Computer Model for Supervisory Control of Discrete Event Systems in Electrical Industry Using PLCs

The Supervisory Control Theory (SCT) is a general technique used to design a controller for Discrete Event Systems (DES) such as production/manufacturing systems, cybernetic systems, communication systems, transportation systems and many others. Resulted controller for the DES is named a supervisor. The SCT involves many formal languages and automata concepts for supervisor synthesis. In SCT, any manufacturing plant can be modeled by using automata. This automaton is a true event sequence generator. By using SCT, a supervisor can be synthesized for avoiding plant from some undesired states in all conditions. The Programmable Logic Controllers (PLC) is widely used to perform control tasks in modern industry. It is also clear that, the supervisor is commonly implemented by means of PLCs. The most popular computing language for programming PLCs is Ladder Logic Diagrams (LLD). The supervisors in automata form can be easily converted to LLD code. In this paper, fundamental information about SCT is presented. As an example a small manufacturing systems that consist of two machines and a buffer is considered. This is a new approach for solving an industrial process issue consisting on a PCB which is transferred from a component soldering machine to another, using a buffer. The implementation methodologies of all supervisor techniques are also provided, in order to increase the speed/productivity of the whole process.