Towards Using Behavior Trees in Industrial Automation Controllers.

Abstract

The Industry 4.0 paradigm manifests the shift towards mass customization and cyber-physical production systems (CPPS) and sets new requirements for industrial automation software in terms of modularity, flexibility, and short development cycles of control programs. Though programmable logical controllers (PLCs) have been evolving into versatile and powerful edge devices, there is a lack of PLC software flexibility and integration between low-level programs and task-oriented control frameworks. Behavior trees (BTs) are a novel framework that enables the rapid design of modular hierarchical control structures. It combines improved modularity with a simple and intuitive design of control logic. This paper proposes an approach for improving the control software design by integrating BTs into PLC programs and separating hardware-related functionalities from the coordination logic. Several integration strategies are shown. The first two integrate BTs with the IEC 61131 PLCs and are based on the use of the PLCopen Common Behavior Model. The last one shows an event-based BTs version for the IEC 61499 controllers. An application example demonstrates the approach. A new PLC software design improves modularity, supports better separation of concerns, and enables rapid development and reconfiguration of the control software. It also provides better integration of low-level PLC code and AI-based task-oriented frameworks.