Vector VFD => motor => clutch => gearbox => encoder??

[eeinpa]

We have a large planing mill which is in need of some upgrades. It originally had a DC motor driving a multi-speed gearbox. Overall gearbox transfer ratio is selected by a series of multiple-plate clutches built into the gearbox.

Originally I was hoping to eliminate the gearbox entirely, but duplicating its max torque AND speed range is really tough The gear ratios vary from 9:1 to 360:1!

Instead, I am now thinking about using a vector-grade motor with vector VFD to drive the gearbox, and keeping the gearbox (with new shift actuators).

The catch is, we'd like to have simple positioning ability (really just a programmable stop/reverse point). Because of the clutches in the gearbox and the possibility of them slipping a bit, it would seem desirable to have a feedback encoder on the OUTPUT of the gearbox. But that means the motor's feedback device is going to turn anywhere from 1/9 to 1/360th the motor rpm! Worse yet, that ratio will vary when you change gears.

Anyway know of a vector VFD that will cope with this situation? I have not used vector mode much, and never with encoder feedback.

Or do I just put a PLC reading the gearbox output encoder, and delivering commands to the drive?

Useful suggestions appreciated.

 

[eeinpa]

Hmmm, the more I think about this, the less likely it seems that it could work. I would think you wouldn't get nearly enough feedback about the motor dynamics. In our case the load is going to be pretty constant and we aren't that interested in that feature, more so in the position feedback, but I can't imagine the drive is designed to look at it that way...

 

[niallnz]

eeinpa

Have look at the ABB ASC800. ABB does a version of this drive that does positioning via encoder feedback, and with the adaptive programming feature could control the clutch selection. However, if all you want is reverse /stop a simple limit switch will do that for you.

 

[eeinpa]

Thank you for the tip! I will download the ABB manual.

What I envision is a _programmable_ reverse/stop point. The operator could put the machine in lowest speed, manually control it to the desired point, press a button to set the reverse/stop point, then switch to a higher speed range to work and have the machine stop close (not necessarily within thousandths) of the original point.

Regards!

 

[DickDV]

I agree that the positioning ACS800 would be a good drive to investigate. You will need an absolute encoder tied to the machine position (after the gearbox) to provide position data to the drive. You will not need an encoder to provide torque and speed regulation for the motor as the ACS800's DTC capability will do that for you without any encoder or tach feedback.

 

[eeinpa]

Nice! This isn't a super high value project (being in-house on an infrequently-used machine), so the simpler the solution, the better.

Anybody needs keyways cut in 30 foot long shafts, give us a yell

Thanks!

 

[sreid]

I believe that the latest drive offerings from Yaskawa [one of many possibilities]

http://www.yaskawa.com/site/products.nsf/productGroup/ACDrives.html

include mini PLC functions including a second encoder input.