高精度時刻同期と経路冗長化を実時間で両立するEtherCAT通信制御手法の提案と実機評価

抄録

Industrial Ethernet has been widely spread and applied to industrial applications thanks to its good connectivity with ICT systems, high communication performance, and economical advantages, and it becomes a dominant element for enhancing industrial automation. The performance of Industrial Ethernet is mainly characterized by delivery time, time synchronization accuracy, and redundancy recovery time. EtherCAT, an Industrial Ethernet, employs unique features to achieve high level performance for each index. However, to balance those indexes at the same time is difficult for EtherCAT. To solve the issue, the author proposes a communication control architecture for a controller based on EtherCAT features such as loopback function and logical addressing. The architecture determines routes for frames inside the controller based on the network condition and corrects timestamps on the frames conveying reference clock time by adding a changed delay in case of link-down. The processing is executed without buffering the frames, thus the architecture can provide low latency, accurate time synchronization, and communication redundancy simultaneously. The architecture is evaluated by measuring synchronization accuracy of periodical synchronized output of 100µs among four EtherCAT devices for more than ten seconds under reference time delivery at intervals of 1ms. The maximum synchronization error was 290ns after a cable was disconnected. Therefore, the effectiveness of the proposed architecture was confirmed.