Integrating machine scheduling and transportation resource allocation in a job shop: a simulation approach

In scheduling problems with fixed routing, usually the transportation of jobs among the machines is not considered (i.e., the transportation time between two stages is negligible, and the number of transportation resources is unlimited). However, in real contexts, this assumption can be unrealistic, especially when human supervision is needed for transportation, and hence not considering transportation can lead to low quality scheduling solutions. This paper considers a job shop in which transportation resources are limited and free to move among all the machines (no fixed routes). The aim is the integration of machine scheduling and transportation resource allocation, i.e., to decide for each machine the job sequence, and for each free transportation resource the routing. Due to the complexity of the problem, a Discrete Event Simulation approach is used to compare different scheduling and transportation resource allocation policies through scenario analysis