Template-Type: ReDIF-Paper 1.0
Author-Name: Azadeh, K.
Author-Name-Last: Azadeh
Author-Name-First: Kaveh
Author-Name: Roy, D.
Author-Name-Last: Roy
Author-Name-First: Debjit
Author-Name: de Koster, M.B.M.
Author-Name-Last: de Koster
Author-Name-First: René
Title: Vertical or Horizontal Transport? - Comparison of robotic storage and retrieval systems
Abstract: Autonomous vehicle-based storage and retrieval systems are commonly used in e-commerce fulfillment as they allow a high and flexible throughput capacity. In these systems, roaming robots transport loads between a storage location and a workstation. Two main variants exist: Horizontal, where the robots only move horizontally and use lifts for vertical transport and a new variant Vertical, where the robots can also travel vertically in the rack. This paper builds a framework to analyze the performance of the vertical system and to compare its throughput capacity with the horizontal system. We build closed-queueing network models for this that in turn are used to optimize the design. The results show that the optimal height-to-width ratio of a vertical system is around 1. As a large number of system robots may lead to blocking and delays, we compare the effect of two different robot blocking protocols on the system throughput: robot Recirculation and Wait-On-Spot. The Wait-On-Spot policy produces a higher system throughput when the number of robots in the system is small. However, for a large number of robots in the system, the Recirculation policy dominates the Wait-On-Spot policy. Finally, we compare the operational costs of the vertical and the horizontal transport system. For systems with one load/unload (L/U) point, the vertical system always produces a similar or higher system throughput, with a lower operating cost compared to the horizontal system with a discrete lift. It also outperforms the horizontal system with a continuous lift in systems with two L/U points.
Length: 51
Creation-Date: 2016-12-19
File-URL: https://repub.eur.nl/pub/94838/ERS-2016-009-LIS.pdf
File-Format: application/pdf
Series: RePEc:ems:eureri
Number: ERS-2016-009-LIS
Keywords: internal transportation, robotic technology, queueing networks, performance analysis, blocking
Handle: RePEc:ems:eureri:94838