What I have been up to (4th axis)

A couple of days ago, I started working on getting my 4th axis rotary
table to work.
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I mounted it on the milling table a while ago and started integrating
it on Sunday or thereabouts. Constantly being interrupted by the
family, of course.
For feedback, it has a separate tachometer and a "resolver". This
resolver has six leads, two for rotor excitation and two for stator.
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I would use Jon's resolver to encoder converter board:
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For some reason, two resolver leads (two from separate stators) were
interconnected. At first I thought that I could reuse that old
arrangement instead of the lead pairs being fully isolated and
differential.
Yesterday I had a revelation and changed my mind. I decided that an
extra week spent on doing things the right way would be time well
spent. I decided to replace the terminal strip on the rotary table
to accommodate completely isolated stators, add a connection for home
switch, etc.
So I ripped everything apart again and will use a 12 lead cable, with
every lead pair shielded individually.
1) 6 wires (3 pairs) for the resolver
2) 2 wires for the tachometer
3) 2 wires for home switch
4) (possibly) 2 wires for limit switch.
As of now, not much has been done after ripping things out, but
perhaps tonight I will get 25% of work done.
i
Reply to
Ignoramus24647
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That resolver model is used as feedback on your typical Fadal DC rotary axis system.
If you still have the pigtail I would perhaps buy it from you if the price is right and provided it is a -35pin male milspec connector.
FWIW, almost nobody pays Danaher their listed retail price for resolvers--last time I bought a new one IIRC I paid around $230 for it...Also, at least one of the Fadal service houses offers "rebuilt" resolver units for around $120 last I checked.
Rather than considering use of a resolver at all I would suggest go to a encoder instead if it is at all possible--size 11 resolvers are highly prone to rapid bearing failure given even the slightest shaft misalignment and they will also will develop an internal open circuit at basically the drop of a pin.
Reply to
PrecisionmachinisT
Did not know
What pigtail are you talking about?
What I know is that this particular resolver is mounted the way it was originally mounted. Since this is a troyke table, I expect they did a good job at mounting.
I thought a lot about resolver vs encoder issue, and right or wrong, decided that I want to reuse the resolver with "resolver converter".
i
Reply to
Ignoramus24647
35 pin male amphenol
Mil-C-5015
Similar to :
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Well, if I could find a converter that allows replacing the resolvers here with an encoder likely that I would immediately purchase about ten of them--because I have about 6 bad resolvers mostly harowe from glentek motors in my desk drawer but have yet to see a single encoder failure on fanuc motors.
Reply to
PrecisionmachinisT
Do not have one
Do you know how hard is it to drill and tap a shaft of that servo motor, coaxially, to install a stem to mount the encoder disk?
Is the shaft hardened?
i
Reply to
Ignoramus24647
Motor shafts are generally fairly soft in my experience though I suggest check and see if it can be easily molested with a file.
I would probably spin in a lathe using a roller support opposite the chucked end and spot, drill then ream.
Reply to
PrecisionmachinisT
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Hmm ... the resolver has specs at 400 Hz (aircraft use) and at 2.5 KHz -- but the board seems to want to talk at 10 KHz. Any certainty that this one will handle the 10 KHz frequency?
Probably for experimentation without long signal leads.
Hmm ... I would instead put each of the secondary windings from the resolver in a separate shielded twisted pair instead of individual leads shielded. Better common mode rejection.
Best of luck, DoN.
Reply to
DoN. Nichols
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I have NO idea, this is a good question. I wondered about the same thing.
Yes, this is what I tried to say, every pair is shielded.
thanks.
Any thoughts on this excitation frequency?
i
Reply to
Ignoramus24647
Whatever the resolver wants. The datasheet provided above says 400 Hz through 2500 Hz. I bet it is not critical within that range, but 10 KHz is too high. I would ask Pico. Much more important to accuracy than excitation frequency is good shielding.
Joe Gwinn
Reply to
Joseph Gwinn
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I believe that that board has a freq select jumper and the max freq is 10kc.
John
Reply to
John
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That is the min frequency.
i
Reply to
Ignoramus26424
I use a multiconductor cabnle where each pair is shielded.
i
Reply to
Ignoramus26424
That's good and usually necessary. Pico may have an opinion on how best to connect the shields and pairs so the capacitance from pair to shield has little effect. The point of the shielding is to prevent leakage of excitation drive signals into the signals coming from the resolver, which will cause phase shifts and thus angle errors.
The resolver angular accuracy is +/- 10 minutes of arc, according to the datasheet. If we assume leakage in quadrature with the true signal, then leakage ratio exceeding Tan[10' of arc]= 0.0029:1 voltage, or about -51 dB will cause that magnitude of error. Now, it is not hard to achieve this much shielding effectiveness, if one does a reasonable job.
Joe Gwinn
Reply to
Joseph Gwinn

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