Stepper motors and linear scale closed loop setup?

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.

Tuned and tested in the video.



Now the Y axis.

Finishing off the X axis. Aligning the reading head, mounting the cover.
Another of these un-polished videos that show every detail.

Hi Peter.
Re: PID command-deriv pins on all stepgens
Could you elaborate a bit more on this?
Does it apply to open loop PID setups, or both open & closed?

I am on LCNC V. 2.7.14

Thank you!

Ray

The Y axis is now done. The Y axis is in poor mechanical shape with a backlash of 0.2-0.3 mm.
Nevertheless I test to see if the encoder can improve things.



I think the result was interesting, although not perfect. The Y axis will be rebuilt later on.

I test the stepper motors' resolution and try to see if that has an influence on the following error.
The locking screw from from the video is finally added.

Prepare a BK15 bearing block with angular contact bearings for use on the Y-axis.
This will, when mounted, improve backlash and stiffness in the Y-axis.

HI,
any news about Y axis?

Hi, can you share your latest .ini and .hal files?
Thank you!!!