Decentralized execution of Sequential Function Charts

Programmable Logic Controllers (PLCs) are widespread in the control of industrial production system. For the specification and the implementation of PLC programs, the language Sequential Function Charts (SFC) is increasingly used in industry. The reaction time of a PLC is a fundamental matter in discrete event control systems. Most industrial PLCs run their programs in an interpreted and centralized manner. The PLC reads the inputs, runs the SFC interpreter (also called coordinator in this paper) and writes the outputs. In this work we propose and analyze a new technique for the execution of SFC programs, the decentralized implementation, where several interpreters execute the SFC program of the PLC in concurrence. This implementation is compared to the centralized one. Also, a new technique with the aim of optimizing the degree of decentralization is proposed.