An Adapted Variable Neighborhood Search based algorithm for the cyclic multi-hoist design and scheduling problem

International audienceThis paper studies both the design and the cyclic scheduling of multi-hoist treatment surface facilities. Former research have always assumed that the design of the production line is already available with a fixed material handling fleet size. However, in this study, the number of hoists is considered as a decision variable of the problem. The latter is then bi-objective and called the Cyclic Hoist Design and Scheduling Problem (CHDSP). The optimization objective is to determine an optimal cyclic schedule for each possible number of hoists that minimizes the cycle time and thus maximizes the line throughput rate. The achieved results will contribute to building a decision support system that will enable to choose the required number of transportation resources for the production line regarding both aims of productivity maximization and cost savings. An original encoding approach is proposed that both assigns a number of hoists to the line and generates their move sequences, which are evaluated thanks to a mixed integer linear programming model. A rich and well-structured solving algorithm based on variable neighborhood search is developed and adapted to solve efficiently the whole problem. It is also improved by a backtrack procedure that further enhances the findings. Computational experiments are conducted on benchmark problems and demonstrate the high performance and effectiveness of the proposed algorithm that was, in most cases, even able to reach the optimal solutions