Object Oriented Structuring of Real Time Control Systems

A real time system consists of two parts, a physical system further dissecteable into physical subsystems, and a ‘psychical’ system, comprising the computer control software. The structuring of such a real time control system is a major problem within the control engineering research area. As the number of I/O-signals increase, the system complexity manifolds exponentially. In this paper we will discuss how modern techniques borrowed from the computer science and artificial intelligence community can be used to handle that complexity. We propose the following: • Separate the control of the individual physical subsystems from the synchronization of the system as a whole. • This can be achieved by building software models of the physical subsystems, using the object oriented paradigm. • Encapsulate the control of the physical subsystem by implementing these models in two distinct parts, a general and a specific part. • Make the software models communicate by high level messages, specially designed for expressing the synchronizing aspects of the system. • Incorporate an application specific entity, a controller, that administers the message handling, and synchronization. Furthermore we discuss how this method fits into control of systems from discrete event manufacturing, as well as process industry. We also view our approach in relation to MMS, which utilizes a similar scheme, though not so intent on handling the synchronizing functions. Finally, we describe an FMS-workcell, controlled by software created with the above scheme in mind.