Hello everyone.
Gantry here with two servo axes on the Y side, one per rail. Beckhoff CX5230, TwinCAT 3.1 4024, two AX8000 drive modules on EtherCAT, NC task 1 ms. Y2 is gantry slaved to Y1 in the NC.
Over a 2 m move at full speed the two rails finish a few tenths apart. The following error on Y2 grows steadily right through the move, a clean ramp, then settles as soon as it stops. Short moves are fine.
I've been up and down on Kv and it changes nothing, and when I swapped the two drive modules over the ramp stayed with the axis, not the drive. I'm outside my own brand here, on Kinetix CIP Sync does all this in the background. Is there something in the sync setup I'm meant to do per drive that CIP Sync just does for you?
What are the drives running in, DC-Synchron or SM-Synchron? Each AX8000 has a DC tab in TwinCAT. A ramp that grows with the move and resets when it stops is two clocks, not two gains. That's the same on any EtherCAT master, it isn't a Beckhoff thing.
DC tab on both AX8000 says SM-Synchron. Never looked in there, I took whatever the scan gave me. Y1 and Y2 are both on the same setting though, so I'm not sure why they'd drift apart rather than together. Or is that the point?
That's the point. In SM-Synchron each drive runs on its own oscillator and reacts to frames as they arrive. Two oscillators are never quite the same, so over a long move each drive samples its setpoint at a slightly different moment and the difference piles up, which is your clean ramp, and it stops growing when the move stops. That's my understanding of it anyway. With DC every slave runs off one network clock, the first DC capable slave in the chain is the reference by default, and the drives fire their sync interrupt at the same instant.
Set both to DC-Synchron on the DC tab, Activate Configuration. One question, what's the first slave in your chain?
Both drives to DC-Synchron, activated. First slave is an EK1100 then EL1008s, the drives are boxes 6 and 7. Long move now, the ramp's gone, Y2 error is flat noise around zero. But on every restart the drives show a sync error for a couple of seconds before they go OP, which they didn't do before. Trend of the restart attached.