論理間移行の頻度判定によるラダー図から制御フローへの変換方式

抄録

In sequential controllers of plants, ladder diagram is one of major programming languages. However, it is difficult to understand their control sequence and to maintain them because ladder diagram does not clearly represent the sequence of plants' behaviors. Sequential Function Chart (SFC), which is based on Petri net, recently spreads as a powerful graphical description of sequential logic. SFC can represent clearly the sequence of control programs. Therefore, the method to translate ladder diagram into SFC is required.
In this paper, control sequence extraction method is proposed. In this method, a tentative SFC is created by searching all actually possible states by using transitions in the ladder diagram. However, the tentative SFC description can be complicated because of existance of non-order control, which does not depend on fixed sequence, for example manual control. Therefore, sequential flows of plants' behaviors in the tentative SFC are extracted according to the difference of transfer frequency between order control and non-order control, and the check of both-way control included by non-order control.
Through an application of the proposed method to a practical plant model, it is confirmed that the adequate sequence which represents the original plants' behaviors is extracted from ladder diagram.