Servo motor overheating

[Azalin]

The servo motor is a brushless AC servo. Drive is ABB branded. I did the servo setup as per the servo user manual and the values are:

Max current: 17.84
Continuous stall current: 5.55
Voltage constant: 37.6
Winding resistance: 1.24
Winding inductance: 4.14

Servo runs very smooth actually. No vibration, no surging however the only part that is overheating is the output shaft of the rotor. The case remains stone cold. To me, since the case (and the winding in it) is cold so the heating could be because a mechanical problem. However I disassembled checked and I could not find anything bad.

If it is not a mechanical problem then the PC software of the drive has an Auto Tune feature. When I run the test the drive changes the electrical values for the servo (max current, voltage constant etc). So which setting do I need to use? The values from the servo pdf or the values the drive decides?

Thanks

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[Azalin]

By the way, does this Thermal class mean that temperature up to 155 degrees C is normal?

https://www.cnczone.com/forums/attac...d=407374&stc=1

[Bdrangdo]

Is the motor free to turn by hand ?, there should be no resistance at all, sounds like the bearing closest to the pulley is binding or misaligned . The winding's are just underneath the case so if they get warm so will the case. Dave

[Azalin]

Dave,

There is actually some resistance on the rotor when I turn it by hand. For that I was thinking on removing the washer (it is there to ad some preload I guess). The rotor is locked by the disabled break so I believe there is no need for the washer.

[Bdrangdo]

The washer that is normally fitted is a kind of wrinkled preload washer that exerts a minimum of force and should make little difference to the pressure needed to turn the shaft. There should be a small amount of end float that is controlled by this washer, you should be able to feel the movement by pulling the shaft away from the motor and feel it spring back again.

[mike_Kilroy]

Shaft gets hot even not hook to load?

a new shaft seal running thousand RPM can Heat 2 point you cannot touch it.

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[Azalin]

Mike,
Yes, it gets hot unloaded

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[mike_Kilroy]

Mike,
Yes, it gets hot unloaded

ok, back at a keyboard so can write more...

so it gets hot unhooked from load, so it is not a load related bearing issue.

To be clear: does it get hot after rotating or does it get hot just sitting there never moving?

From not hot to hot, how long does it take?

What is going on during this time of it getting hot? Is it spinning? still? oscillating back and forth? something else?

What is motor current during this time when it get hot?

Does the 'ac servo motor' have permanent magnets in it? If unknown, unhook the motor from the drive and short all leads together and rotate it: is there significant torque (compared to leads not shorted together)?

[Azalin]

I just removed the preloader spring to see if it resists the rotor but I don't see any big difference. Maybe just a little. So the spring is innocent. The oil seal has two contact points. I guess that is warming up the shaft while spinning.

Motor is permanent magnet 3 ph ac servo. With no load at high speed, like 3000rpm it takes just about a minute or so to get warm enough to not to touch.

I also removed the spiral ring from the oil seal if it makes a difference.

The servo is used but consider it new because the old owner used it very little. So maybe the oil seal hasn't broken in yet? (Forgive me if it's stupid question)

I'll put the servo back in and will try again. I can also record a video if you want. Let me know.

Thanks

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[mike_Kilroy]

So you confirmed your problem is the shaft seal. That is not a problem. Shaft seals require spinning at high speed to flake off little bits of Teflon Etc to lubricate themselves. Let it run 3000 RPM for 30 minutes and it will no longer get hot, by guess. Enjoy knowing your motor is basically non-used.

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[ennab1977]

Dear Azalin,

The servo gets hot when the resolver (encoder) is not working properly

either the cable of the resolver(encoder) or the the resolver(encoder) has the problem

since the resolver(encoder) is missing some feedback signals to the drive then the close loop of the drive try to recover it

as the time is passing then the motor is getting hot

maybe it sounds irregular to you ...never the less this issue happen

To prove that ,, Why most of the manufacturer of the servo drive encoder or the resolver plug pinout temperature sensor is included ?!!

the answer is simply ,,, it means there is common between the angular movement and the protection of the motor it gets hot when there is something wrong with resolver (encoder)

[Azalin]

So you confirmed your problem is the shaft seal. That is not a problem. Shaft seals require spinning at high speed to flake off little bits of Teflon Etc to lubricate themselves. Let it run 3000 RPM for 30 minutes and it will no longer get hot, by guess. Enjoy knowing your motor is basically non-used.

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Thanks Mike. I didn't have the time yesterday but I'll do some test runs today.

[Azalin]

I guess I moved the shaft downwards when I disabled the brake. This caused the bearings to make heat. I gently hammered the shaft back to place and problem solved.

Thank you all.

[Bdrangdo]

If the bearings were so heavily loaded as to produce significant heat they could well be damaged now or the grease has become carbonised. That type of bearing is not designed to be heavily loaded axially. Dave

[Azalin]

Good point Dave. Thanks for the heads up.

[Azalin]

Got new bearings for the servo.https://uploads.tapatalk-cdn.com/201...a4905a2b47.jpg

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[Azalin]

By the way, these bearings are C3 rated. Is C3 good for servo?

[Bdrangdo]

C3 bearings have a little extra clearance to allow for heat expansion so they should be just fine for a servo can get rather warm under normal circumstances. Dave

[Azalin]

Thanks Dave.

I've been looking to cheap Chinese full ceramic bearings. I wonder if they are usable on servos.

[Bdrangdo]

I am not sure about this, ceramic bearings effectively electrically insulate the rotor from the fluctuating magnetic fields and could possibly cause the rotor and the exposed shaft/coupling to radiate interference, which may be picked up by the encoder electronics. For sure I have never seen them used on servos and i can''t imagine what possible advantage you would get from using them. Dave