Distributed clocks

Overview

Synchronization via distributed clocks allows to share the same system time between the master and all slaves.

This feature allows to achieve high performance, especially with sharp tuning.

Without synchronization, unwanted vibration can occur when a slave’s internal clock isn’t synchronized with the master time. Especially when several slaves try to perform complex motion synchronously, periodical vibrations, audible noise and spikes in the torque signal can appear and the slaves may not execute the motion fully synchronously.

This most prevalent in cyclic modes, since in profile modes the slaves compute their trajectories themselves.

Important

For good performance, always enable the feature if possible. Ensure that your master supports it!

Reference Clock

One EtherCAT device will be used as a reference clock. Typically, the reference clock is the first slave with DC capability between master and all the slaves to be synchronized (DC slaves).

The distributed clocks cycle can be set by the user. The maximum is once per cycle (250 µs at 4 kHz). It is recommended to synchronize at least every 4 cycles.

Sample configuration (TwinCAT)

Settings for the slave

  • Select the drive that is used as a reference clock.
  • Switch to “DC” and proceed with Advanced settings.
  • Select the Operation mode: “DC-syncron”
  • Determine the cycle time for that slave.
../../../../../../_images/dc_in_twincat_slave.png

Note

SYNC1 is currently not supported.

Settings for the master

  • Select the EtherCAT master device
  • Switch to EtherCAT and proceed with Advanced settings.
  • Set the drive that is used as a reference clock.
  • Select “External Mode”
../../../../../../_images/dc_in_twincat_master.png

Use the button “Export Configuration File” to export the ENI config file and use it with your master.

Behavior of the feature

When the feature is configured correctly you should notice that the difference between the adjacent EtherCAT timestamps is always equal to the EtherCAT cycle time ( for example 250 µs) and periodic vibrations and distortions in the position signal are eliminated.

../../../../../../_images/beat_wo_dc.png