Need Help!- Fanuc AC servo encoder position

[Jonne]

Hello!


I'm going to use Fanuc servos with TECO servo drives, and there have to change encoder, because Fanuc use some weird communication method. Can any explain which position I install new "standart" encoder (U-, U+, V-, V+, W-, W+) concerning Fanuc's servo axis? There is keyway in axis, anyone knows which coil is it pointing?

[Al_The_Man]

There is a method of testing the original alignment using a DC source on the windings,
But The method I have used is to use a double beam scope while rotating the motor at a low rpm and adjust the U pulse with the A phase.
Tie the three phases to a central reference with 3 10k resistors and use the junction as 3 phase common for the 'scope.
There a few past posts that explain it.
You need the right encoder commutation to suit the pole count, the Fanuc can be either 8 or 6 pole motors.
Al.

[Jonne]

Ok, so its not going to happen like in movies? I have to check older posts about that issue.

Thanks AL!!!

[Jonne]

Al, I have to bother you little bit, but I was wondering how 6 pole motor can work, is there then four coils or what..?

These servos what I'm going to use, was used by servo ampfiliers, which have seven pwm signals for control (six for thyristor bridge, one for current cut). So I think this is sign of 8 pole motor, right..?

Four cables goes inside servo, but this not give any help?

[Al_The_Man]

The standard AC sinusoidal or DCBL have three stator windings and a ground.
http://users.tinyworld.co.uk/flecc/4...otor031102.swf
If you scope either the U,V or W commutation pulse, you will see 4 transitions/rev for 8 pole and 3 for 6 pole.
Al.

[Jonne]

So, I have to get 6 or 8 pole BLDC encoder for this system, depending which one is Fanuc's pole count?

[Al_The_Man]

Yes, usually Fanuc have the pole count on the label.
It is often the Robot motors that seem to be 6 pole, most others are 8 pole.
On the Fanuc motors, I replaced the allen head screw with a shoulder bolt and used a through-hole encoder, I had to make a circular plate to fix the encoder to.
Al.

[Jonne]

Thanks again Al!!!


I check servo type plate and its say "8 pole". But can I use four pole encoder also, or have it exactly 8 pole. Sorry my stupid questions, I'm little bit confused still these poles... Which manufactures encoders have you used in 8 pole Fanucs? Please give a link, Thanks!

[Al_The_Man]

An 8 pole motor has to have a 8pole commutation, I use Renco encoders.
In recent years they have been dumping NOS or overruns on ebay, but now they have been taken over by Heidenhain they seem to have quit the practice.
The Renco are indicated by pole pair, IOW a 1000/4 would be 1000p/rev encoder and 8 pole motor.
The metric shoulder bolts I get from Misumi USA.
Al.