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381  Mach Discussion / General Mach Discussion / Re: Converting Heidenhain sine wave to TTL on: February 28, 2012, 02:04:54 AM
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

382  General CNC Chat / Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit on: February 27, 2012, 08:00:38 AM
Yes, good indeed, Hood Smiley

The clamping and unclamping is so quiet and smooth you can hardly believe it's so powerful.

Dan
383  Mach Discussion / General Mach Discussion / Re: Converting Heidenhain sine wave to TTL on: February 27, 2012, 06:24:42 AM
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
384  General CNC Chat / Show"N"Tell ( Your Machines) / Re: Coil Winder Questions on: February 26, 2012, 05:19:12 AM
Hi Gary,

Machine looks fantastic! Thanks for sharing the pictures.

And I would also like to see it in action Smiley

Dan
385  General CNC Chat / Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit on: February 25, 2012, 09:23:19 AM
Hood,

Nice turret. Wonder if he made the coupling as well.

Any good reason you'd want a curvic coupling dead accurate? Most probably you'll still need to adjust each tool's height so even if it weren't indexing accurately you'd still have all tools aligned in the end. Repeatability will still be there and I think that is what maters in the end.

Dan
386  General CNC Chat / Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit on: February 25, 2012, 02:02:29 AM
Id like to scale this down but need an alternative to the curvic as I don't see them offered in a smaller size.
Maybe pins and bushings ?  Or keys and slots ?

Russ,

You need them tapered for it to work at all. Otherwise a small lash and vibrations are inevitable. If you have an accurate enough CNC mill I think it wouldn't be a problem making one. If your mill isn't accurate you should still get around if you have a rotary table which would index one tooth at a time and the mill would cut each tooth at the same location, thus repeatability is guaranteed.

Dan
387  G-Code, CAD, and CAM / G-Code, CAD, and CAM discussions / Re: Arcs not cutting smoothly on: February 24, 2012, 02:08:01 AM
It's different in this case, I am afraid, as he has arcs programmed in the Gcode and not segments.

Dan
388  General CNC Chat / Show"N"Tell ( Your Machines) / Re: The Laser Project. on: February 22, 2012, 08:00:05 AM
Sorry, Tweakie. Didn't mean to sound that way. Let's just consider the issue closed... till we know better anyway Wink

Dan
389  General CNC Chat / Show"N"Tell ( Your Machines) / Re: The Laser Project. on: February 22, 2012, 05:55:26 AM
Hi Tweakie,

I agree again. I was just trying to say it was not theoretically correct a way of description. There will always be the slightest offset between the two dots. It might be small, but it's there. And without it you wouldn't again be able to produce shades of grey Grin

Dan
390  General CNC Chat / Show"N"Tell ( Your Machines) / Re: The Laser Project. on: February 22, 2012, 04:45:54 AM
Hi Tweakie,

I agree with this. It's just that I think that using the word "power" to describe this process is misleading as the laser is being turned on to the same (predefined by some other means) power each time.

And to be more correct, I think that the laser never really does several pulses on top of one another (well if it's focused fine enough that is), as the axis is in a constant move. I think the correct way of thinking about it is the dots intensity. And the other thing to consider while at it is that the exposure time is determined by the axis feed rate.

Yes, I had read through your PDF and I must say you've done great job there!! Thanks for that!

Dan
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