I know, it was just that the motor never stopped reposition. I thought it should stop doing that once inside the deadband, but it just kept on although not very often, one microstep every 5-20 seconds or so. Wasn't used to that, I guess.
When using the I-parameter it happened that the position was 1 µm off (seen on the DRO). I just let it do its thing and yeah eventually the DRO switched to 0. So it does its work. It is very sensitive to large I-values, it is easy to get the axis to oscillate.
I now have two sets of parameters that work fine.
P=250, I=0, D=0
P=300, I=10, D=0.5
I really can't see much of a difference in the axis response. Had to lower P from earlier post, jogging very short distances 0.01 mm was a bit sensitive.
Also made a quick milling test, milled in the X axis direction. Following error was a bit noisy like in the figure before, but inside 0-10 µm. So load doesn't seem to be a big factor. Admittedly light load.
Also noticed that the f-error from joint.0.f-error is different from "my f-error" which is encoder.00.position - pid.x.command. "my f-error" is larger than joint.0.-f-error (can be seen in prev figure), I wonder if "my f-error" is wrong.
Why do we use velocity mode? I don't know so I switched to position mode and tried to tune the PID loop. Got worse result, the best result f-error was at least double the f-error with velocity mode. So I run velocity mode again. For servo motors I see the point using velocity mode, but for stepper motors at least it felt more logical to use position mode. But that didn't work out in reality.
