Smoking x servos

[Jig Maker]

I have a KTS4014 machine that burned out the x servo about a year after I got the machine. I replaced it and it did it again after maybe a 30 hours. It just burned the 3rd one after 15 maybe 20 hours.


It happens almost instantly. No warning as in slowing down or anything. It's never happened while the machine is running. It only happens at the start of a cycle or at the day's initial power up when I attempt to jog, or reference home. Soon as the servo gets an input to do one (jog or home) the red fault light on the controller will light and within seconds the burnt varnish smell fills the air. Too late to save the motor. Below is a pic. Any ideas on what could be causing this? There doesn't seem to be any undue resistance on the worm screw.









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[ger21]

Sounds like the drive is supplying to much current.

[Jig Maker]

Sounds like the drive is supplying to much current.

They shouldn't run with an over-current condition for a long period right, so do you mean something is causing a sudden current spike?

[Al_The_Man]

There is virtually only one way to burn a Motor out that is as Gerry says is to pass too much current, with a DC motor that is free to move and no load it should not happen,
If you were to accidentally or on purpose, supply max voltage and the motor is free to move it should rapidly accelerate to a rpm where the back EMF equals the applied voltage, =non, or rather very little current depending on motor inertia etc . i.e. the high current should only occur very briefly at start and not normally enough time to do any damage.
As it accelerates, the current gradually diminishes, now if you lock the armature or place an extremely high load, then this can cause enough current to burn it out.
If your drive is rapidly reversing or is passing any kind of AC, a similar result will occur.
Also it does not seem that your drive current limit is working or adjusted way too high?
If I had to hazard a guess, I would say your armature is getting locked up periodically.
Al.

[Jig Maker]

...
Also it does not seem that your drive current limit is working or adjusted way too high?
Al.

I thought there should be a current limiting circuit, but I'm not familiar with the machine like I need to be yet. Would that be on the gecko drive for that axis?

I really appreciate the ideas I'm getting.

[Al_The_Man]

I am not that familiar with Gecko, but I am pretty sure there is a current limit setting, what is the model?
I see most models have a pot setting, but Gecko say set it max??
I would set it as low as possible that does not give 'nuisance' tripping.
Al.

[Jig Maker]

An update. After my first post I'd decided to take the motor off and remove the armature to see how bad this one got before I was able to power it off. When I removed the front cover and armature I saw small droplets of light brown varnish or whatever they use these days to insulate the wiring that makes up the coils, spread throughout the inside of the motor - on the stators & inside the housing etc. I could visualize that the inside had turned to a smoke-filled almost superheated atmosphere and vaporized the coating which collected together to form the droplets once I had removed the power and it began to cool down in there.

I'm in desperate need to run this machine today and figured I have nothing to lose. I figured it was an exercise in futility but since nothing was visually melted down like the last two motors, I cleaned everything and reassembled it. Before I reinstalled the motor I double-checked to make sure the x worm screw moved freely and it did.

I just finished running my first cycle since all that and it ran the entire 11 minutes flawlessly. As I said, a mototr has never failed while running just on startup. If you had told me the motor would still run I wouldn't have believed it. The housing had gotten so hot the two input voltage leads had been melted to the housing in both places where it was tie-strapped. How none of the insulation had yet burned though to short or at least shunt some of the coils is beyond me.

I don't expect the motor to last long but I'm going to run it until it dies as I have to get orders caught up.


Al I will scare up the drive I replaced in the controller the first time I burned a servo. K2 advised me to change both so I did. I don't want to mess with the controller right now. Afraid to do anything except cut parts.

[Al_The_Man]

You were very lucky, apart from windings, usually what happens is the heat melts the solder where the coils are attached to the commutator and this get flung out and destroy the motor.
I would definitely look into the current limit as it does not seem you have pinned the problem origin down.
It seems rather pointless of Gecko to say set the Ilim at max?
Al.

[Jig Maker]

This is the drive I had replaced. It has 3 pots Limit Damp & Gain.





I assume the limit is the I limit. I'm going to their site to see if i can download some instructions for it. I have not had any nuisance tripping, I have had post-smoke tripping.