Home made encoder questions

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04 Sep 2019 06:34 #144130 by Scot
Hello folks,

I'm prepping to make a custom encoder wheel for the lathe I'm retrofitting as an off-the-shelf part won't work. I've asked a bunch of questions and probably wrote way too much but learned volumes. Bear with me as I'm still learning.

I'm currently researching how to etch through 304 stainless. What I've found seems straight forward enough and I should be getting detailed info I need within a few days. But then the fun starts and I get to do some hands-on learning on how to etch this material and keep tolerances. The processes aren't over the top. But I have some detail info needs. The encoder wheel design is what I really need to know before I start. Once I get the basic design down, the details seem pretty simple.

What I don't really understand yet is the layout of the slits on the wheel. I understand the requirement for this application is a quadrature encoder with index. A typical non-quadrature encoder has radial slits evenly spaced with the same width material left over after the etch as the slits created in the wheel. That I understand. A quadrature encoder has the slits that 'jog" so the pulses generated can be read in quadrature half way offset and look like this, right?:

cdn.thingiverse.com/renders/41/9c/b8/b7/...preview_featured.jpg

The index is what I'm curious about. From what I've read, the index is a single pulse point on the wheel so the reader can make one pulse per revolution to identify the position and direction quickly and easily.

On that photo, is the index the line closer to the center?

Basically when I go to make this wheel, I'll be making 3 or 4 of them in various resolutions to see which works best. The other question I have is if I make this wheel, which reader would be applicable? I can pick up a wheel/ reader quadrature encoder that comes without an enclosure. And that's what I planned to do. Then I plan to mount it on the lathe with the homemade wheel running in the groove of the reader and a cover to keep it from getting destroyed. Would anyone be able to help me identify an applicable reader for a wheel that's about 5-6" in diameter and with slits between .016" to .094" wide and a quarter to a half inch long? I know that's a big range in slit width. But the resolutions may vary. So the slits will vary as well.

Thanks in advance, again. All the info I've gotten has helped in volumes.

Scot

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04 Sep 2019 06:40 #144132 by pl7i92
Replied by pl7i92 on topic Home made encoder questions
dont forget for real good use ((if Forward/Backword is needed))
to add a Second detector
one on line one on nonline
and a third detects the full Rev
this is the best you can get
ABI

on304 (X38CrMo16‎)
you need good bits to go and as my advice tage a MDF benned and drill throu that so bits STAY

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04 Sep 2019 11:04 - 04 Sep 2019 11:07 #144143 by PCW
Replied by PCW on topic Home made encoder questions
Note that its more normal to have plain slits and offset detectors or offset
detector masks (gratings) than offset slits in the wheel.
In high resolution encoders its common to have a single piece
mask for the A and B sensors, the mask looks like a section of the
wheel but with a1/4 pitch offset in the slit locations in the A and B sections
Last edit: 04 Sep 2019 11:07 by PCW.
The following user(s) said Thank You: Scot

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04 Sep 2019 16:04 #144159 by Scot
Replied by Scot on topic Home made encoder questions
I understand the explanation of the slits you gave. But I am having trouble understanding the mask explanation. Do you have any photos I can reference?

Thanks,

Scot

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04 Sep 2019 16:08 #144160 by Scot
Replied by Scot on topic Home made encoder questions
Aren't there off-the-shelf readers that I can adapt to my application for this? As for drilling through the material, I don't plan on making a coarse wheel or using a drill on the wheel. The plan is to chemically etch through the stainless to allow the light to pass and to make a wheel that's very close to the type you would see on a commercial product.

I'm also unsure of what you mean to "tage a MDF benned". Could you clarify that for me?

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04 Sep 2019 17:27 #144162 by PCW
Replied by PCW on topic Home made encoder questions
I can't seem to find a good picture but imagine that you made 2 disks instead of one
and mounted one of the disks stationary and very close to the moving disk
Now you have effectively a shutter for the whole disk with 50% maximum transmission or close to 0 transmission every slit period. This means you don't need a very narrow light source or detector because you get a whole disk Moire pattern.
Then imagine that you cut the stationary disk into 2 pieces and rotated 1/2 of the stationary disk 1/4 of a slit period. Now you have 2 1/2 disk sized masks for A and B...

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04 Sep 2019 23:11 #144164 by aleksamc
I have similar encoder that you talking about. If you need I can make photo of inner disk in it.

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05 Sep 2019 03:43 #144190 by Scot
Replied by Scot on topic Home made encoder questions
That would be fantastic, sir. I'm curious for sure. I'm sure I can make the wheel if I have a good idea of how the slits are laid out. The only thing I would need other than that would be etching the encoder to properly match a reader, then.

Thanks again,

Scot

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05 Sep 2019 03:47 #144191 by Scot
Replied by Scot on topic Home made encoder questions
That's confusing! This may end up more challenging than I expected!

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05 Sep 2019 06:10 #144208 by pl7i92
Replied by pl7i92 on topic Home made encoder questions
best for you woudt b to use a LASER CUT
Sorry for my non understanding English
for Cutting 304 i Recommend to put a MDF pice of wood under the Steel Plate to drill/Mill True

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