# Servo troubleshooting



## Black Dog (Oct 16, 2011)

just the cowboy said:


> I have a machine that the motor is oscillating. What is the best way to tell if it Is it the machine or motor?
> It's 9300 lenze servo drive
> Checked the motor reads OK from what I can tell 29 ohms phase to phase nothing to ground. This check was done at the drive so cables read at same time.
> Connected to drive with software, no faults and feedback was changing in a steady state as I rotated the shaft of the motor with out drive enabled. As soon as it was enabled oscillation starts.
> ...


Take a look at this *article...*


----------



## dronai (Apr 11, 2011)

Tricky ! Drive I bet, sounds like the motor is lost


----------



## pjholguin (May 16, 2014)

Lose of the encoder.


----------



## eric7379 (Jan 5, 2010)

just the cowboy said:


> I have a machine that the motor is oscillating. What is the best way to tell if it Is it the machine or motor?
> It's 9300 lenze servo drive
> Checked the motor reads OK from what I can tell 29 ohms phase to phase nothing to ground. This check was done at the drive so cables read at same time.
> Connected to drive with software, no faults and feedback was changing in a steady state as I rotated the shaft of the motor with out drive enabled. As soon as it was enabled oscillation starts.
> ...



Is the motor direct-coupled to the driven load or is it attached to a gearbox? Are there belts involved of any kind and if so, are the belts loose?

Any chance of there being a mechanical issue with the driven load causing the oscillation? 

What size is the drive? I know that it will probably list the size in Kw.


----------



## eric7379 (Jan 5, 2010)

pjholguin said:


> Lose of the encoder.


I thought that, but the 9300 drives will typically toss out a "Eer Trip" error message in the event of the loss or disruption of the encoder signal. At least the ones that I am familiar with, anyways.


----------



## just the cowboy (Sep 4, 2013)

*resolver is working*



eric7379 said:


> I thought that, but the 9300 drives will typically toss out a "Eer Trip" error message in the event of the loss or disruption of the encoder signal. At least the ones that I am familiar with, anyways.


Yes it has that trip setting enabled, and I can watch the counts coming into the drive software count up or down with repeatalby.


----------



## just the cowboy (Sep 4, 2013)

*motor is out of machine*




eric7379 said:


> Is the motor direct-coupled to the driven load or is it attached to a gearbox? Are there belts involved of any kind and if so, are the belts loose?





eric7379 said:


> Any chance of there being a mechanical issue with the driven load causing the oscillation?
> What size is the drive? I know that it will probably list the size in Kw.



The motor is coupled to an eccentric and it only rotates 120 degs back to 0.
unbolted motor from the machine still oscillates. 
motor is 0.5 KW.


----------



## John Valdes (May 17, 2007)

Just because it counts does not mean its counting like it should.
Is the encoder mounted direct couple to the shaft or is there a coupling?
Check where the encoder connects to the shaft. It could be loose.


----------



## just the cowboy (Sep 4, 2013)

*direct mount*



John Valdes said:


> Just because it counts does not mean its counting like it should.
> Is the encoder mounted direct couple to the shaft or is there a coupling?
> Check where the encoder connects to the shaft. It could be loose.


It is part of the servo motor


----------



## John Valdes (May 17, 2007)

just the cowboy said:


> It is part of the servo motor


I know. There is a place where the servo motor shaft connects to the resolver or encoder shaft.
You might not be able to see it without separating the two.

If you can replace the feedback device, it does come apart from the actual motor. I have seen many plastic couplings between the motor and feedback device. And i have seen many loose.

This issue sure does sound to me like the drive has no idea where the shaft is.


----------



## just the cowboy (Sep 4, 2013)

*Just changed motor*

Just got a new motor airshipped from Germany. Changed motor/resolver unit, it did not fix the problem. Pulled drive and sent out for repair.


----------



## AllWIRES (Apr 10, 2014)

Is there an interface involved? I lost a negative connection from a UMI to the analog input on the drive. Gave me a 2.5VDC on the drive and oscillation on the motor.

Just a suggestion.


----------



## John Valdes (May 17, 2007)

Encoder cable been checked or replaced?


----------



## pjholguin (May 16, 2014)

Did this just start or was there any maintenance done on drive lately? Check equipment history.


----------



## just the cowboy (Sep 4, 2013)

*update*

Drive still is not running right.
This one got me stumped!!
Drive oscillates whether it is hooked up to a load or uncoupled from load only .54kw motor. Machine has been running 15 years no problems with drive before. This happened while machine was running and no changes to operation.
1. Did basic checks first found nothing wrong.
2. Changed motor with integral resolver built in. no change
3. Changed drive with one from OEM with original parameters in it. no change.
4. swapped cables from known working drive. no change.
5. Changed Profibus card no change.
Waiting to hear back from OEM to see what is sent over profibus, don't have a copy of the Siemens step 7 program.

Thanks for input so far.
Harvey


----------



## dronai (Apr 11, 2011)

We had one that was giving us a hard time, turned out to be the cable ends had corrosion where it attached the board.


----------



## just the cowboy (Sep 4, 2013)

dronai said:


> We had one that was giving us a hard time, turned out to be the cable ends had corrosion where it attached the board.


Tried cables no good, the are hooked to a new motor and drive. cables for drive that was working still worked with cables from trouble drive, and trouble drive did not run with cables from known good drive.

Keep suggesting


----------



## 8V71 (Dec 23, 2011)

Wear and slop in the mechanism that it's driving? Is it operating OK but hunting during standstill? Gain parameters?


----------



## just the cowboy (Sep 4, 2013)

8V71 said:


> Wear and slop in the mechanism that it's driving? Is it operating OK but hunting during standstill? Gain parameters?


No wear in driven unit, hunts both ways


----------



## just the cowboy (Sep 4, 2013)

*another update*

Went in and lowered the gain, and got rid of most of the oscillating, but still did not find the original problem that is causing it. Have a drive specialest coming out tomorrow, will update again then.


----------



## AutoCtrl (May 16, 2015)

*Interesting case- any new findings?*

Curious if you found a root cause to this-

1.If altering the gain affected it then it sounds like the tuning is off - though you mentioned setting the parameters to a known good set and that it didn't seem to help. Does the saved parameters include tuning parameters?

2. Has anything changed on the communications network ( Profibus) recently? - might it have overwritten some of the tuning parameters accidentally?


----------



## just the cowboy (Sep 4, 2013)

*update*

We changed the velocity gain to a lower number and it dampened the oscillation till it worked. We charted the speed and torque of the motor and it was all over the place, but as we were charting it, it started working properly then went back to the way it was? That was before we changed the gain. I then had a drives person come out and his answer was “it works now why worry" & " It happens, all drives need tuning now and then”. I don’t believe that answer since we replaced all the drive components and the load components it should be the way the factory had it setup, since it worked, didn't work, worked, didn't work. I know my problem is not fixed; it is just a fix that worked.

Thanks for all the input this is the BEST forum out there and everyone has a say.
Harvey


----------



## just the cowboy (Sep 4, 2013)

*reply*




AutoCtrl said:


> Curious if you found a root cause to this-





AutoCtrl said:


> 1.If altering the gain affected it then it sounds like the tuning is off - though you mentioned setting the parameters to a known good set and that it didn't seem to help. Does the saved parameters include tuning parameters?
> 2. Has anything changed on the communications network ( Profibus) recently? - might it have overwritten some of the tuning parameters accidentally?



1. gain worked but factory says original gain setting should of worked
2. no changes it bus


----------

