Re: [Emc-users] Mounting spindle sensors.

[John Dammeyer]

And here's the drawing.  The exact part number of the sensors are:
OPB991T11Z
https://www.digikey.ca/en/products/detail/tt-electronics-optek-technology/OPB991T11Z/1637795

These are already set up with a voltage regulator, Schmitt trigger and a driven 
Open Collector transistor.  

John Dammeyer
 
> Here's the test setup with the protoboard that took me all afternoon to wire 
> up.  When I'm ready I have a TTL to RS422 driver on it in
> case electrical noise is an issue.  At the moment it's not populated.
> 



QuadSensorConnections.pdf
Description: Adobe PDF document
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Re: [Emc-users] four axis foam cutter 2.8 config

[Ralph Stirling]

It'll be a few days, but I'll send you the original 2.7 hal file and the 
converted file, along with some notes.

Thanks!
-- Ralph

On Jul 2, 2021 5:37 PM, andy pugh  wrote:
CAUTION: This email originated from outside the Walla Walla University email 
system.


On Thu, 1 Jul 2021 at 01:38, Ralph Stirling
 wrote:
> The auto conversion doesn't seem to
> be quite sufficient for foam cutter configurations.

I wrote the conversion script, so I guess this is my fault.

If you can send me your HAL file I can try to figure out where I messed up.

I think that this is probably purely a HAL-level problem.

--
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] Mounting spindle sensors.

[John Dammeyer]

> I am prepared to state categorically that it must be a coincidence as
> "math" was not a word in Douglas Adams's lexicon. As a speaker of
> British English he would have always used "maths" as the shorter
> version of "mathematics"
> 
Hi Andy,
That's the same comments I've heard.  However, nothing is to say that someone 
didn't tell him to use that number and may have even explained that to him.  
The chance has to be very very very small that someone would pick a number that 
by luck that worked out to spell MATH which is required for an understanding of 
the universe.

In either case MATH is also required to understand what the scope is showing 
and why the waveforms aren't symmetrical.

A couple of caveats here so don't judge me too harshly.
1. The drawing of the encoder disk was done with the idea of using a 3mm tool 
to cut 3.32mm slots which would result in 3.32 mm tabs at the expected 
diameter.  
2. Using a 4mm tool to cut 3.32 mm slots was a bit of a mistake.  Ever so 
slightly.  Well.  OK.  A big mistake.

However it was a good exercise, using LinuxCNC and a number of different G-Code 
files for the hub, the perimeter, the mounting holes and the slots.

And I'll have to draw up a new larger disk and do this all over again because 
although the sensor bodies do a great job of being clear of the lower pulley 
the actual sensor mounting tabs stick up too high.  Can't get the belt on the 
lower pulley without removing a sensor bracket mounting screw and pivoting it 
out of the way.

Finally, and that would only show up in a video, the ever so slightly larger 
bore of the self-made cast aluminium motor pulley gives that pulley an ever so 
slight wobble which through the V belt is transferred to the spindle pulley 
(also self-made casting with inner cone to fit on cone spindle drive).

It shows up as jitter on the scope.

Didn't really care at the time (wasn't going to do it over) since the intention 
is to change to toothed belts anyway.  Once the full CNC system is operational 
with coolant, mister and splash shields, power draw bar.  And I haven't even 
started on ball screws yet. 

I'll post the schematic of the interface board to the PhotoLogic OPB990 series 
slotted optical switches in another posting.

John Dammeyer





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Re: [Emc-users] four axis foam cutter 2.8 config

[andy pugh]

On Thu, 1 Jul 2021 at 01:38, Ralph Stirling
 wrote:
> The auto conversion doesn't seem to
> be quite sufficient for foam cutter configurations.

I wrote the conversion script, so I guess this is my fault.

If you can send me your HAL file I can try to figure out where I messed up.

I think that this is probably purely a HAL-level problem.

-- 
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] Mounting spindle sensors.

[Chris Albertson]

Do you need a sharp rise and fall time?   I think a sine wave would work
well enough.

The bigger question is how many slots to cut per revolution.  The number
has to "work" at the slowest speed the shaft will be used.   The high end
of the range is "easy" but the slow end requires some thinking...

Those C-shape sensors are easy to use.  Typically, the detection electronic
uses an op-amp wired as a voltage comparator with hysteresis.  It is just
an op-amp with a little POSITIVE feedback. Hysteresis provides a small
dead-band that eliminates noise.

The beam diameter of the IR sensor is not a geometric point but has some
diameter so the interrupter disk wipes a shadow across the detector and the
output voltage depends on the fraction of the beam that is being cut.  The
output is always a voltage ramp.  The positive feedback detector moves the
"trip" and "untrip" points far enough apart on the ramp, so there is no
ambiguity.


On Fri, Jul 2, 2021 at 12:01 AM John Dammeyer 
wrote:

> > From: Gene Heskett [mailto:ghesk...@shentel.net]
> > Subject: Re: [Emc-users] Mounting spindle sensors.
> >
> > On Friday 02 July 2021 01:42:25 John Dammeyer wrote:
> >
> > > Progress.  This will ultimately be metal since I don't trust the
> > > plastic to be stable and the encoder disk is perhaps a tad thick for
> > > the slotted sensors.
>
> > With regard to the comment about disk thickness, its a small effect, but
> > the thicker disk has more effect of the edge diffraction, so you would
> > get sharper rise and fall times from a thinner disk. One way to reduce
> > the rise & fall time if it is a problem would be to cut the disk with an
> > engraving tool, because the 60 degree v would leave a single sharp edge
> > but that would also tend to give small errors if your z depth is shakey
> > or the disk isn't optically flat. If using the engraving tool, turn the
> > disk over to put the sharp edge, narrower opening towad the led in the
> > interruptor, less chance of an errant reflection from the angled face
> > that way.
> >
> > Cheers, Gene Heskett
>
> Thanks Gene. Good suggestions.
>
> I started with a front panel from an old S-100 computer.   Used the mill
> to cut the complete part.  Then after I realized it was too thick I milled
> it thinner.  I should have started with thinner aluminium to start with.
> Or some thinner steel sheet.
>
> Live and learn.  Just a do over.  Project #42.  In fact all my projects
> are #42.
>
> BTW, in case you missed that from the book "Hitchhiker's Guide To the
> Galaxy" the #42 is the answer to Life, the Universe and Everything.  And
> more interesting, although there are claims that it's a coincidence, if you
> take the letters of the alphabet and assign a number to each.
> A=1, B=2, C=3, ... Z=26
> and add but the numbers for the word "MATH" you get 42.
>
> So in fact MATH is the answer to Life, the Universe and Everything!
>
> Some trivia for the last 3 minutes of Canada Day.
> John
>
>
>
>
>
>
>
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Mounting spindle sensors.

[andy pugh]

On Fri, 2 Jul 2021 at 08:01, John Dammeyer  wrote:

>  although there are claims that it's a coincidence, if you take the letters 
> of the alphabet and assign a number to each.
> A=1, B=2, C=3, ... Z=26
> and add but the numbers for the word "MATH" you get 42.

I am prepared to state categorically that it must be a coincidence as
"math" was not a word in Douglas Adams's lexicon. As a speaker of
British English he would have always used "maths" as the shorter
version of "mathematics"

-- 
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] Mounting spindle sensors.

[John Dammeyer]

> From: Gene Heskett [mailto:ghesk...@shentel.net]
> Subject: Re: [Emc-users] Mounting spindle sensors.
> 
> On Friday 02 July 2021 01:42:25 John Dammeyer wrote:
> 
> > Progress.  This will ultimately be metal since I don't trust the
> > plastic to be stable and the encoder disk is perhaps a tad thick for
> > the slotted sensors.  

> With regard to the comment about disk thickness, its a small effect, but
> the thicker disk has more effect of the edge diffraction, so you would
> get sharper rise and fall times from a thinner disk. One way to reduce
> the rise & fall time if it is a problem would be to cut the disk with an
> engraving tool, because the 60 degree v would leave a single sharp edge
> but that would also tend to give small errors if your z depth is shakey
> or the disk isn't optically flat. If using the engraving tool, turn the
> disk over to put the sharp edge, narrower opening towad the led in the
> interruptor, less chance of an errant reflection from the angled face
> that way.
> 
> Cheers, Gene Heskett

Thanks Gene. Good suggestions.

I started with a front panel from an old S-100 computer.   Used the mill to cut 
the complete part.  Then after I realized it was too thick I milled it thinner. 
 I should have started with thinner aluminium to start with.  Or some thinner 
steel sheet.  

Live and learn.  Just a do over.  Project #42.  In fact all my projects are #42.

BTW, in case you missed that from the book "Hitchhiker's Guide To the Galaxy" 
the #42 is the answer to Life, the Universe and Everything.  And more 
interesting, although there are claims that it's a coincidence, if you take the 
letters of the alphabet and assign a number to each.
A=1, B=2, C=3, ... Z=26 
and add but the numbers for the word "MATH" you get 42.  

So in fact MATH is the answer to Life, the Universe and Everything!

Some trivia for the last 3 minutes of Canada Day.
John








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Re: [Emc-users] Mounting spindle sensors.

[Gene Heskett]

On Friday 02 July 2021 01:42:25 John Dammeyer wrote:

> Progress.  This will ultimately be metal since I don't trust the
> plastic to be stable and the encoder disk is perhaps a tad thick for
> the slotted sensors.  What you see underneath the yellow plate are
> stiffeners.  Likely a 6mm thick steel plate wouldn't need this. John

Looks real good John. I'd think 1/8" alu panel stock would be plenty 
stiff enough for that. 1/4"|6mm steel seems like serious overkill.

With regard to the comment about disk thickness, its a small effect, but 
the thicker disk has more effect of the edge diffraction, so you would 
get sharper rise and fall times from a thinner disk. One way to reduce 
the rise & fall time if it is a problem would be to cut the disk with an 
engraving tool, because the 60 degree v would leave a single sharp edge 
but that would also tend to give small errors if your z depth is shakey 
or the disk isn't optically flat. If using the engraving tool, turn the 
disk over to put the sharp edge, narrower opening towad the led in the 
interruptor, less chance of an errant reflection from the angled face 
that way.

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)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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