Optimal Class-Based Storage System with Diagonal Movements

Abstract

With the advent of e-commerce activities, warehouse operations require high storage density and high throughput. When the space is limited, high storage density can be attained by puzzle-based storage solutions. Recently a new solution has been introduced by Logistics 4.0 Lab at NTNU and Wheel.me. Storage racks are moved by autonomous wheels in any direction allowing also diagonal movements which might theoretically achieve high throughput. Even though it is identified as most viable method, retrieval time is dependent upon the characteristics of the system. Previous studies investigated retrieval performance largely based on the escort locations (empty slots), Input/Output points and movement types. The purpose of this paper is to apply two-class-based storage policy where high-turnover items are kept nearby the Input/Output point to lower the response time. We conducted a scenario-based analysis by changing the COI based ABC curve, system size, zone A size, and shape factor to examine the impact of ideal system dimensions and zone A boundaries on the performance of the class-based storage system. According to the findings, two-class-based storage system typically outperforms random storage in terms of cycle time of about 10% to 50% depending on the configuration and COI value.