Title: A simulation framework for studying blocking effects in warehouse systems with autonomous vehicles

Authors: Debjit Roy; Ananth Krishnamurthy; Sunderesh S. Heragu; Charles J. Malmborg

Addresses: Indian Institute of Management Ahmedabad Vastrapur, Ahmedabad 380015, India ' Department of Industrial and Systems Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA ' School of Industrial Engineering and Management, Oklahoma State University, Stillwater, OK 74078, USA ' Department of Industrial and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA

Abstract: Autonomous vehicles-based storage and retrieval systems (AVS/RS) have been shown to offer greater flexibility to improve cycle time and throughput capacity in the transfer of unit loads in high-density storage areas of warehouses. In these systems, loads are transferred by autonomous vehicles that move horizontally along aisles and cross-aisles within a tier, while lifts support vertical movement of loads between tiers. For analytical tractability, prior studies on performance evaluation of AVS/RS have ignored the blocking effects of vehicles and lifts while estimating throughput capacity and cycle times. To evaluate the effects of blocking on system performance, this paper first develops protocols to address vehicle blocking that are subsequently incorporated in a detailed simulation model. The blocking effects are studied for a variety of tier configurations that differ in depth/width ratio, number of locations, number of available vehicles, and transaction arrival rates. Results suggest that blocking delays could account for 2%-20% of the transaction cycle times. [Received 17 October 2013; Revised 28 August 2014; Revised 23 December 2014; Accepted 2 April 2015]

Keywords: storage and retrieval systems; unit load operations; simulation; blocking effects; warehouse systems; autonomous vehicles; warehousing; cycle time; throughput capacity; system performance; vehicle blocking; blocking delays.

DOI: 10.1504/EJIE.2016.075100

European Journal of Industrial Engineering, 2016 Vol.10 No.1, pp.51 - 80

Available online: 03 Mar 2016 *

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