Research on structural analysis for the Petri-net representing sequential function chart

In recent years, sequential control systems have become complex with increasing requirement specifications. Therefore, it is important to find bugs which might be contained in a sequential control system at each development phase. Currently, a main method for analyzing the system is behavior analysis. Though, we consider that it is necessary to analyze control structures of the system before behavior of that is analyzed. The control structures consist of loop, alternative and parallel structures. These structures are corresponding repeat, selection and parallel controls which are typical in control systems. We call structural analysis to detect and to distinguish these controls. By comparing both the results of the structural analysis and requirement specifications, the system can be verified. The purpose of this research is to shake out the bugs. This paper shows a method for analyzing control structures about sequential function chart elements which are defined by IEC 61131-3. Using the method, we can find the bugs, and we can fix the bugs before behavior of the system is analyzed. Therefore, we consider that structural analysis contributes improvement of productivity.