• Journal of Korean Society of Industrial and Systems Engineering
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• v.22 no.52
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• pp.53-68
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• 1999

지금까지 전통적인 EPQ(Economic Production Quantity) 모델에서는 생산율이 수요율보다 큰 경우만을 다루어 왔으나, 실제 시장에서는 그 반대로 수요율이 생산율보다 큰 경우도 종종 발생한다. 그러나 이러한 상황에 대한 EPQ 연구는 찾아보기 어려운 실정이다. 따라서 본 논문에서는 수요율이 생산율보다 큰 상황을 고려한 확장된 EPQ 모델(Extended EPQ Model)을 유도하고, 이를 생산재고의 유한보충률 상황(Finite Replenishment Rate Environment)에서의 MPS(Master production Schedule)와 MRP(Material Requirements Planning)에 적용하였다.

• Journal of applied mathematics & informatics
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• v.12 no.1_2
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• pp.251-260
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• 2003

Generally, in deriving the solution of economic production quantity (EPQ) inventory model, we consider the demand rate and deterioration rate as constant quantity. But in case of real life problems, the demand rate and deterioration rate are not actually constant but slightly disturbed from their original crisp value. The motivation of this paper is to consider a more realistic EPQ inventory model with finite production rate, fuzzy demand rate and fuzzy deterioration rate. The effect of the loss in production quantity due to faulty/old machine have also been taken into consideration. The methodology to obtain the optimum value of the fuzzy total cost is derived and a numerical example is used to illustrate the computation procedure. A sensitivity analysis is also carried out to get the sensitiveness of the tolarance of different input parameters.

• Journal of Korean Institute of Industrial Engineers
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• v.40 no.3
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• pp.313-320
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• 2014

We consider the problem to find economic inventory quantity of a single commodity under stochastic demands and order cancellation. In contrast to the traditional economic production quantity (EPQ) model, we assume that once the amount of inventory reaches to a predetermined level of quantity then the production is not halted but its production speed decreases until the inventory level drops to zero. We establish two probabilistic models representing the behaviors of both the high-production period and low-production period, respectively, and derive the relationship between the level of inventory and costs of production, cancellation, and holding, from which the quantity of economic inventory is obtained.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.5
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• pp.532-541
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• 1997

This article derives an analytic solution to determine the optimal size of multiple noncontinuous process and storage units. The total cost to be minimized consists of the setup cost of noncontinuous processing units and the inventory holding cost of feedstock/product storages. A novel approach, which is called PSW(Periodic Square Wave) model, is applied to represent the material flow among non-continuous units and storages. PSW model presumes that the material flow between unit and storage is periodic square wave shaped. The resulting optimal unit size has similar characteristics with the classical economic lot sizing model such as EOQ(Economic Order Quantity) or EPQ(Economic Production Quantity) model in a sense that the unit size is determined as the balance between setup and inventory holding cost. However, the influence of inventory holding cost of PSW model is different from that of EOQ/EPQ model. EOQ/EPQ model includes only the product inventory holding cost but PSW model includes all inventory holding costs around the non-continuous unit with proportional contribution. PSW model is suitable for analyzing interlinked process-storage system. The optimal lot size of PSW model is smaller than that of EOQ/EPQ model. This is quitea remarkable result considering that the EOQ/EPQ model has been is widely used since last half century.

• Journal of Korean Society for Quality Management
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• v.20 no.2
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• pp.1-10
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• 1992

In this paper, we study a joint lot sizing and inspection policy under an EPQ(Economic Production Quantity) model where a random proportion of units are defectives. Those units can be discovered only through costly inspection. The problem is thus bivariate : both lot size and fraction to inspect are to be chosen. We first analyze a model in which the only penalty for uninspected defectives is financial, and then consider a model where defectives units cannot be used and thus must be replaced by non-defective ones. As a result it can be proved that this inspection policy costs economically and is to be decided effectively for the Economic Production Quantity constraining the fraction to inspect.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.29 no.3
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• pp.70-78
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• 2006

제조업에서는 보다 합리적으로 생산량을 결정함으로써 고객에 대한 납기 준수는 물론, 기업 내부의 비용을 감소시키기 위한 노력을 끊임없이 하고 있다. 합리적인 생산량의 결정은 기업 내적으로는 낭비를 제거하고, 생산 흐름의 안정성을 유지하여 주며, 기업 외적으로는 공급사슬 전체의 자재흐름을 원활히 해주고 고객의 기호 변화에 빠르게 대처할 수 있도록 한다. 이에 본 논문은 보다 높은 고객 만족도와 비용의 절감을 위해서 재고 유지비용과 생산준비비용만을 고려하는 기존의 생산량 결정 모형에 고객의 대기 비용을 추가한 다품목 경제적 생산량 모델을 제시하였다.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.10
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• pp.867-873
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• 2001

The purpose of this study is to find analytic solution of determining the optimal capacity (lot-size) of multiproduct acyclic multistage production and inventory system to meet the finished product demand under the constraint of finite intermediate storage. Intermediate storage is a practical way to mitigate the material flow imbalance through the line of supply and demand chain. However, the cost of constructing and operating storage facilities is becoming substantial because of increasing land value, environmental and safety concern. Therefore, reasonable decision-making about the capacity of processes and storage units is an important subject for industries. The industrial solution for this subject is to use the classical economic lot sizing method, EOQ/EPQ(Economic Order Quantity/Economic Production Quantity) model, incorporated with practical experience. But EOQ/EPQ model is not suitable for the chemical plant design with highly interlinked processes and storage units because it is developed based on single product and single stage. This study overcomes the limitation of the classical lot sizing method. The superstructure of the plant consists of the network of serially and/or parallelly interlinked non-continuous processes and storage units. The processes transform a set of feedstock materials into another set of products with constant conversion factors. A novel production and inventory analysis method, PSW(Periodic Square Wave) model, is applied to describe the detail material flows among equipments. The objective function of this study is minimizing the total cost composed of setup and inventory holding cost. The advantage of PSW model comes from the fact that the model provides a set of simple analytic solutions in spite of realistic description of the material flows between processes and storage units. the resulting simple analytic solution can greatly enhance the proper and quick investment decision for the preliminary plant design problem confronted with economic situation.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.1
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• pp.26-32
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• 2007

This study deals with waiting-time dependent backordering rate during stock-out period in the EconomicProduction Quantity (EPQ) model. Assuming that the backordering rate follows an exponentially decreasingfunction of the waiting time, the backorder rate is developed under First-Come-First-Served (FCFS) andLast-Come-First-Served (LCFS) Policy. The mathematical models are developed based on differential equations.Through numerical examples, the validity of the developed models is illustrated.

• Journal of Korean Society for Quality Management
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• v.47 no.1
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• pp.87-96
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• 2019

Purpose: The purpose of this paper is to determine an optimal production time for economic production quantity model with preventive maintenance and random defective rate as the function of a machinery deteriorates. Methods: If a machinery shifts from "in-control" state to "out-of-control" state, a proportion of defective items being produced increases. It is assumed that time to state shift is a random variable and follows an arbitrary distribution. The elapsed time until process shift decreases stochastically as a production cycle repeats and quasi-renewal process is used to implement for production facilities to deteriorate. Results: When the exponential parameter for exponential distribution increases, the optimal production time increases. When Weibull distribution is considered, the optimal production time is closely affected by the shape parameter of Weibull distribution. Conclusion: A mathematical model is suggested to find optimal production time and optimal number of production cycles and numerical examples are implemented to validate the patterns for changes of optimal times under different parameters assumptions. The real application is implemented using the proposed approach.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.4
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• pp.398-405
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• 1997

This article presents a new model which is called Periodic Square-Wave(PSW) to describe the material flow of the periodic processes involving intermediate buffer. The material flows incoming into and outgoing from the intermediate buffer are assumed to be periodic square shaped. PSW model gives the same result as that of Economic Production Quantity(EPQ) model for determining optimal lot size of single stage batch storage system. However, for batch storage serial train system, PSW model gives a different optimal solution of about 6 % reduced total cost. PSW model provides the more accurate information on inventory and production system than the classical approach by maintaining simplicity and increasing computational burden.