![]() Subsequently we used the discrete cycle time model, which is more accurate but for which the used exact methods require a significant computation time. First, we used a commonly used method to find the optimal ratios between the three spatial dimensions of the rack, using the continuous cycle time model. Finally, we proceeded to optimize the design of the studied system for a minimal cycle time. acceleration/deceleration and maximum velocity before validating these formulas by simulation. In a second step we developed new cycle time models but taking into consideration the operational characteristics of the S/R machines, i.e. This could be made using two modelling approaches, discrete and continuous. First, we modelled storage, retrieval and dual cycle times by considering constant velocities for the S/R machines (Storage/Retrieval). The main purpose was to carry out various mathematical models of different cycle times of this system in order to be able to evaluate its performance. In this Ph.D thesis we were interested in the study of the bidirectional flow-rack Automated Storage/Retrieval (AS/RS) system. Although the phased algorithm avoids the waiting of stacker in operation, the average value of its objective function is 12.14% higher than that of the proposed method, and the maximum deviation is more than 30%. Various numerical experiments show that the average deviation of the objective function value between the proposed method and CPLEX is no more than 0.4%, and the maximum deviation is only 1.22%. In order to adapt to the integrated optimization characteristics of the problem, a node structure with multi-I/O points is considered, and the probability selection formula of ant colony algorithm is improved for multiple pheromones. The complexity of the problem is analyzed without considering the I/O point assignment and double units transport (DUT). The problem is formalized as an integrated optimization problem with noncrossing constraint for the I/O point assignment and the storage/retrieval (S/R) requests grouping and scheduling. This paper researches the problem of operational optimization in the multiple-input/output (multi-I/O) points automated storage and retrieval system (AS/RS), where the destination addresses of the retrieval requests are unknown, twin stackers work simultaneously in the same aisle and cannot cross each other, and each stacker can carry two cargo units at the same time.
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