Research On Modeling And Task Scheduling Optimization Of Double-deep Shuttle-based Storage And Retrieval Systems

With the rapid development of e-commerce,the form of products is becoming more and more diversified,the scale of products has been decreasing but the varieties have been increasing.Meanwhile the products can be delivered in a short cycle.As a core component of logistics transit,warehousing has an extremely important impact on the transportation cycle of products.The shuttle-based automated storage and retrieval system(SBS/RS)has attracted many industrial applications thanks to its high throughput and expandability in handling mini-load commodity.At present,there are some literature of analytical and simulation models for the SBS/RS used to analyze related performance data,in which,the work about the single-deep SBS/RS is more than the double-deep SBS/RS.It is a consensus that the lift has an extremely important impact on the warehousing efficiency.But the impact of different elevator patterns on the performance of a defined SBS/RS is not considered when they establish the model.For reducing delivery time,some researches concern about task scheduling optimization for a SBS/RS,and the objectives include one or more of the follows,as the shuttle carrier waiting time,and the total outbound time,etc.The rearrangement time of blocked totes caused by double-deep rack will directly affect the effective running time of the shuttle carrier.So in order to improve the efficiency of the shuttle carrier,the rearrangement time of blocked totes need to be considered.Hence,the thesis dedicates to these work for analyzing and optimizing the double-deep tier-captive SBS/RS with alternative elevator-patterns.On one hand,this thesis builds simulation models of single elevator pattern and double-elevator pattern,and analyzes the outbound workflow under the two models.Besides,the impact of different elevator patterns on the performance of a defined SBS/RS is analyzed.On the other hand,a multi-objective task scheduling optimization model is established,and the non-dominated genetic algorithm based on the elite strategy(NSGA-II)is applied to solve the problem of task scheduling optimization.A series of experiments are designed to verify this work.The contribution of this thesis have comprehensively improved the efficiency of warehouse from multiple perspectives.The main achievements of this paper are as follows:(1)In order to fill the current system modeling deficiencies,this thesis designs a double-deep tier-captive SBS/RS with both single elevator pattern and double-elevator pattern,analyzes the outbound simulation process,and calculates the critical running time and elevator efficiency.In addition,the elevator experiment was designed for verification,and the elevator efficiency in the shuttle waiting time and total outbound time was proposed,so as to help warehouse managers choose the appropriate elevator configuration under different throughput requirements.respectively on these two elevator-patterns(2)Aiming at the problem of task scheduling optimization,this thesis considers the rearrangement time of double-deep rack,and establishes a task scheduling optimization model with three objective of shuttle waiting time,rearrangement time,and total outbound time.the elite strategy based NSGA-II multi-objective optimization algorithm is adopted.In addition,the task scheduling experiment is designed respectively on these two elevator-patterns.This contribution improving the utilization rate of shuttle carrier and elevator,and reducing the time for outbounds.(3)To determine the storage density,this thesis designs storage load factor experiments on the basis of task scheduling optimization,verifies the characteristics of the shuttle system for dense storage and presents the best reference for the storage load factor range.This contribution improving the utilization of storage space rate.