Robust Solutions to Job-Shop Scheduling Problems with Operators

The job-shop scheduling problem with operators is an extension of the classical job-shop scheduling problem where each operation has to be assisted by one operator from a limited set of them. We confront this problem with the objective of obtaining robust schedules and minimizing the make span. In this way the problem becomes more difficult but more interesting from a practical point of view. We propose to solve the problem in three steps. In the first one, the JSP relaxation (without operators) is modeled and solved using a CSOP solver with the objective of minimizing the make span. Then, the solution is modified to include operators, in this step robustness is introduced by means of a set of buffers in the operators sequences. Finally, these buffers are uniformly distributed among the operations that are not involved in a critical path. We have conducted an experimental study showing that the proposed method reaches a good trade-off between robustness and optimality.