Multi-Objective Approach with a Distance Metric in Genetic Programming for Job Shop Scheduling

The goal of the Fourth Industrial Revolution is to develop smart factories that ensure flexibility and adaptability in complex production environments, without human intervention. Smart factories are based on three main pillars: integration through digitalization, employment of flexible structures, and the use of artificial intelligence (AI) methods. Genetic programming (GP) is one of the most promising AI approaches used in the automated design of production-scheduling rules. However, promoting diversity and controlling the bloating effect are major challenges to the success of GP algorithms in developing production-scheduling rules that deliver high-quality solutions. Therefore, we introduced a multi-objective technique to increase the diversity among GP individuals while considering the program length as an objective to avoid the bloating effect. The proposed approach employs a new diversity metric to measure the distance between GP individuals and the best rule in the current generation. Subsequently, the non-dominated sorting genetic algorithm II (NSGA-II) was used to select individuals based on three objectives: solution quality, similarity value, and program length. To assess the effectiveness of the proposed approach, we compare the two versions with three GP methods in the literature in terms of automatically generating dispatching rules on 10 benchmark instances of the job-shop scheduling problem. The experimental results show that the proposed distance measure enhances the phenotypic diversity of individuals, resulting in improved fitness values without the need for additional fitness assessments. In addition, the integration of NSGA-II with the GP algorithm facilitates the evolution of superior job shop dispatching rules with high diversity and shorter lengths under the makespan and mean tardiness objectives.