Replacing DC Motor to AC Motor

[kamenges]

This, or something very similar, is what Charly is dealing with:

http://www.bollina.it/inglese/frameitinf.htm

I would be somewhat surprized if the drive did it's own indexing. I expect there is a separate machine controller on here somewhere that is already getting a feed roll encoder input. The question is, where is that encoder? If it is piggybacked in the DC motor then getting an AC motor with the same resolution encoder would probably be helpful. In that case Charly probably doesn't want to change the drive ratio either, unless it's relatively easy to redefine the encoder counts/mm in the controller. But if the material measurement encoder is mouinted separately from the motor then we are back to DickDV's point about relative motor/drive performance.

So, Charly, where is the material measurement encoder on the system right now?

Keith

 

[rsdoran]

I converted several Elsner paper converting systems from DC drives and they used a measuring wheel to determine length and when to cut. Technically all we did was do a straight changeover on the drives and left the system as was.

We also had several "tube" winders, the tubes were the kind you find christmas paper wrapped onto. We converted them to AC motor/drive leaving the system intact to determine when to cut.

I dont know that system but if the cut to length system is independent of the drive then all you would need to do is change the drive system over and match the control to what was previously used.

We did the changeovers because the old DC drives/motors were high maintenance and costly to repair...old Reliance VS drives, Ward Leonard motor generator, and sheave drive systems, 50 & 60's made equipment.

 

[Charly]

1024 ppr Incremental Encoder mounting in rolls (separetly from DC Motor) that drived from dc motor. This encoder measure material length (calculated from count/mm factor, roll diameter and roll speed). The encoder signal is send to Compact Logix PLC (1769-HSC with 1769-L32C processor). Speed ref and stop signal is send from PLC analog output to analog dc drive.
For upgrading, we will connect Powerflex 700 to compact logix processor using controlnnet. Any comment?
Thank you.

 

[kamenges]

You are going to like the ControlNet interface to the drive. Logix5000 has a pre-made drive communication structure for the PF700. It will get entered as a controller tag as soon as you configure the drive on the ControlNet port. You will have alot more info available to you if you want it.


I found a rather interesting thing on the AB website. The 'Joe off the Street' price you get from the AB website is less for a PF700 with the feedback option installed than it is for the PF700 with the standard interface. If that holds true through your distributor you probably want to buy the PF700 with the vector control interface and just run it sensorless vector. That gives you added flexibility for a lower price.

Keith

 

[Gerry]

There may be an inertia concern

Since this is a positioning system

This motor will pull material from uncoiler section and use the encoder to measure length of material and motor will stop in length setpoint and cutter will cut the material. Machine speed is 30 meter/min with cutting length variation is maximum 0.2 mm.

motor rotor inertia may need to be considered.

Speaking from painful experience with servo motors - DC servo motors tend to have 2-3 times higher rotor inertia than a equivalently rated AC servo motor. Simply replacing a 10 NM DC servo with a 10NM AC servo results in higher load:rotor inertia ratio which demands de-tuning and less performance.

From what others have said here, a 5HP AC motor will be smaller than the original 5HP DC motor and so I would assume its rotor inertia will be less.

The point is: you may need to install a larger HP AC motor, not because you need the extra HP, but because you need more rotor inertia to enable tuning to an acceptable performance level.