Multi-Load AGV의 생산성 효율 평가를 위한 지표 개발

임대은 ( Dae Eun Lim ),서민석 ( Min Seok Seo ) 한국생산성학회 2011 生産性論集 Vol.25 No.4

The use of Multi-Load AGV (AGV capable of simultaneously transport two Lots with different pick-up and drop-off points) that can significantly enhance operation efficiency of the conventional AGV (Single-Load AGV able to only handle one Lot at a time) is increasing. However, indices for the transportation of Multiple-Load AGV Lot remain unchanged from those for the conventional Single-Load AGV carrying a single Lot, resulting in difficulties to accurately analyze transportation effectiveness of Multiple-Load AGV and troubles to use the indices as a mean to set future direction for additional research. This paper proposes indices to understand transportation and operation effectiveness of Multiple-Load AGV, and based on the new indices, presents a calculation algorithm. Furthermore, it compares the results of the old index calculation method with the new one to analyze the effectiveness of improved algorithm.

A Heuristic Derivation of the Waiting Time Distribution of a GI/G/1 Queue

Dae Eun Lim(임대은),Bokeun Kim(김보근),Nam K. Kim(김남기),Kyung C. Chae(채경철) 한국경영과학회 2015 한국경영과학회지 Vol.40 No.1

This paper presents a heuristic approach to derive the Laplace-Stieltjes transform (LST) and the probability generating function (PGF) of the waiting time distributions of a continuous- and a discrete-time GI/G/1 queue, respectively. This is a new idea to derive the well-known results, the waiting time distribution of GI/G/1 queue, in a different way.

일반품질연구 : 열화가 감마과정을 따르는 경우 가속열화시험의 최적 계획

임헌상 ( Heon Sang Lim ),임대은 ( Dae Eun Lim ) 한국품질경영학회 2015 품질경영학회지 Vol.43 No.2

Purpose: This paper is concerned with optimally designing accelerated degradation test (ADT) plans based on a gamma process for the degradation model. Methods: By minimizing the asymptotic variance of the MLE of the q-th quantile of the lifetime distribution at the use condition, the test stress levels and the proportion of test units allocated to each stress level are optimally determined. Results: The optimal plans of ADT are developed for various combination of parameters. In addition, a method for determining the sample size is developed, and sensitivity analysis procedures are illustrated with an example. Conclusion: It is important to optimally design ADT based on a gamma process under the condition that a degradation process should be always nonnegative and strictly increasing over time.

시스템 내 고객 수에 따라 서비스율과 도착율을 조절하는 M/G/1/K 대기행렬의 분석

최두일,임대은,Choi, Doo-Il,Lim, Dae-Eun 한국시뮬레이션학회 2015 한국시뮬레이션학회 논문지 Vol.24 No.3

대기행렬 시스템에는 고객들의 대기시간이 지나치게 길어지는 것을 막기 위해 다양한 정책들이 적용되는데, 본 연구에서는 고객숫자에 따른 제어 정책을 갖는 유한용량 M/G/1/K 대기행렬을 분석한다. 고객의 숫자에 따라 서버의 서비스율과 고객의 도착율을 조절하는 정책이다. 두 개의 한계점(thresholds) $L_1$과 $L_2$($${\geq_-}$$L1)를 설정하고 시스템 내 고객의 숫자가 $L_1$보다 작을 때는 시스템은 보통(또는 상대적으로 느린)의 서비스율(service rate)과 보통의 도착율(arrival rate)을 갖는다. 고객의 숫자가 증가하여 $L_1$이상이고 $L_2$보다 작으면 도착율은 그대로 이지만 서비스율을 증가시켜 빠르게 서비스한다. 이후 고객의 숫자가 더욱 증가하여 $L_2$ 이상이면 고객의 도착율도 작은 값으로 바꾸어 고객을 덜 입장시킨다. 위 정책을 갖는 M/G/1/K 대기행렬을 내재점 마코프 체인과 준-마코프 과정을 이용하여 분석하고 수치예제를 제시한다. We analyze an M/G/1/K queueing system with queue-length dependent service and arrival rates. There are a single server and a buffer with finite capacity K including a customer in service. The customers are served by a first-come-first-service basis. We put two thresholds $L_1$ and $L_2$($${\geq_-}L_1$$ ) on the buffer. If the queue length at the service initiation epoch is less than the threshold $L_1$, the service time of customers follows $S_1$ with a mean of ${\mu}_1$ and the arrival of customers follows a Poisson process with a rate of ${\lambda}_1$. When the queue length at the service initiation epoch is equal to or greater than $L_1$ and less than $L_2$, the service time is changed to $S_2$ with a mean of $${\mu}_2{\geq_-}{\mu}_1$$. The arrival rate is still ${\lambda}_1$. Finally, if the queue length at the service initiation epoch is greater than $L_2$, the arrival rate of customers are also changed to a value of $${\lambda}_2({\leq_-}{\lambda}_1)$$ and the mean of the service times is ${\mu}_2$. By using the embedded Markov chain method, we derive queue length distribution at departure epochs. We also obtain the queue length distribution at an arbitrary time by the supplementary variable method. Finally, performance measures such as loss probability and mean waiting time are presented.

고객수 기반의 오버로드 제어 정책이 있는 M/G/1/K 대기행렬의 바쁜기간 분석

임헌상,임대은,Lim, Heonsang,Lim, Dae-Eun 한국시뮬레이션학회 2018 한국시뮬레이션학회 논문지 Vol.27 No.3

We consider the busy period of an M/G/1/K queueing system with queue-length-dependent overload control policy. A variant of an oscillating control strategy that was recently analyzed by Choi and Kim (2016) is considered: two threshold values, $L_1({\leq_-}L_2)$ and $L_2({\leq_-}K)$, are assumed, and service rate and arrival rate are adjusted depending on the queue length to alleviate congestion. We investigate the busy period of an M/G/1/K queue with two overload control policies, and present the formulae to obtain the expected length of a busy period for each control policy. Based on the numerical examples, we conclude that the variability and expected value of the service time distribution have the most influence on the length of a busy period. 대기행렬에 고객 (또는 패킷 등)이 몰리는 오버로드(overload)가 발생하는 경우 긴 대기열이 발생하여 서비스 품질에 좋지 않은 영향을 줄 수 있다. 오버로드 상황에서 혼잡을 완화하기 위해 대기하는 고객숫자에 기반한 다양한 오버로드 제어 정책들이 고안, 적용되고 있다. 본 연구는 대기 중인 고객 숫자에 한계점 (threshold)을 두고, 한계점을 넘으면 서비스 속도를 빠르게 하거나 고객의 도착 간격(시간)을 증가시키는 제어정책을 대상으로 한다. 이러한 정책을 갖는 M/G/1 대기행렬에 대해 바쁜 기간(busy period)을 분석하는데, 연구결과는 비용구조가 주어졌을 때 최적 시스템 제어 정책을 찾는데 필수적이다.

반도체 EDS 검사 공정의 설비 용량 계획에 관한 최적화 모델

김해중 ( Hae Joong Kim ),임대은 ( Dae-eun Lim ) 대한설비관리학회 2021 대한설비관리학회지 Vol.26 No.1

In this paper, a mixed-integer programming (MIP) based capacity planning model for the electrical die sorting (EDS) process where probe cards are used as consumables in semiconductor facilities is presented. The model is designed to satisfy the demand while maximizing the utilization of testers and probe cards in hand. As a result, the level of resource procurement can stay at the minimum level in which directly can be translated into positive profitability. This research employs the decomposition methodology to convert the MIP formulation into a “solver recognizable” format. By doing so, the decomposed model can provide near-optimal solutions instantaneously for practical application and the positive outcome is projected to be over several million dollars.

주문량에 따라 생산 속도를 조절하는 제조시스템의 분석

최두일 ( Choi Doo Il ),임대은 ( Lim Dae-eun ) 한국경영공학회 2016 한국경영공학회지 Vol.21 No.4

In this study, we analyze a manufacturing system with a variable production rate. The system produces an item upon a request. If an arriving request finds the system occupied, the request waits in the queue. The production (or service) time distribution of requests (or customers) upon production initiation is changed if the number of requests in the system reaches a predefined threshold L₂. Then, the changed production time distribution continues until the number of requests in the system is reduced to another threshold L₁(≤ L₂), and this process is repeated. We model this system as an MMPP/G/1/K queue with a modified state-dependent service rate and analyze the system using an embedded Markov chain and a supplementary variable method. The performance measures of the queue-length distributions at a customer`s departure epochs and at an arbitrary time are derived. Numerical examples are also presented.

반도체 제조라인 레이아웃 평가를 위한 실용적인 Lot 이동거리 계산방법

서민석 ( Min Seok Seo ),임대은 ( Dae Eun Lim ) 한국생산성학회 2014 生産性論集 Vol.28 No.1

In this paper, a practical estimation method is developed for the lot travel distance in order to evaluate semiconductor unified fabrication layouts using the absorbing Markov chain. The lot travel distance is defined as the total distance that a lot travels from the first process to the last process; it can be used to investigate whether a fabrication layout design is reasonable. Furthermore, unified fabrication has not yet been introduced in the literature; it is a fabrication method that uses only one type of automated material handling system (AMHS). When designing semiconductor fabrication layouts, every aspect of all alternatives should be investigated meticulously. The widely known and accepted methods, such as sophisticated simulations and mathematical modeling with high accuracy, require an extensive time period to build the model. However, in the early stages of the layout design, simple and insightful methods are required in order to investigate the numerous alternatives during a short time period. This paper presents a simple estimation method for the travel distance of a lot during its lifetime in a fabrication.

낮은 교통밀도 하에서 서버 고장을 고려한 복수 서버 대기행렬 모형의 체제시간에 대한 분석

김우성(Woo Sung Kim),임대은(Dae Eun Lim) 한국산업경영시스템학회 2016 한국산업경영시스템학회지 Vol.39 No.2

In this paper, we present a new way to derive the mean cycle time of the G/G/m failure prone queue when the loading of the system approaches to zero. The loading is the relative ratio of the arrival rate to the service rate multiplied by the number of servers. The system with low loading means the busy fraction of the system is low. The queueing system with low loading can be found in the semiconductor manufacturing process. Cluster tools in semiconductor manufacturing need a setup whenever the types of two successive lots are different. To setup a cluster tool, all wafers of preceding lot should be removed. Then, the waiting time of the next lot is zero excluding the setup time. This kind of situation can be regarded as the system with low loading. By employing absorbing Markov chain model and renewal theory, we propose a new way to derive the exact mean cycle time. In addition, using the proposed method, we present the cycle times of other types of queueing systems. For a queueing model with phase type service time distribution, we can obtain a two dimensional Markov chain model, which leads us to calculate the exact cycle time. The results also can be applied to a queueing model with batch arrivals. Our results can be employed to test the accuracy of existing or newly developed approximation methods. Furthermore, we provide intuitive interpretations to the results regarding the expected waiting time. The intuitive interpretations can be used to understand logically the characteristics of systems with low loading.

재구성가능 제조시스템과 다계층 구조를 가지는 분배센터로 구성된 공급사슬망을 위한 웹기반 시뮬레이터 개발

서민석(Minseok Seo),임대은(Dae-Eun Lim) 대한산업공학회 2011 대한산업공학회지 Vol.37 No.4