Encoders & their wiring to the UHU servo controllers

[cnc2]

Hi everybody !

I meant this thread for collecting information about the different encoder models used with the UHU, their price, reliability & the way they are connected to the UHU. (direct connection or through a differential interface ?)

Feel free to post your wiring diagram !

Here's what i found on the net as a DIY alternative :

1) http://users.on.net/%7Emerrifield/opto/index.html it's an optical incremental quadrature encoder i think it has a 5V output, TTL ?

2)Maybe the end of expensive encoders for UHU servo driver board didn't try it yet & have no idea if it can work.


As i'm not an electronician i ain't sure this will work with the UHU so, if you know the answer let us know !


Thanks !
cnc2.

[Al_The_Man]

Those are both crude low resolution encoders, the second link appears to be ~80p/rev, which would come out to ~320p/rev after x4 conversion.
a 1200p/rev (before x4) encoder would require a huge diameter wheel using this technique.
In order to make a compact hi-res encoder, it requires a bit of smoke and mirrors called the Moiré effect grating.
A search in the forums will show an explanation.
A 26LS31 can convert to differential line drive for a $1 or so.
Al.

[vroemm]

A few years ago i have been playing around with making a DIY encoder.
Made a drawing of a encoder disk with qcad.
Had it printed on transparent foil at a copyshop.
Here is part of the result, with pictures.
http://home.wanadoo.nl/vroemm/cnc/encoder/index.html

A other possible way to make encoder wheels:
Take a big white paper, like 1 x 1 meter.
Draw a very big encoder wheel on it.
Take a 6x6 cm photo camera, which has slides or negatives of 6x6 centimeter.
There must be a lot of 6x6 cameras around doing nothing, because of the digital cameras revolution.
Put high resolution (?) slide film in it.
Take a few photos with it of the paper with the encoder wheel.
Develop the film.
Then you have a encoder wheel, but how good will it be ?
A lot depends on the quality of the lens.
Some questions remain open, like:
How expensive is 6x6 slide film ?
How expensive is it to develop the film ?

Other tip.
Put the light sensors and leds on a line in the direction of the center of the encoder wheel.
This reduces the errors in pulse width.

Vroemm.

[Al_The_Man]

Did you happen to test the 50mm 500 line? How successful was it?
The usual problem is the line density is too high for a conventional photo cell arrangement to read.
For example the line spacing on 500 line, 50mm disc will be around .0065" or .165mm.
This is going to make it almost impossible for common photocell transmitter/receiver to distinguish between the lines.
Al.

[contactirfu]

Hi Guys,

I have with me the US digital ones the mini's EP4's I think, at 250ppr they are low res. but still i think will work for me, when I bought them it was like 17 usd now they are 30+,

have to see if they are good for my router or I need to switch over to the 500ppr or more.

and yes I made the Differential line drivers using the 26LS31 based of schematic on the US digital website.

RGDS
Irfan

[vroemm]

Did you happen to test the 50mm 500 line? How successful was it?
The usual problem is the line density is too high for a conventional photo cell arrangement to read.
For example the line spacing on 500 line, 50mm disc will be around .0065" or .165mm.
This is going to make it almost impossible for common photocell transmitter/receiver to distinguish between the lines.
Al.

It is a long time ago.
I used CNY37 led barriers.
And i got a sinus like signal floating somewhere between 0 and 5 volt.
A comparator made it into a square wave.
There was instability in the signal, never found out if it mattered.

Then i stopped experimenting, other priorities :-)
It never was used to actually control a servo motor.

Still interesting puzzle to make a encoder, my hobby hart itches again, but lots of other things to do. :-)

Could a laser from a old cd player be used ?
It has a much narrower beam, i think.

Vroemm.

[cnc2]

Those are both crude low resolution encoders, the second link appears to be ~80p/rev, which would come out to ~320p/rev after x4 conversion.
a 1200p/rev (before x4) encoder would require a huge diameter wheel using this technique.
In order to make a compact hi-res encoder, it requires a bit of smoke and mirrors called the Moiré effect grating.
A search in the forums will show an explanation.
A 26LS31 can convert to differential line drive for a $1 or so.
Al.

Thanks for the reply Al !

For the second link, if you enlarge the picture you will see that the encoder wheel isn't the toothed gear but a 50mm plastic disk stuck (glued) on it, it has so many lines that they appear to be a grey band, you can distinguish the lines if you look at a lamp bulb through the disk, it's 200LPI (i think it stands for Line Per Inch) & 1200CT (count).

I was thinking about using this disk with a mouse sensor, but i ain't sure it can detect such a thin lines ?

About the 26LS31 can you post a pinout or a diagram for connecting it to an encoder ?

Thanks !
cnc2.

[Al_The_Man]

The link for the data sheet is one http://pdfdata.datasheetsite.com/web/58498/26LS31.pdf
Example hookup would be:
Pin1 = Ain
Pin2 = Aout
pin3 = /Aout
pin4 = 5v+
pin5 = /Bout
pin6 = Bout
pin7 = Bin
Pin8 = Gnd
pin9 = Zin
pin10 = Zout
pin11 = /Zout
pin12 = NC or GND
pin13,14,15 spare fourth channel
pin16 +5v
Al.

[cnc2]

Thanks Al !

An encoder like the digikey amt102 has A & B channels, what about the /Aout & /Bout.
from what i uderstand Ain is from the encoder before the diferential interface & Aout is from the diferential interface to the UHU, am i right ? but what about the /Aout (not Aout ?) is it needed for the UHU ?

Zin, Zout & /Zout can be used for an index channel, am i right ? so, if i don't have an index channel Z won't be used ? like the remaining fourth channel.

Is there any redy made layout for such an interface or a bread board will do the job ?

Thanks !
cnc2.

[Al_The_Man]

The advantage to differential driver comes when both A & /A etc are used for noise elimination on long conductor runs, if using only one output, you may as well use the single ended output direct as shown in the first link.
If you really wanted to use differential but only had single ended input at the receiver, a 26LS32 receiver could be used.
Al.

[cnc2]

Thanks Al !

After verification the AMT102 from digikey has only A,B,Index,5V & GND. And i ain't sure if UHU uses (needs) /Aout /Bout.

is there any way of implementing the /Aout /Bout from Aout & Bout on the differential board before the 26LS31 ?

Else, how to make the differential interface assuming we only have A & B, 5V & GND (index isn't used by UHU) can i expect any noise elimination this way ?

Thanks !
cnc2.

[kreutz]

Thanks Al !

After verification the AMT102 from digikey has only A,B,Index,5V & GND. And i ain't sure if UHU uses (needs) /Aout /Bout.

is there any way of implementing the /Aout /Bout from Aout & Bout on the differential board before the 26LS31 ?

Else, how to make the differential interface assuming we only have A & B, 5V & GND (index isn't used by UHU) can i expect any noise elimination this way ?

Thanks !
cnc2.

The original UHU does not use differential signals, so your encoder seems to be OK.

In order to use a differential interface you need then a differential transmitter chip on the encoder side and a differential receiver chip on the UHU side. The interface cable should be shielded twisted pair (with 4 pairs minimum) for best results.

Regards,

Kreutz.