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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

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 January 2012 (has links)
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, which set an international standard for the its calculation. Still, few studies have addressed the interface between the measurement uncertainty and other aspects of industrial quality, in particular process control tools like control charts. The objective of this work is to study the effects of measurement uncertainty on control charts and to identify the situations in which its application exerts greater influence. A research was made, mapping of the articles published between 2004 and 2010 regarding measurement uncertainty, aiming to identify which calculation methods and approaches are most widely used. After, a method was developed to include uncertainty of the measurement system in control charts, modifying the probabilities of type I and type II errors. Finally, it was created a computer simulation using the method developed, to make it possible to analyze those situations in which the measurement uncertainty must be considered and which it can be neglected.
52

Ferramentas para modelagem e monitoramento de características de qualidade do tipo taxa

Biguelini, Cecília Brasil January 2012 (has links)
Esta dissertação apresenta a modelagem e o monitoramento de características de qualidade do tipo taxa, que apresentam valores restritos ao intervalo [0,∞). A motivação inicial é que a característica de qualidade do tipo taxa pode ser modelada pela distribuição Poisson e, geralmente, a modelagem e o monitoramento não utilizam tal distribuição. Os objetivos desta dissertação são: (i) Propor uma nova carta de controle (CC), Carta Poisson, para monitorar características de qualidade do tipo taxa, com adaptação no cálculo dos limites de controle utilizando a distribuição Poisson; (ii) Propor uma CC baseada em modelo de regressão utilizando a distribuição de Poisson para monitorar características de qualidade do tipo taxa em função das variáveis de controle do processo e (iii) Propor índices de capacidade MRPOISSON Cp e MRPOISSON Cpk para avaliar processos monitorados por CCs baseadas em modelos de regressão utilizando a distribuição de Poisson. As cartas de controle e os índices de capacidade propostos foram avaliados aplicando exemplos retirados da literatura. As cartas de controle foram comparadas através do número médio de amostras (NMA) via simulação de Monte Carlo. Concluiu-se que as cartas de controle propostas são adequadas para a modelagem e o monitoramento de características de qualidade do tipo taxa pois detectaram mais rapidamente todas as alterações induzidas, apresentando melhor desempenho em comparação com outras cartas similares encontradas na literatura. / This paper presents the modeling and monitoring of quality features like rate, which have values restricted to the interval [0, ∞). The initial motivation is that the quality characteristic of the type rate can be modeled by the Poisson distribution, and generally, modeling and monitoring do not use such a distribution. The objectives of this dissertation are: (i) to propose a new control chart (CC), Poisson Charter, to monitor quality characteristics of the type rate, adapted to calculate the control limits using a Poisson distribution, (ii) propose a CC based on regression model using the Poisson distribution to monitor quality characteristics like rate as a function of the control variables of the process and (iii) Propose capability indices MRPOISSON Cp and MRPOISSON Cpk to evaluate processes and monitored by CCs based on regression models using the distribution of Poisson. The control charts and capability indices were estimated by applying the proposed examples from the literature. The control charts were compared using the average number of samples (NMA) via Monte Carlo simulation. It was concluded that the proposed control charts are suitable for modeling and monitoring of quality characteristics of the type detected faster rate because all the changes induced, showing better performance in comparison with other similar letters found in the literature.
53

Cartas de controle multivariadas baseadas no método Kernel-Statis para monitoramento de processos em bateladas

Marcondes Filho, Danilo January 2009 (has links)
Processos industriais que ocorrem em bateladas são empregados com freqüência na produção de alguns itens. Tais processos disponibilizam uma estrutura de dados bastante peculiar e, diante disso, existe um crescente interesse no desenvolvimento de cartas de controle multivariadas mais apropriadas para seu monitoramento. Destaca-se aqui uma abordagem recente que utiliza cartas de controle baseadas no método Statis. O Statis constitui-se numa técnica exploratória que permite avaliar similaridade entre matrizes de dados. Entretanto, esta técnica avalia a similaridade no contexto linear, isto é, investiga estruturas de correlação lineares nos dados. Propõe-se nesta tese a utilização de cartas de controle baseadas no Statis em conjunto com um kernel para monitoramento de processos com presença de nãolinearidades fortes. Através dos kernels, definem-se funções não lineares dos dados para melhor representação da estrutura a ser caracterizada pelo método Statis. Esta 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 some 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, the technique only assesses similarities in a linear context, i.e. investigating structures of linear correlation in the data. In this thesis we propose control charts based on the Statis method in conjunction with a kernel for monitoring processes in the presence of strong non-linearities. Through the kernels we define non-linear functions of data for better representing the structure to be characterized by the Statis method. The new approach, named Kernel-Statis, is developed and illustrated using simulated data.
54

Avaliação da estabilidade do processo de lingotamento contínuo por meio de gráficos de controle com variáveis dependentes / Stability evaluation of continuous casting process by means of control graphs with dependent variables

Casarin, Vanusa Andrea January 2012 (has links)
A presente pesquisa aborda a utilização de gráficos de controle em processo produtivo com variáveis autocorrelacionadas. Tem como objetivo verificar a estabilidade do processo de lingotamento contínuo na fabricação de tarugos por gráficos de controle aplicados aos resíduos oriundos da previsão dos modelos matemáticos por meio da modelagem linear e/ou não linear. Primeiramente, é observada a existência de correlação entre os dados, utilizandose, então, a Análise de Componentes Principais. Com os dados livres de correlação, testa-se a autocorrelação nas Componentes Principais. A partir desse instante, são aplicados os modelos ARIMA, para encontrar os resíduos nos quais será testada a presença de volatilidade, podendo-se aplicar os modelos ARCH e/ou GARCH. Para exemplificar a metodologia utilizada na pesquisa, foi realizado um estudo de caso em uma empresa do RS, na célula da aciaria, especificamente na máquina de lingotamento contínuo onde são fabricados os tarugos para o Aço DIN20MnCr5, seção quadrada 240 mm. Foi possível a avaliação da estabilidade do processo para as variáveis originais por meio do gráfico . Posteriormente, os dados foram decompostos em Componentes Principais, avaliados por meio dos gráficos de controle e EWMA, indicando as componentes com maior instabilidade e as variáveis com maior influência dentro do novo conjunto de dados. Identificado o conjunto de variáveis, essas foram modeladas, utilizando-se a metodologia de modelos lineares e não lineares para encontrar os resíduos e assim construir os gráficos. Os modelos matemáticos encontrados foram capazes de representar os processos produtivos, possibilitar a compreeensão do comportamento das variáveis e auxiliar na monitoração do processo, e, além disso, mostrar as variáveis que contribuem para que o sistema esteja instável e ocasione a produção de sucata para o aço estudado. / This research addresses the use of control charts in the production process with autocorrelated variables. It aims to determine the stability of the continuous casting process in the manufacture of billets through control charts applied to the residues that come from prediction (of waste) from of mathematical models, by means of (modeling) linear and/or nonlinear modelling. First, it is observed existence of correlation among data, then using Principal Component Analysis. With correlation-free data, the autocorrelation is tested in the Principal Components. From that moment ARIMA models are applied to find residues in which will be tested the presence of volatility maybe applying ARCH and/or GARCH models. To illustrate the methodology used in the survey was conducted a case study at the in a Steel Plant in the State of RS, in the Aciaria cell, specifically in the continuous casting machine where steel billets DIN20MnCr5 square section 240mm are manufactured. It was possible to evaluate the stability of the process for original variables through the graph . Subsequently, data were broken down into Principal Components, evaluated by means of control charts and EWMA, indicating the components with higher instability and variables with greater influence within the new data set. Identied the set of variables, they were modeled using the methodology of linear and nonlinear models to find the residues and thus construct the graphs. Mathematical models were found capable of representing the production process, allowing understanding the variables behavior and assisting in process monitoring; showing the variables that contribute to the system is unstable and causes the scrap production for the steel studied.
55

Monitoramento dos registros de condenações na população de frangos abatidos no SIF 2485, no período de 1995 a 2005: avaliação das séries históricas e análise crítica / Monitoring condemnation records for poultry hygienic inspection from a federal inspected abattoir (SIF 2485), for 1995 to 2005: time series evaluation and critical analysis

Leandro d\'Arc Moretti 31 May 2006 (has links)
Apesar do reconhecimento da relevante contribuição epidemiológica dos registros de condenação em abatedouros, é escassa a divulgação sobre estudos referentes às circunstâncias relacionadas com as apreensões em matadouros de frangos. Avaliaram-se dez anos de registros oficiais de condenação em um abatedouro sob inspeção federal no Estado de São Paulo, obtendo-se informações a respeito de 24 causas de apreensão. Análises de tendência, sazonalidade e de componente cíclico foram efetuadas para 21 variáveis. Isto é discutido frente às dificuldades na obtenção sistemática e fidedigna de dados, propondo-se a utilização de programas informatizados para análise dos registros mensais em tempo real, o que possibilita a reavaliação dos programas de controle para as enfermidades desencadeantes das apreensões. Abordaram-se aspectos legislativos da inspeção de aves, enfocando limitações internacionais e particularidades de alguns processos patológicos, sugerindo adequação em determinados procedimentos sanitários. Destacou-se a comparação de dados locais com apreensões de vários países e o impacto interpretativo de diferentes metodologias de análise na concepção das ocorrências. As avaliações permitiram concluir que abordagens informatizadas para sazonalidade e ciclicidade nas séries temporais de apreensões podem incrementar o poder da verificação de programas HACCP. Além disso, observou-se maior poder para revelação de padrões, pela associação dos dois tipos de análise. / There is a lack of studies for circumstances related to poultry abattoir condemnations, despite its wide recognition as a relevant source of epidemiological information. Ten year official condemnation records were issued for one federal inspected slaughterhouse in São Paulo State, Brazil, gathering data about 24 condemnation causes. Global, seasonal and cyclical trends were evaluated for 21 variables, which were further debated concerning trouble reporting of systematic reliable data. Furthermore, the study suggests software packages utilization for real-time monthly data analysis, which in turn leads to control schedules reevaluation for condemnation disease determinants. Legislative approach to poultry inspection, focusing on international limitations and pathological process features were asked for sanitary procedures adequacy. The local and several countries data comparison, besides different analytical methodology impact were highlighted. The conclusion assigns that time series seasonal and cyclical computerized analysis can enhance HACCP\'s verification power and better reveal patterns when combined.
56

Occupational Safety Surveillance Using a Statistical Monitoring Approach

Schuh, Anna Kristine 10 May 2013 (has links)
When unsafe conditions arise in a workplace, they may result in employee accidents and fatalities. However, if these problems are detected early, new hazard controls and safety initiatives can be introduced in order to actively reduce or prevent the occurrence of these events. Unfortunately, many safety systems currently monitor and report data that has been aggregated over long time periods, making it difficult to realize and respond to pattern shifts in a timely manner. When monitoring a process over time, a commonly used tool is statistical process control charting. Traditionally used in manufacturing, control charts indicate a deviation from historically "normal" or "in-control" behavior and have become increasingly common in healthcare and public health monitoring. This dissertation studies the use of control charts to monitor the frequency of occupational safety incidents, with the overarching goal of investigating the effects of data aggregation on the detection performance of these charts. Specifically, this dissertation 1) qualitatively establishes the need for more frequent monitoring of safety incidents; 2) investigates the comparative performance of control charts with aggregated and non-aggregated data for the detection of increased accident frequency, using a case study with data from an industrial partner; 3) more generally compares the performance of these charts for a Poisson process with a range of simulated process shifts; and 4) discusses the potential future challenges of including accident severity in quantitative safety monitoring systems. The comprehensive results indicate that lower degrees of data aggregation are preferred, and suggestions for better data collection and employee communication practices are offered to aid the transition for companies. / Ph. D.
57

Automated Verification of Load Test Results in a Continuous Delivery Deployment Pipeline

Sundbaum, Niklas January 2015 (has links)
Continuous delivery is a software development methodology that aims to reduce development cycle time by putting a strong emphasis on automation, quality and rapid feedback. This thesis develops an automated method for detecting performance regressions as part of a continuous delivery deployment pipeline. The chosen method is based on control charts, a tool commonly used within statistical process control. This method is implemented as part of a continuous delivery deployment pipeline and its ability to detect performance regressions is then evaluated by injecting various performance bottlenecks in a sample application. The results from this thesis show that using a control chart based approach is a viable option when trying to automate verification of load test results in the context of continuous delivery. / Kontinuerlig leverans är en utvecklingsmetodik för mjukvara med målet att reducera ledtid genom att fokusera på automatisering, kvalitet och snabb återkoppling. I det här examensarbetet utvecklas en automatiserad metod för att upptäcka försämringar i prestanda i en deployment pipeline för kontinuerlig leverans. Den valda metoden baseras på kontrolldiagram, ett verktyg som ofta används inom statistisk processkontroll. Metoden implementeras som en del av en deployment pipeline för kontinuerlig leverans och dess förmåga att upptäcka prestandaförsämringar utvärderas genom att olika prestandarelaterade flaskhalsar implementeras i en testapplikation. Resultaten från arbetet visar att en metod baserad på kontrolldiagram är ett tänkbart alternativ för att automatisera verifiering lasttestresultat inom kontinuerlig leverans.
58

Improvement of Statistical Process Control at St. Jude Medical's Cardiac Manufacturing Facility

Edwards, Christopher Lance 01 June 2012 (has links) (PDF)
Sig sigma is a methodology where companies strive to reproduce results ending up having a 99.9996% chance their product will be void of defects. In order for companies to reach six sigma, statistical process control (SPC) needs to be introduced. SPC has many different tools associated with it, control charts being one of them. Control charts play a vital role in managing how a process is behaving. Control charts allow users to identify special causes, or shifts, and can therefore change the process to keep producing good products, free of defects. There are many factories and manufacturing facilities having implemented some sort of statistical process control. St. Jude Medical implemented control charts to monitor different tools on the manufacturing line. How the data is entered and stored poses a difficult situation for the person monitoring the processes. The program used to keep the control charts is not user friendly and difficult to use. Another program can be produced to provide a greater level of efficiency. The goals of this project are to stress how important control charts are in the manufacturing world, what problems are currently seen for operators and supervisors, and how a new and improved program can help fix the current situation. This paper goes into the reasons for the change as well has what has been improved.
59

Multivariate control charts for the mean vector and variance-covariance matrix with variable sampling intervals

Cho, Gyo-Young 01 February 2006 (has links)
When using control charts to monitor a process it is frequently necessary to simultaneously monitor more than one parameter of the process. Multivariate control charts for monitoring the mean vector, for monitoring variance-covariance matrix and for simultaneously monitoring the mean vector and the variance-covariance matrix of a process with a multivariate normal distribution are investigated. A variable sampling interval (VSI) feature is considered in these charts. Two basic approaches for using past sample information in the development of multivariate control charts are considered. The first approach, which is called the combine-accumulate approach, reduces each multivariate observation to a univariate statistic and then accumulates over past samples. The second approach, which is called the accumulate-combine approach, accumulates past sample information for each parameter and then forms a univariate statistic from the multivariate accumulations. Multivariate control charts are compared on the basis of their average time to signal (ATS) performance. The numerical results show that the multivariate control charts based on the accumulate-combine approach are more efficient than the corresponding multivariate control charts based on the combine-accumulate approach in terms of ATS. Also VSI charts are more efficient than corresponding FSI charts. / Ph. D.
60

Enhancing continuous improvement projects with the Blythe S-curve and multivariate control charts

Kelly, William 01 May 2020 (has links)
Successfully implementing continuous improvement and quality methodologies have been challenging over the past century. Challenges occur in managing change in the organization, which can be effectively addressed through relationship building in concert with strong leadership. Even with solid leadership, change management, and relationship building, initiatives have challenges quantifying and identifying when to intervene in order to keep them on track for success. Creating a quantitative model using a 3-parameter logit s-curve, Blythe S-curve, to illustrate the growth and decay of the handoff of projects to the process owner will allow leadership the knowledge and direction to keep the initiative moving in a positive direction. Leveraging the Hotelling T2 multivariate charts on the residuals derived from the Blythe S-curve will give definitive statistical evidence on when to intervene on projects in the earliest possible time frame. Leaders in organizations implementing and actively using change management, relationship building, the Blythe S-curve model, and Hotelling T2 multivariate charts to drive quality and continuous improvement methodologies in their organization will improve the likelihood of success.

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