Signal-Interpreted Coloured Petri Nets: A modelling tool for rapid prototyping in feedback-based control of discrete event systems

Petri nets (PNs) are typically used for design and verification rather than direct control implementation. In this paper, aligning with the Industry 4.0 paradigm's focus on flexible and reconfigurable control systems, we propose a modelling tool for rapidly prototyping feedback-based discrete-event control algorithms on programmable controllers such as PLCs or microcontroller boards. This modelling tool, named Signal Interpreted Coloured Petri Nets (SICPNs), aims to combine the formal modelling expressiveness of Coloured PNs with the capabilities of Signal Interpreted PNs, which are specialised in processing plant measurements and determining actuator commands. This contribution involves: (a) the formal definition of SICPN; (b) the presentation in the IEC61131-3 compliant SCL language of the so-called Token Player, a software entity designed to support feedback-based decision-making within the SICPN; (c) the validation of the effectiveness of the proposed formalism in controlling an extended configuration of the FESTO Modular Processing Station (MPS) using an Arduino microcontroller via two-way UART serial communications; (d) the modelling of a Digital Twin of the FESTO MPS testbed. The tests demonstrate that, during transitions, the colour and signal interpretation conditions enable the microcontroller to accurately schedule and dynamically reconfigure control actions while keeping the size of the PN-based controller small relative to the control problem's complexity.