Deadlock prevention and performance oriented supervision in flexible manufacturing cells: A hierarchical approach

In this paper, a hierarchical control system is proposed for automated flexible manufacturing cells (FMCs) that operate in a job shop flow setting. The control system is made up of a higher level scheduler that optimizes the production flow within the cell, and a lower level supervisor that implements the decisions of the scheduler on the shop floor. To obtain the supervisor, a production schedule is transformed into an augmented Marked Graph (MG) model that can interact with the cell devices. Because of the flow complexities inherent in job shop systems, they are usually prone to deadlocks. Accordingly, this paper also proposes a necessary condition for deadlock occurrence in the scheduling phase. The proposed approach is validated by implementation in an experimental manufacturing cell.