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

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

I suspect Alex means that they are "hot", not literally burning :D 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.

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

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

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.

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.

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?

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

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.

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

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

Do I understand you right that it is a cogged wheel driving a long toothed belt that goes from one end of the slide to the other?
The spring was too tight?? What spring?

Dhe drive. Is it one of these: http://www.nee-controls.com/dr_drivestext.html
I'll be very surprised if it does not in addition to what you mention have either settigs for motor characteristics, or simply a choice between some standard motor types.

The motor. Give the data from the label on the motor. Producer, type, etc. etc.

ESjaavik,
You are right. It is a cogged wheel driving a long toothed rail and it is driving for all long rail. The equipement gotta two axis X and Y only. The system is one cutting machine for plasma and oxy fuel cutting process. The spring belong to the system and it works to keep the mechanical system without slack therefore keeping close the cogged wheel and the toothed rail. The motor I was wrong it is a model from CMC and it is model is: MT3528 - 450CF and the driver is from AMC but the controls I quoted above are the same.
Thanks

I assume you have a spring set up for maintaining the spur gear contact with the rack, normally excess gear pressure does not affect motor current that much. What is the model of the AMC amplifier, these usually have both a current limit setting, what is the dip switch set to on the amplifier? They usually have an output terminal that you can monitor current. It almost sounds like it is ok when the axis is being commanded to move, the following error is high so the command signal is such that the motor overcomes any excess loading, but if the motor is unable to reach the in position band setting then it will sit there with a constant command trying to reach the actual in-position setting. Which in my experience with these amps and motors is that you have a excess loading condition on the motor.
A way of setting the gain is to disconnect the motor gear from the rack and if you remove the +- command signal, the balance pot should be adjusted so that the motor is stopped and does not drift, next adjust the gain untill the motor growls and then back off the potentiometer 1/2 to 1 turn.
Re-conect the command signal and see if the overload occurs with the gear dis-engaged from the rack, this will see if the problem is mechanical.
Al

If the current is exceeding the limits then you have to suspect that something is causing the mechanism from moving, if the mechanism is moving slowly then it may be provinding too much torque for the servo to overcome, if you don't have any mechanical or load constraints does the servo run with a light load? Are you sure you have the servo wired correctly?

What I could understand is: the servomotor, when I stopped it, goes on activited untill it stopped by itself. If the mechanical system is too tight, it is probably the motor will keep running, even "stopped", because it won't find the position for rest. Am I right? If so I think the problem will be solved for the system mechanical of equipament was tight beyond of normal because the spring was compressed too much. I monitoring the current of motor for all rack long while moving and the current changed in varying parts of rack.As i wrote now I am observing the equipment's behaviour.
Al,
I will get the information if the check you suggested was made by someone, I think so but I will get the assure information.

Alex S.A

Hi guys
is: Velocity, offset, gain and derivative gain. I did these adjustments at driver.
BTW the balance I mentioned is the same as offset.
Al

Yes, the servo is attempting to reach the location that the driver is telling it to seek, if the encoder is not moving then the motor is stalled and the driver will continue to supply current to the servo...eventually causing the problem you are encountering....one hot servo...until something fails or preset limits are reached.
(chair)

If it does not buzz, the problem is probably stiction. If it buzzes it may be slack or compliance.
If stiction, first try to find if there is a mechanical problem. Lack of lube, old gummy lube, worn parts etc. If not, try to lower your integral gain, I think that is the one you call offset. When lowered, it will be more "satisfied with" a position that is not exactly right. If increased, it will add current to try to remove the final small error. The longer the error persists, the more current it will add. This final positioning is probably not very important for your machine?

Maybe it just needs a good cleandown and relubrication?

integral gain, I think that is the one you call offset.


Actually on the AMC amplifiers Offset is the zero or balance which should be adjusted for zero drift with no signal input.
Al

The end position happens normally when I move the equipament in manual mode or when it, after execute a program, return the zero point. In these conditions it is not important. but if this adjustment influence the sheet will be cut, there will be more one problem. I will report you the behaviour of equipament. The last adjust I did were those I wrote in mechanical system.
Thanks for all help you have given to my problem. I am a new in CNC machines and I could learned much more after our chat in this site.

Good luck, let us know how it turns out.
Al

hi everyone... Untill now the equipament is working fine
thanks
Alex Sandro