• 한국경영과학회:학술대회논문집
• /
• 대한산업공학회/한국경영과학회 2006년도 춘계공동학술대회 논문집
• /
• pp.1124-1132
• /
• 2006

This paper considers a flow shop scheduling problem where a different WIP (work-in-process) state has different weight on the duration time. The objective is to minimize the sum of the weighted WIP. For the two machine flow shop case, the recognition version is unary NP-Complete. The three simple and intuitive heuristics H0, H1, and H2 are presented for the problem. For each heuristic, we find an upper bound on relative error which is tight in limit. For heuristic H2, we show that H2 dominates the other two heuristics.

• 한국컴퓨터정보학회논문지
• /
• 제4권3호
• /
• pp.13-19
• /
• 1999

본 연구는 TPN (Time Petri Nets) unfolding을 이용하여 가공 machine과 세정 machine으로 구성된 FMC (Flexible Manufacturing Cell)의 WIP (Work In Process)를 분석하는 방법을 제시한다. 여기서, PN의 unfolding은 상태공간폭발이 발생하지 않는 concurrent system의 검증에 사용되는 순서기반 방법이다. 본 연구는 일반적으로 발생하는 순환상태 스케쥴 문제에서 가장 그 작업과정 시간을 최적화하기 위하여 원래의 net을 동일한 비순환 net으로 바꾸어 줄 수 있는 unfolding 개념을 기반으로 한 것이다.

• Bulletin of the Korean Chemical Society
• /
• 제29권8호
• /
• pp.1575-1578
• /
• 2008

• 산업경영시스템학회지
• /
• 제42권1호
• /
• pp.55-63
• /
• 2019

This paper develops an algorithm to determine the batch size of the batch process in real time for improving production and efficient control of production system with multiple processes and batch processes. It is so important to find the batch size of the batch process, because the variability arising from the batch process in the production system affects the capacity of the production. Specifically, batch size could change system efficiency such as throughput, WIP (Work In Process) in production system, batch formation time and so on. In order to improve the system variability and productivity, real time batch size determined by considering the preparation time and batch formation time according to the number of operation of the batch process. The purpose of the study is to control the WIP by applying CONWIP production system method in the production line and implements an algorithm for a real time batch size decision in a batch process that requires long work preparation time and affects system efficiency. In order to verify the efficiency of the developed algorithm that determine the batch size in a real time, an existed production system with fixed the batch size will be implemented first and determines that batch size in real time considering WIP in queue and average lead time in the current system. To comparing the efficiency of a system with a fixed batch size and a system that determines a batch size in real time, the results are analyzed using three evaluation indexes of lead time, throughput, and average WIP of the queue.

• 대한산업공학회지
• /
• 제41권3호
• /
• pp.275-286
• /
• 2015

In this paper, we propose a practical method for setting up a daily production plan which can operate semiconductor fabrication factories more stably and linearly by determining work in process (WIP) targets and movement targets. We first adjust cycle times of the operations to satisfy the monthly production plan. Second, work in process (WIP) targets are determined to control the production progress of operations: earliness and tardiness. Third, movement targets are determined to reduce cumulated differences between WIP targets and actual WIPs. Finally, the determined movement targets are modified through a simulation model which considers capacities of the equipments and allocations of the WIPs in the fab. The proposed daily production planning method can be easily adapted to the memory semiconductor fabs because the method is very simple and has straightforward logics. Although the proposed method is simple and straightforward, the power of the method is very strong. Results from the shop floor in past few periods showed that the proposed methodology gives a good performance with respect to the productivity, workload balance, and machine utilization. We can expect that the proposed daily production planning method will be used as a useful tool for operating semiconductor fabrication factories more efficiently and effectively.

• 한국지능시스템학회논문지
• /
• 제21권3호
• /
• pp.283-289
• /
• 2011

본 논문에서는 차륜형 역진자에 적용되는 속도 추정기 기반 제어기 설계와 다양한 수치 시뮬레이션이 수행되었다. 차륜형 역진자는 불안정한 평형점과 안정한 평형점을 동시에 갖는다. 불안정한 평형점에 대하여 평형을 유지하기 위하여 차륜형 역진자는 지속적으로 제어되어야 한다. 제어기의 입력으로 차륜형 역진자 몸체의 각도, 각속도, 변위 속도 등이 필요하다. 필요한 속도는 모터에 부착된 에코더 신호를 차분하여 얻어지며, 엔코더의 해상도에 민감하게 의존한다. 저해상도 엔코더와 속도 추정기에 기반하여 개선된 속도 검출법이 제안되고 경사면에서 유효함을 보이기 위해서 다양한 수치 시뮬레이션이 수행되었다.

• 정보과학회지
• /
• 제18권6호
• /
• pp.15-22
• /
• 2000

• 산업공학
• /
• 제15권4호
• /
• pp.349-355
• /
• 2002

In order to build a new factory, we must have answers regarding the following questions; 1. what is to be produced? 2. how are the products to be produced? 3. how much of each product will be produced? The answers are related to product-design, process-design and capacity-design respectively and they are used for layout-design as the input data. Especially capacity design decision provides the information regarding the number of equipments required and the balance of the line. This paper introduces a case study on the capacity design for a new factory where the retainers of ball bearing are manufactured. A simulation model is developed with ARENA for analyzing the system considered. The major objectives of the study are evaluating the performance of the line which is originally suggested by the company, and finding out alternatives for improving the system. Number of WIP between the processes are also investigated because it affects the space planning of the layout.

• 한국경영과학회지
• /
• 제36권2호
• /
• pp.51-65
• /
• 2011

We compared a CONWIP(constant work-in-process) system with a kanban system in a production line with constant processing times. Based on the observation that a WIP-controlled line production system such as CONWIP and kanban is equivalent to a m-node tandem queue with finite buffer, we applied a max-plus algebra based solution method for the tandem queue to evaluate the performance of two systems. Numerical examples with 6 workstations were used to demonstrate the proposed analysis. The numerical results support the previous studies that CONWIP outperforms kanban in terms of expected waiting time and WIP. Unlike the kanban case, sequencing workstations in a CONWIP does not affect the performance of the system.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
• /
• pp.1250-1255
• /
• 1990

This paper discusses an optimal cyclic scheduling problem for a FMC (Flexible Manufacturing Cell) modeled by a two-machine flowshop with two machining centers with APC's (Automated Pallet Changers), an AGV (Automated Guided Vehicle) and loading and unloading stations. Cyclic production in which similar patterns of production is repeated can significantly reduce the production lead-time and WIP (Work-In-Process) in such flexible, automated system. Thus we want to find an optimal cyclic schedule that minimizes the cycle time in each cycle. However, the existence of APC's as buffer storage for WIP makes the problem intractable (i.e., NP-complete). We propose an practical approximation algorithm that minimizes, instead of each cycle time, its upper bound. Performances of this algorithm are validated by the way of computer simulations.