Production Activity Model


Category: Type 1 Model


Comments: While the MMCS model is very generic it is challenged by an even more generic model: the PAC (Production Activity Control) model. The PAC model was developed within the ESPRIT Project 477 entitled COSIMA (Control System for Integrated Manufacturing) [14].

One of the basic principles of PAC as shown in Fig. 4.3 is the recognition of five basic building blocks representing the functions required for production control: Scheduler, Dispatcher, Mover, Producer and Monitor. Communication between these building blocks is facilitated through the use of the Application Network which was developed as part of the project. This Application Network also supports message passing across different nodes thus providing the means to develop a distributed PAC system. MMCS and PAC models are limited to the shop and cell levels. A more global model for factory supervision and control was defined in the ESPRIT Project 932 to support decision making at all levels. This model is based on the NBS model and the GRAI model and uses an intelligent workcell controller concept. A controller (see Fig. 4.4) performs three basic tasks (Planning, Quality Control and Preventive Maintenance). Various expert system tools have been developed to support these controllers.

The knowledge based, real-time control, reference model enforces the decision making aspect by introducing some important concepts from the GRAI model, such as the Decision Horizon/Period and the Decision Frame, etc. The implemented system becomes totally goal oriented by means of the use of a 'decision frame'. The ESPRIT Project 932 finds its sequel ina new project; ESPRIT Project 2434 in ESPRIT 2.

The ESPRIT Project 2434 is concerned with real-time controllers for distributed factory supervision. The results achieved in ESPRIT 932 were used directly in ESPRIT 2434. The objective of this latter project is to make modern production philosophies (OPT, JIT, LOP, etc.) available on the factory floor by delivering decision support to each relevant function of the factory using knowledge based software techniques.

[14] Browne, J., Harken, J., and Shivman, J., Production Management Systems, A CIM Perspective, Addison-Wesley Publishing Company, Reading, Massachusetts (1988).


[1] Moss, S.P., 'A Management and Control Architecture for Factory-Floor Systems: From Concept to Reality,' Int. J. Computer Integrated Manufacturing, Vol. 2, No. 2, pp. 106-113 (March-April 1989).