Integrated scheduling of resource-constrained flexible manufacturing systems using constraint programming

• A new constraint programming formulation for the FMS scheduling problem is proposed.
• Machines, tools, as well as empty and loaded AGV trips are taken into account.
• All the FMS critical features are addressed in an integrated way.
• Optimal and good-quality suboptimal solutions were found for the case-studies.
• The transfer/processing times ratio has an important impact on the solution.

This contribution presents a novel approach to address the scheduling of resource-constrained flexible manufacturing systems (FMSs). It deals with several critical features that are present in many FMS environments in an integrated way. The proposal consists in a constraint programming (CP) formulation that simultaneously takes into account the following sub-problems: (i) machine loading, (ii) manufacturing activities scheduling, (iii) part routing, (iv) machine buffer scheduling, (v) tool planning and allocation, and (vi) AGV scheduling, considering both the loaded and the empty movements of the device. Before introducing the model, this work points out the problems that might appear when all these issues are not concurrently taken into account. Then, the FMS scheduling model is presented and later assessed through several case-studies. The proposed CP approach has been tested by resorting to problems that consider dissimilar number of parts, operations per part, and tool copies, as well as different AGV speeds. The various examples demonstrate the importance of having an integrated formulation and show the important errors that can occur when critical issues such as AGV empty movements are neglected.