The authors propose the Mark Flow Graph for the purpose of theoretical systematization of the sequential control.
Sequential control systems are regarded as the event-conditon systems which are activated by mutual connections between events and conditions. These systems have such fundamental features as asynchronism, ordering, concurrency and conflict, and unsafeness and deadlock will happen to them. Petri net is one of the effective means to represent the systems with these properties and phenomena.
The authors modify the concept of Petri net to develop the design and analysis tool for sequential control systems taking the safeness and notation of input/output functions into consideration. Mark Flow Graph (MFG) is proposed as such a new kind of graph. The paper deals mainly with the definitions and rules of MFG, and also with the basic subjects about its structure, structual properties and deadlock phenomenon.