An improved genetic algorithm with an overlapping strategy for solving a combination of order batching and flexible job shop scheduling problem

The problem of flexible job shop batch scheduling represents an extension of the flexible manufacturing problem. Different batching strategy significantly affects the effect of subsequent scheduling optimization. Therefore, collaborative optimization of the batching strategy and subsequent scheduling is crucial for improving production efficiency. In this paper, a flexible job shop batch production model considering the set-up time is established by analyzing the coupling relationship between batching strategies and scheduling optimization. Based on the proposed model, an improved genetic algorithm with a three-layer coding mechanism is developed to solve the problem of the solution space expansion caused by batch collaboration. The three-layer coding mechanism includes the batch strategy, operation selection, and machine selection. In addition, an operation overlapping strategy is introduced to improve production efficiency and make production more resilient. The proposed algorithm is tested by experiments on scheduling problems of different sizes. The experimental result shows that the proposed method can significantly improve and efficiently optimize flexible job shop scheduling in batch production.