Página 1 dos resultados de 728 itens digitais encontrados em 0.029 segundos

Control charts for individual observations of a bivariate Poisson process

HO, Linda Lee; COSTA, Antonio Fernando Branco
Fonte: SPRINGER LONDON LTD Publicador: SPRINGER LONDON LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.37%
In this paper, three single-control charts are proposed to monitor individual observations of a bivariate Poisson process. The specified false-alarm risk, their control limits, and ARLs were determined to compare their performances for different types and sizes of shifts. In most of the cases, the single charts presented better performance rather than two separate control charts ( one for each quality characteristic). A numerical example illustrates the proposed control charts.

Aplicação de cartas de controle como ferramenta de melhoria frente às dificuldades operacionais de laboratórios acreditados na ABNT NBR ISO/IEC 17025 ; Application of Control charts as an improvement tool considering the operational difficulties of accredited laboratories according to ISO/IEC 17025

Turuta, Tatiana Barbosa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/03/2015 PT
Relevância na Pesquisa
56.36%
É crescente o número de laboratórios que têm implantado sistemas de gestão da qualidade conforme a norma ABNT NBR ISO/IEC 17025, entretanto, para continuidade no atendimento aos requisitos da norma e às necessidades dos clientes, os laboratórios podem apresentar dificuldades que precisam ser identificadas e analisadas para melhoria continua da qualidade dos resultados. Desta maneira, uma avaliação preliminar das dificuldades operacionais após implantação do sistema de gestão da qualidade ABNT NBR ISO/IEC 17025 aponta como um dos requisitos de maior dificuldade a garantia da qualidade de resultados (requisito 5.9). Este requisito abrange a importância do monitoramento contínuo para validade dos ensaios realizados e acompanhamento de possíveis tendências das análises realizadas pelos laboratórios. Para realização desse monitoramento são aplicadas as cartas de controle que requerem maior atenção na sua aplicabilidade e interpretação em função do método de análise, da amostra de controle e da periodicidade do acompanhamento. As cartas de controle são ferramentas que possibilitam o monitoramento contínuo dos processos analíticos e permitem a avaliação de possíveis otimizações das atividades técnicas como...

Índices de capacidade para gráficos de controle baseados em modelos de regressão; Capability indices to control charts based on regression models

Souza, Fernanda Siqueira
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
66.22%
Índices de capacidade mal empregados geram conclusões errôneas, comprometendo o estudo e análise do processo, prejudicando o atendimento de exigências gerenciais ou de clientes externos. Assim, o objetivo do presente trabalho é propor índices de capacidade para processos monitorados com gráficos de controle baseado em modelos de regressão conteplando limites simétricos e assimétricos. Realizou-se um mapeamento dos artigos publicados em nove periódicos no período de 2000 a 2009, visando identificar as abordagens pesquisadas sobre capacidade de processos. Um fluxograma orientativo é apresentado, com a finalidade de direcionar a escolha do tipo de gráfico de controle e índices de capacidade para processos com variáveis de resposta: (i) não correlacionadas, (ii) correlacionadas dependentes da variável de controle e (iii) autocorrelacionadas. O uso do fluxograma foi ilustrado através da aplicação do mesmo em um processo de torneamento de uma empresa de máquinas agrícolas.; Capability indices wrongly appointed generate erroneous conclusions, compromising the study and analysis of the process, jeopardizing the fulfillment of the requirements management or external customers. Therefore, the objective of this study is to propose capability indices for processes monitored with control charts based on regression models considering symmetric and asymmetric limits. A mapping of the articles published in nine journals...

Gráficos de controle multivariados para monitoramento de processos não lineares em bateladas; Multivariate control charts for monitoring non-linear batch processes

Marcondes Filho, Danilo; Fogliatto, Flavio Sanson; Oliveira, Luiz Paulo Luna de
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
Relevância na Pesquisa
66.33%
Processos industriais em bateladas são empregados com frequência na produção de certos itens. Tais processos disponibilizam uma estrutura de dados peculiar; diante disso, existe um crescente interesse no desenvolvimento de gráficos de controle multivariados mais apropriados para seu monitoramento. Investiga-se aqui uma abordagem recente que utiliza gráficos de controle baseados no método Statis. O Statis constitui-se em uma técnica exploratória que permite avaliar similaridade entre matrizes de dados. Entretanto, essa técnica considera a similaridade em um contexto linear, investigando estruturas de correlação lineares nos dados. Propõe-se neste artigo a utilização de gráficos de controle baseados no Statis em conjunto com kernels para monitoramento de processos com presença de não linearidades fortes. Através dos kernels, definem-se funções não lineares dos dados para melhor representação da estrutura a ser caracterizada pelo método Statis. Essa nova abordagem, denominada Kernel-Statis, é desenvolvida e avaliada utilizando dados de um processo simulado.; Industrial batch processes are widely used in the production of certain items. Such processes provide a peculiar data structure; therefore there is a growing interest in the development of customized multivariate control charts for their monitoring. We investigate a recent approach that uses control charts based on the Statis method. Statis is an exploratory technique for measuring similarities between data matrices. However...

Influência da incerteza de medição no uso de cartas de controle; Influence of measurement uncertainty in the usage of control charts

Hack, Pedro da Silva
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
66.34%
A incerteza de medição ainda é tema de estudo e desenvolvimento, mesmo quase vinte anos após o lançamento do ISO GUM, que definiu um padrão internacional para o cálculo de incerteza. Mesmo assim, poucos estudos tratam da interface entre a incerteza de medição e outros aspectos da qualidade industrial, em especial ferramentas de controle de processo como cartas de controle. Assim, o objetivo deste trabalho é estudar os efeitos da incerteza em cartas de controle e identificar sob quais situações de aplicação ela exerce maior influência. Foi feito um mapeamento dos artigos publicados entre 2004 e 2010 sobre incerteza de medição, para identificar quais as metodologias de cálculo e abordagem são mais utilizadas. Na sequência, foi desenvolvido um método incluir nas cartas de controle a incerteza do sistema de medição, modificando as probabilidades de erros tipo I e tipo II. Finalmente, foi elaborada uma simulação computacional utilizando o método desenvolvido, para que fosse possível analisar quais as situações nas quais a incerteza de medição deve ser obrigatoriamente considerada e quais ela pode ser negligenciada.; The measurement uncertainty is still subject of study and development, even almost twenty years after the release of the ISO GUM...

Control charts for monitoring the mean vector and the covariance matrix of bivariate processes

Machado, Marcela A. G.; Costa, Antonio F. B.; Marins, Fernando Augusto Silva
Fonte: Springer London Ltd Publicador: Springer London Ltd
Tipo: Conferência ou Objeto de Conferência Formato: 772-785
ENG
Relevância na Pesquisa
66.41%
In this article, we propose new control charts for monitoring the mean vector and the covariance matrix of bivariate processes. The traditional tools used for this purpose are the T (2) and the |S| charts. However, these charts have two drawbacks: (1) the T (2) and the |S| statistics are not easy to compute, and (2) after a signal, they do not distinguish the variable affected by the assignable cause. As an alternative to (1), we propose the MVMAX chart, which only requires the computation of sample means and sample variances. As an alternative to (2), we propose the joint use of two charts based on the non-central chi-square statistic (NCS statistic), named as the NCS charts. Once the NCS charts signal, the user can immediately identify the out-of-control variable. In general, the synthetic MVMAX chart is faster than the NCS charts and the joint T (2) and |S| charts in signaling processes disturbances.

Control charts for individual observations of a bivariate Poisson process

Ho, Linda Lee; Branco Costa, Antonio Fernando
Fonte: Springer London Ltd Publicador: Springer London Ltd
Tipo: Artigo de Revista Científica Formato: 744-755
ENG
Relevância na Pesquisa
66.37%
In this paper, three single-control charts are proposed to monitor individual observations of a bivariate Poisson process. The specified false-alarm risk, their control limits, and ARLs were determined to compare their performances for different types and sizes of shifts. In most of the cases, the single charts presented better performance rather than two separate control charts ( one for each quality characteristic). A numerical example illustrates the proposed control charts.

Adaptive control charts: A Markovian approach for processes subject to independent disturbances

De Magalhaes, M. S.; Costa, AFB; Neto, FDM
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 236-246
ENG
Relevância na Pesquisa
56.35%
Recent studies have shown that adaptive X control charts are quicker than traditional X charts in detecting small to moderate shifts in a process. In this article, we propose a joint statistical design of adaptive X and R charts having all design parameters varying adaptively. The process is subjected to two independent assignable causes. One cause changes the process mean and the other changes the process variance. However, the occurrence of one kind of assignable cause does not preclude the occurrence of the other. It is assumed that the quality characteristic is normally distributed and the time that the process remains in control has exponential distribution. Performance measures of these adaptive control charts are obtained through a Markov chain approach. (c) 2005 Elsevier B.V. All rights reserved.

A hierarchy of adaptive (X)over-bar control charts

De Magalhaes, M. S.; Costa, A. F. B.; Moura Neto, F. D.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 271-283
ENG
Relevância na Pesquisa
56.34%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); The purpose of this article is to present a statistical design of a hierarchy of two-states adaptive parameters (X) over bar charts. We assume that the shift in the process mean does not occur at the beginning of the production process but at some random time in the future. The occurrence time of the shift is assumed to be an exponentially distributed random variable. This assumption allows the application of the Markov chain approach for developing performance measures. Seven adaptive (X) over bar charts result from the combinations of the design parameters, that is, the sample size, the sampling interval, and the factor used to define the control limits, when one, two, or all of them are allowed to vary. arranged in a hierarchy. When comparing the performance between different two-state charts one sometimes can use a chart with fewer parameters varying and yet achieve good performance, however this depends on the size of process shift. One can change the probability of the control system to be in a state of loose control: considering that, its effect on the adjusted average time to signal and on the design parameters was analyzed numerically. (C) 2009 Elsevier B.V. All rights reserved.

Joint economic design of X̄ and R control charts for processes subject to two independent assignable causes

Costa, Antonio F B
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 27-33
ENG
Relevância na Pesquisa
66.22%
A model for the joint economic design of X̄ and R control charts is developed. This model assumes that the process is subject to two assignable causes. One assignable cause shifts the process mean; the other shifts the process variance. The occurrence of the assignable cause of one kind does not block the occurrence of the assignable cause of another kind. Consequently, a second process parameter can go out-of-control after the first process parameter has gone out-of-control. A numerical study of the cost surface to the model considered has revealed that it is convex, at least in the interest region.

The use of principal components and univariate charts to control multivariate processes

Machado, Marcela A. G.; Costa, Antonio F. B.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 173-196
ENG
Relevância na Pesquisa
56.41%
In this article, we evaluate the performance of the T2 chart based on the principal components (PC chart) and the simultaneous univariate control charts based on the original variables (SU X̄ charts) or based on the principal components (SUPC charts). The main reason to consider the PC chart lies on the dimensionality reduction. However, depending on the disturbance and on the way the original variables are related, the chart is very slow in signaling, except when all variables are negatively correlated and the principal component is wisely selected. Comparing the SU X̄, the SUPC and the T 2 charts we conclude that the SU X̄ charts (SUPC charts) have a better overall performance when the variables are positively (negatively) correlated. We also develop the expression to obtain the power of two S 2 charts designed for monitoring the covariance matrix. These joint S2 charts are, in the majority of the cases, more efficient than the generalized variance |S| chart.

Tabular cusum control charts of chemical variables applied to the control of surface water quality

Follador,Franciele A. C.; Boas,Márcio A. Vilas; Schoenhals,Marlise; Hermes,Eliane; Rech,Clovis
Fonte: Associação Brasileira de Engenharia Agrícola Publicador: Associação Brasileira de Engenharia Agrícola
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2012 EN
Relevância na Pesquisa
66.29%
The aim of this study was to evaluate the application possibility of tabular CUSUM control charts in the quality control of chemical variables in surface water. It was performed bibliographic and field research to collect water samples from 2003 to 2009, totaling 30 samples, some monthly and others semi-annual in order to observe the variables that regulate water quality. It was found that these charts may be applied to control the quality of river water; showing to be effective in the perception of changes during the process, especially for small samples (n=1) which there is no repetition as in this research. It was also concluded that the Mandurim River does not presents significant levels of pollution.

The use of principal components and univariate charts to control multivariate processes

Machado,Marcela A. G.; Costa,Antonio F. B.
Fonte: Sociedade Brasileira de Pesquisa Operacional Publicador: Sociedade Brasileira de Pesquisa Operacional
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2008 EN
Relevância na Pesquisa
56.41%
In this article, we evaluate the performance of the T² chart based on the principal components (PC X chart) and the simultaneous univariate control charts based on the original variables (SU charts) or based on the principal components (SUPC charts). The main reason to consider the PC chart lies on the dimensionality reduction. However, depending on the disturbance and on the way the original variables are related, the chart is very slow in signaling, except when all variables are negatively correlated and the principal component is wisely selected. Comparing the SU , the SUPC and the T² charts we conclude that the SU X charts (SUPC charts) have a better overall performance when the variables are positively (negatively) correlated. We also develop the expression to obtain the power of two S² charts designed for monitoring the covariance matrix. These joint S² charts are, in the majority of the cases, more efficient than the generalized variance chart.

A novel experience in the use of control charts for the detection of nosocomial infection outbreaks

Gomes,Isabel Cristina; Mingoti,Sueli Aparecida; Oliveira,Cláudia Di Lorenzo
Fonte: Faculdade de Medicina / USP Publicador: Faculdade de Medicina / USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 EN
Relevância na Pesquisa
56.37%
OBJECTIVE: This study aims to compare different control charts to monitor the nosocomial infection rate per 1,000 patient-days. METHODS: The control charts considered in this study were the traditional Shewhart chart and a variation of this, the Cumulative Sum and Exponentially Weighted Moving Average charts. RESULTS: We evaluated 238 nosocomial infections that were registered in the intensive care unit and were detected by the Committee for Nosocomial Infection Control in a university hospital in Belo Horizonte, Brazil, in 2004 and 2005. The results showed that the traditional Shewhart chart was the most appropriate method for monitoring periods with large deviations, while the Exponentially Weighted Moving Average and Cumulative Sum charts were better for monitoring periods with smaller deviations of the mean infection rate. CONCLUSION: The ability to detect nosocomial outbreaks was improved by using the information provided by all three different control charts.

Behavior prediction models and control charts for safety control of concrete dams

Lopes,R. A. C.; Santos,E. P.; Veloso,L. A. C. M.
Fonte: IBRACON - Instituto Brasileiro do Concreto Publicador: IBRACON - Instituto Brasileiro do Concreto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
Relevância na Pesquisa
66.29%
This paper presents a study for improving measurement procedures on concrete dams based on the development of behavior prediction models using multiple regression and control charts. The series of displacements of the TA-2 concrete block crest of the Tucuruí Hydroelectric Power Plant, the largest Brazilian hydroelectric power plant, was taken as an example of application. The methodology that was used generated a behavior prediction model that is in good agreement with the measured displacements. Two types of control charts were tested, both of which identified the change in structural behavior of the block.

Adaptive EWMA Control Charts with a Time Varying Smoothing Parameter

Ugaz, Willy; Sánchez, Ismael
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/draft; info:eu-repo/semantics/workingPaper
Publicado em 01/05/2015 ENG
Relevância na Pesquisa
66.46%
It is known that time-weighted charts like EWMA or CUSUM are designed to be optimal to detect a specific shift. If they are designed to detect, for instance, a very small shift, they can be inefficient to detect moderate or large shifts. In the literature, several alternatives have been proposed to circumvent this limitation, like the use of control charts with variable parameters or adaptive control charts. This paper has as main goal to propose some adaptive EWMA control charts (AEWMA) based on the assessment of a potential misadjustment, which is translated into a time-varying smoothing parameter. The resulting control charts can be seen as a smooth combination between Shewhart and EWMA control charts that can be efficient for a wide range of shifts. Markov chain procedures are established to analyze and design the proposed charts. Comparisons with other adaptive and traditional control charts show the advantages of the proposals.; Acknowledgements: financial support from the Spanish Ministry of Education and Science, research project ECO2012-38442.

Use of control charts for multi-temporal analysis of geodetic auscultation data from dams

Quintanilha,José Alberto; Ho,Linda Lee; Machado,Cláudia Aparecida Soares; Blitzkow,Denizar
Fonte: Universidade Federal do Paraná Publicador: Universidade Federal do Paraná
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
Relevância na Pesquisa
66.32%
Geodesic auscultation can be used to monitor the movement of dam structures by measuring the distance, at different epochs from fixed positions (pillars) to other positions (targets). It is important to identify the targets that present atypical measurements to permit managers to take corrective actions. After fitting a model using the Least Squares Method (LSM), the residuals normally display random behavior. Multivariate control charts are then applied to the residuals of the fitted model from data taken of geodesic survey campaigns conducted at different epochs. Control charts have been widely applied in other fields of research than production processes such as public health, marketing, services. The results show that it is possible for monitoring the multi-temporal stability by the multivariate control charts. The method provides complementary information than the classical univariate statistical analysis.

A novel experience in the use of control charts for the detection of nosocomial infection outbreaks

Gomes, Isabel Cristina; Mingoti, Sueli Aparecida; Oliveira, Cláudia Di Lorenzo
Fonte: Universidade de São Paulo. Faculdade de Medicina Publicador: Universidade de São Paulo. Faculdade de Medicina
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; ; Formato: application/pdf
Publicado em 01/01/2011 ENG
Relevância na Pesquisa
56.37%
OBJECTIVE: This study aims to compare different control charts to monitor the nosocomial infection rate per 1,000 patient-days. METHODS: The control charts considered in this study were the traditional Shewhart chart and a variation of this, the Cumulative Sum and Exponentially Weighted Moving Average charts. RESULTS: We evaluated 238 nosocomial infections that were registered in the intensive care unit and were detected by the Committee for Nosocomial Infection Control in a university hospital in Belo Horizonte, Brazil, in 2004 and 2005. The results showed that the traditional Shewhart chart was the most appropriate method for monitoring periods with large deviations, while the Exponentially Weighted Moving Average and Cumulative Sum charts were better for monitoring periods with smaller deviations of the mean infection rate. CONCLUSION: The ability to detect nosocomial outbreaks was improved by using the information provided by all three different control charts.

Joint economic design of X̄ and R control charts for processes subject to two independent assignable causes

Costa, Antonio F B
Fonte: Chapman Hall Ltd Publicador: Chapman Hall Ltd
Tipo: Artigo de Revista Científica Formato: 27-33
ENG
Relevância na Pesquisa
66.22%
A model for the joint economic design of X̄ and R control charts is developed. This model assumes that the process is subject to two assignable causes. One assignable cause shifts the process mean; the other shifts the process variance. The occurrence of the assignable cause of one kind does not block the occurrence of the assignable cause of another kind. Consequently, a second process parameter can go out-of-control after the first process parameter has gone out-of-control. A numerical study of the cost surface to the model considered has revealed that it is convex, at least in the interest region.

Uma comparação de gráficos de controle para a média de processos autocorrelacionados; A comparison of control charts for the average of autocorrelated processes; A comparison of control charts for the average of autocorrelated processes

Mingoti, Sueli A.; UFMG; Yassukawa, Fabiane R. S.; UFMG
Fonte: Universidade Federal Fluminense - LATEC Publicador: Universidade Federal Fluminense - LATEC
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; Formato: application/pdf
Publicado em 29/05/2009 POR
Relevância na Pesquisa
66.44%
Gráficos de controle são amplamente utilizados com o objetivo de monitorar parâmetros doprocesso. Em geral esses gráficos são fundamentados nas suposições de normalidade eindependência entre as unidades amostrais. No entanto, em muitos casos como emprocessos químicos ou no monitoramento on-line, a suposição de independência não severifica. Neste artigo comparamos os gráficos de controle construídos via metodologias degeoestatística e de séries temporais com os gráficos de controle muito conhecidos naliteratura como Shewhart, CUSUM, EWMA, quando usados para monitoramento da médiade processos autocorrelacionados. A comparação foi feita via simulação de Monte Carlorealizada com o uso do software estatístico R para Windows.; Control charts are extensively used with the purpose of monitoring some parameters of theprocess. In general these charts are based on the normality and independence assumptionsof the sample observations. However, there are situations where the independence is notvalid such as in chemical processes or sampling on-line. In this paper we compared thecontrol charts based on geostatistics and time series methodologies with the well-knowncharts Shewhart, CUSUM and EWMA, when used to monitor the average of autocorrelatedprocesses. The comparison was performed by using Monte Carlo simulation implemented inthe software R for Windows.; Control charts are extensively used with the purpose of monitoring some parameters of theprocess. In general these charts are based on the normality and independence assumptionsof the sample observations. However...