Servo motor is burning

[Alex S.A]

Hi There,
I have faced one problem at equipament with servo motor. They're burning constantlly. I just change the drivers, checked the parameters and adjusted some of them but the servo motor goes on to burn. The mechanical system is one rack. Does someone have any suggestion for check in order to solve my problem?
I see no way to solve it.
If someone wish more information please tell me.
Thanks in adavance,
Alex

[Ken_Shea]

Alex, I do not know your specific setup but I do know that DC motors burning up are normally caused by underrated for the job/binding/under or over voltage. Check these issues out.

Good Luck

Ken

[HuFlungDung]

I suspect Alex means that they are "hot", not literally burning If these motors are servo motors, then that would be strange behaviour and would indicate overloading, but if they are stepper motors, then it could be normal behaviour of the motors.

[Ken_Shea]

Thanks Murray, I am glad you clarified that, I guess now I can cancel the 911 call to the fire dept

[Al_The_Man]

Usually the only reason a servo will overheat is because of mechanical overload, most amplifiers have a means, either by potentiometer or parameter to set the current limit. The current can be monitored on some sytems from the operator screen, others you will require to hook up an ampmeter. The correct setting will prevent motor burn out.
Al

[Alex S.A]

Originally Posted by Alex S.A Hi There, I have faced one problem at equipament with servo motor. They're burning constantlly. I just change the drivers, checked the parameters and adjusted some of them but the servo motor goes on to burn. The mechanical system is one rack. Does someone have any suggestion for check in order to solve my problem? I see no way to solve it. If someone wish more information please tell me. Thanks in adavance, Alex

Thanks for all suggestion!!!!
I shall check the suggestions out to find the cause of problem.

[ESjaavik]

Yes, more info is needed. What drive/amplifier?
If it's a "hobby amplifier" I don't know, but "pro" drives have RMS (average) and max current/torque settings and temperature monitoring of the motors. If the settings are correct they protect the motors.
In addition to what is mentioned by Ken, Hu, Al also check for lack of stiffness between motor and load. That will make the motor continously hunting for a stable position even when not moving. It will never get a rest.

[Alex S.A]

They are a pro driver/amplifier. How about what you said. I would like to inform that the conditios that the motor burnt was such as you wrote, that is to say, the motor burning while it is "stopped", after I pressed the stop buttom. It keeps its nominal current and melt itself causing its burning. Not righ away but after some time. Can you explain me better why what you wrote happen?

[Al_The_Man]

Assuming they are servo's and not steppers, I would think there is a couple of possibilities, First if the gain is set too high there can be high current at stand still if they are typical PWM drives, I would still also check for tightness and binding. At standstill the motors should not be humming,buzzing or emitting a high pitch noise, there is usually a way of monitoring the current, sometimes by an output on the amplifier itself.
Al

[ESjaavik]

If there are compliance or outright play between the motor and the load, it will hunt because it will be tuned for the load but it is unloaded. It's the same as if you try to uncouple the motor from it's load. It will become "spastic" until it is re-tuned for the no load situation. It's a bit difficult to explain without going through a lot of servo tuning stuff. And it's not possible to tune it out without also ending up with very sluggish movements. So the best remedy is to remove the slack. Too much compliance will give the same behaviour but to a lesser extent. So don't use softer couplings than really necessary, avoid helical couplers. And if using toothed belts make them as short and wide as possible, and don't re-use worn belts and pulleys.

Of course I assume your servos are properly tuned for the machine.

What drive and motor are you using?
You wrote that you did some adjustments. What did you adjust?
What kind of machine?

And check that the drive is configured for the motor you have. It should not burn up the motor regardless of any bad settings or mechanical problems. It should just shut down with an overcurrent fault. That would still leave you with a problem to solve, but not the cost of a new motor.

[Al_The_Man]

Another thought, High current in a servo can be caused if the axis is operating a heavy overhung load that is not counter-balanced properly, as in a Z axis in a large mill.
As Esjaavik suggests, you really need to post some specifics on the control/machine etc.
As general questions only invoke general answers.
Al

[Alex S.A]

Hi guys
I got more info about the servodriver. It is a model from axor and the adjustments that is possible to do is: Velocity, offset, gain and derivative gain. I did these adjustments at driver. The mechanical system is pulley tothed and rail tothed.
I re-checked the mechanical set up and I could see the the spring was too much squeezed. The spring effect does not happen. I slacked the spring and now I am observing the equipment's behaviour. The driver warning us whe the current was exceding. What let me worried a lot is the fact that the motor burn after some days and when it is stopped. with the explanation supplied for you i can understand the servo's behaviour. Do you know any site where I can draw more informations regarding to servomotor's working?
Thanks