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This paper analyzes a proposed release controlmethodology, WIPLOAD Control (WIPLCtrl), using a transfer line case modeled by Markov process modeling methodology. The performance of WIPLCtrl is compared with that of CONWIP under 13 system configurations in terms of throughput, average inventory level, as well as average cycle time. As a supplement to the analytical model, a simulation model of the transfer line is used to observe the performance of the release control methodologies on the standard deviation of cycle time. From the analysis, we identify the system configurations in which the advantages of WIPLCtrl could be observed. / Singapore-MIT Alliance (SMA)

No description available.

O processo de microencapsulação vem sendo bastante aplicado em alimentos e um dos objetivos que vem se destacando atualmente é o controle da liberação do agente ativo no tempo e local desejado. Portanto, o objetivo do trabalho foi microencapsular agentes refrescantes (xilitol e mentol) a aplicá-los em gomas de mascar, objetivando prolongar a duração da sensação de refrescância. Xilitol e mentol foram microencapsulados utilizando o método de coacervação complexa. As microcápsulas foram caracterizadas quanto ao tamanho médio, morfologia (microscopia ótica, confocal e eletrônica de varredura), cor instrumental, higroscopicidade, umidade, atividade de água (Aw), solubilidade em água, isotermas de sorção, espectroscopia no infravermelho por transformada de Fourier (FTIR), comportamento térmico (por Caloria Diferencial de Varredura - DSC), eficiência de encapsulação e controle de liberação. As gomas de mascar foram produzidas no laboratório de pesquisa e desenvolvimento de uma indústria de alimentos. Oito formulações foram produzidas, sendo quatro com as microcápsulas e quatro com os ingredientes livres. As gomas foram analisadas em relação à umidade, Aw e cor instrumental; por meio da análise do perfil de textura (TPA) avaliou-se a dureza, elasticidade, mastigabilidade e a coesividade das gomas. Análise de tempo-intensidade (TI) das gomas de mascar foi realizada com 19 provadores treinados para avaliar a duração da sensação de refrescância fornecida por esses ingredientes. As microcápsulas obtidas apresentaram características adequadas para aplicação em alimentos, como tamanho médio de partículas de aproximadamente 100 µm e baixos valores de umidade, Aw, solubilidade e higroscopicidade. Por meio da microscopia confocal e da análise de FTIR confirmou-se que os núcleos foram completamente encapsulados pelo material de parede, demonstrando o sucesso da técnica empregada. A eficiência de encapsulação foi alta para o mentol, mas relativamente baixa para o xilitol. Por meio da análise de DSC constatou-se que o xilitol e o mentol passam do estado cristalino para o estado amorfo após o processo de microencapsulação, o que não interfere nas propriedades do mentol, mas no caso do xilitol sim, pois sua refrescância é atribuída ao seu calor de dissolução endotérmico. As gomas de mascar apresentaram baixos valores de Aw e umidade, o que favorece a estabilidade microbiológica. Em relação ao perfil de textura, observou-se que a presença do xilitol melhorou os parâmetros de textura das gomas, pois as gomas produzidas com este composto apresentaram os menores valores de dureza, mastigabilidade e elasticidade. A presença das microcápsulas não interferiu significativamente em nenhum dos parâmetros de textura analisados. A análise de TI confirmou que as microcápsulas foram hábeis para promover liberação gradual do mentol e do xilitol, pois a refrescância das gomas de mascar contendo as microcápsulas durou mais tempo que as gomas de mascar com os ingredientes livres. / The microencapsulation process has been widely applied in food and one of the aims that have been highlighted is to control the release of the active agent at the desired time and local. Therefore, the objective was to microencapsulate cooling agents (menthol and xylitol) to apply them in chewing gum, aiming to prolong the feeling of freshness. Xylitol and menthol were microencapsulated using complex coacervation method. The microcapsules were characterized by particle size, morphology (optical microscopy, confocal and scanning electron), instrumental color parameter, hygroscopicity, moisture, water activity (Aw), solubility, sorption isotherms, Fourier transform Infrared Spectroscopy (FTIR), thermal behavior (Differential Scanning Calorie -DSC), encapsulation efficiency and release control. The chewing gums were produced in the research and development laboratory of a food industry. Eight formulations were produced, four with microcapsules and four with free ingredients. The gums were analyzed for moisture, Aw and instrumental color parameter; by texture profile analysis (TPA) was evaluated hardness, springiness, chewiness and cohesiveness of the gum. Analysis of time-intensity (TI) of chewing gum was conducted with 19 trained panelists to evaluate the duration of the freshness sensation provided by such ingredients. The microcapsules obtained had characteristics suitable for application in foods such as average particle size of approximately 100 µm and low levels of humidity, Aw, solubility and hygroscopicity. By confocal microscopy and FTIR analysis it was confirmed that the cores were completely encapsulated by wall material, ensuring the success of the technique. The encapsulation efficiency was high in menthol microcapsules but relatively low for xylitol microcapsules. By the DSC analysis it was found that xylitol and menthol crystalline state transform to the amorphous state after the microencapsulation process, which does not affect the properties of menthol, but in the xylitol yes, because their freshness is attributed to its endothermic heat of dissolution. Chewing gums showed low values of Aw and moisture, which favors the microbiological stability. Through TPA, was observed that the presence of xylitol improved the texture parameters of the gums because the gums produced with this compound showed the lowest hardness, chewiness and elasticity. The presence of the microcapsules was not significantly influenced the texture parameters analyzed. Time-Intensity analysis confirmed that the microcapsules were able to promote gradual release of menthol and xylitol, because the freshness of chewing gum containing microcapsules lasted longer than the chewing gum free ingredients.

O processo de microencapsulação vem sendo bastante aplicado em alimentos e um dos objetivos que vem se destacando atualmente é o controle da liberação do agente ativo no tempo e local desejado. Portanto, o objetivo do trabalho foi microencapsular agentes refrescantes (xilitol e mentol) a aplicá-los em gomas de mascar, objetivando prolongar a duração da sensação de refrescância. Xilitol e mentol foram microencapsulados utilizando o método de coacervação complexa. As microcápsulas foram caracterizadas quanto ao tamanho médio, morfologia (microscopia ótica, confocal e eletrônica de varredura), cor instrumental, higroscopicidade, umidade, atividade de água (Aw), solubilidade em água, isotermas de sorção, espectroscopia no infravermelho por transformada de Fourier (FTIR), comportamento térmico (por Caloria Diferencial de Varredura - DSC), eficiência de encapsulação e controle de liberação. As gomas de mascar foram produzidas no laboratório de pesquisa e desenvolvimento de uma indústria de alimentos. Oito formulações foram produzidas, sendo quatro com as microcápsulas e quatro com os ingredientes livres. As gomas foram analisadas em relação à umidade, Aw e cor instrumental; por meio da análise do perfil de textura (TPA) avaliou-se a dureza, elasticidade, mastigabilidade e a coesividade das gomas. Análise de tempo-intensidade (TI) das gomas de mascar foi realizada com 19 provadores treinados para avaliar a duração da sensação de refrescância fornecida por esses ingredientes. As microcápsulas obtidas apresentaram características adequadas para aplicação em alimentos, como tamanho médio de partículas de aproximadamente 100 µm e baixos valores de umidade, Aw, solubilidade e higroscopicidade. Por meio da microscopia confocal e da análise de FTIR confirmou-se que os núcleos foram completamente encapsulados pelo material de parede, demonstrando o sucesso da técnica empregada. A eficiência de encapsulação foi alta para o mentol, mas relativamente baixa para o xilitol. Por meio da análise de DSC constatou-se que o xilitol e o mentol passam do estado cristalino para o estado amorfo após o processo de microencapsulação, o que não interfere nas propriedades do mentol, mas no caso do xilitol sim, pois sua refrescância é atribuída ao seu calor de dissolução endotérmico. As gomas de mascar apresentaram baixos valores de Aw e umidade, o que favorece a estabilidade microbiológica. Em relação ao perfil de textura, observou-se que a presença do xilitol melhorou os parâmetros de textura das gomas, pois as gomas produzidas com este composto apresentaram os menores valores de dureza, mastigabilidade e elasticidade. A presença das microcápsulas não interferiu significativamente em nenhum dos parâmetros de textura analisados. A análise de TI confirmou que as microcápsulas foram hábeis para promover liberação gradual do mentol e do xilitol, pois a refrescância das gomas de mascar contendo as microcápsulas durou mais tempo que as gomas de mascar com os ingredientes livres. / The microencapsulation process has been widely applied in food and one of the aims that have been highlighted is to control the release of the active agent at the desired time and local. Therefore, the objective was to microencapsulate cooling agents (menthol and xylitol) to apply them in chewing gum, aiming to prolong the feeling of freshness. Xylitol and menthol were microencapsulated using complex coacervation method. The microcapsules were characterized by particle size, morphology (optical microscopy, confocal and scanning electron), instrumental color parameter, hygroscopicity, moisture, water activity (Aw), solubility, sorption isotherms, Fourier transform Infrared Spectroscopy (FTIR), thermal behavior (Differential Scanning Calorie -DSC), encapsulation efficiency and release control. The chewing gums were produced in the research and development laboratory of a food industry. Eight formulations were produced, four with microcapsules and four with free ingredients. The gums were analyzed for moisture, Aw and instrumental color parameter; by texture profile analysis (TPA) was evaluated hardness, springiness, chewiness and cohesiveness of the gum. Analysis of time-intensity (TI) of chewing gum was conducted with 19 trained panelists to evaluate the duration of the freshness sensation provided by such ingredients. The microcapsules obtained had characteristics suitable for application in foods such as average particle size of approximately 100 µm and low levels of humidity, Aw, solubility and hygroscopicity. By confocal microscopy and FTIR analysis it was confirmed that the cores were completely encapsulated by wall material, ensuring the success of the technique. The encapsulation efficiency was high in menthol microcapsules but relatively low for xylitol microcapsules. By the DSC analysis it was found that xylitol and menthol crystalline state transform to the amorphous state after the microencapsulation process, which does not affect the properties of menthol, but in the xylitol yes, because their freshness is attributed to its endothermic heat of dissolution. Chewing gums showed low values of Aw and moisture, which favors the microbiological stability. Through TPA, was observed that the presence of xylitol improved the texture parameters of the gums because the gums produced with this compound showed the lowest hardness, chewiness and elasticity. The presence of the microcapsules was not significantly influenced the texture parameters analyzed. Time-Intensity analysis confirmed that the microcapsules were able to promote gradual release of menthol and xylitol, because the freshness of chewing gum containing microcapsules lasted longer than the chewing gum free ingredients.

Since 1970s, ever growing attention has been devoted by worldwide researchers and practitioners to the investigation of job release control. However, the need for control of flow of job/wafer into the wafer fabrication system is identified in the late 1988s. Subsequently, many release policies are developed and presented in the literature for improving its performance with respect to cycle time and throughput. Even though it is pointed out in the literature that there is a need for the development and analysis of policy that control the flow of job/wafer through the manufacturing process, still there is no exhaustive study in view of the previously developed release policies in the literature. Moreover, many new opportunities have evolved in the field of release policy in wafer fabrication industry due to the advancement in technology and computer science. It implies that near real-time decision making for efficient release policy is possible based on the global factory state. However, it appears from the literature that still to date the release policies, which are employed in real wafer fabrication system, are usually based on the static information. Release control/policy is emerging as an important research topic in the wafer fabrication industry given the extremely large capital investment and sales revenue of this industry. Release policy also hold practical significance for manufacturing managers, since neglecting it can lead to wide variations in shop workloads, can cause excessive backlogs, accomplishment of orders will be either too early or too late and there can be frequent need for expediting. All the challenges associated with the performance of the wafer fabrication system discussed here and the puzzle around the release policies and its impact on the wafer fabrication process, this research attempts to investigate existing release policies and proposing a few efficient release policies based on the knowledge gained from the existing release policies strength and weakness. Based on the insights gained from the existing release policies, three new closed loop release policies constant workload (CONSTWL), constant batch machine workload (CONSTBWL) and layer wise control (LWC) are developed by considering the parameters: workload in general, workload in batch machine, and re-entrant characteristics of the wafer fabrication system respectively. The conceptual significance in favour of these proposed closed loop release policies in improving performance of the wafer fabrication system is also outlined in this study. In the literature, few researchers clearly indicate that dispatching rule(s) influence the performance of wafer fabrication system either independently or in integration with release policies. Therefore, to empirically validate this fact, release policy is integrated with dispatching rule particularly applying on bottleneck (discrete processing machine) work station in this study. With these, the aims of proposed release policies are to efficiently improve the system performances in terms of average cycle time, standard deviation of cycle time and throughput. Accordingly, a simulation model is proposed and developed using Arena software for evaluating the performance of release policies in integration with dispatching rule applied on bottleneck work station in wafer fabrication environment. Further, to set the values of parameters in the simulation model, the cause and effect analysis is explored in this study by considering eight critical parameters or factors of the simulated wafer fabrication environment. It includes arrival rate, arrival distribution, processing time, maintenance schedule, operator’s schedule, batch size, dispatching rule and release policy. Simulation based cause and effect analysis not only helps in setting up the values of parameters in the proposed simulation model, but it also helps in strengthening the face validity of the developed simulation model. The verification and validation of the developed simulation model, which is a vital and fundamental aspect of simulation is discussed in detail in this study. Based on the analysis and the results observed from the cause and effect analysis, some modifications are incorporated and subsequently, the parameters values are set in the proposed simulation model for evaluating the performance of release policies integrating with dispatching rules. A series of simulation experiments are conducted using the proposed simulation model with systems conditions such as product mix, complexity of the process, level of machine unreliability, and system congestion level to study the relative effects of each of 18 release policies (one open loop release policy, 14 existing closed loop release policies, and 3 proposed release policies) in integration with dispatching rules (FIFO, LIFO and SRPT), considered in this study, at various throughput levels in the wafer fabrication environment. Particularly, the relative effect of integrating release policies and the dispatching rules are observed and analysed in terms of (a) the effect of dispatching rule on release policy, and (b) the effects of release policies on dispatching rules. It is observed from the overall inferences that dispatching rule: SRPT outperformed both FIFO and LIFO dispatching rule for all the considered release policies, except for the release policy: ‘TOTAL_CT’. Additionally, it is observed that for each of the eighteen release policies integrated with considered, the dispatching rule: SRPT produces less WIP inventory at the bottleneck work station for all throughput levels. The maximum deviation in delay (cycle time) is produced by dispatching rule: LIFO in all the release policies considered except for the release policy: ‘TOTAL_CT’ in which dispatching rule: SRPT produces maximum deviation in delay. Moreover, it is observed that the difference in mean delay with all three dispatching rules (FIFO, LIFO and SRPT) increases with the increase in throughput levels. Furthermore, it is observed that the throughput rate under all release policies (except ‘TOTAL_CT’) is more for dispatching rule: SRPT in comparison with both dispatching rules: FIFO and LIFO for nearly the same threshold values. The experimental results showed that proposed release policy: LWC reliably improves the system performance followed by the proposed release policy: CONSTWL and CONSTBWL with respect to both mean delay and standard deviation for corresponding throughput levels in wafer fabrication system. The characteristics of the proposed release policy: LWC are summarized and the same is presented as follows because this is proven to be best release policy among all the release policies considered in the proposed simulation model. The proposed release policy: LWC is a new measure of the work quantity on the shop floor system, which takes into account the location of jobs/wafers along the production line by employing re-entrant property of wafer fabrication system. As a result, it offers quick response to the stochastic events of the manufacturing system and can compensated the system disturbances in time. The proposed release policy: LWC offers more efficient control of flow of job/wafer in the wafer fabrication system with reduced delay (cycle time) and the standard deviation of delay (cycle time) for a given throughput level in comparison with almost all the release policies considered in this study in integration with all three dispatching rules considered and applied on bottleneck work station. For instance, from the analysis of simulation model, the proposed release policy: LWC reduces the average delay up to 98%, 95%, 90%, 89%, 49%, 35%, 21%, 17%, 13%, 12%, 10%, 9%, 9%, 9%, 6% and 4%, and reduces the standard deviation of delay up to 96%, 98%, 94%, 93%, 34%, 22%, 4%, 13%, 11%, 6%, 9%, 14%, 4%, 4%, 10% and 7% for a given throughput level, respectively in relation to other release polices: FRCP, EWIP, TOTAL_CT, PWR, EWC, DRCP, CONLOAD, WIPLCtrl, Droll, DEC, CONWIP, SA, RCONWIP, WR, CONSTBWL and CONSTWL respectively in integration with dispatching rule: SRPT. These improvements can also be understood from another aspect, that is, LWC can increase the system throughput rate for a given cycle time. The improvement is statistically significant according to the two sample t-test for all throughput values with a 95% confidence level. As the improvement of the proposed release policy: LWC is relatively less on the proposed release policies: CONSTWL and CONSTBWL with respect to mean delay, it can be inferred that the performance of CONSTWL and CONSTBWL is relatively better than other existing closed loop release policies for the scenarios considered in the simulation model. However, the best release policy: LWC provides satisfactory performance in comparison with other release policies for almost all scenarios considered in the simulation model. It is important to note that these proposed release policies can be easily applied in real wafer manufacturing systems because it possesses a simple logic and only the reference level need to be prescribed. The performance of four existing closed release policies that are FRCP, EWIP, TOTAL_CT and PWR are relatively worst in comparison with open loop release policy CONST. This is contradicting to the conclusions given in the literature by many authors that closed loop release policies are always better than open loop release policy with respect to cycle time and throughput measures. In fact, a reasonable closed loop release policy can provide better results than open loop release policy, if its objective and the release parameter are designed carefully, so that the release parameter can respond effectively to the dynamics of the manufacturing system. The reason for worst performance of these four existing closed loop release policies in comparison with open loop release policy and other existing policies is described in detail in this study. In order to see the impact of dispatching rules on a particular work station, batch machine work station, which usually has highest processing time in fabrication process, is considered in this study. The entire simulation experiments are replicated in the same manner except the basis that dispatching rules are applied on batch machine work station instead of bottleneck work station. Based on the analysis of the simulation results, the important observations are as follow: It is observed from the overall inferences that the influence of dispatching rules when applied to batch processing machine (diffusion) work station was not much on individual release policies, since the performance of all three dispatching rules provides nearly same performance at higher throughput level in the proposed simulation model. However, the performances of dispatching rule: SRPT in integration with all release policies considered in this study are summarized here because it produces less mean delay at most of the throughput values. In addition, from the analysis of simulation model, the proposed release policy: LWC reduces the average delay up to 97%, 93%, 87%, 85%, 22%, 17%, 15%, 15%, 13%, 11%, 10%, 10%, 9%, 6%, 6% and 2%, and reduces the standard deviation of delay up to 96%, 97%, 92%, 93%, 21%, 5%, 10%, 2%, 16%, 7%, 14%, 4%, 20%, 10%, 10% and 11% for a given throughput level, respectively in relation to FRCP, EWIP, PWR, TOTAL_CT, EWC, DEC, Droll, CONLOAD, SA, RCONWIP, WIPLCtrl, WR, DRCP, CONWIP, CONSTWL and CONSTBWL in integration with dispatching rule: SRPT, when applied on batch processing machine work station. The improvement is statistically significant according to the two sample t-test for most of the throughput values with a 95% confidence level. It is observed from overall inferences that the performance of all the release policies, considered in this study, in integration with dispatching rule: SRPT is better with respect to both mean delay and standard deviation of delay, when the dispatching rule is applied on the bottleneck (discrete machine, lithography) work station in the proposed simulation model. The performance of most of the release policies, considered in this study, in integration with dispatching rule: LIFO is better with respect to standard deviation of delay, when the dispatching rule is applied on the batch (batch machine, diffusion) work station. These results indicate that there is an influence of dispatching rule on the performance of wafer fabrication system if applied on batch machine work station or on bottleneck work station in integration with release policies. In addition, the effects of dispatching rules are highly dependent upon both the type of release policy used and the work station on which it is applied. Overall, the performance of the proposed release policies is proven to be very effective to system variability’s in scenarios considered in the simulation model. The significant impact of the choice of release policies on wafer manufacturing system performance is justified by the simulation experiments. It can be safely concluded that the efficient closed loop release policies that utilizes system information carefully based on the global factory state data can significantly improve the performance of wafer fabrication system. This thesis provides an extensive literature review covering several aspects of wafer fabrication process. Thereafter, a three new efficient closed loop release policies are developed and their workability are conceptually demonstrated with a framework and a flow diagram. The strength and the weakness of the existing release policies are conceptually highlighted and later it is proven to be true through comprehensive simulation study. A simulation model is developed by considering all the real-life fabrication environment for evaluating the performance of release policies in integration with dispatching rules. Cause and effect analysis is explored in proposed simulation model to set the parameters value. A series of simulation experiments are also constructed to empirically justify the conceptual significance of the proposed release policies.