Another "what do I need" thread. Vmc retrofit

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12 Jan 2015 00:35 #54883 by thewho
Hello

Excuse my English as it´s not my first language

I recently bought a old Modig MD5000 vmc with TNC150Q. Didn't take much effort to find out it´s pretty much useless compared to today´s alternatives.
Bad picture:


Quick specs:
X,Y,Z drives = +-10V analog servo drives with tacho feedback. Contraves NC710 on X,Y and NC720 on Z
DC servos with resolvers on all axis
5100rpm DC spindle motor with tacho
Spindle drive with many control options. Uses +-10V now
15slot tool changer

Did some digging around the machine and found out that´s really easy to mount encoders on X,Y,Z and the spindle.

So my plan is (or was depending on your answers):
Mesa a 5I25+7I77 kit
And mount AMT102 encoders instead of the resolvers.

Will it work? And is this the right way to go?

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12 Jan 2015 01:10 - 12 Jan 2015 01:10 #54887 by PCW
That should work but note that some have had issues with the AMT encoders as they
are interpolated capacitive encoders and dont have particularly good dynamic response
(indicated position lags real), but then resolvers have this issue to some extent also

You might consider retaining the resolvers if they are standard excitation-in and sine/cosine out devices
Standard resolvers will work with the Mesa 7I49 interface card
Last edit: 12 Jan 2015 01:10 by PCW. Reason: 7I49, not 7I48

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12 Jan 2015 01:39 - 12 Jan 2015 02:35 #54890 by emcPT
Sometimes using a standard incremental encoder from the start makes the retrofit more straight forward and makes the machine more easy to maintain (for example if one of the resolvers brakes in the next year, what will you do?).

________________
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Last edit: 12 Jan 2015 02:35 by emcPT.

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12 Jan 2015 02:21 #54895 by PCW
Sure maintenance is an issue but but resolvers tend to be much
more reliable than encoders, especially in dirty environments.

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12 Jan 2015 02:35 #54896 by emcPT
A full sealed motor back can work in heavy dirty conditions. I opened several Fanuc and Okuma motors with more than 15 years working, and the inside looks like they were just shipped from factory.

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12 Jan 2015 02:40 - 12 Jan 2015 02:51 #54897 by PCW
Sure but resolvers are passive and much simpler than encoders so much more reliable

(and the motors on this VMC dont look all that well sealed)
Last edit: 12 Jan 2015 02:51 by PCW.

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12 Jan 2015 03:15 #54899 by thewho
I wanted encoders because I´m pretty much screwed if a resolver breaks as emcPT said.
Don´t worry about the placement. It´s only the X axis motor that is inside the enclosure. Z and Y is located inside the electrical cabinet on the back.
And there is two covers removed that normally covers the X motor seen in the picture.

How serious is the "lag" issue on the AMT encoders? It´s not a particularly fast machine. 10m/min rapids and 5krpm spindle in hi gear.

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12 Jan 2015 03:30 #54900 by PCW
wiki.linuxcnc.org/cgi-bin/wiki.pl?GantryPlasmaMachine for example

scroll down to the section on encoders = 2.3.5

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12 Jan 2015 05:31 #54905 by thewho
Oh crap :( But I could use them on Z and spindle right? I have no plans for hi speed 3d machining.

So what options does I have on encoders then?
emcPT does sell some that apparently does work well with Linuxcnc and Mesa.

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12 Jan 2015 19:23 #54927 by emcPT
You can use encoders on all axis or you can use resolvers.
PCW is not saying that they will not work, he is saying that you should probably keep your resolvers. Encoders have advantages and so do resolvers. If one would be much better than the other, the industry only would use one of them.
I have machines running at 20m/min with encoders. Also not all encoders are born the same, and there are encoders with much better performance than others.

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