy rather than traditional "Quality Control" or "Quality Assurance". Nowadays, downstream costs has been increased, that made cost accountants' attention to costs of quality. Many countries have developed their own quality awards system in order to improve overall national quality level. The Deming Prize of Japan and Malcolm Baldrige National Quality Award (MBNQA) of United States are two representatives of quality prizes. We compared the two awards by means of their history, objective, coverage, and judging criteria. Deming Prize has a longer history than MBNQA. Deming Prize selects five winners a year, while MBNQA has two or three areas. The biggest difference is judgement criteria. The Deming Prizes focuses on statistical control which is a traditional quality control method, while MBNQA concentrates on modem business concept such as customer satisfaction. The suggestions to these awards are: evaluate more on information of quality; evaluate more on inter-functional relationship between quality control function and other link more financial success.e financial success.

• 한국데이터정보과학회:학술대회논문집
• /
• 2005.04a
• /
• pp.7-17
• /
• 2005

Consider a stuffing process where sausage-casings are filled with sausage-kneading. One of the most important factors in the stuffing process is weights of stuffed sausages. Sausages weighting above the specified limit are sold in a regular market price for a fixed price, and underfilled sausages are reworked at the expense of reprocessing cost. In this paper, the sausage stuffing process is inspected for improving productivity and quality levels. Several statistical process control tools are suggested by using real data obtained from a Korean Vienna sausage company.

• Communications for Statistical Applications and Methods
• /
• v.6 no.2
• /
• pp.413-422
• /
• 1999

Multivariate EWMA control charts to simultaneously monitor correlation coefficients of correlated quality characteristics under multivariate normal process are proposed. Performances of the proposed charts are measured in terms of average run length(ARL). Numerical results show that smalle values for smoothing constant with accumulate-combine approach are preferred for detecting smalle shifts.

• Journal of the Korean Data and Information Science Society
• /
• v.16 no.2
• /
• pp.391-399
• /
• 2005

Consider a stuffing process where sausage-casings are filled with sausage-kneading. One of the most important factors in the stuffing process is weights of stuffed sausages. Sausages weighting above the specified limit are sold in a regular market price for a fixed price, and underfilled sausages are reworked at the expense of reprocessing cost. In this paper, the sausage stuffing process is inspected for improving productivity and quality levels. Several statistical process control tools are suggested by using real data obtained from a Korean Vienna sausage company.

• Journal of Korean Society for Quality Management
• /
• v.44 no.2
• /
• pp.245-264
• /
• 2016

Purpose: This article focuses on the reviewing the papers published in the Journal of the Korean Society for Quality Control (JKSQC) and the Journal of the Korean Society for Quality Management (JKSQM) since 1965, in the area of design of experiments. In this paper, moreover, some other contents of another statistical quality control areas is included. Methods: The reviewed articles are classified into the three main categories: theory and application of experimental designs, response surface methodology and mixture experiments, and roust designs. Some omitted papers in the other areas of reviewing works are also included in this paper, and the contents and relationships of the published articles are examined and summarized in each sub-field. Results: We summarize the reviewed papers in the chronological road-maps for each sub-field, and outline the relations of the connected papers. We provide comments on the contents and the contributions of the reviewed papers. The future direction of the research in the theory and application areas of experimental designs can be provided by the contents of this research. Conclusion: The diverse topics on the improving the quality in the various industry fields are studied and published on the theory, methodology and the empirical application in the fields of designs of experiments. We can see that the Korean Society for Quality Management (KSQM) has tremendously contributed on the improvement of quality in the manufacturing and service industries by publishing the reviewed articles in this paper.

• Journal of Korean Society for Quality Management
• /
• v.21 no.2
• /
• pp.17-26
• /
• 1993

Process fault diagnosis is a complicated matter because quality control problems can result from a variety of causes. These causes include problems with electrical components, mechanical components, human errors, job justification errors, and air conditioning influences. In order to make the system run smoothly with minimum delay, it is necessary to suggest heuristic remedies for the detected faults. Hence, this paper describes a heuristic methodology of fault diagnosis that is performed using statistical patterns generated by quality characteristics The proposed methodology is described briefly as follows: If a sample pattern generated by random variables is similar to the number of prototype patterns, the sample pattern may be matched by any prototype pattern among them to be resembled. This concept is based on the similarity between a sample pattern and the matched prototype pattern. The similarity is calculated as the weighted average of squared deviation, which is expressed as the difference between the relative values of standard normal distribution to be transformed by the observed values of quality characteristics in a sample pattern and the critical values of the corresponding ones in a matched prototype pattern.