No description available.

No description available.

No description available.

This thesis examines the use of variable sampling intervals as they apply to control charts that use count data. Papers by Reynolds, Arnold, and R. Amin developed properties for charts with an underlying normal distribution. These properties are extended in this thesis to accommodate an underlying Poisson distribution. / Master of Science

An improved quality control model is suggested in this thesis. The improved quality control model is derived by treating the quality control problem as a process control problem. The quality control model is developed by formulating a process control model in terms of product quality parameters and control variables which affect the product quality parameters. SQC is used in the model to provide estimates about the state of the product quality variable as the product is processed by the plant. A state variable approach is used to determine the optimal control strategy. An example quality control model is formulated for a coke size-reduction process. Numerical values are assumed and sensitivity analysis results are discussed. The results show that the proposed quality control model is reasonable. Extensions to more complicated models are discussed. / M.S.

Given the continuing deployment of total quality control and total quality management initiatives by organizations, employees have seen changes in their work environment. Furthermore, the impact of downsizing has resulted in operators becoming responsible for the quality of their own processes. This study tested the impact of various display alternatives of control chart data on decision performance and mental workload.  The control charts were shown as multiple two dimensional displays, a composite two dimensional display, and a composite three dimensional perspective display. Multiple two dimensional displays were found to have significantly higher decision accuracy and decision confidence ratings than either composite displays. No significant difference in decision accuracy and decision confidence ratings was found among the composite displays. The type of display did not have a significant effect on decision time. Mental workload was also found to be significantly affected by the type of display used. Multiple two dimensional displays imposed significantly lower levels of mental workload than either composite display. No significant difference in mental workload was found among the composite displays. These results indicated that multiple two dimensional displays should be used when control chart data from multiple processes must be displayed. / Master of Science

[pt] Este trabalho mostra a implantação de técnicas de Controle Estatístico de Processo (CEP) em uma indústria de cosméticos, em uma situação em que as técnicas convencionais não são aplicáveis. O processo a ser controlado é constituído de oito canais, que produzem em um mesmo instante de tempo oito unidades de um mesmo produto. Tal processo possui a peculiaridade de ter médias variáveis no tempo, mesmo em estado de controle estatístico. Como os métodos de controle propostos na literatura para processos com múltiplos canais têm como premissa médias constantes ao longo do tempo e os canais terem médias e variâncias semelhantes, tais métodos não são aplicáveis ao processo em questão. Para o CEP do processo, então, foi desenvolvida uma metodologia adaptada à realidade da empresa, que conjuga os princípios de group charts e de gráficos de controle de aceitação. Foi ainda realizada uma revisão bibliográfica de algumas técnicas de controle estatístico de processos com múltiplos canais, contemplando métodos tradicionais e não tradicionais. / [en] This study shows the implantation of techniques of Statistical Process Control (SPC) in a cosmetics industry, in a situation in which conventional techniques are not applicable. The process to be controlled is composed of eight streams, which produce eight units of the product at a time. The process has the peculiarity that the means of the streams change in time, even in a condition of statistical control. The control schemes proposed in the literature hitherto for multiple-stream processes assume constant means, and streams with similar means and variance, and are therefore not applicable to this process. A new scheme was then developed for the statistical control of the process, which blends the principles of the group charts and of acceptance control charts. A review was also presented of some techniques of statistical control of multiple-stream processes, including traditional and more recent methods.

[pt] Esta dissertação trata do controle estatístico de processos (CEP) multi-canal, assunto pouco tratado na literatura especializada. As técnicas encontradas na literatura pressupõem condições de validade nem sempre verificadas na prática, a saber: medidas sucessivas efetuadas em cada canal independentes e identicamente distribuídas; todos os canais ajustados, com mesma média e desvio-padrão; e (na maioria dos trabalhos) canais independentes, sem correlação cruzada. O estudo foi motivado por um caso real, em que nenhuma dessas condições se verifica. Este trabalho propõe adaptações e extensões de técnicas existentes para lidar com processos nessa situação; detalha como aplicá-las; ilustra sua aplicação no caso prático analisado; discute limitações e propõe alternativas, e inicia uma discussão sobre as diferentes condições (características das situações práticas) em que cada uma das alternativas é mais apropriada. O trabalho iniciou- se com uma análise exploratória dos processos da empresa, de modo a permitir um diagnóstico do CEP que vinha sendo realizado, e fundamentar a proposta de um novo esquema de controle, mais adequado. O esquema proposto, aplicado aos dados, sinalizou problemas com os processos que as técnicas empregadas não sinalizavam. Embora, em virtude dos prazos para finalização da dissertação e da programação da produção da empresa, que teve interrupções, não tenha sido possível incluir nesta análise a investigação de causas especiais, com revisão dos limites de controle e utilização dos gráficos assim revistos no monitoramento on line, para fins de acompanhamento do desempenho do esquema proposto, mesmo assim a aplicação desse esquema aos dados disponíveis demonstrou ser ele mais sensível a causas especiais que os gráficos que vinham sendo utilizados, e levantou algumas questões, não abordadas na literatura, que são indicadas para pesquisa futura. / [en] This dissertation tackles the problem of statistical control of multi-channel processes, which has been scarcely dealt with in the specialized literature. The techniques found in the literature assume validity conditions which are not always verified in practice, namely: successive measurements taken in each channel should be independent an identically distributed; all the channels should be adjusted, with same mean and standard deviation; and most works assume the channels to be independent, with no cross correlation. The study was motivated by a real case, in which no one of these conditions holds. This work proposes adaptations and extensions of existing techniques in order to deal with this and similar real situations; details the application of the adapted/extended techniques; illustrates their application in the case under analysis; discusses limitations and proposes alternatives, and initiates a discussion about the different conditions (practical situations´ characteristics) in which each alternative is most appropriate. The work began with an exploratory data analysis of the enterprise´s production processes, so as to enable a diagnosis of the statistical process control procedures that were in use, and serve as a basis for the proposal of a new, more adequate, control scheme. The proposed scheme, when applied to the data, signalled problems with the processes which the techniques in use did not signal. Due to the deadlines for ending this dissertation and to programmed interruptions in the production, it has not been possible to include in the analysis the search for special causes with corresponding revisions of the charts´ control limits and the use of the revised charts in on-line monitoring, for the purposes of feedback on the proposed scheme´s performance. Its application to the available data has nevertheless shown it more sensitive to special causes than the charts that were in use, and raised some issues not approached in the literature, which are left as indications for future research.

Quality, as well as stability of processes check is nowadays gaining on its significance. The main driving force of its increasing importance is the rapid expansion of series production. Large-scale manufacturing processes are concerned, in terms of the number of operators, direct and indirect influence on rejects, but also on process stability. There are several quality characteristics, defined by utility properties, that can be easily measurable (linear dimensions, solidity, elongation, humidity, concentration) or directly immeasurable, mostly subjective (fragrance, taste, color, comfort while using, appearance). Statistical Process Control-SPC features the preventive tool of quality control, because based on the early detection of significant divergences of the process from the predetermined level, it is possible to execute interventions in the process with the aim of maintaining the acceptable and stable level and improving the process. This manufacturing process check will be the topic of my thesis. At first, Shewhart's control charts analysis will be done to determine strong process instability. Consequently, analysis will be carried out in test chi-square, used to determine the influence of each factor on the process of stability (operators, type of shift, type of product, type of defect on the product). All the practical part will be processed in statistical software MINITAB15. The thesis will be complemented by the findings from the examination of the features of interval estimates of parameter p for binomial distribution - numeric stability in the various statistical software (specifically Minitab 15, Statistica, Matlab 7.8.0). Master's thesis was supported by project from MSMT of the Czech Republic no. 1M06047 Center for Quality and Reliability of Production.

[pt] Processos com diversos canais em paralelo são muito comuns na indústria; um exemplo são operações de enchimento, encontradas nas indústrias farmacêutica, alimentícia, cosmética e de bebidas. O método clássico para o controle estatístico desse tipo de processos, as group charts (Boyd, 1950), é pouco eficiente, por não considerar que uma parcela da variação nestes processos é comum a todos os canais. Mortell e Runger, em 1995, propuseram um esquema alternativo que leva este fato em conta. No ano seguinte, Runger, Alt e Montgomery propuseram um outro esquema. A presente dissertação propõe um terceiro esquema para o controle de tais processos. O seu modelo formal detalhado, as expressões para cálculo dos limites de controle e a análise de seu desempenho são contribuições originais. As probabilidades de sinal e o número esperado de amostras até a sinalização de alterações na média da parcela individual de um dos canais foram obtidas analiticamente e/ou por simulação, e utilizadas para comparação de desempenho com o esquema de Mortell e Runger. Os resultados demonstram a superioridade do esquema proposto para a detecção de variações superiores a um desvio-padrão na média da parcela individual de um canal do processo. Para detectar variações menores, nenhum dos dois esquemas é eficiente. O esquema de Runger et al. (1996) tem, para o caso de alteração em um canal apenas, desempenho igual ou inferior a ambos. Assim, o esquema aqui proposto revela-se o mais eficiente de todos. Uma série de extensões e questões em aberto para pesquisa futura são indicadas. / [en] Processes with several streams in parallel are very common in industry. Filling operations, such as the ones found in the pharmaceutical, cosmetics, or food and beverage industries are a typical example. The classical scheme for the statistical control of multiple-stream processes (MSP) is the group chart (Boyd, 1950). Its efficiency is impaired by its underlying model of the process not considering that part of the variation in MSP is common to all streams. In 1995, Mortell and Runger (M&R) proposed an alternative scheme which takes this fact into account. In the next year, Runger, Alt and Montgomery proposed another scheme. This dissertation proposes a third scheme for statistical control of MSP. The detailed mathematical model, the expressions for establishing the control limits, and the performance analysis here are original contributions. The probabilities of a signal and average run lengths in the case of shifts in the mean of one individual stream were obtained either analytically or by simulation and compared with the ones of M&R´s scheme. The results show the superiority of the proposed scheme for signaling shifts greater or equal to one standard deviation. For smaller shifts, neither scheme can be said to be really efficient. As to the scheme proposed by Runger et al. (1996), it is in some cases slower and in some cases just as fast as M&R`s, so the proposed scheme is the fastest of all. A number of extensions and open issues are indicated for future research.