Study on a transformation method of ladder diagram into sequential function chart on the basis of linear programming technique

Ladder diagrams (LD) have been widely used in industries as a programming language for PLCs. However, the LD can not represent sequential flows of control logic explicitly. On the other hand as the sequential function chart (SFC) can explicitly represent the sequential flow in the control logic: the SFC is expected used more widely than the LD. Because much know-how with respect to sequential controls have been accumulated in the LD of the existing systems, for the promotion of SFC, it is preferable to develop a transformation technique from the LD to the SFC. In this paper, first we suggest the necessity of the modeling of control plants for the LD transformation into the SFC using a conceptual example. Secondly we proposed a new algebraic analysis method that transforms the state equations of the total system into simultaneous linear inequalities whose solution can be sought with linear programming techniques