Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
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Evaluation of EtherCAT Clock Synchronization in Distributed Control Systems

분산 제어 시스템을 위한 EtherCAT 시계 동기화의 성능 평가

  • Kim, Woonggy (Dept. of Mechanical and Information Engineering, Univ. of Seoul) ;
  • Sung, Minyoung (Dept. of Mechanical and Information Engineering, Univ. of Seoul)
  • 김웅기 (서울시립대학교 기계정보공학과) ;
  • 성민영 (서울시립대학교 기계정보공학과)
  • Received : 2014.04.09
  • Accepted : 2014.05.20
  • Published : 2014.07.01
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Abstract

Support for the precise time synchronization of EtherCAT, known as distributed clock (DC), enables the design of highly synchronized operations in distributed real-time systems. This study evaluates the performance of the EtherCAT DC through extensive experiments in a real automation system. We constructed an EtherCAT control system using Xenomai and IgH EtherCAT stack, and analyzed the clock deviation for different devices in the network. The results of the evaluation revealed that the accuracy of the synchronized clock is affected by several factors such as the number of slave devices, period of drift compensation, and type of system time base. In particular, we found that careful decision regarding the system time base is required because it has a fundamental effect on the master operation, which results in significantly different performance characteristics.

EtherCAT의 시계 동기화 기법인 DC(Distributed Clock)는 실시간 분산 제어 시스템에서 고도로 동기화된 기능의 설계를 가능하게 한다. 본 논문은 실제 자동화 시스템에서의 광범위한 실험을 통해 EtherCAT DC 기법의 성능을 평가한다. Xenomai와 IgH EtherCAT 스택을 이용하여 EtherCAT 제어 시스템을 구축하고, 네트워크 내의 노드 간 시계 편차를 분석한다. 실험 결과, 동기 시계의 정확도는 슬레이브 장치의 개수, 드리프트 보정의 주기, 시스템 기준 시계의 종류 등 많은 요소에 의해 영향을 받음을 알 수 있었다. 특히, 시스템 기준 시계의 종류에 따라 마스터 장치의 동작이 근본적으로 상이하며 매우 다른 성능 특성을 초래하므로, 기준 시계의 선택은 신중히 이루어져야 함을 알 수 있었다.

Keywords

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