Re: [CAD_CAM_EDM_DRO] Re: re:cleaning, lovejoy, black box tach, linear scales, making pulleys

Oohhhh...from what I remember of electronics, this sounds sounds really cool
and logical. Hope you get it to the "practical" stage Mariss.

Smoke
-----Original Message-----
From: Mariss Freimanis <geckohall@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
Date: Wednesday, November 29, 2000 2:28 PM
Subject: [CAD_CAM_EDM_DRO] Re: re:cleaning, lovejoy, black box tach, linear
scales, making pulleys

>--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:
>
>>
>> I find this VERY hard to believe. Maybe, with no realistic band-
>limiting
>> it is only 25 Db, but with reasonable band limiting (just a simple
>RC
>> at the input to the servo amp) I think I have demonstrated a SNR of
>> over 40 Db on my own system. The tach is still working WELL down
>> into the tens of uV region, but the finite gain of the amplifiers
>is eventually
>> overcome by stick-slip friction somewhere below .01 IPM. Maybe
>> I'm just picking at rediculous straws, here, but I want it SMOOTH
>down
>> as far as I can possibly get it. (The idea is partly that if it is
>smooth
>> down to rediculously low velocities, it will also perform well
>while holding
>> position against intermittent external loads, ie. cutting forces.)
>>
>> Jon
>
>Hi,
>
>Jon, could you clear up something for me? Assuming a PID loop, it
>seems there is no simple way to keep the motor from dithering or
>bouncing between adjacent encoder edges due to the "infinite" DC gain
>of the integral term. Does your system exhibt this phenomena, and if
>it does, what is the frequency?
>
>On an allied subject, quasi sine-cosine encoders are intriguing. If
>you strip the slope information for sine -45 deg to sine +45, it is
>pretty darn linear. Stitch these 90 degree segments together and you
>get continuous position feedback.
>
>I've got a very simple breadboarded circuit doing this right now with
>a cheap ($100) DRC sine-cosine encoder I'm using in conjuction with a
>hacked G320. The motor is completely still between steps because the
>servo nulls at the sine=cosine points.
>
>What is really exciting is when I replaced the STEP/DIRECTION
>interface with a variable freq. constant amplitude sawtooth waveform.
>The fast edge of the sawtooth is differentiated and forms the STEP
>input; positive going is CW, negative going is CCW. This same
>sawtooth is scaled and injected into the servo summing node.
>
>The result is an absolutely smooth, monotonic motion down to zero
>speed! On a much lesser note, the interface requires only a single
>signal line. I am going to pursue this further to see if it is
>practical.
>
>Mariss
>Geckodrive Inc.
>
>
>
>
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