Research On Optimal Scheduling For The 2-RGV System With Circular Rail During Storage Operations In Automated Storage And Retrieval System

A reasonable schedule for the rail-guided vehicle system,which is a vital part of the material handling system in the Automated Storage and Retrieval system(AS/RS),determines the efficiency of the AS/RS.However,during operation,the system can suffer from RGV collisions,unreasonable RGV assignments,and improper cooperation between RGVs and stackers,all of which impact the efficiency of the AS/RS and negatively affect its operation.There is little research on RGV collision avoidance,as almost all the existing research focuses on RGV dynamic scheduling,RGV scheduling rules,and RGV scheduling algorithms.Scholars have rudimentary discussed the problem of RGV collision avoidance under the zoned operation mode,but there are significant differences between RGV collisions in this operation mode and RGV collisions in general terms,as well as significant differences between adaptability of solutions.The paper deals with the storage scheduling problem of 2-RGV systems with circular rails in an AS/RS.A mixed-integer linear programming model is constructed to obtain an accurate solution to the problem.Taking into account the properties of the RGV scheduling problem,the VNTS-PSO algorithm is designed to achieve a feasible and satisfactory solution in a short time.The main research contents are described as follows:Firstly,this paper analyzes the optimal scheduling problem for a 2-RGV system with circular rail during storage operations in an AS/RS.The parameters and variables are derived from the realistic research hypothesis of the collision problem.To minimize the total storage time,constraints such as RGV sequence of transportation,RGV assignment,RGV priority,coordinated operation between the RGV and stacker,and RGV collision avoidance constraints are taken into consideration.A mixed-integer linear programming model is developed for the problem.Secondly,this paper presents two important topics,including RGV transportation order and RGV assignment by identifying the important variables that should be considered in the design of the algorithm.This paper explores the adaptability of intelligent optimization algorithms(genetic algorithm,particle swarm algorithm,variable neighborhood search algorithm,and tabu search algorithm),which are mainly used in the existing research on RGV scheduling,as well as the characteristics of the warehousing scheduling problem of a 2-RGV system with circular rail,and then proposes the initial idea of a VNTS-PSO algorithm.Furthermore,the key steps of the algorithm are explicitly presented from the perspectives of feasible solution coding,initial solution construction,fitness evaluation,tabu search strategy,variable neighborhood search strategy,particle swarm optimization algorithm,and termination criteria,which represent a possible normative deduction of the algorithm.Finally,based on the layout of an actual AS/RS,the series parameters of the 2-RGV system for the example experiment are developed and 15 examples of different scales of calculation examples are presented.Using CPLEX software,the VNTS-PSO algorithm,and hybrid scheduling rules,the examples are solved and results are compared.The experimental results show that CPLEX is capable of solving small-scale problems accurately,but is less efficient at solving larger-scale problems within the specified time.The VNTS-PSO algorithm proposed in this paper can facilitate the solution of small-scale problems,obtain an approximate optimal solution in a short time,and provide a more feasible and high-quality solution for medium-scale problems.In comparison with hybrid scheduling rules,the average storage time obtained by the VNTS-PSO algorithm is reduced by 31.35%.Furthermore,by analyzing the sensitivity and warehousing strategy of the same example under a variety of I/O stations,storage density,and storage location,three warehousing operations strategies for a 2-RGV system with circular rail are presented,which provides theoretical guidance for the efficient operation of real storage problems using a 2-RGV system with circular rail.