High-precision time synchronization in real-time Ethernet-based CNC systems

This paper presents a time synchronization method to achieve high-precision distributed clocks in real-time Ethernet-based computer numerical control (CNC) systems with a ring topology. The proposed synchronization method adopts the frequency compensation and peer-to-peer transparent clock mechanisms, and utilizes a real-time synchronization protocol to embed the time synchronization into the real-time communication cycle. An optimal proportional-integral controller is then designed for the frequency compensation mechanism based on the model and analysis of the time synchronization process. Besides, the hardware implementation of this time synchronization strategy is described. Finally, a real time Ethernet-based CNC system with a ring topology is built, and experiments are conducted to verify the performance of the presented synchronization scheme. The experimental results demonstrate that the proposed time synchronization method achieves high synchronization precision. The peak-to-peak jitters are measured to be only 42.42 and 95.5 ns for one and four hops, respectively.