A generic event control framework for modular flexible manufacturing systems

A generic event control framework is presented for a class of modular flexible manufacturing systems (FMSs). A modular FMS is characterized as a set of flexible workstations inter-connected by a material handling system consisting of a transporter and a stocker. Many of the existing FMS implementations in industry fall into this class. Furthermore, the modularity also allows the capability to effectively model a complex FMS by decomposing it into several modular FMSs. In order to achieve reconfigurability of control system for various FMS implementations and control policies, the proposed control framework is defined as a set of distributed resource controllers and a central system supervisor coordinating them. The resource controllers are further classified into workstation, transporter, and stocker controllers. As the controllers exchange a series of events according to pre-defined protocols, they are modelled as event handlers in which control actions are made based on the event occurrences. Specifically, for each controller, an event-based control structure specified in terms of generic logical and performance control functions, is presented. Since the proposed framework is defined by the use of the interacting distributed processes with the well-defined protocols and computationally efficient algorithms, it is expected that the framework is easily implementable for most industrial FMSs. Finally, the performance and reconfigurability is demonstrated by the distributed simulation from which we can also verify the correctness of the proposed algorithms.