Travel time model for double-deep shuttle-based storage and retrieval systems

Abstract

Technological developments in the global supply chain have changed processes in warehousing. This reflects in short response time in handling the orders, which has a consequence on high automation degree in warehousing. An important part of automated warehouses is presented by shuttle-based storage and retrieval systems (SBS/RS), which are used in practice when demand for the throughput capacity is high. In this paper, analytical travel time model for the computation of cycle times for double-deep SBS/RS is presented. The advantage of the double-deep SBS/RS is that fewer aisles are needed, which results in a more efficient use of floor space. The proposed model considers the real operating characteristics of the elevators lifting table and the shuttle carrier with the condition of rearranging blocking totes to the nearest free storage location during the retrieval process of the shuttle carrier. Assuming uniform distributed storage locations and the probability theory, the expressions for the single and dual-command cycle of the elevators lifting table and the shuttle carrier have been determined. The proposed model enables the calculation of the expected cycle time for single- and dual-command cycles, from which the performance of the double-deep SBS/RS can be evaluated. The analysis show that regarding examined type of the double-deep SBS/RS, the results of the proposed analytical travel time model demonstrate good performances for evaluating double-deep SBS/RS.

Keywords:

• Automated warehouses
• Double-deep system
• Shuttle-based storage and retrieval systems
• Analytical modelling, performance analysis

Disclosure statement

No potential conflict of interest was reported by the author.

Notes

1. For a detailed representation of the above mentioned conditions, see papers from Lerher et al. (2005) and Hwang and Lee (1990).

2. For a detailed representation of the above mentioned conditions, see papers from Lerher et al. (2005) and Hwang and Lee (1990).

3. Since the elevator Config. 3 proves to be the most efficient, the expected dual-command cycle times and the throughput capacity of Config 3. with the velocity profile vp₃ (Table 5), have been used.