Two servos controlled by one drive

[ziyaddin2015]

Hi All,
We have encountered a problem with one of two servos that feed paper. The infeed roll was replaced and diameter of a new one is slightly bigger. Its pulling a bit hard and dropping dancing bar all the way down to the bottom sensor which then errors out if not cleared in four cycles? I dont want to change outfeed roll because its still in good shape but I was wondering if there anything else can be done logicwise?? Thank you
Sero motors MPL-B220T-Exx
Powerflex 40
Rslogix5000

 

[Aabeck]

A PowerFlex is a VFD, not a servo controller. One servo controller would never drive 2 motors, unless it was a 2 axis (or 4, 6..) as each servo motor has a position encoder to tell the controller where it is precisely.

The PowerFlex output is a frequency/voltage combination that can be sent to more than one motor, but all motors will spin at the same frequency.
EDIT: 'Frequency" not RPM, as 2 motors may have different spec's and at the same frequency rotate at different RPM's.

The only fix here would be mechanical. If direct drive the rollers would have to be the same size, if belt or chain driven you may be able to change a sheave/sprocket on one motor to change its speed.

 

[GaryS]

If I understand it correctly you have 2 motors each powering a feed roll
You have 1 drive powering both motors
If that is correct then you do not have a servo motor or servo drive it’s just a single vfd powering 2 motors
( A servo controller can only control 1 motor )
With the rolls at a different diameter the material they feed will travel at a different rate
That’s a common configuration but since the one vfd is running 2 motors your options are limited
1. Rebuild the 2nd roller so the diameters are the same
2. Install a 2nd vfd one for each motor and set the output speed with a small offset so the smaller roller vfd is running slightly faster than the other
Personally I like option 2 it will give you greater flexibility in controlling the feed rolls

 

[ziyaddin2015]

My bad. I found that they do have two separate kinetix6000 drives after looking into it more. It was not labeled correctly. What would you recommend doing in this case? Thank you, Ziya

 

[widelto]

If you change roll diameter (bigger) while maintaining angular speed then your linear speed will be increased, please take into account change in diameter in order to lower angular speed and keeping linear speed the same as before changing roll.

 

[GaryS]

Option 2 above
offset the 2 servo's speed reference so the feeder speed match

 

[ziyaddin2015]

I am new to all of this. Gary how do you off set the two motor speed reference or where do you make the change. Is this located in axis properties? I have attached a pic as well. Thanks

 

[Aabeck]

Go to the drive parameters and change the MAX Speed setting. That will change the output speed of that motor with the same input signal.

 

[GaryS]

Youe picture did not come out check the size
there are several ways to offset the drives
change the setting vfd you would be better off bringing somebody in to do it

 

[ziyaddin2015]

The fix was. ...Motor ratio modified and tuned in.