METHOD FOR DRAWING LADDER DIAGRAM USING PETRI NET

摘要

PURPOSE: A method for drawing a ladder diagram using a petri net is provided to form a PLC(Programmable logic Controller) program by converting a petri net to a ladder diagram. CONSTITUTION: A petri net is drawn by analyzing operations and states requested from a controlled system(S101). All activated places are obtained from input places connected to a normal arc and an enabling arc on the basis of input transition in the petri net(S102). All places which do not have tokens are obtained from the input places connected to a prohibition arc in the petri net(S103). Each state condition of the obtained places, conditional inputs and event inputs of the input transition are obtained(S106). The tokens are added to the corresponding place if the input transitions related to the conditional inputs of the corresponding place are started(S107,S108). The number of the activated transitions is obtained from the output transitions satisfying a starting condition connected to the normal arc of the corresponding place(S109). The tokens are removed from the corresponding place if the output transitions are started(S110,S111). A Boolean numerical expression for the corresponding place is obtained(S112). A ladder diagram is drawn by using the Boolean numerical expression for the corresponding place(S115).