A Study on Transformation from Ladder Diagram to SFC

A Ladder Diagram (LD) has been widely used in industrial world as a language for sequential control. LD, however, can not represent the sequential flow of control logic explicitly. This leads to the difficulty in understanding the control logic for a third party. To overcome this problem, Sequential Function Chart (SFC) has been proposed and used in many industrial applications. As SFC can represent the sequential flow exlicitly, it is expected to be used more widely in industrial world. To spread SFC in industrial world, it is necessary to develop the transformation algorithm from LD to SFC. This problem essencially means how to extract the information on the sequential flow of control logic from LD. In this paper, we propose a new technique to extract the information on the sequential flow of control logic from LD. The key ideas are firstly, to model the controlled machine with finite state automaton via synchronized composition technique and secondly to couple LD and the controlled machine so as to form the closed loop system. We show the concrete aigorithm to extract the information on the sequential flow of control logic based on this closed loop system.