Encoders for EMC

1. ## Encoders for EMC

Hi,

I'm collecting information on hard-wear for EMC. (I am in the process a very slow process of CNCing a 1944 Colchester lathe!) What I need to know that I couldn't find a clear novices answer to was what kind of encoder set up do I need on the spindle to do threading. My project will be running steppers so no encoders. I have a mechanical bent, but am electronically challenged!

Matthew

2. if your going to use the printer port to read the encoder back - then I would look for a low count one. Somewhere around 100 line. Remember you need to have an index pulse also - so find an encoder with A,B and Z channels.

To be safe - you should only count 1/2 of your base period. So if your base period is a 50us (most computers have no problem with this). This is (1/50us)/2 = 10khz. so at 100 line - that would give you (10khz/(100line*4edges))*60 = 1500 rpm max threading. 50us is really safe - most computers will do much better. So say if you had a 250line encoder and could do a base period of 20us

(1/20us)/2=25khz max counting rate

(25khz/(250line*4edges))*60=1500rpm. (it just happend to come out the same )

sam

3. ## 100 line encoder

Sam

First of all thank you for your rapid reply. I was thinking about making a 100 slot disk and use a photo switch. I had the intention of running two discs one with a single or double 90° apart slot for position. 100 slots is quite easy for me to make using my home made dividing head I could also gear it up with a toothed belt to take the 100 slot disk up to 250 slot per revolution, leaving the single or double wheel directly on the shaft.

Thoughts, thanks

4. acondit is doing something similar..

http://www.cnczone.com/forums/showth...t=37656&page=4
notice the single index 'hole' in the outer edge. (you only need one)
He is going to use 3 sensors - a,b and index (z).

sam

5. Having more than one pulse per rev allows emc to track the spindle more accuratly. You can do some pretty cool stuff... (more than just threads ) emc will blend many spindles synced motions togather.. For things like this

(like a fusee in a clock.)
He is going to make a video at some point... I can't wait.

You could even do rigit tapping if you can reverse the spindle under emc control.

sam

6. ## Gearing up

If I gear up a disk, I then need a separate one to have a one per RPM. Is 100 pulses/rev sufficient? I have no idea about any of this!

Matthew

7. You cannot have more than one index pulse per rev. So if you do gear up the encoder disk - keep the index separate.

I think that a 100 line encoder will work just fine. This guy converted an emco lathe - it has a 100 line encoder on it.

http://www.lerneaenhydra.net/index.p...d=15&Itemid=28

sam

8. ## 100count

Oooops! I didn't read the first line closely enough! you answered my question about the 100 pulses. I presume that this is an adjustable parameter. I'm going to make my own disk.

[QUOTE=samco;420662]if your going to use the printer port to read the encoder back - then I would look for a low count one. Somewhere around 100 line. Remember you need to have an index pulse also - so find an encoder with A,B and Z channels.

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