AB Servo Motor Keeps tripping out on excessive velocity error

[tetcie]

Hi all,

I am having a problem with my servo motor and I'm absolutely stuck as to why it wont run.

Without any gearbox or any load attached to the motor - when I am sending a jog command to it - it is tripping out on excessive velocity error. When trending what is happening, the torque reference is shooting up massively, way above the limit, causing the motor to stop, which is then building a velocity error which then cause the motor to fault and trip.

What I don’t understand though is when I do the motor and feedback test, the motor runs perfectly, it just trips out when sending MAM/MAJ commands to it. Does anybody know why this is the case?

I've looked at the knowledge base and tried its suggestions like checking all the wiring etc and the wiring into the drive is correct.

Has anybody seen this before and have any ideas as to why the torque reference is shooting up, and how to fix it? Or what other troubleshooting ideas I can look at? Is it simply just a broken motor and that a new one will fix it?

 

[dmroeder]

Can you screenshot your MAM/MAJ (expanded)

My limited experience, assuming you are not asking it to do the impossible in the MAM/MAJ parameters, puts tuning up on the list. The first thing I'd do is delete the axis, create a new one, using default parameters. Just input the catalog number of the motor, use motion direct command to move it, use very slow speed. Don't change any other parameters.

 

[Maxkling]

I have had this issue with Siemens servos before. If the gain or other parameters are set for when a load is applied but are too high for when there is no load, this can happen.

 

[tetcie]

Can you screenshot your MAM/MAJ (expanded)

My limited experience, assuming you are not asking it to do the impossible in the MAM/MAJ parameters, puts tuning up on the list. The first thing I'd do is delete the axis, create a new one, using default parameters. Just input the catalog number of the motor, use motion direct command to move it, use very slow speed. Don't change any other parameters.

Hi that's exactly what I've tried. The MAJ I've used in the motion direct command is just 5 units per second, rest of the MAJ is default applied any tuning yet - i figured I'd tune it after I know its working lol

 

[tetcie]

I have had this issue with Siemens servos before. If the gain or other parameters are set for when a load is applied but are too high for when there is no load, this can happen.

Unfortunately it still occurs with the gearbox attached and when the gearbox is in mesh with the rack. I have an another machine on site which uses the exact same motor/gearbox etc doing the same job, which has the same parameters and that machine has no bother at all

 

[kamenges]

What's your drive/motor platform? Keep in mind that when the system is doing a feedback test it is NOT using the feedback to control anything. So anything odd with the feedback will not affect the motor durring a feedback test but WILL affect the motor during normal run. The system is acting like you have a feedback to motor rotation mismatch of some kind. When you do a feedback test does it tell you that the test passed successfully?

Keith

 

[tetcie]

What's your drive/motor platform? Keep in mind that when the system is doing a feedback test it is NOT using the feedback to control anything. So anything odd with the feedback will not affect the motor durring a feedback test but WILL affect the motor during normal run. The system is acting like you have a feedback to motor rotation mismatch of some kind. When you do a feedback test does it tell you that the test passed successfully?

Keith

Hi Keith, I am using an AB VPL servo motor with a Kinetix 5500. That makes sense I guess it could be feedback related causing the issue - but yes the feedback tests are passing successfully so thats confusing me a bit. Is there anything I can check feedback wise? I've only commissioned a couple of motion control systems so I'm still a bit of a noob when it comes to this sort of stuff

 

[kamenges]

If this is a VPL motor and it is passing the feedback test then there really isn't much that you can do to change anything with wiring. If the feedback was wired wrong (only two wires) it wouldn't communicate at all. It sounds like you checked the motor power wires and have U-U, V-V and W-W.

The only other thing to look at is the polarity settings for the system. When you do a feedback test the system with ALWAYS evaluate the results in the positive context (positive motion / positive feedback / positive motor rotation). It does not take into account the current settings of these three items. When using any of the AB servomotors you will want to make sure that the motor and feedback polarity selections are set to positive and use the motion polarity selection to change what is forward. Making either motor or feedback polarity negative is about the only way I know that you can create a feedback conflict with a VPL motor.

Keith

 

[tetcie]

I have checked and the polarity is set to normal for both motor and motion. I have previously played around with the polarity when I was troubleshooting but nothing with the polarity has seemed to work so it is now set back to default after deleting the motion group and starting again from scratch

 

[tetcie]

Hi All,

Quick update on this - bit the bullet and bought a new motor which works perfectly. So yeah don't know why the motor was acting as it was - our Rockwell supplier seems to think feedback issue - but at least the project has moved forward.

Thanks everyone for your suggestions anyway