• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.43-49
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• 2005

The high rate of voltage rise (dv/dt) in motor terminals caused by high-frequency switching and impedance mismatches between inverter and motor are known as the primary causes of irregular voltage distributions and insulation breakdowns on stator windings in IGBT PWM inverter-driven induction motors. In this paper, voltage distributions in the stator windings of an induction motor driven by an IGBT PWM inverter are studied. To analyze the irregular voltages of stator windings, high frequency parameters are derived from the finite element (FE) analysis of stator slots. An equivalent circuit composed of distributed capacitances, inductance, and resistance is derived from these parameters. This equivalent circuit is then used for simulation in order to predict the voltage distributions among the turns and coils. The effects of various rising times in motor terminal voltages and cable lengths on the stator voltage distribution are also presented. For a comparison with simulations, an induction motor with taps in the stator turns was made and driven by a variable-rising time switching surge generator. The test results are shown.

• 산업공학
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• 제9권2호
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• pp.143-158
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• 1996

This paper deals with the development of a software module for production planning and scheduling activities of an actual die-production management system. Scheduling problems, such as master schedule and detailed schedule, are the focal point of the whole article and they are considered in terms of operation procedures. Schedule-explosion module and load levelling module are the essential components of schedule management. The scheduling module allocates the resources, determines the process priority and the planned start and completion dates of processes. Rescheduling can be done to manipulate unforeseen situations that schedule is delayed owing to inducing defectives, machine breakdowns and lumpy demands. This study indicates a practical model for the die-producation management and helps to apply it for jobs in the real situation.

• 대한산업공학회지
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• 제19권3호
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• pp.91-102
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• 1993

This paper suggests an approach to quantitative evaluation of a manufacturing flexibility in automated manufacturing systems. The flexibility of a cell is newly defined and evaluated in use of the environmental change factors which may influence flexibility for satisfying a manufacturing performance objective. The number of machines, the number of operations, machine breakdowns and processing times are considered for this cell flexibility measure. The cell flexibility measures the extent that the cell utilizes the processes to acquire high throughput. Simulation program written in SLAM System was used to help measure cell flexibility. The proposed cell flexibility measure provides a prediction of the influence of the factors on throughput performance, and applies in case of comparison of existing system and a new system, changes in operation conditions of a cell, and comparison of rival machines. Therefore it can be used as decision making criteria for system justification.

• 산업경영시스템학회지
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• 제29권1호
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• pp.109-115
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• 2006

Exact solutions for practical-size problems in job shop will be highly inefficient. Scheduling heuristics, therefore, are typically found in the literature. If we consider real-life situations such as machine breakdowns, the existing scheduling methods will be even more limited. Scheduling against due-dates addresses one of the most critical issues in modern manufacturing systems. In this paper, the method for weighted tardiness schedule using a graph theoretic decomposition heuristic is presented. It outstands the efficiency of computation as well as the robustness of the schedule.

• 대한전기학회논문지
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• 제39권5호
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• pp.527-537
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• 1990

This paper describes an intelligent control-based job scheduler, named ESIJOBS, for flexible manufacturing system. In order to construct rulebase of this system, traditional rules of job scheduling in FMS are examined and evaluated. This result and the repetitional simulations with graphic monitoring system are used to form the rulebase of ESIJOBS, which is composed of three parts:six part selection rules, four machine center selection rules, and twenty-one metarules. Appropriate scheduling rule sets are selected by this rulebase and manufacturing system status. The performances of all simulations are affected by random breakdowns of major FMS components during each simulation. Six criteria are used to evaluate the performance of each scheduling. The two modes of ESIJOBS are simulated and compared with combinational 24 rule-set simulations. In this comparison ESIJOBS dominated the other rule-set simulations and showed the most excellent performance particularly in three criteria.

• 산업공학
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• 제6권2호
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• pp.53-65
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• 1993

This paper deals with the development of a software module for production planning and scheduling activities of an existing Flexible Machining and Assembly System (FMAS). The Production Planning Module uses the hierarchical and sequential scheme based on "divide and conquer" philosophy. In this module, routes are determined based on the production order, orders are screened, tools are allocated, and order adjustments are executed according to the allocated tools. The Scheduling Module allocates the resources, determines the task priority and the start and completion times of tasks. Re-scheduling can be done to handle unforeseen situations such as lumpy demands and machine breakdowns. Since all modules are integrated with a central database and they interface independently, it is easy to append new modules or update the existing modules. The result of this study is used for operating the real FMAS consisting of a machining cell with 2 domestic NC machines and a part feeding robot, an assembly cell with a conveyor and 3 robots, an inspection cell, an AGV, an AS/RS, and a central control computer.

• 한국지능시스템학회논문지
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• 제18권5호
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• pp.718-723
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• 2008

베어링은 각종 설비에서 활용되는 중요한 기계요소 중 하나이다. 설비고장의 상당수는 베어링의 결함이나 파손에 기인하고 있다. 따라서 베어링에 대한 온라인모니터링기술은 설비의 정지를 예방하고 손실을 줄이는 데 필수적이다. 본 논문은 진동 신호를 이용하여 베어링의 상태를 예측하기 위한 온라인모니터링에 대해 연구한다. 프로파일로 주어지는 진동신호는 이산 웨이블릿 변환을 통해 분석되고, 분해수준별 웨이블릿 계수로부터 얻은 통계적 특징 중 유의한 것을 선별하고자 분산분석 (ANOVA)을 이용한다. 선별된 특징벡터는 Support Vector Machine (SVM)의 입력이 되는 데, 본 논문에서는 다중클래스 분류문제를 다루기 위한 계층적 SVM 트리를 제안한다. 수치실험 결과, 제안된 방법은 베어링의 결함을 분류하는 데 우수한 성능을 갖는 것으로 나타났다.

• 산업과 과학
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• 제2권4호
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• pp.11-16
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• 2023

지하철은 현대 도시의 교통 체계에서 중요한 역할을 하는 대중 교통 수단이다. 하지만, 갑작스런 고장 및 시스템 불통 등의 이유로 혼잡을 야기시키는 경우가 종종 발생하여 불편을 초래하고 있다. 따라서, 본 논문에서는 지하철 시스템의 효율적 운영을 위해 머신러닝을 활용한 고장 예측 및 예방 연구를 진행하였다. UC Irvine의 MetroPT-3 데이터셋을 활용하고, 로지스틱 회귀를 이용하여 지하철 고장 예측 모델을 구축하였다. 모델은 0.991의 높은 정확도로 비고장 상태를 예측하나, 정밀도와 재현율은 상대적으로 낮아 고장 예측에 있어 오류 가능성을 시사하고 있다. ROC_AUC 값이 0.901로, 모델이 무작위 추측보다 뛰어난 분류를 할 수 있다. 구축한 모델은 지하철 시스템의 안정적인 운영 운영에 유용하나, 성능 개선을 위한 추가 연구가 필요하다고 생각한다. 따라서 학습 데이터가 많고 데이터의 정제가 잘 이루어진다면 고장 예측을 통해 사전 점검을 하여 예방할 수 있다.

• 제어로봇시스템학회논문지
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• 제4권2호
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• pp.235-245
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• 1998

This paper presents the fuzzy optimization model based scheduling methodology for the efficient production control of a FFS(FIexible Flow Shop) under the uncertain production environment. To develop the methodology, a fuzzy optimization technique is introduced in which the uncertain production capacity caused by the random events like the machine breakdowns or the absence of workers is modeled by fuzzy number. Since the problem is NP hard, the goal of this study is to obtain the near optimal but practical schedule in an efficient way. Thus, Lagrangian relaxation method is used to decompose the problem into a set of subproblems which are easier to solve than the original one. Also, to construct the feasible schedule, a heuristic algorithm was proposed. To evaluate the performance of the proposed method, computational experiments, based on the real factory data, are performed. Then, the results are compared with those of the other methods, the deterministic one and the existing one used in the factory, in the various performance indices. The comparison results demonstrate that the proposed method is more effective than the other methods.

• Industrial Engineering and Management Systems
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• 제14권2호
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• pp.129-158
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• 2015

It is necessary for retailers to determine the optimal ordering policy of products considering supply disruptions due to a natural disaster and a production process failure as quality and machine breakdowns. Under the situation, a dualsourcing supply chain (DSSC) is one of effective SC for retailers to order products reliably. This paper proposes the optimal ordering policy of a product in a DSSC with a retailer and two manufacturers. Two manufacturers may face supply disruptions due to a natural disater and a production process failure after they received the retailer's order of products. Here, two scenarios of demand information of products are assumed: (i) the demand distribution is known (ii) mean and variance of the demand are known. Under above situations, two types of DSSC are discussed. Under a decentralized DSSC (DSC), a retailer determines the optimal ordering policy to maximize his/her total expected profit. Under the integrated DSSC (ISC), the optimal ordering policy is determined to maximize the whole system's total expected profit. Numerical analysis investigates how demand information and supply disruptions affect the optimal decisions under DSC and ISC. Besides, profitability of supply chain coordination adjusting the wholesale price is evaluated to encourage the optimal decision under ISC.