Optimization Of Real-time Storage Location Assignment In Automated Storage And Retrieval System

Automated Storage/Retrieval System (AS/RS) is the most important tool used in modern logistics, so it is desirable to optimize the storage location assignment problem in AS/RS for reducing travel time of crane. This paper concerns storage location assignment in unit load AS/RS. It can be divided into two aspects: assign the bin for the storage unit; choose the bin for retrieval command.With the consideration of the impact of crane's acceleration and deceleration on crane's velocity,the total travel time of crane's current operation and subsequent operations is used as the optimization object. Then three optimization goal functions are developed by changing the weights of the crane's subsequent operations. To prevent the situation that some items stay in the racks too long, the upper limit for the items'storage time is setted.The problem is solved by the genetic algorithm combined with simulated annealing while kinds of methods are used to improve the algorithm's efficiency. To reduce the running time of the program, another algorithm which only uses simulated annealing is also designed.The algorithm is evaluated in different conditions by changing the number of product types, the strategy of setting the weights in the objective function, the sequencing rule of retrieval queue, crane's dwell point and capacity in numerous simulations. The result shows that the crane's dual command cycle travel time can be reduced less by the algorithm when the capacity of crane is one unit. When the capacity of crane is large than one unit, the crane's expected travel time can be reduced quite large by the algorithm. Besides, the difference between the functions using the changeable weight and fixed weight is small. The algorithm which only uses simulated annealing can reduce the running time greatly, but it is not good at reduing the crane's expected travel time.