Using a Petri-net-based approach for the real-time supervisory control of an experimental manufacturing system

A new Petri-net-based design technique, called the inhibitor arc method, fo r the synthesis of compiled supervisors for discrete event systems is used to solve a forbidden state problem in an experimental manufacturing system. The technique used offers the following advantages: 1. The closed-loop (i.e. controlled) behaviours of the systems are non-bloc king and do not contradict the forbidden state specifications. 2. The closed-loop behaviours of the systems are maximally permissive withi n the specifications. The supervisors to be synthesised consist of a controlled automation Petri net (APN) model of the system. Automation Petri nets include the following extensions to the ordinary Petri-net framework: sensor readings as firing c onditions at transitions and actions assigned to places. Ladder logic diagr am (LLD) code is used to implement the supervisors on programmable logic co ntrollers (PLC). It is important to note that the supervisors obtained are correct by construction, therefore there is no need for verification. This paper particularly shows the applicability of previous results [1] to low-l evel real-time control where the role of the supervisor is to arrange low-l evel interaction between the control devices, such as motors, actuators, et c. This is done by considering an experimental manufacturing system.