Multiple-Rack Strategies Using Optimization of Location Assignment Based on MRCGA in Miniload Automated Storage and Retrieval System

Abstract

This paper aimed to introduce multiple-rack strategies in miniload automated storage and retrieval systems (AS/RSs), which included first fit (FF) and best fit (BF) assignment methods based on a matrix real-coded genetic algorithm (MRCGA) in the storage and retrieval process. We validated the probability occurrence of item sizes as a contributory factor in multiple-rack strategies, and compared their capacities, utilization of units and space by equal probabilities or the 80/20 law. According to the analytical methods, BF showed a reduction of more than 11.2% than FF on travel distance, and Type B-FF, Type B-BF and Type C-BF were better able to meet high-density requirements. These strategies provide diversified storage and retrieval solutions for the manufacturing and express delivery industry.

A Novel Parts-to-Picker System with Buffer Racks and Access Racks in Flexible Warehousing Systems

“…The storage capacity (in the large-scale model, the storage capacity is 13440, as listed in Table 7) is significantly bigger than the KIVA system (2000 to 4000, [5,6]). At the same time, the picking efficiency (in the large-scale model, the picking efficiency can reach 2430 boxes per hour, as listed in Table 7) is significantly better than the SBS/RS (between 500 and 800 boxes per hour, [1]) and the miniload AS/RS (less than 300 boxes per hour, [22]). Furthermore, when the number of AMRs reaches the max, the picking efficiency (2430 in the large-scale model, as listed in Table 7) is no less than the KIVA system (nearly 2000 per hour, [5,6]).…”

“…Considering the various sizes of materials in industrial warehouses, the unified-size-unit rack design is not suitable for all parts, components, and entire pieces. In [22], the authors propose different-unit-size racks to maximize space utilization and storage capacity. At the same time, the pod design in the KIVA system is not suitable here because, on the one hand, the height of the storage pods is two to three meters, which is significantly lower than that of industrial warehouses (more than eight meters) and means a significant waste of vertical space.…”

“…In order to improve space utilization, we consider different unit sizes for materials of different sizes, such as tiny parts, medium-sized components, and large-sized entire pieces [22]. The rack design should reduce the gaps in racks to increase the utilization of the warehouse.…”

“…According to the 80/20 rule [22] and the reality material probabilities of manufacturing enterprises [1,2], for example, in some cases, we set the proportions of small, medium, and big as 8, 8, and 1. The racks' length and height are 30 m and 16 m, respectively, and we set the different unit sizes as 2 m × 2 m (big), 1 m × 1 m (medium), and 0.5 m × 0.5 m (small), and the number of shelves is two for big, eight for medium, and four for small, as shown in Figure 7.…”

“…The operation time of a DC is obviously less than the sum of loading and unloading. When the rack has different unit sizes, as shown in Figure 11, the first fit (FF) and best fit (BF) rules are considered in DC processes [22]. FF gives the loading position, which is first searched with a space big enough for loading an item, and BF gives the loading position, which is the best for loading an item with low space waste.…”