• 산업공학
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• 제9권2호
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• pp.219-229
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• 1996

Most studies on the operation policy for AS/RS concluded that the class-based storage policy has better performance than random storage policy does. However ASRS performances are examined only with the assumption of fixed production quantity in the studies. It is true that production quantity of each item changes frequently in practice. If an ASRS keeps the current storage policy regardless of production quantity variation, the performance of present storage policy will be worse. The effect of production quantity variation per product between 10 and 80% with random storage policy and class-based storage policy with reassignment and relocation are studied. The results are compared with both of the randomized and class-based storage policies without reassignment nor relocation cases. A typical ASRS system is developed using GPSS/PC for operation policy evaluation purposes.

• 한국경영과학회지
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• 제24권3호
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• pp.39-47
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• 1999

It has been concluded that the performance of class-based storage policy is better than the performance of random storage policy in the literature. However, the rack shortage problem assigned to the 1st class items makes the decision hard to apply the class-based storage policy in practice. In this paper, a new common zone concept is introduced between two classes to resolve the problem with class-based storage policy. The common zone is the area to accept items from both classes. An AS/RS model is developed for computer simulation study and the effect of common area sizes with various AS/RS operation conditions is analyzed.

• Journal of applied mathematics & informatics
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• 제23권1_2호
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• pp.505-516
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• 2007

In this paper, we provide some fundamental properties and basic theoretical results of K-class-based dedicated storage policy in a unit load system assuming the constant-space assumption that the number of storage locations for a class is not the maximum aggregate inventory position for a class but the sum of space requirement for products assigned to the class. The main theorem is that there exists a (K+1) -class-based storage layout whose expexted single command (SC) travel time is not greater than that of a K-class-based storage layout, i.e, $E(SC^*_{K+1}){\leq}E(SC^*_K)\;for\;K=1,{\cdots}$, (n-1).

• Industrial Engineering and Management Systems
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• 제11권4호
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• pp.331-338
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• 2012

This research proposes a Pareto-based multi-objective optimization approach to class-based storage warehouse design, considering a two-block warehouse that operates under the class-based storage policy in a low-level, picker-to-part and narrow aisle warehousing system. A mathematical model is formulated to determine the number of aisles, the length of aisle and the partial length of each pick aisle to allocate to each product class that minimizes the travel distance and maximizes the usable storage space. A solution approach based on multiple objective particle swarm optimization is proposed to find the Pareto front of the problems. Numerical examples are given to show how to apply the proposed algorithm. The results from the examples show that the proposed algorithm can provide design alternatives to conflicting warehouse design decisions.

• 한국경영과학회지
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• 제23권3호
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• pp.91-108
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• 1998

Automated Storage and Retrieval Systems (AS/RSs) are an important facility for modern material management. The expected benefits of these capital-intensive facilities are gained when their control policies and their physical design parameters are determined simultaneously. In this paper we present several analytical models that capture the impact of the storage assignment policy and of the rack design on the expected storage and retrieval times. Sequential and interleaved service modes are considered for sequencing the storage and retrieval requests. We further investigate the impact of the rack structure on the relative performance of the following storage assignment policies : closest open location (random), full turnover-based policy, and class-based. Our analysis clearly indicates that significant savings in crane travel time are realized when implementing full turnover-based policy, rather than random. These savings become more and more pronounced as the profile of the storage racks approaches the square-in-time shape. Furthermore, it is shown that a class-based policy, with a small number of storage classes, will capture most of these savings and be easier to manage in practice.

• 대한산업공학회지
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• 제22권2호
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• pp.179-188
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• 1996

We study n-class-based storage policy for an automated storage/retrieval system (AS/RS) and derive the closed form expressions of expected travel times under single command cycle. In order to confirm the correctness of the derivations, we consider both discrete and continuous storage racks, and show that the expressions for expected travel times of discrete rack converge to those of continuous one. We also derive the expected travel times when the coordinate locations for storages or retrievals are triangularly distributed and we try to solve class layout problem using the obtained results. Numerical examples are given in case of 3-class-based storage policy.

• 대한산업공학회지
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• 제25권2호
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• pp.274-281
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• 1999

In this paper, we determine the required storage capacity of a unit-load automated storage/retrieval system(AS/RS) under random storage assignment(RAN) and n-class turnover-based storage assignment(CN) policies. For each of the storage policies, an analytic model to determine the optimal storage capacity of the AS/RS is formulated so that the total cost related to storage space and space shortage is minimized while satisfying a desired service level. A closed form of optimal solutions for the RAN policy is derived from the model. For the CN policy, an optimal storage capacity is shown to be determined by applying the existing iterative search algorithm developed for the full turnover-based storage(FULL) policy. Finally, an application of the approach to the standard economic-order-quantity inventory model is provided.

• 대한산업공학회지
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• 제16권1호
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• pp.99-106
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• 1990

With two-class-based storage assignment policy and dual command cycle in Automated Storage/Retrieval Systems(AS/RS), the problem of determining the region dedicated for class-one item is considered. First, the expected travel time of the S/R machine is derived when the boundary of the class-one region is square. Secondly, a heuristic procedure is proposed which determines sequentially the class-one region in a discrete rack. An application of the procedure generates leaf shape region which confirms that the L-shape partition is not necessarily optimal.

• 한국컴퓨터정보학회논문지
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• 제8권4호
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• pp.159-164
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• 2003

물류창고의 적재위치는 창고를 이동하는 물품의 총 자재취급비용에 의해 직접전인 영향을 받는다. 본 논문의 목적은 물류 창고에서의 총 오더피킹 시간을 감소하기 위한 물품 저장방식인 블록 저장방식을 개발하고자 한다. 블록저장방식은 랙들을 블록으로 분할하고, 각 물품은 회전율과 도크와 블록간의 평균 거리를 기준으로 할당한다. 제시한 저장방식의 수행도를 평가하기 위해 다양한 주문 결합 방법들을 이용하여 기존의 등급별 저장방식과 비교 연구한다.

• 대한산업공학회지
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• 제27권4호
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• pp.384-393
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• 2001

The performance of a double carousel system depends on its design and operation strategy. The two-class based assignment policy is expected to be an appropriate storage policy for its efficient operation, since it has two independently-moved carousels, lower and upper sub-carousels. This paper conducts a comparative analysis of the effects of the two-class based assignment policy and those of randomized assignment policy on the throughput of a double carousel system. We also show that, by allowing the sub-carousels not to be equal in size, a further improvement in the throughput can be obtained.