A Model and a Task Scheduling Method for Double-Deep Tier-Captive SBS/RS With Alternative Elevator-Patterns

The last decade has brought the blooming of shuttle-based automated storage and retrieval system (SBS/RS) in many industrial applications thanks to its high throughput and expandability in handling mini-load commodity. In the paper, we focus on a double-deep tier-captive SBS/RS. Specifically, we propose a simulation model to support analyzing the performance related data of a double-deep tier-captive SBS/RS with both single-elevator and double-elevator patterns. The data includes shuttle carrier waiting time, elevator idle time, and total outbound time. Then, the impact of system performance due to two different elevator-patterns has been analyzed quantitatively. Based on the model, an optimization model and an improved NSGAII algorithm for task scheduling are designed, which can make the SBS/RS achieve the shortest shuttle carrier waiting time, rearrangement time and total outbound time. Experiments are conducted considering diverse task sizes and load factors, and the two elevator-patterns in a SBS/RS. The results show that our work can optimize the performance of the SBS/RS and assist stakeholders to decide more economical elevator-pattern.