On Wed, 8 Jul 2009, Jon Elson wrote:
> Date: Wed, 08 Jul 2009 12:24:34 -0500
> From: Jon Elson <el...@pico-systems.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Servo tuning
>
> Leslie Newell wrote:
>> I have just got the lathe on the internet so I uploaded a screen shot of
>> the I weirdness <http://imagebin.ca/view/Yh4hGxr.html>. It shows a long
>> move followed by the term returning the axis to position. The big spikes
>> are accel/decel. Here is a shot with the I term turned down to 0 but
>> everything else the same <http://imagebin.ca/view/3Uj1P_1.html>. I still
>> need to play around with the tuning to get rid of those acceleration
>> spikes. The accel is set very high at the moment for testing purposes.
>>
> Reading the calibration dialog box to the right of Halscope, I see the
> first pic has I at 500. That is WAY too high.
> I don't know the exact dynamics of the I calculation, but I never set it
> anywhere near that high. I usually have it at a few % of P, max.
> I note that FF1 and FF2 are not zero, they can muddy the waters a lot.
> The 2nd pic looks fairly good, although I don't know what speed these
> moves were. As for the accel spikes, FF2 is easy to overdo, and is very
> sensitive, so a change from .002 to .0025 can make a big difference.
>
> Jon
Actually it may be that the HostMot2 tuning parameters are different for some
reason. Once the P/D/FF1 are tuned, I would think a much larger value of I
should be used, as 500 seemed to take more than a second to pull in a many
count error (I'm guessing the counts from the steps in the second half of the
trace). I would think that the I term should fix that large of an error in a
small fraction of a second. Also if the I term is too high relative to P you
will get oscillation (P is damping relative to I)
Peter Wallace
Mesa Electronics
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