Motor control for long feed and collection rollers 2

[matbob]

Hi all,

I am new to the group and hope my question is relavent.

I have 2 11' long spools of 6" OD. I am transfering a 60' long sheet of 10' foot wide plastic from one to the other and then back again. the system needs to advance 6' and stop then advance another 6' and stop and so on. When it gets to the end it should reverse and do it all again the other direction. The plastic between the spools should stay to firm (not sag). The system will do this all day long... the total weight of the spool and 60' of plastic is about 180 lb.

I plan to directly connect a Leeson right angle gear motor to the shaft of each spool (1/3 hp 88 rpm). However, when all the plastic is on one spool the empty spool needs to spin a bit faster to keep pace with the other spool. I need ideas on how to deal with this issue or the overall control of such a system.

Any help welcome,

Thanks

Rob

 

[Skogsgurra]

This application seems to be a typical reel-to-reel center driven winder/rewinder. Many frequency inverters can do this for you, using built in diameter servos and torque control. You will need to know the line speed and also the RPM of the motors if you need real good indirect tension control.

If your material is sensitive to touch, it is often possible to get a good diamater measurement with an analogue ultrasonic transducer. You need one for each reel. You can then use the diameter and the required torque and let either an external PLC or the built-in functions of the inverter calculate RPM and torque to give you the right web tension.

I do not think that you need "real" tension control, where the tension is measured using a load cell. If your requirements are "no sag and no elongation" it is usually OK to use indirect tension control.

The possibilities are many and I think that you should discuss this with a good drives salesman.

The sequence control (starting/stopping every 6') is best done in an external PLC.

 

[matbob]

Thanks skogsgurra,

You are correct that I do not need "real" tension control.

Yes, I am controlling with a PLC.

To simplify it all I had an idea to make one of the reels spring loaded with a torsion spring and use the motor on the other reel to wind or unwind. Any comments?

If that is a bad idea can anybdy recommend a "good driver salesmmn" in the US (south Florida if possible)?

 

[blacksea]

Instead using standard PLC or motion controller maybe suggested special web tension controller from Montalvo or Warner. Both of them have tension controller with direct connection of ultrasonic sensor - U-3000 from Montalvo or MCS2000 from Warner. Pls pay attention that such sensor hasn't high accuracy.
But if you want use tension sensor produced by yourself motion controller with analog input would be suggest -for example from Galil.

 

[jraef]

Is this by chance a moving sign / banner application? If so you need to consider braking capabilities if the rollers are oriented vertically (one over the other).

"Venditori de oleum-vipera non vigere excordis populi"

 

[sreid]

You might try Contrex.

http://www.contrexinc.com

 

[Barry1961]

A 50:1 worm gear's efficiency is so poor you should not need a brake. You should add a little fudge factor since the efficiency for a worm is even worse on start up. Also if you are going to mount it where the shaft will be vertical you need to let Leeson know or it will leak bad.

In general if over about 30:1 and you do not need the braking effect of a worm gear you can get a good gear motor for close to the same money. This is because you can usally go down a motor size due to the high efficiency. Then you could just run one gear motor at a time and let it back drive the other. This would do away with the VFD. Of course you may need a brake motor to keep it from free wheeling.

With 1/3hp worm gear at 50:1 you should be able to use a 1/6hp hypoid. Brother, Sumitomo and I think GAM make small right angle boxes with solid and hollow bore outputs. They all can mount in any position without leaking.

Do you have marks/holes on the sheet ever 6' for the index or are you going to calculate revs?

Barry1961

 

[matbob]

Thanks for all the feedback,

A few clarifications:

The motor I was looking at is 88 rpm 20:1 1/3 hp and 177 inlb as seen here I was told by a person at Leeson that is would not free-spin and would have a braking action as the motor stops. Is that correct?

jraef,
Yes this is a mobile billboard application. The reels are horizontal and one above the other.

Barry1961,
Yes I am using holes to index the billboards and sensors on the sides to stop the system if it goes out of alignment (eg walking down the reels). My output shaft will be horizontal so I do not need to worry about leaking.

Blacksea,
Thanks but I think that would be overkill in my application.

While you were all being so kind and answering my question I was doing a quick trial and error test with the torsion spring from my garage door. I used it to provide the rewind and breaking while I hand cranked the other reel. It looks like it will work for me except that I do not get enough rotaions our of the sring I used and will need a longer spring or a bigger drum for cable at the end of the spring... Can one of you tell me why I should not persue this idea further (please save me from myself)?

Thanks to all

Rob

 

[Skogsgurra]

limeads,

I think that you should avoid following my advice. I was thinking process equipment. Forget about torque and speed control. All you need is a motor and some breaking. Your spring seems quite OK if you use a longer one to get more turns out of it. Your index holes and your PLC does the rest. Sorry that I recommended overkill.

 

[Skogsgurra]

Not my day. Read BRAKING!

 

[Barry1961]

Don't know how I got a 50:1 reduction, must have been sleeping. A 20:1 worm does have a braking effect but is usually not self locking, it can back drive.

You might consider a counter weight instead of a spring. You would need some type of reduction to get the travel you would need but it would be constant force.

Barry1961

 

[jraef]

I have done billboard drive controls in the past. You will need a dynamic brake package, trust me. Without it, the pay-out reel overspins from the weight of the sign material.

"Venditori de oleum-vipera non vigere excordis populi"