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Splitting differential servo signals
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OM222O:

--- Quote from: jmelson on April 22, 2019, 09:59:51 pm ---
--- Quote from: Corryl on April 22, 2019, 08:47:49 pm ---So what I’m trying to do is take the signal directly from the “motor” (the encoder to be precise) have it go to the original lace it was going, but pull a duplicate in real time which after some conditioning would feed into a micro controller.  So I’m receiving the same data the proprietary control is receiving at the same time.

--- End quote ---
What you want is a digital comparator with differential output.  There are tons of these made.  Just make sure the one you pick has a TTL voltage input range and it ought to work.  The inputs will have high impedance.

Jon

--- End quote ---
The signals from rotary encoders are not differential ... just repeating myself over and over again lol
duak:
Corryl, you haven't indicated what control, servos and encoders are in this machine.  The big iron CNC machine tools have their way of doing things, Fanuc in particular.  If the encoders are serial, this TI product will give you an idea of what you are up against: http://www.ti.com/lit/ug/tiduan5a/tiduan5a.pdf  The time delay introduced by a serial link is no big deal if it is short and predictable - we're talking megbit/sec rates here.  Since the mid-90's most servo systems are implemented in DSP to get the performance they need and I guess the simple quadrature A/B/I wasn't good enough, although I don't know why.  Maybe they were getting ready for fibre interconnections where everything has to be serialized anyway.

These guys make a protocol converter for Fanuc serial to quadrature:  http://pico-systems.com/osc2.5/catalog/product_info.php?products_id=27  I don't know if it will work in parallel with the existing servo-encoder interface. ie., if it can be set to monitor a bidirectional bus.

This may not apply to all CNC systems but the interface between the control, where the axis position interpolators are, and the servos are increment/decrement position pulses.  It's conceptually quite simple to slave an independant axis to an existing one and can be a clever way to get a compound motion without having to mess with the control itself.
Corryl:
I did say it’s a haas control, they roll their own.  I’m actually back home where the machine is now, so I should be able to throw a scope on it and see what I’m up against (unless anyone has worked with haas controls already! :) )

As for encoder outputs being differential, yes, in environments where they expect a lot of interference, like huge currents going to giant spindle motors (54KW is what it claims when revving up, though my sense energy monitor disagrees, but maybe they’ve got a huge cap bank on a bldc motor driver board or something.  No the motors isn’t hooked directly to 3 phase, it’s powered off 320V DC).  So yeah, in environments like these they often do run differential signaling.  A propritary serial protocol would actually make sense since they could put some FEC on there as well. 
H.O:
If the encoders are just your ordinary incremental encoders with then splitting the signal (be it differential or single ended) obviously won't be much of a problem. But, as have been indicated already, if the machine is fairly new it's likely that the encoder interface is serial which makes it harder. Not so much from an electrical standpoint but how to interpret the signal. There are standards (like EnDat for example) and there are propriatary format.

With that said, many off the shelf drives (Mitsubishi and Lenze springs to mind) can be setup to output a subset of the encoder signal as an "ordinary" quadrature signal. I don't know if HAAS rolls there own drives or uses off the shelf ones or how much documentation is available on the drives used in your machine but it might be worth looking into.
duak:
Corryl, I believe you may have Yaskawa Sigma axis drives, motors and encoders: https://www.haascnc.com/service/troubleshooting-and-how-to/troubleshooting/sigma-5---axis-servo-motor-and-cables---troubleshooting-guide.html  This good because Yaskawa was good at putting information on their site about their products.  Not to the schematic level but probably enough to solve your problem.

The Sigma servos could have serial or quadrature encoders: https://www.yaskawa.com/delegate/getAttachment?cmd=docurl&doc=workspace/SpacesStore/1c3a9511-5767-48d7-8093-4644ec17fc94/absenc.pdf

It occured to me why the manufacturers went to a serial encoder interface: it allowed the encoder to have the position counter rather than the control and thus simplifies battery backup.
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