Bongju Jeong

An available-to-promise system for TFT LCD manufacturing in supply chain

This paper presents development of an available-to-promise (ATP) system for thin film transistor liquid crystal display (TFT LCD) manufacturing in global supply chain environment where the worldwide headquarter, distribution centers, and manufacturing facilities are globally networked. ATP activity is simply to give the delivery date promise to customers for their specific orders. However, the ATP process is not simple due to the complexity of supply chain and information integrity. In this paper, we build up a global ATP system architecture whose functions and information flows are comprehensively defined. To do so, we developed an ATP model in a global supply chain for estimating the promising delivery date for new orders, and the capacity available-to-promise (CATP) model for calculating the unused production capacity at shop floor level with given production schedules. We proposed an efficient heuristic for scheduling TFT LCD module assembly process for effectively using the unused capacity at shop floor level. Efficiency of the scheduling system was investigated using the data collected in a real TFT LCD manufacturing site. The validity of the proposed ATP system was also explored by comparing with other ATP procedures including the current practice.

Decentralized supply chain planning framework for third party logistics partnership

As the complexity of a supply chain continuously increases and the importance of prompt delivery to end customers grows, an independent company, so called a third party logistics provider, to perform all or part of a manufacturers product distribution function has emerged. In this situation, collaboration between the manufacturer and the third party logistics provider is indispensable in order to generate a supply chain plan. However, information sharing for collaboration between two companies is getting complicated by privacy issues associated with information provided by and shared among different independent companies. In this paper, we propose a decentralized supply chain planning framework based on minimal-information sharing between the manufacturer and the third party logistics provider. Extensive computational tests have shown that the proposed approach generates a good supply chain plan in terms of total costs comparing with the ideal centralized supply chain planning approach.

A computerized causal forecasting system using genetic algorithms in supply chain management

Forecasting activities are widely performed in the various areas of supply chains for predicting important supply chain management (SCM) measurements such as demand volume in order management, product quality in manufacturing processes, capacity usage in production management, traffic costs in transportation management, and so on. This paper presents a computerized system for implementing the forecasting activities required in SCM. For building a generic forecasting model applicable to SCM, a linear causal forecasting model is proposed and its coefficients are efficiently determined using the proposed genetic algorithms (GA), canonical GA and guided GA (GGA). Compared to canonical GA, GGA adopts a fitness function with penalty operators and uses population diversity index (PDI) to overcome premature convergence of the algorithm. The results obtained from two case studies show that the proposed GGA provides the best forecasting accuracy and greatly outperforms the regression analysis and canonical GA methods. A computerized system was developed to implement the forecasting functions and is successfully running in real glass manufacturing lines.

Product sequencing problem in Mixed-Model Assembly Line to minimize unfinished works

Abstract This study is concerned about how to optimize the input sequence of product models with sequence-dependent setup time in Mixed-Model Assembly Line (MMAL) using conveyor system. Usually MMAL consists of a number of stations linked by a conveyor belt and each station has a work zone limited by upstream and down stream boundaries. To avoid improper interference between operators in the adjacent stations and excess of machine moving range, operators are forced to complete their operations within their predetermined work zone. In this study, our goal is to determine the sequence of models for minimizing the total unfinished work within their work zone. A generalized formulation of the product sequencing problem in MMAL is presented. We developed an optimal procedure using Branch & Bound technique and a heuristic procedure using lower bound and local search. Experimental results show that the heuristic procedure provides reasonably good solutions with low computational costs.

An assembly scheduler for TFT LCD manufacturing

This paper presents development of a scheduling system for Thin Film Transistor Liquid Crystal Display (TFT LCD) assembly process. With given daily production plan that is rough-cut capacitated, the scheduler generates shift-based capacity feasible schedules at each assembly step. The scheduling problem is a parallel-machine scheduling problem with sequence dependent setups and some manufacturing environments, which make the problem considerably difficult. The scheduling objective is to minimize the mean flow time and maximize the production progressiveness. Two scheduling heuristics are proposed for each production step of assembly process. The first scheduling heuristic is applicable for the first three steps of assembly process, i.e. coating, rubbing, and attaching step, and for the later steps another similar heuristic is employed. We also propose a simple method for computing production requirements for each step where daily production demand is unknown. The proposed scheduling procedures are implemented in a real TFT LCD manufacturing line and their performances are investigated. The experimental results show that the proposed scheduler provides quite better schedules than the current practice employed in the line in terms of both mean flow time and fulfillment of production demands.

A production-distribution coordinating model for third party logistics partnership

Recently, independent third party logistics providers who perform all or part of the firms product distribution function allow many manufacturers to focus on its core competencies rather than on the distribution expertise. In this situation, collaboration between a manufacturer and a third party logistics provider is indispensable for successful production-distribution coordination. However, while information must be shared between them for coordination purpose, they hope to communicate with each other using minimum proprietary information regarding their own business. For efficient coordination of this type of supply chain, a new decentralized coordinating model based on minimum information sharing is proposed. This decentralized coordinating model is implemented on a multi-agent system. The preliminary result with a numerical example shows a very promising performance of the proposed model, when compared with that of an ideal centralized model.

Measuring greenhouse gas emissions for the transportation sector in Korea

This paper presents a methodology of measuring greenhouse gas emissions (mainly CO2) for the transportation sector and illustratively applies it in Korea. The transportation sector is one of the most critical sectors concerning environmental pollution and represents about 20 percent of the yearly total greenhouse gas emissions for the energy sector in Korea. In spite of the increasing importance of the transportation sector in the eco-environment, current methodologies to analyze greenhouse gas emissions use a Tier 1 method, which is the simplest type among the methodologies recommended by IPCC guidelines. For a new methodology, we consider characteristics of transportation modes and operational environments in Korea. The proposed methodology can analyze the amount of greenhouse gas emissions for each transport mode and integrate it through transportation environments. It also provides a decision-making tool for governments to make transportation polices. As a result, the Korean government can manage the transportation sector in an eco-friendly manner and improve the national eco-environment.

Site symmetry of Er3+ in In0.5Ga0.5P

The site and site symmetry of Er3+ in LPE grown In0.5Ga0.5P have been investigated for the first time through Raman and polarized luminescence spectroscopic techniques. The Er3+ site was found to be ErIn in In0.5Ga0.5P. The site symmetry of Er3+ in In0.5Ga0.5P was positively confirmed asC2v.

Zn diffusion of In0.5Ga0.5P investigated by photoluminescence measurements

Abstract Zn diffusion of an In 0.5 Ga 0.5 P layer grown on semi-insulating GaAs substrate by the liquid phase epitaxy technique has been investigated using photoluminescence (PL) measurements. The PL spectrum shows a characteristic emission peak of In 0.5 Ga 0.5 P at 1.934 eV after diffusion. From temperature-dependent studies of this peak and depth profiling of this luminescence, it was found that this peak behaves like D-A (donor-acceptor) pair recombination and is associated with the interstitial Zn donor to substitutional Zn acceptor band transition. Also it was found that recombination due to interstitial Zn donor is dominant near the surface and decreases with increasing depth. The calculated activation energy of substitutional acceptor was found to be 47 meV.

The band offset measurement at the In0.5Ga0.5P/GaAs heterojunction by using properties of transition metal☆

Abstract It is well known that the energy level of a transition metal (TM) such as manganese is tied to the vacuum level rather than to a particular band extreme in semiconductors. Therefore, TM can be used as a common reference energy level in all the semiconductors. We have investigated for the first time the photoluminescence spectrum of Mn-doped In0.5Ga0.5P/GaAs heterojunction and by using the Mn acceptor level in photoluminescence (PL) spectra, the fractional band offsets Qc and Qv for the In0.5Ga0.5P/GaAs heterojunction are determined as 0.63 and 0.37, respectively.