I tried this on my little circuit board milling machine and it can make
a difference there as well.
I retuned with the hostmot2 high-quality velocity estimate, and then ran
with and without it. The new tuning parameters I ended up with were
Component Pins:
Owner Type Dir Value Name
10 float I/O 5 pid.0.Dgain
10 float I/O 0 pid.0.FF0
10 float I/O 0.615 pid.0.FF1
10 float I/O 0.0045 pid.0.FF2
10 float I/O 0.01 pid.0.Igain
10 float I/O 150 pid.0.Pgain
in the old tuning, Dgain was 2.
http://emergent.unpy.net/files/sandbox/pid-old-zenbot.png
http://emergent.unpy.net/files/sandbox/pid-new-zenbot.png
red: axis.0.joint-pos-cmd
purple: Xpwm-cmd
cyan: pid.0.error
cream: pid.0.feedback-deriv (note change in scale: 10m vs 50m)
what you don't see in the picture is the difference in the noise.
Without the improved velocity estimate, there's a sickly hum or honk
coming from some part of the machine resonating -- actually, you can see
it in all those reversals of the purple trace, Xpwm-cmd. The overall
following during a cruise isn't much different, but I'd sure rather have
it without the noise! (lowering Dgain also gets rid of it).
It's also interesting to note that the pattern of lead/lag is nearly the
same in both traces. That variation seems to be something physical
about the machine, and can't be cured by PID tuning. Of course, it's
also tiny compared to all the other kinds of slop in this flimsy little
machine...
Jeff
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