On the Implementation of Discrete Event Supervisory Control with Focus on Flexible Manufacturing Systems
Doctoral thesis, 2002
In modern day production, the ability to quickly implement a control system is of increasing importance. In order to meet demands on shorter development times and easier reconfigurability, the design and implementation of the control system should be automated and provably correct. A reference architecture and methodology that supports automated design and implementation of flexible manufacturing systems has been developed at Chalmers.
Following the methodology, there are typically four phases from design to implementation. The phases are modelling of the plant, specification of the desired and legal behaviour, controller synthesis and implementation. Typically, the implementation consists not only of the synthesised controller, but also of functionality related to bookkeeping and diagnosis.
Tools are developed for obtaining deterministc models while still adopting object-oriented modelling principles. These models, representing a plant and a specification, may then be used within the framework of the supervisory control theory to synthesise a controller that keeps the closed-loop system within the specification. By using modular techniques, state space explosion may be avoided, or at least alleviated. For a certain class of resource allocation systems, often encoutered in flexible manufacturing, a non-brute-force synthesis procedure is developed.
Finally, we are able to implement modular supervisors in Programmable Logic Controllers using Sequential Function Charts. This is not straightforward since the operating conditions of the implementation is not the same as those that are assumed when modelling and synthesising controllers.