Gráficos adaptativos de controle por atributos e seu projeto na prática

Resumo Os gráficos de controle clássicos para variáveis contínuas monitoram, separadamente, as medidas de posição central e de dispersão, conhecidas também como medidas de locação e escala. O monitoramento desses parâmetros tem como pressuposto que a distribuição de probabilidade dos dados seja conhecida e siga o padrão normal, o que, em situações práticas, nem sempre ocorre. Para isso foram desenvolvidos os chamados gráficos de controle não paramétricos. Este trabalho tem como objetivo desenvolver um método para determinar os limites de controle estatístico de gráficos de controle com distribuição de probabilidade desconhecida e que monitore simultaneamente as medidas de locação e escala. O método de pesquisa utilizado integra técnicas de experimentos computacionais com técnicas de planejamento de experimentos. Assim, foi possível: i) determinar os limites de controle de gráficos não paramétricos que monitorem simultaneamente as medidas de posição e escala para situações particulares; ii) a partir dos limites de controle calculados, estimar os erros tipo I e tipo II; e iii) comparar o desempenho desses gráficos com as cartas de controle estatístico de Shewhart para diferentes combinações de amostras (m, n) nas fases I e II. O método proposto foi aplicado em um processo de manufatura com o objetivo de identificar a combinação que minimize os erros tipo I e II. Com base nos resultados, observou-se que o gráfico de controle não paramétrico tem desempenho superior aos gráficos tradicionais de Shewhart quando a distribuição de probabilidade dos dados é assimétrica.

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Método de estimativa dos limites da carta de controle não paramétrica que monitora simultaneamente a média e variância

Oprime

Toledo

González

et al. 2015

Gest. Prod.

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A bibliometric analysis of 50 years of worldwide research on statistical process control

et al. 2016

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Resumo: Um crescente número de trabalhos sobre controle estatístico do processo (CEP) emergiu nos últimos cinquentaAbstract: An increasing number of papers on statistical process control (SPC) has emerged in the last fifty years, especially in the last fifteen years. This may be attributed to the increased global competitiveness generated by innovation and the continuous improvement of products and processes. In this sense, SPC has a fundamentally important role in quality and production systems. The research in this paper considers the context of technological improvement and innovation of products and processes to increase corporate competitiveness. There are several other statistical technics and tools for assisting continuous improvement and innovation of products and processes but, despite the limitations in their use in the improvement projects, there is growing concern about the use of SPC. A gap between the SPC technics taught in engineering courses and their practical applications to industrial problems is observed in empirical research; thus, it is important to understand what has been done and identify the trends in SPC research. The bibliometric study in this paper is proposed in this direction and uses the Web of Science (WoS) database. Data analysis indicates that there was a growth rate of more than 90% in the number of publications on SPC after 1990. Our results reveal the countries where these publications have come from, the authors with the highest number of papers and their networks. Main sources of publications are also identified; it is observed that the publications of SPC papers are concentrated in some of the international research journals, not necessarily those with the major high-impact factors. Furthermore, the papers are focused on industrial engineering, operations research and management science fields. The most common term found in the papers was cumulative sum control charts, but new topics have emerged and have been researched in the past ten years, such as multivariate methods for process monitoring and nonparametric methods.

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Synthetic control charts with two-stage sampling for monitoring bivariate processes

Costa

Machado

2007

Pesqui. Oper.

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In this article, we consider the synthetic control chart with two-stage sampling (SyTS chart) to control bivariate processes. During the first stage, one item of the sample is inspected and two correlated quality characteristics ( x; y ) are measured. If the Hotelling statistic 2 1 T for these individual observations of ( x; y ) is lower than a specified value 1 UCL the sampling is interrupted. Otherwise, the sampling goes on to the second stage, where the remaining items are inspected and the Hotelling statistic 2 2 T for the sample means of ( x; y ) is computed. When the statistic 2 2 T is larger than a specified value 2 UCL , the sample is classified as nonconforming. According to the synthetic control chart procedure, the signal is based on the number of conforming samples between two neighbor nonconforming samples. The proposed chart detects process disturbances faster than the bivariate charts with variable sample size and it is from the practical viewpoint more convenient to administer.

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Gráficos adaptativos de controle por atributos e seu projeto na prática

Cited by 3 publications

References 25 publications

Método de estimativa dos limites da carta de controle não paramétrica que monitora simultaneamente a média e variância

Método de estimativa dos limites da carta de controle não paramétrica que monitora simultaneamente a média e variância

A bibliometric analysis of 50 years of worldwide research on statistical process control

Synthetic control charts with two-stage sampling for monitoring bivariate processes

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