An approach for performance evaluation of SBS/RS with shuttle vehicles serving multiple tiers of multiple-deep storage r
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ORIGINAL ARTICLE
An approach for performance evaluation of SBS/RS with shuttle vehicles serving multiple tiers of multiple-deep storage rack Michael Eder1 Received: 5 March 2020 / Accepted: 1 September 2020 / Published online: 21 September 2020 © The Author(s) 2020
Abstract This paper presents a method for determining the performance of shuttle-based storage and retrieval systems (SBS/RS) with tier-captive, single-aisle shuttles serving various numbers of tiers of multiple-deep storage. The use of this approach takes place in the design process of SBS/RS. The proposed approach considers the real operating characteristics of the shuttle and lifts. The basis of this calculation method is a continuous-time, open-queueing system with limited capacity. The cycle times of the lifts and shuttles, determined by a spatial value approach, can be used directly in the presented method with an assumed uniform distribution of storage locations and a probability-based model of storage depth. This approach is validated by a comparison with a discrete-event simulation. Finally, an example based on a system provided by a European material handling provider is presented to outline how this calculation model can be used for designing SBS/RS that fulfill predefined requirements. The result of this example is a decrease in the needed ground space with an increasing number of tiers served by each shuttle and with increasing storage depth. Keywords Automated warehouses · SBS/RS · Queue modeling · Multiple-deep storage rack · Performance analysis
1 Introduction Technological developments in the global supply chain have increased the requirements for physical storage technology. The reasons why warehouses are needed include the following: (i) an imbalance in the inflow and outflow of goods due to the mismatched dynamics of production and consumption, (ii) the combining of goods from numerous producers in single shipments, (iii) the realization of the daily supply of goods in their production and distribution, (iv) the realization of additional activities, such as packaging and final assembly [1]. An important part of meeting these requirements of automated warehouses is the autonomous vehicle storage and retrieval system (AVS/RS). The type of AVS/RS treated in this paper is a tier-captive system. In these systems, the shuttle is confined to a tier that it cannot leave. The main movement of the shuttle is in the horizontal direction, with limited mobility in the vertical Michael Eder
[email protected] 1
Institute for Engineering Design and Product Development, Vienna University of Technology, Getreidemarkt 9, 1060, Wien, Austria
direction. The shuttle vehicles are like short single-lane stacker cranes of AVS/RS. Furthermore, the lifts, positioned at the end of every storage aisle, transport totes only in the vertical direction. The common system treated in this paper has two lifts, one for input and one for output. Between these two transportation devices, buffer slots are located in each main tier. This leads to the indep
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