Retrofit of Precix 5x10 CNC

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22 Nov 2019 21:40 #150977 by randypetersen
Awesome, thanks Todd, ya, probably didn't fix that from when I was first setting it up.

It's definitely an encoder problem. With LinuxCNC open and drives not powered, if I manually push the Y axis I can see the DRO change. Same on Z, but not on X, so I am guessing my X encoder lost connection mid run. I am going through trying to check connections now.

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22 Nov 2019 23:45 - 22 Nov 2019 23:49 #150985 by PCW
Replied by PCW on topic Retrofit of Precix 5x10 CNC
Yes, much smaller following error limits should be used so even a small commanded
move will result in a following error if the encoder position does not "follow" the move,
this would likely have prevented your runaways
Last edit: 22 Nov 2019 23:49 by PCW.

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01 Dec 2019 04:19 #151629 by wefixprecix
Do you think it may be an encoder cable seperating as it bends through the flexible raceway...have a look at my username.

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07 Dec 2019 19:28 #152277 by randypetersen
Thanks PCW!

I will get those changed, but if the cable lost connection, then would anything have prevented that?

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07 Dec 2019 19:30 #152278 by randypetersen
Thanks!

Got your email too, and I will see about getting some spare parts.
With my broken belt, the guy I got the CNC had a spare so I was able to get up and running.

That older servo concerns me, might have to look at getting a replacement. Might be nice to have one on the shelf...

Thanks,
Randy

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07 Dec 2019 19:32 #152279 by randypetersen

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07 Dec 2019 19:55 - 07 Dec 2019 19:56 #152281 by PCW
Replied by PCW on topic Retrofit of Precix 5x10 CNC
A non-working encoder in a velocity mode servo can lead to
a runaway situation but typically only slow runaway (drift)

With lost feedback a static axis could drift without the controller noticing
but this would only be at a quite low speed. As soon as the controller
commanded a motion larger than the following error, the loss of encoder
feedback or erroneous feedback should cause an immediate following error
and disable the drives.

If a motion smaller than the following error limit was commanded, you will get
a slow runway with a maximum velocity proportional to the PIDs P term
times the commanded motion.

(this will typically be quite a low velocity with reasonable ferror limits)

This is why it is so important to have reasonable ferror limits...
Last edit: 07 Dec 2019 19:56 by PCW.

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07 Dec 2019 19:57 #152282 by randypetersen
Thanks for clarifying that PCW, I will get those fixed!

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