On 10/3/22 07:48, Sam Sokolik wrote:
Our 80's vintage matsuura started losing counts when the 5v supply started
to lower.. don't remember how far down..
Maybe 4.7v?
Wearing my C.E.T. hat, at 4.7 volts, all it can do is crash, and if
there is a resistively terminated scsi drive
involved, it will get flaky below 4.95 volts. The culprit there is the
isolation diode, engineering speced
a schotky, spedificly for its very low fwd drop, and some MBA had a cow
over the price and substituted
a std si power diode on the way to production, killing .7 volts of the
5 it had. By-by to any logic 1 noise
margin it might have had on the drawing board with the proper parts
installed. Your trivia factoid for the day.
On Sun, Oct 2, 2022, 11:54 PM gene heskett <ghesk...@shentel.net> wrote:
On 10/2/22 22:25, John Figie wrote:
So if you missed an A or a B pulse from the encoder I think you should
see
the position count go in the opposite direction for one count. Another
words, instead of a position sequence of 0,1,2,3,4,5,6,7 you might see
instead 0,1,2,3,2,3, and in addition the time spent in 3 followed by 2
would each be twice as long. So maybe if you can trigger on a non
monotonic position sequence you can capture the event.
John Figie
On Sun, Oct 2, 2022, 7:49 PM Jon Elson <el...@pico-systems.com> wrote:
On 10/2/22 19:34, John Dammeyer wrote:
Oh boy does that bring back memories.
I started with the US Digital Encoders on the DC Servos. According to
the designer of the PIC upgrade board for the HP_UHU Servo drive the US
Digital were crap and caused nothing but problems.
I switched to CUI and it appeared to be better. Until one day circle
milled inside a piece was off center. See photo.
That’s when I started doing what you did and discovered that at very
slow speeds I could return to the same 0 position but faster moves lost
steps. The error happened in only one direction.
Eventually I discovered that if I swapped the motor+encoder with the Y
axis the problem moved to the Y so it wasn’t the HP_UHU drive. Further
research showed the X axis motor winding resistance was almost double
that
of the working Y axis motor.
It's possible I might have been able to fix the problem by doubling the
current setting on the motor. They were bought at the same time and
were
supposed to be identical.
I don't know why the HP_UHU servo drive didn't catch the position loss.
Like yours, the encoder signals looked nice. The CUI encoders seem
to be
high
One other point. I switched to the Bergerda AC Servo drives which to
date have been great. Talking to Donald Chen the sales guy at Bergerda
he
mentioned that their encoders are Japanese and more expensive than ones
used on a lot of their competitors. After that conversation I took one
apart and checked part numbers. Sure enough, Japanese design made in
China.
So try different encoders.
Yes, I did see some really strange signals on the scope
before. I tore the whole motor/encoder set apart and cleaned
the inside of the encoder. But, optical components in the
encoder are held in place with glue, 39 year old glue! I'm
having doubts that everything is still properly aligned in
there.
So, I'm leaning toward replacing the encoders with newer
high-end encoders with higher line count. But, that will
require machining adapter plates and making sure the
encoders are well-centered.
Thanks,
Jon
Jon and John, I'd vote for a lack of good "star' grounding. Somehow the
encoder is picking up noise from the
motors reversal. So you are getting an extra noise pulse into the
encoder wireng and its going to be direction
switch related. A good star ground, and all that just goes away. Even
with unshielded cables.
The whole point of the star ground is that this common ground may not be
quiet. But everything is
referencing the same bolt. that bolt may not be grounded to earth, and
can be bouncing around 500 volts, but its
carrying ALL the logic with it and the logic is only sensitive to the
logic level between the wire from the encoder
and that star bolt. As far as individual line cords are concerned, only
one third pin should actually get to the wall,
More than one third pin is a ground loop and a noise src.
.
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Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
_______________________________________________
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_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
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