Abstract-Flexible job-shop scheduling problem (FJSP) is very important in many research fields such as production management and combinatorial optimization. The FJSP problems cover two difficulties namely machine assignment problem and operation sequencing problem. In this paper, a hybrid of particle swarm optimization (PSO) algorithm and tabu search (TS) algorithm are presented to solve the FJSP with the criterion to minimize the maximum completion time (makespan). In the novel hybrid algorithm, PSO was used to produce a swarm of high quality candidate solutions, while TS was used to obtain a near optimal solution around the given good solution. The computational results have proved that the proposed hybrid algorithm is efficient and effective for solving FJSP, especially for the problems with large scale.Index Terms -Flexible job shop scheduling problem; Particle swarm optimization; Tabu search algorithm; makespan
I. INTRODUCTIONFlexible job-shop problem (FJSP) is harder than the classical job-shop problem. In FJSP, one operation can be operated on a set of machines [1][2][3][4][5]. Therefore, FJSP should solve two problems: first, assign a proper machine from a set of machines to operation each operation; second, sequence each operation on every given machine. The former problem can be seen as a parallel machine problem, which is also a NP-hard problem. The latter is equal to a classical job-shop problem.The FJSP recently captured the interests of many researchers. The first paper about FJSP was proposed by Brucker and Schlie (Brucker & Schlie, 1990) discuss a simple FJSP model with two jobs and operations performed on any machines with the same processing time. To solve more genera FJSP problems with more than two jobs and machines, many researchers proposed hierarchical approaches, i.e., decomposing the problem into two stages: machine assignment sub-problem and job shop sub-problem. The first author to use the hierarchical idea was Brandimarte (Brandimarte, 1993) [3], who solved the first stage with some existing dispatching rules and the second stage with tabu search heuristic algorithms. Mati (Mati Rezg & Xie, 2001) [4] proposed a greedy heuristic for simultaneously dealing with the two stages. Liouane (Liouane, 2007) [5] illustrated a combined ant system optimization with local search methods, including tabu search for solving the FJSP problems. Saidi-mehrabad (Saidi-mehrabad, 2007) [6] gave a detailed solution for solving FJSP with tabu search method.In this paper, we give a new chromosome representation for the FJSP solutions, and propose some novel crossover and mutation functions for the particle swarm optimization algorithm. In each generation, we use tabu search algorithm to find near optimum solutions for the given best solution. After a detailed experiment, the result verifies that our novel method can get better solutions in very short period. The paper is organized as follows: in section 2, we introduce the problem definition; in section 3, some related algorithms such as particle swarm opt...