Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Holt on February 21, 2012, 06:38:03 PM
-
Hello everybody
I have scored an Heidenhain glass scale,i would like to run with Mach3, the scale puts out a sine wave, but Mach3 only handles TTL signals.
Have anyone made a working Schmitt trigger for this, and are you willing to share the schematics. I am able to read schematics, make PCB's and solder, but i can't figure it out if you only says "just use part no. ********* and it will work"
Hope somebody are able to help.
Holt
-
To show you what i got to work with, this is a scan of the Heidenhain manual
(http://i253.photobucket.com/albums/hh64/kristianholt/Drejebaenk/IMG.jpg)
What i need is a signal looking like this
(http://i253.photobucket.com/albums/hh64/kristianholt/Drejebaenk/DSC02941-2.jpg)
Any help much appreciated
Holt
-
What you need goes FAR beyond simply using a Schmitt trigger to convert the sine wave to TTL. What you have is an anlog resolver, which will output one cycle of sine wave for each full revolution of the resolver. To get useful position information from that, you need to do an a very precise analog to digital conversion. You'd be far better off replacing those with digital encoders.
Regards,
Ray L.
-
Thanks Ray
I wont replace the scale, one scale costs as much as my entire lathe!
If i can't build anything myself, i will be watching the bay for a cheap Heidenhain interpolation box
(http://i253.photobucket.com/albums/hh64/kristianholt/Drejebaenk/KGrHqZnkE63Ug-DYBPDiKCfsnQ60_12.jpg)
-
You can buy a good digital encoder for under $30....
-
You can buy a good digital encoder for under $30....
Could you suggest any
Holt
-
I just got a Heidenhain EXE 610 C interpolation box on ebay Germany for 12.50 Eur, no need to warm up the solder iron then :D
-
You can buy a good digital encoder for under $30....
Could you suggest any
Holt
These are the ones I use - about US$23 each:
http://products.cui.com/CUI_AMT102-V_Datasheet.pdf?fileID=7573
Regards,
Ray L.
-
For what it's worth, it's not a resolver. It's rather a variation of a Sine quadrature encoder. It's implemented on a scale rather than on a rotary encoder. The sine/cosine signals are decoded in the Heidenhain controller with a AD converter of some resolution. For instance an 8-bit converter will break the sine wave into 256 parts and thus it will get a resolution multiplied by that amount compared to the scale resolution.
Considering the above, while you would be able to use a simple Schmitt trigger to produce digital quadrature signals from the sine/cosine ones, you would lose resolution to such an extent making the scale not efficient. A further electronic gearing circuit could be added, but that would make things much more complicated.
Dan
-
As a point of interest, all optical encoders and scales of this type, TTL included, start off with an optically detected signal that is sine wave in nature, in a TTL Incremental quadrature encoder type, the sine wave is squared up and converted to TTL and/or Differential output.
In these Heidenhain and similar scales or encoders, the arc tangent function is used to produce a high resolution absolute encoder count from the sine/cosine signal.
As suggested, you could use an op amp to amplify this signal and square it up and produce a TTL quadrature signal.
Nosmo.
-
"you could use an op amp to amplify this signal and square it up and produce a TTL quadrature signal." - Of very LOW resolution.
Regards,
Ray L.
-
"you could use an op amp to amplify this signal and square it up and produce a TTL quadrature signal." - Of very LOW resolution.
Regards,
Ray L.
Not really, we are not dealing with a resolver here, these heidenhain scales/encoders are very high resolution before taking advantage of the arc tangent convertor.
Nosmo.
-
As a point of interest, all optical encoders and scales of this type, TTL included, start off with an optically detected signal that is sine wave in nature,
All optical encoders?! Of what type? Those I see typically have lines on the disk.
In these Heidenhain and similar scales or encoders, the arc tangent function is used to produce a high resolution absolute encoder count from the sine/cosine signal.
Don't think "absolute" is applicable to scales. In a rotary encoder I could see how they could possibly do this by matching a full sin/cos cycle to a single rotation, although I have never seen this. Usually a sine/cos encoder is just treated as an incremental encoder. I am not familiar with Heidenhain encoders in particular though.
Dan
-
I found thse to be great for converting Heidenhain to TTL:
http://www.deva.co.uk/product/deva018.shtml
Very helpful guys. Their PCI drive cards are also very nice :)
-
All optical encoders?! Of what type? Those I see typically have lines on the disk.
The lines you see cannot be read or distinguished by the simple infra red transmitter and detector that is used in all optical encoders, in order to read the individual lines something called the Moiré effect is used, this produces a much larger 'shutter effect' in order to read individual lines, the output of the detectors results in a sine/cosine signal due to the varying degree of exposing the detector by the shutter.
This is then squared up by the subsequent electronics, this method has not really changed since the inception of optical encoders, which used incandescent lamp and photo cell.
Don't think "absolute" is applicable to scales. In a rotary encoder I could see how they could possibly do this by matching a full sin/cos cycle to a single rotation, although I have never seen this. Usually a sine/cos encoder is just treated as an incremental encoder. I am not familiar with Heidenhain encoders in particular though.
Mitsubishi and others use the arctangent detection to produce an absolute digital value.
http://www.opticalencoder.com/copi-high-resolution-optical-encoders-tutorial-article.html
Nosmo.
-
Thanks for the information, Nosmo. That is very interesting. I didn't know that.
Dan
-
Incidentally the Moiré effect is produced by the reading head carrying a small piece of scale in front of the detector, but slightly skewed by a few degrees.
This produces a wide shutter that 'rotates' at right angles to the direction of travel with a width of half the height of the scale but an incidence equal to the resolution of the scale lines.
The direction of the shutter will reverse with a change in head direction.
This way lines can be read which are only µm wide.
N.
-
If you have a link with a detailed description and some pictures, I would love to read.
Dan
-
I don't have much available, I originally learned from a course I took under Ferranti-Packard that covered the theory of this in depth.
There is a simple explanation in this pdf of the Moire effect.
N.
-
Thanks Nosmo. will read it later.
Dan