Distributed clocks for synchronized EtherCAT (KRC4 and Kollmorgen AKD)

Robot:
KR 16 R2010-2

KSS:
8.5.8

WoV 6.0
RSI 4.0.9

Hi everyone,

We are controlling a KR 16 R2010-2 using RSI from a Beckhoff C6015, and want to incorporate an external 7th axis (Kollmorgen AKD with AKM64Q Servo Motor). We are able to successfully send packets to both the Kollmorgen AKD via EtherCAT and the KRC4 via RSI, but we are having clock synchronization issues. Currently the AKD and the KRC4 request a new packet every 4ms, but due to clock drift, every 2 minutes and 50 seconds the Kollmorgen Drive and the KUKA robot get out of sync for a brief period, causing shuddering motion on our system.

We are controlling the external axis exclusively through the C6015 PLC, not configuring it as an external axis as part of the robot's kinematic chain. Part of our end requirements is for the external axis control to NOT be part of the KUKA project configuration.

Is there a way to configure the KUKA EL6695-1001 clock on the KUKA with the clock on the PLC to avoid these clock drift issues? It seems like this is possible with a standard Beckhoff EL6695 (using DC Sync 0) but this option is not available on the 1001 variant. We are also utilizing the FSoE lines on the PLC, so we cannot use a non-KUKA EL6695 Beckhoff slice.

I have also seen numerous posts on the forums about using the EL6695-1001, but it seems like most of those questions are around using I/O through the Beckhoff slice, not synchronizing to an external clock.

We actually spoke with Beckhoff this afternoon and they provided us with this solution (which they received from collaborating with engineers from KUKA). I decided to post this on here anyways in case anyone else has this problem in the future.

The recommended way to do this is to use an EL6688 PTP Time Sync slice and connect it to the KRC using X46. The recommended PTP version (from KUKA) is Version 1, although Beckhoff encouraged us to try out using Version 2 instead, because it's a newer protocol and would have better support with other peripherals.

The EL6688 can be run in Master Mode to synchronize the PLC and the KRC, or it can be used in Slave Mode to reference an external Grandmaster clock or GPS to synchronize multiple systems within a single facility.

Update: For those who have a hard time finding the Time Synchronization option in WorkVisual, it's under Additional Controller Settings:

After testing PTPv2, we have found this also works for synchronizing the KRC to an external clock. The advantage of using this configuration is that the KRC looks to the KLI port instead, so you do not have to connect a cable to X46 inside the KRC.

Update from KUKA:
PTPv2 is only supported on KSS 8.5 and above. If you have a robot with KSS 8.3, you must use PTPv1