Copyright © IFAC Low Cost Automation, Buenos Aires, Argentina, 1995 THE APPLICATION OF ENHANCED MARK FLOW GRAPH IN REAL TIME CONTROL SYSTEMS P. E. Miyagi*; L. M. Camarinha-Matos**; D. J. Santos Filho*; J. Barata** and J. Arakald* *Universil/ade de Siio Paulo - Escola Politecnica Av. Pro! Luciano Gualberto - Trav 3, N.,380, CEP 05508-900 - Sao Paulo, SP,- Brasil **UniversUiade Nova de Lisboa and Uninova Institute Quinta da Torre - 2825 Monte Caparica - Portugal Abstract: The aim of this work is the evaluation of the modeling power of Enhanced Mark Flow Graph (E- MFG) when dealing with flexible manufacturing systems and the presentation of an approach to link the models to the real system. Main concepts regarding E-MFG and its application in the description of the control part are described as well as the operative part of production systems. Through the information associated with the structural components of E-MFG it is possible to represent complex control strategies involving different tasks of the manufacturing systems in a highly flexible environment. An object oriented approach for integrating the various heterogeneous controllers available in a manufacturing system is presented, resulting in an abstract machine that realizes the operative part and, thus, ensures the link between the E-MFG models and the physical system. Keywords: discrete event dynamic system, Petri nets, Mark Flow Graph, manufacturing system, system integration 1. INTRODUCTION The difficulty in controlling a flexible manufacturing system is strongly related to its level of automation and flexibility. On the other hand, the concept of automatic process control can be generalized to the case in which the control object is a dynamic production system driven by events, i.e., a discrete event dynamic system - DEDS (Santos F", 91) (Ho, 89). Therefore, this work approaches the problem of controlling a flexible manufacturing system with high functional flexibility which can be treated as DEDS. Recently, the technological evolution of the equipments used in automated manufacturing systems has increased substantially the degree of automation of these systems. In this way, increases in the functional flexibility of manufacturing systems meet the changes of the market dynamics with high degree of autonomy. Nevertheless, in a shop floor we can find a large variety of controllers, representing various generations of technology. 147 Mark Flow Graph - MFG (Hasegawa, 84) (Masuda, 81) is a technique derived from Petri nets (Reisig, 92) that is effective to represent and control the dynamic behavior of DEDS in special cases where the system must be described and controlled in a distributed way. The major property of the MFG is that it explicitly describes the control strategy of independent, sequential and concurrent events. However, there are some problems related to the modeling of systems with complex dynamic behavior involving non trivial control rules. To represent the control rules in a consistent manner it is necessary to consider several sub-graphs that need to be synchronized. The resultant graph is difficult to be interpreted and analyzed. This aspect motivated the proposition of extensions to MFG to increase i;s modeling power and a methodology to represent Integrated Manufacturing Systems (IMS) by subsystems that operate cooperatively. In this context, the Enhanced Mark Flow Graph - E-MFG (Santos P, 93) is based on individualized marks* and additional rules to control the transitions firing. * These concepts will be presented in detail in the following sections.