Powerflex 700

Hello we are using a Powerflex drive with a 10 hp motor. in our application we run at a fairly low speed and the motor is used on a take-up and holds constant tension. we changed the gear box on the take-up to help the motor out, we were using a 4-1 and we replaced it with a 28-1. now the motor jerks and doesn't seem to be able to keep constant tension no matter how high we turn the motor up. It pulls then lets go at any speed.

Is it running in torque mode?

yes it is.

Are you using encoder feedback?

Did you autotune the drive?

If so, how was is coupled to the load during tuning?

Does the display show the correct amount of torque when you say it "jerks", and when it "pulls and then lets go at any speed"?

Are there any alarms present when it acts up?

How about faults? Are there faults occuring on this drive? If so, please list them.

Yes I autotuned the drive. I uncoupled the motor and tuned it and later I tried a static tune but nothing changed. There are no alarms or faults. It is coupled to a gear box with a belt. I spoke to an AB drive rep. and he said the drive was only seeing the current from the gear box with the change in gearbox size. And that a change in gear size is not always a good thing when trying to run in constant tension mode. He did suggest trying to scale the signal to get the drive to appear to see the same conditions that it saw before we changed the gear box.

Oh and it is in encoder feedback

Well, I imagine the A/B guy is right. The change in ratio was probably too drastic. The product tension "felt" by the motor is now approximately 1/7 what it was before.

It would be helpful to put some real numbers on this, particularly torque and tension.

What is the desired tension? And what torque does this translate to in the tensioning roll? What is torque then on the output of the gearbox? From that, we can calculate the torque at the input to the gearbox. Now, how many poles is the motor? or if you will, what is the base speed? From that, we can determine the motor's full load torque and, by comparing it to the torque required on the input of the gearbox, we can find the percent of load torque the tension represents on the motor.

If the tension is somewhere in the range of 25-100% of motor torque, then we stand some chance of getting the drive to regulate it smoothly. If, on the other hand, it is down in the noise, say, under 10% of motor torque, then regulation becomes very difficult.

It might be useful to do the same exercise with the older 4/1 gearbox.

Let us know what some of these values are. We can draw some conclusions about the drive if we have them.

Thanks

Thanks, Dick, I am glad you jumped on this one. You always ask the right questions on these subjects, and mine weren't getting the numbers out of him!

Paul