Servo Motor Failure?

Kabir · Nov 16, 2011

We have had a three servo motor failures in the last 5 years on a auger filling machine, each time after replacing a motor we would open the motor to investigate what caused the failure and they all seamed to have failed in the same manner.

The rotor magnets adhesive appears to have come loose causing the rotor magnets to rub on the stator and hence lock the rotor. I was wondering if anyone has much experience with this sort of failure and would care to share possible reasons for failure.

robo77 · Nov 16, 2011

not that familiar with servo's but sounds like excessive heat. Either by conditions..or under sized.

OkiePC · Nov 16, 2011

It could also be caused by mechanical shock (think lone forktruck driver on third shift...)

Most servo systems have protection for high temps but it might not be set up correctly. Heat was my first thought too, and if that's the cause, I would check sizing, and contact the mfg. They may be able to tell you more by looking at the damage.

Kabir · Nov 16, 2011

One thing I noticed is that the manufacturer of this equipment had the default acceleration and deceleration time set to 30ms which from experimentation appears to be much faster than what was required by the system. I was thinking that perhaps that would have forced the motor to develop too large of an acceleration torque.

robo77 · Nov 16, 2011

I hear ya Okie on mechanical.. but I would think you would find more of a catastrophic failure with excessive "cuts", and would be fairly instant to the situation.

And I agree send them in to MFG for inspection...they built em.. they know em best.

robo77 · Nov 16, 2011

I don't belive under "normal usage" the acceleration would cause the glue to relive itself of it's duty.

robo77 · Nov 16, 2011

you should be able to PM the drives and check vibrations for the "loose" magnets.. just another thought

OkiePC · Nov 16, 2011

I would change the acceleration time though (as long as it doesn't break something else or slow production too much). That is crazy fast for an auger.

robo77 · Nov 16, 2011

High torque on the magnets and excessive heat could cause it to fail early

Kabir · Nov 16, 2011

I really wanted to check out this system from a math prospective since one of my plans for this would be to eventually change the servos out. I can determine the frictional torque but any suggestions on determining the load inertia for an auger?

robo77 · Nov 16, 2011

well... load inertia might be difficult as it will change due to frictional changes. But if possible could you place a torque wrench on it and check?

OkiePC · Nov 16, 2011

Another method to determine load would be to monitor the power required by the existing system under various conditions and add a safety margin to the worst case when you spec replacement motors.

leitmotif · Nov 16, 2011

Cannot remember where I read this but crash reversal can pull the magnets loose if I recall correctly - are you reversing augers and if so how fast?

Dan Bentler

Kabir · Nov 17, 2011

We never reverse the augers.

iant · Nov 17, 2011

is it possible that the motors are undersized for the load.
Servo Motor magnets are the effective stop/start control for the motor other than external brakes.
if the motor is undersized the excess torque would be translated back to the magnets.
I would recomend - if possible - that you get a servo supplier to examine the load.
What is the current duty cycle of the drive?

Servo Motor Failure?

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