Modelling and analysis of autonomous vehicle storage and retrieval systems

Autonomous Vehicle Storage and Retrieval Systems (AVSRS's) utilize bi-directional, rail-guided vehicles moving in rectilinear paths within and between the aisles of storage racks and vertically movement from lifts installed at fixed locations along the storage rack periphery. They represent an alternative technology for automated unit load storage and retrieval, an industry now dominated by crane-based automated storage and retrieval systems (ASRS's) where aisle captive cranes provide more efficient movement patterns owing to simultaneously horizontal and vertical movement. However, AVSRS technology offers other advantages including lower cost and greater flexibility to adjust capacity to the throughput demand of a system. This technology has the potential to dramatically increase the cost effectiveness of automation in lower throughput unit load storage systems. This research investigates computationally efficient design conceptualization models for automated unit load storage and retrieval systems based on autonomous vehicle technology. Vehicle and lift travel times and the probability distribution for alternative service scenarios occurring under realistic operating assumptions are modelled to generate expected transaction service times for all types of unit load storage configurations. Additional issues including transaction and vehicle queuing dynamics and the impact of alternative storage policies are investigated in order to develop practical design tools for predicting key aspects of system performance based on the key drivers of system cost.