Intelligent Production Systems Reconfiguration by Means of Petri Nets and the Supervisory Control Theory

Abstract

The current trend in industrial production processes is to have agile and flexible systems that respond quickly to the permanent changes and disturbances in the production environment. This trend has created an important volume of research and papers aimed at having production control, supervision and programming systems that respond to these demands. Most of the proposals are grouped inside what has been labeled as Intelligent Manufacturing Systems (IMS). Among them are virtual, fractal, bionic, holonic manufacturing. These proposals initially appeared for discrete manufacturing processes. However, continuous production processes such as oil and gas, chemical plants, and power generation, also face demands for flexibility and rapid response. Therefore the IMS proposals can be applied to these types of processes. Holonic Production Systems (HPS) is one of the proposals that has advanced the most. It already shows evidence of its application in industrial systems. In general terms, a HPS is formed by autonomous entities that cooperate proactively to reach a common goal. These entities are labeled holons and, through aggregation relationships, they can form groups to form the so called holarchies. The grouping of various holons or holarchies with the objective of carrying out a productive process is called a Holonic Production Unit (HPU). The principal attributes of holons are: autonomy, cooperation, proactiveness, and reactivity. Other key characteristics are the distribution of intelligence and self-similarity to build complex structures from simpler systems. In order to achieve agility and flexibility, HPSs need distributed coordination and supervision functions. These functions enable them to dynamically reconfigure the production structure and the control laws to accommodate to the new operative conditions. Reconfiguration can only be faced if the production system has flexibility with regards to the allocation of manufacturing operations and of control architectures, which enable using different control policies for different types of services, or adapting control strategies to achieve new requirements.