Servo Drive tuning

[Pivotman]

I have a Allen Bradley Ultra 5000 controlling the motion of a drill head. After a year of intermittent use the drive started to display a E 19 Error code. Which is Excess Position Error. To correct this the book says increase feed forward gain. Since this application has been running for almost a year should this value need to be changed. Or do I have to look at some other area to find the root cause of my problem. Any help on this one would be great.

Thanks.

 

[rdub]

I would examine the mechanism and make sure that it is not binding in anyway. Sounds like the system friction has increased. As a last resort, I would attempt to modify the tuning parameters.

 

[Skogsgurra]

Absolutely. Give it a good grease!

 

[Pivotman]

Thanks for the tip. While I was waiting I checked over the assembly and found the the servo motor mounts had loosened. Would that also cause the condition I discribed?

Thanks for the help. I did check the ball screw that it drives and that moves freely and is well greased.

 

[rdub]

It sure could. A loosely mounted motor may cause binding at the coupler. I would examine the coupler for damage. Generally, you can specify in the servo configuration how much position error is allowed before an error is generated. Your system maybe set so tightly that the little amount of position error generated by the loose motor may have caused it to trip out.

 

[blacksea]

One more tip: take Position Error plot during motion (I hope your AB driver has such feature) and check when Position Errror excesses Position Error limit. The servo system with higher friction has higher position error by steady-state speed.

 

[bscontrols]

I have been using some A-B Ultra 3000 drives for about a year now. Their auto-tuning feature in the RSLogix software tuned my light duty application very tightly. It worked fine for about two weeks until one began oscillating and eventually tripped for motor overtemp. The solution was to cut the gains down considerably. Positioning accuracy did not decrease significantly. Since then I have had no issues.

Just beware of aggressive auto-tuning.