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Mixing Industrial Ethernet Protocols

Standard Ethernet is inherently not capable of real time communications, and thus industrial Ethernet protocols that can run on stock Ethernet hardware cannot be real time.  The best they can do is provide synchronization (for example, using hardware or software implementations of the IEEE-1588 Precise Time Protocol).

Of course, coordinated multi-axis motion using distributed Ethernet servo drives need real time communications, but the problem with real time industrial Ethernet networks is that they cannot use commercial switches and maintain good real time behavior.

One solution I’ve seen from several manufacturers is to put a motion controller in the middle.  Instead of directly connecting the Ethernet servo drives to the main industrial network, the drives are connected to a multi-axis motion controller, which then connects to the main industrial network using a different protocol.  The controller receives higher level motion commands, and sends out lower level motion commands over its own, private real time network to the distributed drives.

Similar motion controllers exist for CANOpen (Ethernet or other network in, coordinated CANOpen motion out), but I find the use of multiple Ethernet protocols interesting.  The result is potentially very good: appropriately using the strengths of the different protocols to make the overall automation system better.

I haven’t needed to use of any these yet, since I don’t have a requirement for Ethernet speed or advanced coordinated motion.  However, here are the controllers I’ve come across:

  • Parker ACR9000-EPL series motion controllers.  They can communicate with Ethernet/IP networks, and talk to servo drives using Ethernet PowerLink.
  • Omron NJ series controllers.  They can communicate with Ethernet/IP networks, and communicate with servo drives using EtherCAT.
  • Elmo Gold Maestro motion controllers.  They can communicate with Modbus/TCP networks, and communicate with servo drives using EtherCAT.
  • ACS SpiiPlus controllers (including the soft controller, I believe).  They can communicate with Ethernet/IP networks and talk with servo drives using EtherCAT.

 

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