Stochastic models for unit-load operations in warehouse systems with autonomous vehicles

This paper presents stochastic models for multi-tier warehouse systems that handle unit load transactions using autonomous vehicle-based technology. In this system, self-powered autonomous vehicles carry out unit-load transactions by moving along rails within a tier and using lifts or conveyors for vertical movement between tiers. We develop semi-open queuing network models to evaluate congestion effects in processing storage and retrieval transactions in this system. The queuing network is evaluated using a decomposition-based approach. The queuing model provides design insights on the effect of vehicle interference and vertical transfer mechanism on various system performance measures of interest. Insights from such studies can be especially useful during the conceptualization stage of warehouses that use autonomous vehicle technology.