Distributed clocks (DC 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!

Distributed Clock configuration

SOMANET supports 2 DC modes:

  • Slave mode - Master device will be used as a reference clock. All the slaves in the chain will be adjusted according to the master time.
  • Master mode - 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).

This feature has to be configured on the master side. We recommend user to use the Master mode as it has better performance than the Slave mode.

Additionally, the synchronization options have to be configured:

  • SYNC 0 has to be enabled with recommended cycle time equal to the EtherCAT communication.
  • SYNC 0 Shift time is usually 0.
  • SYNC 1 is not supported yet and needs to be disabled.