Integer Programming Scheduling Model for Tier-to-Tier Shuttle-Based Storage and Retrieval Systems

Abstract

Shuttle-based storage and retrieval systems (SBS/RSs), a new type of “part-to-picker” system, have attracted public attention because of their flexibility and robustness. The systems consist of two sub-systems—shuttles and lifts—which are responsible for horizontal movements and vertical movements, respectively. SBS/RSs are categorized into tier-to-tier shuttles and tier-captive shuttles. This paper mainly researches SBS/RSs with tier-to-tier shuttles. New challenges have emerged since the commercial simulation-based optimization software has become widely applied for, for instance, task scheduling problems. Specifically, to decrease the idle time of lifts and the waiting time of shuttles, an integer programming scheduling model is proposed to minimize total task time with constraints on orders and devices. The Gurobi linear programming solver was utilized to obtain the optimal order sequence and the shortest operation time. The overall system efficiency was improved using our model. Moreover, the results are significant for reducing capital investment and operating cost.