ControLogix/Kenetix issue

Hey All,

Not sure what to make of this, maybe someone has seen this before......

We have a small wrapping machine, run with a ControLogix PLC that talks to a Kenitix Servo drive rack.
I'm am not really well versed in this system, but I do have RS5000, and can go online with it.
The system has five servo "axis" motors that derive their run/speed from a "virtual axis"in the program.
That is, when the machine is started the five servo drives follow the speed of the virtual.
And I believe that the servo drives are always in a run condition, and starting /stopping the machine just enables/disables
the virtual axis (maybe I'm wrong, but that's how it looks to me).

In the past week, I have witnessed two times when the machine was "stopped" that one of the servo drives continued to run,
and I saw nothing that looked abnormal in the program (but, of course, I'm not exactly sure what I'm looking at).

If the other four servos are stopping, then I would imagine the virtual is stopping, but why would this one continue to run?
one difference I see between the servos is that the other four are indexed while this one seems to just follow a speed reference.

Am I possibly seeing a feedback issue from the motor (encoder going bad or cabling)?
If it doesn't know where it's at, does it just keep running?

Any input is appreciated.

Regards,
JohnR

From what I have experienced:

Beginning issues with feedback cabling / connectors result in Feedback Noise Errors or Feedback Loss Errors. Faulty Encoders may drop Position Error Faults and Feedback Loss Errors. If the axis is in control and the actual motor feedback is not following its internally calculated position this will result in a position error.
Select the axis from the motion group and look at its status when it behaves like you wrote. If the status is running then open the cross reference for this axis and look for MAS instructions as these could be used to stop an axis.

I hope someone else with more experience can chime in to correct me if I'm wrong, but this is what I would do, based on night shifts where all you have is some pdfs and cold coffee

Even if the axis is cammed or geared from a master virtual axis there is no reason why it can't have a life of its own. Servo actions can be superimposed or merged on an axis.

As mareka says - check the axis status bits and see what it thinks it is doing (movestatus,jogstatus,camstatus etc) when the wrong thing is happening and contrast it to the normal operation.

The axis could just be jogging. Look for MAJ instructions operating on the axis and check out the MAS instructions too.

If in doubt flash the processor again or check for a newer revision of the firmware you are using. There has been bugs in the motion firmware before.