Research Of AGV Assignment Considering Charging Factors At Automated Container Terminals

The horizontal transportation system is responsible for connecting the two complex operating systems of the berths and the yard.It is considered to be one of the key links that affect the overall efficiency of the automated container terminal.The automated terminal horizontal transportation system dispatches a limited number of Automated Guided Vehicles(AGVs)to repeatedly transport import and export containers in a closed operation area.Because the number of containers is too large,it is difficult to allocate AGVs to form a reasonable operation sequence,which further leads to lower AGV utilization and increases transportation costs.In addition,the AGV is usually driven by pure electric power,which has the characteristics of high efficiency and no emissions.However,due to the limited battery capacity,the AGV has a shorter maximum travel distance.So,this paper choose the suitable charging time when assigning operation tasks to the AGV.This can improve the utilization of AGV,reduce the operation cost of the horizontal transportation system and also ensure the efficiency of the operation of the automated terminals.At first,this paper design a space-time network diagram to describe the AGV transportation task and charging process.On the basis of the diagram,we construct an optimization model for AGV task allocation and charging timing selection with the goal of minimizing AGV transportation costs.This model can effectively reduce the complexity of the traditional task allocation model and accurately characterize the charging process in the AGV scheduling process at same time.Secondly,the model is decomposed by the Dantzing-Wolfe principle into a path-based set partitioning main problem and the shortest path sub-problem with resource constraints.Placing the constraints of different properties in different part and solving them separately can reduce the complexity of the model.Thirdly,a solution algorithm based on the branch and price algorithm is designed to improve the accuracy of the solution and even get the exact solution of the model.Finally,in order to verify the effectiveness of the model and algorithm,the nonlinear constraints of the model are linearized and accurately solved by CPLEX,whose results is compared with the results of the algorithm in this paper.The algorithm of this paper is also tested by solving the practical examples of different sizes in terminals.A large number of experimental results show that the models and algorithms proposed in this paper can get a reasonable charging time,optimize AGV task allocation and operation sequence,and effectively reduce the operation cost of horizontal transportation systems.The algorithm in this paper can greatly improve the solution quality of the model and obtain the AGV task sequence containing the charging task within an acceptable time,which can be effectively applied to the actual scheduling of the terminal AGV.At the same time,the sensitivity analysis of the maximum driving distance reveale the influence of AGV battery capacity changes on the number of AGVs used and the number of charging times.