touch off don't zero the axis

Hi.

We have a problem. When we do touch off on the X and Z axis, the DRO

show this values, when it should show zeros.

this values seem to be constant all the times, but I can't understand the reason behind this. the scales of the Z and X axis are the same.

Thanks

Actual coordinates, relative.
The commanded are zero indeed. Is not clear why the actual position coordinates are not "near" zero. We understand the small flotation that we have (0.002), but we do not understand the value around witch the flotation is.

This brings another interesting question.
The drives that we are using have a built in PID that can used to set and tune the motor directly in the drive (a PC connected to the drive with manufacturers software).
In linuxcnc we have set a PID 1,0,0 for all the axis as we are using the drive PID (that we calibrate before connect the drive to linuxcnc)

It is possible that we would get a better response (not only related with the zeroed, but overall moving response), if we used the linuxcnc PID instead of the drives PID? Would this be a better "by the book" setup?

Thank you

Now we cannot have a MIN_FERROR less than 0.1, that I suppose is 0.1mm what is too much. If fast movements this goes up to 6.4mm (in 10m/min movements)
The drive tuning shows a very good response what appears nothing to do with the actual error.

We will try now to use the Linuxcnc PID and do not use the drive PID (that I suppose need to set to P=1, I=0 and D=0).

If not already set-up this way, I would set the drives in velocity mode
(so the drive itself closes the velocity loop). I would also set the analog scale
in HAL so the output scale is LinuxCNC's maximum per axis velocity (with 10V at the drive)
so for example if you X full axis speed at 10V is 100 mm/s you would:

setp hm2_5i25.0.7i77.0.1.analogout0-maxlim 100
setp hm2_5i25.0.7i77.0.1.analogout0-minlim -100
setp hm2_5i25.0.7i77.0.1.analogout0-scalemax (100 or -100 depending on feedback direction)

Then I would follow JT's velocity mode tuning tutorial:

gnipsel.com/linuxcnc/tuning/servo.html

With one proviso: If you set analog out scaling as shown above, a FF1 value of 1 is the best starting value

Thank you, your suggestion is to maintain the PID on the drives?
It was not clear to me.

Drives are already at velocity mode.

Yes, you want the drives to be in velocity mode which means they have a PI
velocity loop running in the drive.

LInuxCNC runs a PID position loop, the output of which is a velocity command.

The PID loop in linuxCNC will be mainly tuned with P, FF1 and FF2.
(I and D will normally be close to 0 if the drive itself is well tuned)