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Heteroscedastic latent variable modelling with applications to multivariate statistical process control

Reis, Marco S.; Saraiva, Pedro M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
65.68%
We present an approach for conducting multivariate statistical process control (MSPC) in noisy environments, i.e., when the signal to noise ratio is low, and, furthermore, noise standard deviation (uncertainty) affecting each collected value can vary over time, and is assumingly known. This approach is based upon a latent variable model structure, HLV (standing for heteroscedastic latent variable model), that explicitly integrates information regarding data uncertainty. Moderate amounts of missing data can also be handled in a coherent and fully integrated way through HLV. Several examples show the added value achieved under noisy conditions by adopting such an approach and a case study illustrates its application to a real industrial context of pulp and paper product quality data analysis.; http://www.sciencedirect.com/science/article/B6TFP-4GX1HVW-2/1/c5e6b0a181b2fb4ffd7803ff38c9dace

An RT-Linux based control system of a pilot plant for reaction kinetics and process control studies

Romanenko, Andrei; Castro, José A. A. M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
65.81%
The pilot plant under study is designed for determining the kinetics of the heterogeneous non-catalytic reaction of chemical pulping of wood and for teaching system dynamics and batch process control in an appropriate university course. The natura complexity of the system includes time varying dynamics and stepwise behavior and this makes it attractive for highlighting some important features of the real world of process control. Due to its specific design, the pilot is also very useful for kinetic studies of heterogenous reactions involving wood, ensuring a high level of the repeatability of results. The pilot plant and its control system have been used in teaching of chemical kinetics of heterogeneous reactions and are also part of the experimental program in a process control course.; http://www.sciencedirect.com/science/article/B6TFT-448HNR0-4P/1/c5da9115a1c3b9603689dd138bef0923

Effects of the preventive and corrective adjustments in economical designs for online process control for attributes with misclassification errors

QUININO, Roberto C.; HO, Linda Lee
Fonte: TAYLOR & FRANCIS LTD Publicador: TAYLOR & FRANCIS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.84%
The procedure for online process control by attributes consists of inspecting a single item at every m produced items. It is decided on the basis of the inspection result whether the process is in-control (the conforming fraction is stable) or out-of-control (the conforming fraction is decreased, for example). Most articles about online process control have cited the stoppage of the production process for an adjustment when the inspected item is non-conforming (then the production is restarted in-control, here denominated as corrective adjustment). Moreover, the articles related to this subject do not present semi-economical designs (which may yield high quantities of non-conforming items), as they do not include a policy of preventive adjustments (in such case no item is inspected), which can be more economical, mainly if the inspected item can be misclassified. In this article, the possibility of preventive or corrective adjustments in the process is decided at every m produced item. If a preventive adjustment is decided upon, then no item is inspected. On the contrary, the m-th item is inspected; if it conforms, the production goes on, otherwise, an adjustment takes place and the process restarts in-control. This approach is economically feasible for some practical situations and the parameters of the proposed procedure are determined minimizing an average cost function subject to some statistical restrictions (for example...

Integrating on-line process control and imperfect corrective maintenance: An economical design

Ho, Linda Lee; Quinino, Roberto C.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.77%
Existing studies of on-line process control are concerned with economic aspects, and the parameters of the processes are optimized with respect to the average cost per item produced. However, an equally important dimension is the adoption of an efficient maintenance policy. In most cases, only the frequency of the corrective adjustment is evaluated because it is assumed that the equipment becomes "as good as new" after corrective maintenance. For this condition to be met, a sophisticated and detailed corrective adjustment system needs to be employed. The aim of this paper is to propose an integrated economic model incorporating the following two dimensions: on-line process control and a corrective maintenance program. Both performances are objects of an average cost per item minimization. Adjustments are based on the location of the measurement of a quality characteristic of interest in a three decision zone. Numerical examples are illustrated in the proposal. (c) 2012 Elsevier B.V. All rights reserved.; CNPq Universal [472636/2009-0]; CNPq Universal

Um modelo de tráfego de rede para aplicação de técnicas de controle estatístico de processos.; A network traffic model for statistical process control techniques.

Angelis, André Franceschi de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/03/2003 PT
Relevância na Pesquisa
65.72%
O objetivo deste trabalho é construir um modelo do tráfego de redes de computadores e aplicar a este modelo o conjunto de técnicas de Controle Estatístico de Processo (CEP) de forma a viabilizar ações preventivas sobre a rede. Trabalhou-se com a hipótese de que é possível determinar estatisticamente o comportamento da rede em um dado número de variáveis de interesse. O modelo, representado em sua forma final por um conjunto de variáveis que descrevem o tráfego modelado, foi construído a partir da observação da rede local do Instituto de Física de São Carlos (IFSC). Recolheram-se aproximadamente 10 milhões de registros, pelo software NeTraMet, classificados em fluxos e posteriormente processados por aplicativos criados especificamente para esta finalidade. Dado que o CEP pressupõe a normalidade dos dados, cuidou-se de verificar formalmente esta propriedade nas amostras colhidas, pela aplicação do teste qui-quadrado aos valores individuais. Em conformidade a referências da literatura, fez-se o mesmo em relação aos valores médios das amostras. Em ambas as situações, comprovou-se a não-normalidade das distribuições. Investigaram-se os efeitos desta constatação no CEP e desenvolveu-se uma nova metodologia de cálculo dos limites de controle...

Parâmetros de controle do processo de coqueificação das baterias de fornos de coque da COSIPA.; Cocking process control parameters of the COSIPA's coke plant.

Costa, Luiz Cláudio
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 26/02/2008 PT
Relevância na Pesquisa
65.78%
O controle de processo de uma planta de fabricação de coque depende de muitas variáveis particulares de cada planta. A busca de modelos de controle próprios torna-se necessário. O presente trabalho apresenta um projeto de experimentos, em forno piloto, para investigar a influência dos principais parâmetros de controle de fabricação do coque quanto à produção e consumo de calor e utilizá-los futuramente num modelo de automação do controle do processo dessa planta. O resultado do experimento apresentou significância estatística para os fatores temperatura e umidade da mistura enfornada e para as interações entre umidade e temperatura e entre umidade e granulometria com relação ao consumo de calor e também o fator temperatura com relação ao tempo líquido de coqueificação. Além do projeto de experimentos em forno piloto foi feito também um experimento em um forno industrial cuja metodologia mostrou-se adequada para um projeto em escala industrial. Com os dados dos experimentos obtiveram-se também equações matemáticas de previsão do consumo de calor e do tempo líquido de coqueificação.; The process control of a coke plant depends on a lot of particular parameters. This work describes an experimental design in a pilot oven aiming at getting the influence of the main control factors of a coke oven battery...

Estudo e implementação de estruturas de controle reconfigurável aplicado a processos químicos; Study and implementation of reconfigurable control structures applied to chemical processes

Thiago Vaz da Costa
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/03/2014 PT
Relevância na Pesquisa
55.85%
A consideração sistemática relacionada ao tratamento de falhas na estrutura de controle é essencial para se atingir as metas de um processo ao mesmo tempo seguro e produtivo. Nesse sentido, este trabalho propõe o estudo e a implementação de técnicas baseadas no controle reconfigurável com aplicações em processos químicos. Essa técnica está relacionada à etapa que lida com a falha no sistema em malha fechada, por meio de sua reconfiguração, evitando a evolução dos seus efeitos na estrutura de controle. Nesse estudo, a atenção é voltada ao rastreamento do comportamento nominal do sistema considerando as técnicas baseadas nos atuadores virtuais. O método considera o desvio da planta em relação ao seu comportamento nominal na presença de falhas em seus atuadores. Deste modo, se o distanciamento em relação ao comportamento nominal pode ser estabilizado por meio das redundâncias físicas e analíticas presentes no processo, o comportamento da planta sujeita à falha também pode ser estabilizado. Neste sentido, uma consideração sobre esse desvio no futuro é proposta, permitindo que técnicas baseadas no controle ótimo e preditivo sejam utilizadas. São consideradas especificamente falhas que comprometam o desempenho do processo quando existe a perda total ou parcial de suas variáveis de entrada. Com os componentes comprometidos devidamente localizados...

Desenvolvimento e avaliação de sistemas de controle plantwide aplicados na produção de biodiesel; Plantwide control systems design and evaluation applied to biodiesel production

Bruno Firmino da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/06/2015 PT
Relevância na Pesquisa
55.86%
Os processos químicos apresentam dinâmicas complexas devido a presença de reciclos, integrações energéticas e diversas operações unitárias interconectadas, gerando problemas de interação entre as variáveis e dificultando um efetivo controle do processo. Metodologias de controle global ou plantwide buscam estabelecer sistemas de controle contemplando a planta química como um todo, porém, geram mais de uma solução de controle. Este trabalho propõe avaliar diferentes estruturas de controle global para uma mesma planta química através do uso de indicadores chave de desempenho (KPI ¿ Key Performance Indicator) para o processo, determinando assim qual sistema de controle melhor atende aos objetivos estratégicos da indústria. Como caso de estudo simulou-se uma planta típica para a produção de biodiesel através dos softwares Aspen Plus e Aspen Plus Dynamics. O processo implementado busca representar a produção do biocombustível obtido na transesterificação do óleo de soja com metanol, por meio da rota de catálise alcalina e homogênea. Para simulação dinâmica do processo, utilizaram-se dois conjuntos de controladores obtidos da metodologia de controle global heurística, configurando-se duas propostas de controle para o processo. Para avaliação das propostas de controle...

Cycle to Cycle Manufacturing Process Control

Hardt, David E.; Siu, Tsz-Sin
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 1111042 bytes; application/pdf
EN_US
Relevância na Pesquisa
55.84%
Most manufacturing processes produce parts that can only be correctly measured after the process cycle has been completed. Even if in-process measurement and control is possible, it is often too expensive or complex to practically implement. In this paper, a simple control scheme based on output measurement and input change after each processing cycle is proposed. It is shown to reduce the process dynamics to a simple gain with a delay, and reduce the control problem to a SISO discrete time problem. The goal of the controller is to both reduce mean output errors and reduce their variance. In so doing the process capability (e.g. Cpk) can be increased without additional investment in control hardware or in-process sensors. This control system is analyzed for two types of disturbance processes: independent (uncorrelated) and dependent (correlated). For the former the closed-loop control increased the output variance, whereas for the latter it can decrease it significantly. In both cases, proper controller design can reduce the mean error to zero without introducing poor transient performance. These finding were demonstrated by implementing Cycle to Cycle (CtC) control on a simple bending process (uncorrelated disturbance) and on an injection molding process (correlated disturbance). The results followed closely those predicted by the analysis.; Singapore-MIT Alliance (SMA)

Non-traditional statistical process control for commercial irradiation

Donovan, J; Murphy, Eamonn
Fonte: Irish Statistical Association Publicador: Irish Statistical Association
Tipo: info:eu-repo/semantics/conferenceObject; all_ul_research
ENG
Relevância na Pesquisa
65.73%
non-peer-reviewed; Commercial irradiation typically involves applying electron beam or gamma radiation to a product with a view to sterilizing the product and killing any bacteria present. This is extremely important in the medical device industry where packaged products or pallets require irradiation between a minimum and maximum dose. As packaged product provides a level of shielding it is difficult to monitor such processes to ensuring that all prod- ucts on the pallet received a dose greater than the minimum and yet less than the maximum. This di±culty was solved for both the gamma ray and electron beam radiation facilities by the use of non-traditional Statistical Process Control (SPC) techniques. By combining standardized charts and group charts, a single control chart could accommodate both minimum and maximum doses while e®ectively monitoring the entire process. In addition, guidance tables were developed the allowed operations to determine a win- dow of suitable dosages that would simultaneously satisfy the irradiation requirements of di®erent groups of products.

Statistical Process Control for the Fairness of Network Resource Distribution

Liu, Qingyun
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
65.7%
The purpose of this research is to develop a statistical method to monitor the fairness of network resource distribution. The newly developed fairness score function allows users to have the same or different priority levels. Especially, this function possesses all the necessary properties required as a quality characteristic for the purpose of statistical process control. The main objective is to find the critical values for the statistical test. Monte Carlo simulation is used to find the critical values. When the users have the same priority level, a table of the critical values is given for different sample sizes and different significance levels. When the users have different priority levels, it is difficult to generate a similar table since the users’ priority levels vary. Therefore, the critical values are computed for given priority levels. In both cases, an example is given to demonstrate the approach developed in this study.

Statistical process control of mortality series in the Australian and New Zealand Intensive Care Society (ANZICS) adult patient database: implications of the data generating process

Moran, J.; Solomon, P.
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
65.82%
BACKGROUND Statistical process control (SPC), an industrial sphere initiative, has recently been applied in health care and public health surveillance. SPC methods assume independent observations and process autocorrelation has been associated with increase in false alarm frequency. METHODS Monthly mean raw mortality (at hospital discharge) time series, 1995–2009, at the individual Intensive Care unit (ICU) level, were generated from the Australia and New Zealand Intensive Care Society adult patient database. Evidence for series (i) autocorrelation and seasonality was demonstrated using (partial)-autocorrelation ((P)ACF) function displays and classical series decomposition and (ii) “in-control” status was sought using risk-adjusted (RA) exponentially weighted moving average (EWMA) control limits (3 sigma). Risk adjustment was achieved using a random coefficient (intercept as ICU site and slope as APACHE III score) logistic regression model, generating an expected mortality series. Application of time-series to an exemplar complete ICU series (1995-(end)2009) was via Box-Jenkins methodology: autoregressive moving average (ARMA) and (G)ARCH ((Generalised) Autoregressive Conditional Heteroscedasticity) models, the latter addressing volatility of the series variance. RESULTS The overall data set...

ON-LINE PROCESS CONTROL OF THE NUMBER OF NON-CONFORMITIES IN THE INSPECTED ITEM

Vasconcelos, Renata Mendonça Rodrigues; medeiros, pledson guedes de; Ho, Linda Lee
Fonte: Brazilian Association for Industrial Engineering and Operations Management (ABEPRO) Publicador: Brazilian Association for Industrial Engineering and Operations Management (ABEPRO)
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Peer-reviewed Article; Formato: application/pdf
Publicado em 14/05/2013 ENG
Relevância na Pesquisa
65.86%
Generally, production systems that use automatic control as automatic welding process, production of ceramic products, making clothes use on-line process control to evaluate the quality of their production processes. The control system consists of a periodic inspection of one item after every m produced items. If the number of non-conformities meets the control limit then it is decided that the process is in-control, otherwise the process is stopped for adjustment. The process starts in-control with a non-conformities rate and, after an assignable cause, this rate increases leading the system to operate out of control. The process remains in these conditions until the change is detected and the process adjusted. After adjustment, the process returns to operate in-control. The aim of this paper is to present an economic approach to monitor the rate of non-conformities in a production by on-line process control. To design such type of process, an average cost per item produced is achieved through the properties of an ergodic Markov chain and the two required parameters: the inspection interval and the upper control limit are obtained by minimizing the average cost per produced item.  A numerical example illustrates the proposed procedure.

Forging process control: Influence of key parameters variation on product specifications deviations

ALLAM, Zakaria; BECKER, Eric; BAUDOUIN, Cyrille; BIGOT, Régis; KRUMPIPE, Pierre
Fonte: Elsevier / Takashi Ishikawa and Ken-ichiro Mori Publicador: Elsevier / Takashi Ishikawa and Ken-ichiro Mori
EN
Relevância na Pesquisa
65.79%
Process control in forging industry is essential to ensure a better quality of the product with a lower cost at the end of the manufacturing process. To control the process, a number of key parameters must be monitored to prevent product or forging plan deviations. This paper will illustrate how a variation in a process parameter can create product specifications deviations and how key parameters influence product final state. The illustration work is done on a part obtained via hot forging. An analysis is made on product parameters such as geometry, by varying the key process parameter values previously determined from a created methodology. This later is represented as a decision support system that connects product specifications (geometry, absence of defects…) or other forging specifications (tool wear, involved energy...) to the process parameters.

Diagnosis expert system with automated query to a process control system

Winslow, Richard
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
65.79%
This thesis describes the development of a diagnosis expert system for an automated process control facility. To reduce the number of user responses to the expert system, a network interface was created between the expert system and the process control computer. This document focuses on the unique concerns associated with the development, validation, and implementation of an expert system that is directly interfaced to a process control system.

Using descriptive statistics in statistical process control

Holmes, Donald; Mergen, A. Erhan
Fonte: Northern Decisions Sciences Institute Publicador: Northern Decisions Sciences Institute
Tipo: Proceedings
EN_US
Relevância na Pesquisa
65.7%
The purpose of this paper is to demonstrate the various uses of descriptive statistical analysis in statistical process control (SPC). Some fairly well-known descriptive techniques, along with the lesser known methods, will be discussed for their potential use in SPC. A numerical example will be provided.

An Approach to remote process monitoring and control

Dracos, John
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
55.83%
The purpose of this thesis is to present an approach to remote monitoring and operation of distributed real time process control systems. Conventional monitoring of process control systems currently requires a great deal of close supervision from trained personnel located on-site. In many cases, researchers, developers or maintenance personnel cannot be at every location where such a system is installed. Currently, a standardized architecture for remote access to such systems is not available. In addition, most of these systems are very expensive and under-utilized. Researchers would benefit by having access to different parts of a system concurrently The benefits of a layered architecture for remote process monitoring and control will be analyzed through the use of a demonstration system that was realized to examine the real time performance of the interconnection mechanisms between the process controller(s) and the system monitoring interfaces. Low level, real-time process control is achieved by using specialized networking schemes called fieldbusses to interconnect all control devices. In this system, fieldbus controllers will also assume the role of servers connected to the Internet, in order to make device information available to any local or remote clients. In the proposed architecture...

Effectiveness of OPC for systems integration in the process control information architecture

Zachariah, Philips
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
65.84%
A Process is defined as the progression to some particular end or objective through a logical and orderly sequence of events. Various devices (e.g., actuators, limit switches, motors, sensors, etc.) play a significant role in making sure that the process attains its objective (e.g., maintaining the furnace temperature within an acceptable limit). To do these things effectively, manufacturers need to access data from the plant floor or devices and integrate those into their control applications, which maybe one of the "off the shelf tools such as Supervisory Control and Data Acquisition (SCADA), Distributed Control System (DCS), or Programmable Logic Controllers (PLC). A number of vendors have devised their own Data Acquisition Networks or Process Control Architectures (e.g., PROFIBUS, DEVICENET, INTERBUS, ETHERNET I/P, etc.) that claim to be open to or interoperable with a number of third party devices or products that make process data available to the Process or Business Management level. In reality this is far from what it is claimed to be. Due to the problem of interoperability, a manufacturer is forced to be bound, either with the solutions provided by a single vendor or with the writing of a driver for each hardware device that is accessed by a process application. Today's manufacturers are looking for advanced distributed object technologies that allow for seamless exchange of information across plant networks as a means of integrating the "islands of automation" that exist in their manufacturing operations. OLE for Process Control (OPC) works to significantly reduce the time...

A Test chip approach to routine process control

Meisenzahl, Eric J.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
65.78%
A procedure for determining process control and yield prediction is presented which primarily serves to evaluate the quality and repeatability of critical fabrication steps, but also serves to quantify process capabilities and limitations for future design considerations. This can be accomplished through the use of a specially designed test chip. The test chip is designed for use in determining the process control and fabrication capability of the Microelectronic Engineering Department's fabrication lab of Rochester Institute of Technology.

A Test chip approach to routine process control

Meisenzahl, Eric J.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
65.78%
A procedure for determining process control and yield prediction is presented which primarily serves to evaluate the quality and repeatability of critical fabrication steps, but also serves to quantify process capabilities and limitations for future design considerations. This can be accomplished through the use of a specially designed test chip. The test chip is designed for use in determining the process control and fabrication capability of the Microelectronic Engineering Department's fabrication lab of Rochester Institute of Technology.