Re: [Emc-users] losing encoder counts

[andy pugh]

On Sun, 2 Oct 2022 at 23:51, Jon Elson  wrote:

> I am using my PPMC boards, and I've never
> seen this on my older Bridgeport using the same hardware.

Do you have quadrature error detection in your firmware? ie something
that sets a flag if the speed is non zero but you see an
out-of-sequence transition.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] losing encoder counts

[gene heskett]

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  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  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 



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Re: [Emc-users] losing encoder counts

[Sam Sokolik]

Our 80's vintage matsuura started losing counts when the 5v supply started
to lower..  don't remember how far down..
  Maybe 4.7v?

On Sun, Oct 2, 2022, 11:54 PM gene heskett  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  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.
> >> .
> >>
> >>
> >> ___
> >> Emc-users mailing list
> >> Emc-users@lists.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/emc-users
> >>
> > ___
> > Emc-users mailing list
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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 
>
>
>
> ___
> Emc-users mailing list
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>

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