Time Synchronization Extension for the IO-Link Industrial Communication Protocol

Modern industrial automation systems are real-time, distributed systems utilizing industry and manufacturer-specific, competing communication technologies. These networks are built using Industrial Ethernet Networking solutions today, such as PROFINET, EtherCAT, EtherNet/IP, CC-Link, etc. Hopefully, the industry will move towards the IEEE Time Sensitive Networking (TSN) standard in the near future. However, Ethernet-based technologies are not viable under a certain price point, nor they will be in the coming decades. Therefore, low-cost sensor and actuator networking solutions are used to aggregate sensors and actuators on the Industrial Ethernet Network. One of these is IO-Link. IO-Link has no concept of synchronized system time, and therefore, IO-Link devices cannot participate in real-time distributed systems based on a time-driven operation. The paper introduces a time synchronization extension for IO-Link to allow IO-Link devices to acquire global time and operate based on that with sub-microsecond precision. The extension is fully additive, i.e., backward compatible with standard IO-Link protocol and functions, and requires minimal hardware modification to current IO-Link devices. A proof of concept implementation is presented in the paper showing how an actual IO-Link master can be augmented for time synchronization, and how relevant hardware features of the IO-Link devices, such as timer bit numbers, influence the achievable precision.