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 d...

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

This paper presents a multi-objective optimisation solution procedure for the design of the Shuttle-Based Storage and Retrieval System (SBS/RS) An efficient SBS/RS design should take into account multi-objectives for optimization In this study, we considered three objective functions in the design concept which are the minimization of average cycle time of transactions (average throughput time), amount of energy (electricity) consumption and total investment cost By also considering the amount of energy consumption as an objective function for minimization, we aimed to contribute to an environmentally friendly design concept During the optimization procedure, we considered seven design variables as number of aisles, number of tiers, number of columns, velocities of shuttle carriers, acceleration/deceleration of shuttle carriers, velocity of the elevators lifting tables and acceleration/deceleration of the elevators lifting tables Due to the non-linear property of the objective function, we ut

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Multi-objective optimisation model of shuttle-based storage and retrieval system

The performance of a storage policy in a warehouse is usually evaluated on the basis of the average one-way travel distance/time needed to store/retrieve a load. Dividing the storage space into zones based on item turnover frequency can reduce the travel distance. However, for a given number of stored items, a larger number of storage zones also requires more storage space, because of reduced space sharing between the items, which increases travel time. This study considers the required space consumption by storage zoning in comparing the performance of random, full turnover-based and class-based storage policies for a unit-load warehouse operated by a forklift in single-command mode. A generalised travel distance model that considers the required space consumption is developed to compare the performance of these policies. Results show that the one-way travel distance of a random policy decreases with the increase in skewness of the demand curve. By considering the required space consumption, a class-base...

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Impact of required storage space on storage policy performance in a unit-load warehouse

Multi-tier shuttle warehousing systems are increasingly popular because of their high flexibility and robustness. These systems consist of a multi-tier shuttle sub-system that controls horizontal movement and a lift sub-system that manages vertical movement. The combination of shuttles and lifts undertakes inbound/outbound tasks instead of the stacker crane in conventional automated storage and retrieval systems. Scheduling different devices to reduce expected cycle time is an important concern. Thus, we propose a time sequence mathematical model of task operation on the basis of the movement characteristics of shuttles and lifts. The task scheduling problem between shuttles and lifts is converted into an assembly line parallel job problem by analysing the mathematical model, which generates the scheduling task queue model in the specified time window. In addition, a Pareto optimal based on an elitist non-dominated sorting genetic algorithm is adopted to solve the multi-objective optimisation function in ...

Task scheduling for multi-tier shuttle warehousing systems

Comparing with traditional single-deep single-shuttle automated storage/retrieval systems, double-deep dual-shuttle AS/RS have the advantages of high space utilisation and more efficient, since less number of aisles and less empty travel of S/R machine. This warehousing systems have been developed for use in factories and distribution centres. In this paper, we first develop analytical models of quadruple command cycle to estimate the performance of such system, then taking the single shuttle and dual command cycle as the benchmark model, the potential improvement by dual shuttle has been analyzed, the results show that the efficiency of the system has a significant improvement using dual shuttle S/R machine. In addition, we have extended the proposed travel time to a special case that the double empty storage locations will take place and some management insights are given.

Travel time analysis for the double-deep dual-shuttle AS/RS

Acceleration and deceleration of the AS/RS machine in automated storage and retrieval systems are considered in this paper instead of uniform speed, and there are curve channels in the warehouse. Based on the above hypothesis, the time function and distance function are studied in this paper. The distribution function of the distance and time is given. On this basis, the expected travel time of the automated storage and retrieval system is studied. Finally, a numerical example is given to draw the conclusion that this model is more practical.

Analytical travel time models for multi-aisle automated storage and retrieval systems

Multi aisle automated storage and retrieval systems correspond to multiple picking aisles served by a single storage and retrieval machine. We use this system for saving the initial investment costs due to single aisle systems. The objective of the presented study is to develop analytical travel time models for multi aisle automated storage and retrieval systems considering the operating characteristics of the storage and retrieval machine. Acceleration and deceleration of the storage and retrieval machine is considered in this paper instead of uniform speed, and there are curve channels in the warehouse. Based on the above hypothesis, the time function and distance function are studied in this paper. The distribution function of the distance and time is given. On this basis, the expected travel time of the automated storage and retrieval system is studied. Finally, a numerical example is given. The results show that proposed analytical travel time models perform satisfactory according to the results and could be very useful tools for designing of multi aisle automated storage and retrieval systems in real-world applications.

Hong-yuan Shi

Papers

Analytical travel time models for multi-aisle automated storage and retrieval systems

Travel time analysis of the single and dual command of AS/RS