• Journal of the Korean Operations Research and Management Science Society
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• v.12 no.1
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• pp.111-111
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• 1987

With the increasing interest of reducing process variation, statistical process control has served the pivotal tool in most industrial quality programs. In this study, system analyses have been performed associated with a cost incorporated version of a process control, a quadratic loss-based X over bar control chart model. Specifically, two issues, the capital/research investments for improvement of a system and the precision of a parameter estimation, have been addressed and discussed. Through the analysis of experimental results, we show that process variability is seen to be one of the most important sources of loss and quality improvement efforts should be directed to reduce this variability. We further derive the results that, even if the optimal designs may be sensitive, the model appears to be robust with regard to misspecification of parameters. The approach and discussion taken in this study provide a meaningful guide for proper process control. We conclude this study with providing general comments.

• Journal of Korean Society for Quality Management
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• v.36 no.1
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• pp.7-19
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• 2008

During the past two decades, a huge amount of research on adaptive control charts has been accomplished. Especially, variable sampling interval (VSI), variable sample size (VSS), and variable sample size and sampling interval (VSSI) charts have been focused by many researchers due to their simplicity and efficiency. On the other hand, the difference among notations, assumptions, methodologies may cause confusions in per forming further studies or practical implementations. This research analyses and compares diverse models so as to provide a unified view on statistical and economical characteristics. As a result, we perform comparative study on economical design models of VSI, VSS, and VSSI charts, respectively, We also present practical guidelines to utilize those adaptive control charts.

• Journal of Korean Society for Quality Management
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• v.26 no.1
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• pp.126-142
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• 1998

Traditional statistical process control(SPC) assumes that consective observations from a process are independent. In industrial practice, however, observations are ofter serially correlated. A common a, pp.oach to building control charts for autocorrelatd data is to a, pp.y classical SPC to the residuals from a time series model fitted. Unfortunately, one cannot completely escape the effects of autocorrelation by using charts based on residuals of time series model. For the detection of variance change in the process we propose a CUSUM of squares control chart which does not require the model identification. The proposed CUSUM of squares chart and the conventional control charts are compared by a Monte Carlo simulation. It is shown that the CUSUM of squares chart is more effective in the presence of dependency in the processes.

• The Journal of Korean Physical Therapy
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• v.28 no.6
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• pp.355-363
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• 2016

Purpose: In this study, we investigated the effectiveness of a 12-week virtual reality exercise program using the Nintendo Wii console (Wii) in improving balance, emotion, and quality of life among patients with cognitive decline. Methods: The study included 30 patients with cognitive decline (12 female, 18 male) who were randomly assigned to an experimental (n=15) and control groups (n=15). All subjects performed a traditional cognitive rehabilitation program and the experimental group performed additional three 40-minute virtual reality based video game (Wii) sessions per week for 12 weeks. The berg balance scale (BBS) was used to assess balance abilities. The short form geriatric depression scale-Korean (GDS-K) and the Korean version of quality of life-Alzheimer's disease (KQOL-AD) scale were both used to assess life quality in patients. Statistical significance was tested within and between groups before and after treatment, using Wilcoxon signed rank and Mann-Whitney u-tests. Results: After 36 training sessions, there were significant beneficial effects of the virtual reality game exercise on balance (BBS), GDS-K, and KQOL-AD in the experimental group when compared to the control group. No significant difference was observed within the control group. Conclusion: These findings demonstrate that a virtual reality-training program could improve the outcomes in terms of balance, depression, and quality of life in patients with cognitive decline. Long-term follow-ups and further studies of more efficient virtual reality training programs are needed.

• Computers and Concrete
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• v.14 no.2
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• pp.145-161
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• 2014

The article presents the statistical method of grouping the results of the compressive strength of concrete in continuous production. It describes the method of dividing the series of compressive strength results into batches of statistically stable strength parameters at specific time intervals, based on the standardized concept of "concrete family". The article presents the examples of calculations made for two series of concrete strength results, from which sets of decreased strength parameters were separated. When assessing the quality of concrete elements and concrete road surfaces, the principal issue is the control of the compressive strength parameters of concrete. Large quantities of concrete mix manufactured in a continuous way should be subject to continuous control. Standardized approach to assessing the concrete strength proves to be insufficient because it does not allow for the detection of subsets of the decreased strength results, which in turn makes it impossible to make adjustments to the concrete manufacturing process and to identify particular product or area on site with decreased concrete strength. In this article two independent methods of grouping the test results of concrete with statistically stable strength parameters were proposed, involving verification of statistical hypothesis based on statistical tests: Student's t-test and Mann - Whitney - U test.

• Journal of Korean Society for Quality Management
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• v.40 no.4
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• pp.577-588
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• 2012

Purpose: This paper aims to evaluate the quality of Small & Medium Enterprises(SMEs) Survey and to provide some desirable directions and improvements for the future SMEs Survey, conducted by the Government. Methods: The diagnosis were performed by employing the quantitative and qualitative approaches with the official guideline provided by the Ministry of Statistics. Results: Results show that follow-up management are evaluated relatively low in specific processes, and timeliness are evaluated relatively lower than accuracy, accessibility, relevance, comparability and consistency in statistical qualities. Conclusion: we propose the alternatives which enhance the quality level of SMEs by using the 6 tools of Quality Management for Statistics.

• Journal of Korean Society for Quality Management
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• v.37 no.2
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• pp.68-77
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• 2009

There are many quality control(QC) tools useful for solving quality problems. In this paper, QC 7 tools, new QC 7 tools, and other quality tools are first compared with respect to their frequency of use. We suggest an integrated problem-solving procedure to systematically deal with various quality problems. For each step a streamlined flow chart is presented to help the practitioners to adopt relevant tools depending on certain situations they face. The procedure will help quality practitioners solve field quality problems.

• Journal of Korean Society for Quality Management
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• v.29 no.1
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• pp.128-139
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• 2001

For small sized companies in Korea, it is crucial to have a systematic way of collecting and storing quality data, and extracting relevant information when necessary. This paper Is concerned with developing a quality information system which is mainly focused on processing quality inspection data, converting the data into meaningful quality information, and illustrating a case study of a small sized company in Gyeongnam province. First, we review the current quality Inspection system and reorganize a quality system which is more efficient than the current one. Second, incoming material, process, and product inspection modules are developed. Finally, a statistical process control module is integrated to see the manufacturing process behavior over time.

• Journal of the military operations research society of Korea
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• v.27 no.1
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• pp.73-88
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• 2001

Designing high quality products and processes at a low cost is central technological and economic challenge to the engineer. The combination of engineering concepts and statistical implementations offered by Taguchi\`s off-line design technique has proven t be invaluable. By examining some deficiencies in designs from the Taguchi\`s highly fractional, orthogonal main effect plan based on orthogonal arrays, alternative method is proposed. The maximum resolution or the minimum aberration criterion is commonly used for selecting 2$^{n-m}$ fractional designs. We present new high resolution (low aberration) linear graphs to simplify the complexity of selecting designs with desirable statistical properties. The new linear graphs approach shows a substantial improvement over Taguchi\`s linear graphs and other related graphical methods for planning experiment. The new set of linear graphs will allow the experimenter to maintain the simple approach suggested by Taguchi while obtaining the best statistical properties of the resulting design such as minimum aberration as a by-product without dependency on complicated computational algorithm or additional statistical training.g.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.2
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• pp.246-255
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• 1998

This paper presents a novel method for real-time malfunction detection of plasma etching process using EPD signal traces. First, many reference EPD signal traces are collected using monochromator and data acquisition system in normal etching processes. Critical points are defined by applying differentiation and zero-crossing method to the collected reference signal traces. Critical parameters such as intensity, slope, time, peak, overshoot, etc., determined by critical points, and frame attributes transformed signal-to symbol of reference signal traces are saved. Also, UCL(Upper Control Limit) and LCL(Lower Control Limit) are obtained by mean and standard deviation of critical parameters. Then, test EPD signal traces are collected in the actual processes, and frame attributes and critical parameters are obtained using the above mentioned method. Process malfunctions are detected in real-time by applying SPC(Statistical Process Control) method to critical parameters. the Real-time malfunction detection method presented in this paper was applied to actual processes and the results indicated that it was proved to be able to supplement disadvantages of existing quality control check inspecting or testing random-selected devices and detect process malfunctions correctly in real-time.