Anilam Crusader linear scales

Yes I was using the glass scales for abs position.
When I say the servos would not 'stop' I mean they drift 1 encoder count the Linuxcnc would have to correct.
So it was just 1 count drift back and forth. I could zero the offset on the amps and it was OK for a while.
Seems that temperature of something would cause it to change ever so slightly.
I thought about maybe putting back to back diodes in the +-10 volt signal line to create a dead zone but never tried it.
Using Mesa 5i20 and 4 axis servo card.

I just wanted to share the way I added encoders to the SEM motors while keeping the tachometers.

I would think a little bit of dither like that should be expected.

I don't think the PID dead band would fix it either. It would only change the distance from the commanded position where it would be correct.

Did switching to the AMC drives fix the problem or was it the addition of the encoders? I would think the only solution would be to find a better more stable drive, one that is/can be tuned better so zero velocity was and stayed at zero.

Your adaptation of the encoders to the motors looks very nice. Their finer scale, would also have reduced the size of your dither with the old drives, but not eliminated it.

A 1 or 2 count dither is pretty much unavoidable with velocity mode drives,
and any added deadband is likely to make the following error worse.
basically you have lost analog feedback at this point and have a
digital bang-bang control system
(one reason high end CNC equipment has 1million count/turn or higher encoders)


This is especially true if there is any static load (deadband will just make it worse)

Thank you all.
Changing to the digital encoders did fix the problem. (minor problem)
The main reason I brought this up is to show how I added encoders to the SEM motors and kept the tachometers.

Good info on this thread. I will be opening up the motors on my Lagun Crusader II and looking at the tach/encoder setup you have there for mine. I have a Mesa 6i25-7i77 setup for it. The Crusader always dithered when it was idling. sometimes it would start and then error and have to have the drive enable reset, but usually good to the .0005 scale accuracy. I had been waiting for Peter to have the ENCY encoder splitters in stock again, as I could use the Crusader in DRO mode while tuning and checking the LinuxCNC setup. They have them in the MESA store again, so I need to re establish my order.