Servo Tuning Help

Hi all,

I am having trouble getting my servo's tuned especially the slaved Y to A.

What I did was up the P until it stats to oscillate. Then I go back on the P until it stops oscillating. Then I have it like in the pic. But whatever I do, I cannot get the f-error to straight.



The other drives are much worse.

I tried, raising ff1, and it distorts the oscillating, but never can get it to go away.

I'd say that is still too much P, back it off until the oscillation is minimized during the movement, as well. Then set FF1 to minimize flowing error.

Do you have an I-Gain?

andypugh wrote: Do you have an I-Gain?

Yes, This is on the X and it has to be - or it goes a bit crazy.

OK, here it is with positive scale. And I fixed the div so it is more readable.

These are KRS drives, I have removed the option of the drives handling internal pid, so it is sending out to Linuxcnc the encoder and linuxcnc is handling the PID.

Here are some pics of the machine.

Anyone have an at_pid config I can look at?

Are the drives programmed for velocity or torque mode operation?
(if torque mode, you will likely need to run a faster servo thread to get decent performance)

Peter, brings up a very good point. You said earlier that you disabled the drives PID. That may have been a mistake, if you disabled the drives velocity loop. Without that the drive would be operating in "torque mode" where the analog input would be a force command. This is much more difficult to tune in Linuxcnc that the usual velocity command. But to have a velocity control the drive needs to have some kind of feedback loop that needs to be tuned. You may need to study the manuals for your drives a bit more.