Implementing a discrete-event-system-based supervisory controller for a flexible manufacturing workcell

In this paper, a generalized implementation of DES-based supervisory controller methodology, that utilizes recent theoretical advances in conjunction with programmable-logic-controller (PLC) technology, is presented. The two primary advantages of the proposed methodology are: 1) the utilization of limited-size control strategies that can be efficiently generated online, and which are conflict and deadlock free by construction; and 2) the use of PLCs, which are currently the most suitable and widely employed industrial process-control technology. In our proposed methodology, a host personal computer (PC) possesses an online capability for the automatic generation of supervisory-control strategies, and their downloading to a PLC as required. The PLC, in turn, is responsible for monitoring the workcell reacting to events and enforcing device behaviour based on the current control strategy residing in its processor. A supervisory controller developed based on this approach, was successfully implemented for a manufacturing workcell in our laboratory