Implementation of Petri Nets Based Controller using SFC

Abstract

This paper presents a method for implementing a controller synthesized by PN-based SCT theory. Despite the great acceptance of SCT in controller design, there are problems with its practical implementation. Sequential Function Chart, as an international standard programming language, is used for implementing PN-based controllers. One problem in the implementation step is the occurrence of simultaneous events in mutually exclusive transitions. In SFC standards, it is possible to define a constant priority (e.g. left to right). A method for developing dynamic priority is presented in this research. If two users have requests for a common resource simultaneously, priority goes to the one that did not use the resource in the earlier turn. Existence of non-safe places in PN model is another problem in the implementation process. In this paper an alternative for this problem is also presented. Therefore, if the controller model becomes non-safe, it could implement using SFC. Finally the idea is demonstrated using an example.