"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