Class-based Storage Assignment Research Articles

Increasing Throughput in Warehouses: The Effect of Storage Reallocation and the Location of Input/Output Station

Automatic warehousing systems are a sort of green technology that is becoming increasingly popular in the logistics business. Automated Storage/Retrieval Systems (AS/RS) are one of the most significant components of advanced automated logistics and manufacturing systems. The majority of AS/RS systems use input/output (I/O) points located in the lower left corner of the rack. These systems are reaching their maximum capacity because of their layout design limitations. Breakthrough solutions are needed to enhance the performance of existing systems. In this study, we examined how the location of I/O station can affect the total travel time. Another strategy for enhancement is a two-step preparation method. In this strategy, the allocation of the storage is changed, in the idle time, to be closer to the I/O point to reduce the service time for a class-based storage assignment. An analytical model was used to introduce for the first time optimal configurations of this strategy. We tested the suggested strategy using a simulation model created using R software, specifically designed for this purpose. Results showed that the two-step preparation strategy took between 1.2 and 1.9 h before the shift starts. The enhancement on throughput is almost the same for both possible locations of the I/O point. The results also showed that the two strategies (location of the I/O point and reallocation of storage) could increase throughput by about 21% to 28%, depending on parameters such as the number of orders and the height of the storage rack.

INCREASING WAREHOUSE THROUGHPUT THROUGH THE DEVELOPMENT OF A DYNAMIC CLASS-BASED STORAGE ASSIGNMENT ALGORITHM

This study investigates the problems faced by an agricultural wholesaler arising from an inefficient random storage assignment policy. Research was conducted on warehouse operations and storage policies. The ABC classification technique was used to create a class-based storage assignment policy. This policy was then input into an algorithm that packs products according to how frequently they are ordered. The aim of the algorithm is to store fast-moving products closest to the shipping area. If this is done, the order picking times would decrease by an average of 3 hours 20 mins per day. This would increase the warehouse’s throughput and profitability. Keywords Storage policy; SLAP; Inventory Management

Study and Comparison of Automated Material Handling Systems used in Warehouses

Order picking is an important part of order processing in warehousing and dispersal operations and can be achieved using manual, automated, or semi-automated systems. This thesis evaluates two automated systems, carousel system and AS/RS (automated storage and retrieval system). The main goal of this research is to develop mathematical model to analyze the performance of both AS/RS and carousel systems under random storage assignment and classbased storage assignment.

Designing an automated storage/retrieval system with a single aisle-mobile crane under three new turnover based storage policies

ABSTRACT This article considers a multi-aisle AS/RS employing a single aisle-mobile crane and develops analytical travel time models for three new storage policies with turnover-based product allocation to aisles. In addition to product turnover, these storage policies also take into account the demand skewness and the characteristics of storage and transport equipment. Based on the proposed travel time models, analytical expressions are derived to determine the physical dimensions of the AS/RS that are optimized with respect to crane travel time. AS/RS designs employing the newly developed storage policies are compared with designs employing three other (non-turnover based) storage policies, using a design methodology proposed in a recent study. The analysis shows that among the three turnover-based storage policies, class-based storage assignment performs better than full turnover-based storage policy when subjected to different evaluation criteria. It is concluded that the inclusion of storage policies in the AS/RS design process, is highly beneficial in the selection of the right storage and transport equipment.

Design of diagonal cross-aisle warehouses with class-based storage assignment strategy

Non-traditional warehouses shorten the travelled paths to store and retrieve (S/R) the loads, thanks to additional aisles crossing the parallel racks. This paper provides the analytic model to best design a non-traditional warehouse for unit-load (UL) with diagonal cross-aisles and storage policy according to the class-based storage (CBS) strategy. The model minimizes the average single-command cycle time to S/R the loads, best sizing the classes, their shape, and the position/numbers of additional aisles. The focus is on both 2- and 3-CBS optimizing the number of diagonal cross-aisles to best balance the travel time reduction and the loss of storage space due to the aisles. Furthermore, benchmarking toward standard warehouses with no diagonal cross-aisles and random assignment strategy allows quantifying the positive impact of the proposed design configuration on the daily warehouse operations.

Modeling class-based storage assignment over life cycle picking patterns

This paper aims to introduce a new approach for the design and management of warehousing systems, which involves variable demand patterns in agreement with the life cycle of stock keeping units (SKUs). Two cost-based mixed integer linear programming (MILP) models are formulated to address both the technology selection, e.g. part-to-picker systems (as automated storage and retrieval systems – AS/RS, miniloads, etc.) and picker-to-part order picking systems, and the SKU assignment to the storage areas. In particular, a class based storage assignment over a life cycle picking metric is adopted. This metric is a rolling measure of popularity.The proposed approach, the adopted measure of popularity and the developed models can support (1) decision making for the selection of warehousing and material handling (W&MH) systems, (2) the determination of the storage capacity for the storage classes, (3) the assignment of SKU to the storage classes and (4) the dynamic, i.e., time-based, management of re-warehousing handlings. Two significant numerical examples illustrate the application and the potential of the proposed approach and models.

Class-Based Storage Assignment in a Unit-Load Warehouse Employing AS/RS with Inventory Space Allocation Considering Product Specific Setup to Holding Cost Ratio

Many authors have used continuous optimization models for class-based storage allocation for unit load warehouses employing AS/RS system assuming the same setup to holding cost ratio for all products in their EOQ inventory policy. Accordingly, an ABC curve based on demand ordering of products is used to determine pallet turnovers in their travel distance models which is not applicable in many practical situations and can be inaccurate. This paper develops a new model to determine two/three class optimal partitions while relaxing assumption of constant setup to holding cost ratio in the EOQ formula and as a consequence uses an ABC curve based on decreasing ranking of product turnovers rather than that based on demand. Computational experience shows that this new continuous model approximates pick travel distances which are very close to as compared to that of a semi-discrete model (SDM) proposed in this paper. Further computational experiments are also provided comparing traditional models with our formulations.

A review of methodologies for class-based storage location assignment in a warehouse

The class-based storage distributes the products among a number of classes and reserves a region for each class within the storage area. This paper discusses three important issues in class-based storage location assignment: reduction in storage space requirements under class-based policy compared to dedicated policy, cube-per-order index (COI) and general orderings of products in storage class formation and combined inventory staggering and class-based storage assignment. Accordingly, class-based storage assignment problems are classified and methodologies for class-based storage assignment available in the literature are reviewed. The paper concludes by suggesting some future research in the area of class-based storage assignment.

The impact of acceleration/deceleration on travel-time models in class-based automated S/R systems

The travel time models of Automated Storage and Retrieval systems (AS/RS) machines under randomized storage proposed by Chang et al. (IIE Transactions, 27(1), 108–111, 1995), which consider the speed profiles in real-world applications, are extended in this paper. In the present study, travel time models are proposed that consider various travel speeds with known acceleration and deceleration rates. Compact forms of expected travel times under the class-based storage assignment and full-turnover-based storage assignment have been determined. The results show that both the proposed exponential travel time model and the adjusted exponential model perform satisfactorily and could be useful tools for designing an AS/RS in real-world applications.

A BOM Oriented Class-Based Storage Assignment in an Automated Storage/Retrieval System

A storage assignment policy based on the needs of manufacturing operations can increase not only the performance of the automated storage/retrieval system (AS/RS) but also the performance of the production system. In general, the needs of manufacturing operations are embedded in material attributes, and the bill of material (BOM) is the best source to link material attributes. By employing the BOM as the backbone structure of a production system, a CIM system can be thoroughly integrated. Past work has identified a class-based assignment method for an AS/RS as a reasonable and efficient storage assignment policy. This study presents a BOM oriented class-based storage assignment method for an AS/RS. The proposed method possesses not only the advantage of a class-based storage method, but also the feasibility to integrate an AS/RS into a CIM system. To illustrate the effectiveness of the proposed method, a case study is presented. A random storage assignment method is also employed to obtain the solution for the illustrative example. The results are used to compare with those obtained by the proposed method. From the results of comparative studies, the proposed BOM-oriented class-based AS/RS assignment method is shown to be efficient.

The impact of acceleration/deceleration on travel-time models in class-based automated S/R systems

The travel time models of Automated Storage and Retrieval systems (AS/RS) machines under randomized storage proposed by Chang et al. (IIE Transactions, 27(1), 108–111, 1995), which consider the speed profiles in real-world applications, are extended in this paper. In the present study, travel time models are proposed that consider various travel speeds with known acceleration and deceleration rates. Compact forms of expected travel times under the class-based storage assignment and full-turnover-based storage assignment have been determined. The results show that both the proposed exponential travel time model and the adjusted exponential model perform satisfactorily and could be useful tools for designing an AS/RS in real-world applications.

An optimal boundary for two class-based storage assignment policy in carousel system

Abstract This paper examines the effects of 2-class-based turnover assignment policy on the throughput performance of the carousel system in which a storage/retrieval machine performs pickup/discharge operations. Two alternative configurations in class boundary shape are considered. For each alternative, the expected cycle time is developed for single and dual command cycles based on the continuous analytical models. It is shown that with 2-class-based turnover assignment policy(C2) significant reductions in cycle time are obtainable over randomized storage assignment policy. The effects of the system parameters such as the skewness of the inventory distribution, the shape factor and the pickup/discharge time are studied on the optimal boundary.

Class-based storage assignment policy in carousel system

The carousel storage system is an automated warehousing system which has been widely used in a broad range of applications. This paper examines the effects of storage assignment policy on the throughput performance of the carousel system in which a storage/retrieval machine performs pickup/discharge operations. For 2-class-based storage assignment policy, the expected cycle time models are developed for single and dual command cycles. It is shown that with 2-class-based storage assignment policy significant reductions in cycle time are obtainable over randomized storage assignment policy. The effects of the system parameters such as the skewness of the inventory distribution, the shape factor and the pickup/discharge time are studied on the optimal boundary.