A. Grafcet and Petri nets

Overview

Grafcet is often used as a tool for specification of logic controllers. Many control system used in industry today, uses Grafcet (or the similar SFC, sequential function chart).  

The paper presents the fundamentals of logical controllers, i.e. a discrete system that changes its state depending on events. Further, the papers presents how Gracfet can be used to implement logical controllers. It describes the syntax of Grafcet (steps and transitions) and how to use conditions and actions, and gives an example of a logical controller implementation. The paper also discusses Petri nets.

Paper

R.David, 1993. Petri Nets and Grafcet for Specification of Logic Controllers. IFAC Proceedings Volume 26 Issue 2 part1, p. 683-688.  https://doi.org/10.1016/S1474-6670(17)49215-9 Links to an external site.

Assignment 

• What are the main similarities and differences between Grafcet and Petri nets?
• Is Grafcet a suitable tool for specification of a logical controller? Is Petri nets a suitable tool?
• Show how you would make a specification of a PID-controller in Grafcet (e.g. the controller in Lecture X)?
• In order to implement the specification of the PID controller, an interpretation algorithm is needed? Explain the purpose of the interpretation algorithm. 

Communication

There are scheduled sessions on zoom where a group can discuss their questions with Charlotta, you can book a time here.

Project discussion

The three groups will meet in a Zoom meeting and discuss their results and working process on Tuesday May 26, 13.15-15.00. https://lu-se.zoom.us/j/68900702902