Task Scheduling Model of Double-Deep Multi-Tier Shuttle System

Abstract

As a new type of part-to-picker storage system, the double-deep multi-tier shuttle system has been developed rapidly in the e-commerce industry because of its high flexibility, large storage capacity, and robustness. The system consists of a multi-tier shuttle sub-system that controls horizontal movement and a lift sub-system that manages vertical movement. The combination of shuttles and lifts, instead of a stacker crane in conventional automated storage and retrieval system, undertakes inbound/outbound tasks. Because of the complex structure and numerous equipment of the system, task scheduling has become a major difficulty in the outbound operation of the double-deep multi-tier shuttle system. Figuring out methods to improve the overall efficiency of task scheduling operations is the focus of current system application enterprises. This paper introduces the task scheduling problem for the shuttle system. Inspired from workshop production scheduling problems, we minimize the total time of a batch of retrieval tasks as the objective function, applying the modified Simulated Annealing Algorithms (SAAs) to solve the task scheduling problem. In conclusion, we verified the proposed model and the algorithm efficiency, using case studies.

Relocation and storage assignment strategy evaluation in a multiple-deep tier captive automated vehicle storage and retrieval system with undetermined retrieval sequence

“…Shuttle carriers can travel on different tiers by using an elevator. Wang et al discussed a double-deep AVS/RS [21]. They assumed that the SKU dispatch order is not predetermined but that each SKU has a predefined time window in which it must also be retrieved.…”

“…In some cases, a numerical simulation was used for the verification of the analytical models. Only two scientific papers assumed some (partial) information of SKU shipping sequence [19], [21]. The rest were studying storage systems with undetermined SKU retrieval sequence.…”

“…The second strategy, also applied by other researchers, is the nearest neighbour (NN) strategy [4], [6], [7], [21], [22]. The SKU is stored or relocated to the nearest available empty location (Figure 3 left).…”

Task Scheduling Problem of Double-Deep Multi-Tier Shuttle Warehousing Systems

“…Their study also illustrated the relationship between the fill-grade factor and the total cost. Wang et al [5] and Lerher [22] studied task scheduling models for double-deep SR. Moreover, research on AS/RS has been widely conducted; Roodbergen et al [23] and Gu et al [24] have presented literature reviews in this area.…”

“…In a DMSWS, the double-deep SR has two storage position depths for storing SKUs. In most studies, the double-deep SR increases storage positions by 40-50%, compared with a single-deep SR [4,5]. The double-deep SR requires fewer aisles, resulting in higher space utilization.…”