Application of Ethernet Powerlink for communication in a Linux RTAI open CNC control system

In Computerized Numerical Control (CNC) systems the communication bus between the controller and axis servo drives must offer high bandwidth, noise immunity and time determinism. More and more CNC systems use real-time Ethernet protocols such as Ethernet Powerlink (EPL). Many modern controllers are closed costly hardware-based solutions. In this article the implementation of EPL communication bus in a PC-based CNC system is presented. The CNC system includes a PC computer, software CNC controller running under Linux Real Time Application Interface (RTAI) Real-Time Operating System (RTOS) and servo-drives communicating via EPL. The EPL stack was implemented as a real-time kernel module. Due to software-only implementation this system is a cost-effective solution for a broad range of applications in machine control. All software is based on GNU General Public License (GPL) or Berkeley Software Distribution (BSD) licenses. Necessary modifications to the EPL stack, Linux configuration, computer BIOS and motherboard configuration were presented. Experimental results of EPL communication cycle jitter on 3 different PC’s were presented. The results confirm good performance of the presented system.