• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2006년도 추계학술대회
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• pp.525-528
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• 2006

This paper considers the vehicle dispatching problem in the automated material handling system (AMHS) of a large scale semiconductor fabrication line, which consists of 18 bays, 468 equipments and uses more than 130 overhead hoist transporters (OHT). We propose an assignment problem based vehicle dispatching approach to take advantage of simultaneous vehicle reassignment based on up-to-date system status. The proposed approach compares fsvorably with the shortest travel distance first rule and with the reassignment based rule which was recently proposed by the authors, in the number of vehicles required and the average lead time.

• 한국시뮬레이션학회:학술대회논문집
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• 한국시뮬레이션학회 1997년도 춘계 학술대회 발표집
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• pp.124-127
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• 1997

A key element in the control of Automated Guided Vehicle Systems (AGVS) is dispatching policy. This paper proposes a new dispatching algorithm for an efficient operation of AGVS. Based on an evolutionary operation, it has an adaptive control capability responding to changes of the system environment. The performance of the algorithm is compared with some well-known dispatching rules in terms of the system throughput through simulation. Sensitivity analysis is carried out varying the buffer capacity and the number of AGVS.

• 한국경영과학회지
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• 제26권1호
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• pp.97-108
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• 2001

Design and evaluation of AGV-based material handling systems are very complicated due to the randomness and the large number of variables involved Vehicle travel time is a key parameter for designing and evaluating AGV systems. Although loaded travel time is relatively easy to estimate, determination of empty vehicle travel time is difficult due to the inherent randomness of material handling systems. Most previous studies assume that the empty vehicle travel time is the same as the loaded travel time or assume very specific environments. This paper presents new vehicle travel time models for AGV-based material transport systems. The research effort is focused on the estimation of empty vehicle travel time under various vehicle dispatching policies. Simulation experiments are used to verify the proposed travel time models.

• 한국시뮬레이션학회논문지
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• 제6권1호
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• pp.41-52
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• 1997

It is essential to construct an efficient material flow system for the successful introduction of automated manufacturing systems. Automated Guided Vehicle System (AGVS) plays a significant role more and more in modern manufacturing environments, because of the flexibility and the precision they offer. However, as the size and the complexity of systems increase, the problems of dispatching, routing and scheduling of AGVs become complicated due to their independent and asynchronous demands. In this paper, we review relevant papers, and provide a new and more efficient method for dispatching AGV, named MEVTT (Minimum Empty Vehicle Travel Time) and demonstrate its performance and efficiency using simulation.

• 산업공학
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• 제16권spc호
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• pp.93-98
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• 2003

This paper addresses an AGV dispatching problem in semiconductor clean-room bays where AGVs move cassettes of wafers between machines or machines and a central buffer. Since each machine in a bay has a local buffer of limited capacity, material flow should be controlled in a careful way to maintain high system performance. It is regarded that two most important performance measures in a semiconductor bay are throughput rate and lead-time. The throughput rate is determined by a bottleneck resource and the lead-time depends on smooth material flow in the system. This paper presents an AGV dispatching procedure based on the concept of theory of constraints (TOC), by which dispatching decisions are made to utilize the bottleneck resource at the maximum level and to smooth the flow of material. The new dispatching procedure is compared with existing dispatching rules through simulation experiments.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.249-252
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• 2004

The automatic determination of vehicle operation status as well as continuous tracking of vehicle location with intelligent management is one of major elements to achieve the goals. Especially, vehicle operation status can only be analyzed in terms of expert experiences with real-time location data with scheduling information. However the scheduling information of individual vehicle is very difficult to be interpreted immediately because there are hundreds of thousand vehicles are run at the same time in the national wide range workplace. In this paper, we propose the location-based knowledge management system(LKMs) using the active trajectory analysis method with routing and scheduling information to cope with the problems. This system uses an inference technology with dispatching and geographic information to generate the logistics knowledge that can be furnished to the manager in the central vehicle monitoring and controlling center.

• 대한산업공학회지
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• 제37권4호
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• pp.331-341
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• 2011

This paper considers an inbound lot-sizing and outbound dispatching problem for a single product in a thirdparty logistics (3PL) distribution center. Demands are dynamic and finite over the discrete time horizon, and moreover, each demand has a delivery time window which is the time interval with the dates between the earliest and the latest delivery dates All the product amounts must be delivered to the customer in the time window. Ordered products are shipped by multiple vehicle types and the freight cost is proportional to the vehicle-types and the number of vehicles used. First, we formulate a mixed integer programming model. Since it is difficult to solve the model as the size of real problem being very large, we design a conventional genetic algorithm with a local search heuristic (HGA) and an improved genetic algorithm called adaptive genetic algorithm (AGA). AGA spontaneously adjusts crossover and mutation rate depending upon the status of current population. Finally, we conduct some computational experiments to evaluate the performance of AGA with HGA.

• 한국시뮬레이션학회논문지
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• 제9권1호
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• pp.21-38
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• 2000

A fuzzy dispatching algorithm with adaptable control scheme is proposed for more flexible and adaptable operation of AGV system. The basic idea of the algorithm is prioritization of all move requests based on the fuzzy urgency. The fuzzy urgency is measured by the fuzzy multi-criteria decision-making method, utilizing the relevant information such as incoming and outgoing buffer status, elapsed time of move request, and AGV traveling distance. At every dispatching decision point, the algorithm prioritizes all move requests based on the fuzzy urgency. The performance of the proposed algorithm is compared with several dispatching algorithms in terms of system throughput in a hypothetical job shop environment. Simulation experiments are carried out varying the level of criticality ratio of AGVs , the numbers of AGVs, and the buffer capacities. The rule presented in this study appears to be more effective for dispatching AGVs than the other rules.

• 산업공학
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• 제15권3호
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• pp.316-324
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• 2002

Automated Guided Vehicles are widely used as an essential material handling system for FMS to provide flexibility and efficiency. We suggest a new dispatching rule based on priority function which considers urgency and empty vehicle travel time under finite buffer capacity. We evaluate the performance of the proposed rule by comparing the performance of Shortest Travel Time/Distance(STT/D) rule in terms of machine utilization, throughput and WIP level using simulation. The simulation results show that the suggested dispatching rule is robust and provides better machine utilization, throughput with comparable WIP level compared to STT/D rule.

• 한국시뮬레이션학회논문지
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• 제23권4호
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• pp.97-109
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• 2014

Personal Rapid Transit (PRT)는 차세대 대중교통 수단으로 에너지 효율적이며 높은 수준의 고객 서비스를 제공한다. 정류장에 동적으로 도착한 고객이 운송 서비스를 요청하면 PRT 시스템은 차량을 배차한다. 본 연구에서는 PRT 시스템을 위한 새로운 온라인 배차 알고리즘을 제시하였다. 제시된 알고리즘은 최근린(nearest neighbor) 배차 규칙을 기반으로 개발되었으며, 이분 매칭(bipartite matching)을 사용하여 다수의 PRT 차량과 고객을 동시에 고려하여 배차를 결정한다. 이 경우 전체 차량 중 배차 대상 차량의 선택 범위가 성능지표에 영향을 줄 수 있다. 따라서 본 연구에서는 차량의 상태를 고려하여 체계적으로 배차 차량을 선택하는 방법을 제시한다. 성능지표로 공차 이동거리와 고객 대기시간을 고려하였으며, 시뮬레이션 기법을 사용하여 배차 선택 범위에 따른 성능지표의 차이를 확인하였다. 그리고 기존의 배차 규칙과 비교하여 본 연구에서 제시하는 방법론이 우수하며 PRT 시스템에 적합한 것을 확인하였다.