Web Unwind and Rewind Control

[Stuntman]

Peter-I have had good success in the past applying somewhat what you are saying to a rewinder but I had a dancer.

This sequence sets the "gear ratio"
Upon pressing the start button the rewind would take up slack in the web until the dancer was 50% full, once 50% full the unwind would start feeding material to the rewind.

Think of it this way, say we have a unwind and rewind that are driven from the same motor at the the exact same gear ratio, both roll diameters are the same and never change. No stretch perfect material. You should be able to use a dancer to take up the slack in the material and provide a specific tension. once the tension is set lock the dancer in place and hit the start the drive/motors. We are able to keep tension without a gear ratio.

OK out of the perfect world and back to my application. Have the Unwind set the web speed and have the rewind respond with speed to hold tension. I think the key to the process is the speed set point that is given to the rewind drive that is controlling tension. Then having the speed trimmed above and below this an equal amount using load cells i.e. +/- 10rpm. If our rewind speed set point is off so will be our actual usable +/- trim.

I am apologize I am not very good at articulating my ideas.

I should be able to make this work by setting the rewind speed setpoint but honestly my biggest worry now is that the rewind will start pulling the unwind and regenerate energy. The unwind needs a brake.

I quick read on tension basics
http://www.tappi.org/content/events/07place/papers/whiteside.pdf

 

[DickDV]

Most drive manufacturers and surely Siemens will have pre-packaged software for this type of application. I'd check that out before trying to reinvent the wheel.

 

[JRW]

How's this application going?

 

[Stuntman]

Its going good, I have had to switch off of that project for a few days to get a set of drawings done but I will post some details and maybe code when I get a chance.

 

[OkiePC]

What Peter last described is the best method for control if you want to do it yourself, calculate your best estimate of the diameter, and trim it as necessary to adjust for material thickness variations...You want surface speed to begin with, and tension as a trimming influence.

In most of those tire material and web winders/rewinders, we had one loadcell, and it was allowed to trim the letoff speed along with another scaled offset for any dancer postion. The dancer and tension contolrs sometimes went through PID math, but often just one "P" calculation was used.

Before I did all that to the math, what was in these machines was "dumb" PID math. There had to be an error before it would react, and you had to limit how fast it would react or adjust when the diameter was at either extreme.

I added some calculations to estimate the diameter at all times to get in the ballpark and allow a limit to how much influence the tension feedback or dancer position would have at the end. Sometimes, the "gain factor" for the dancer would need to be stepped depending on the line speed. I may want the dancer to have 80% control of the motor speed following a splice or abnormal stoppage, and then only 10% during product X which is pretty uniform...

Doing the geometry in the PLC and starting really close to known velocities makes starting, stopping, and overall machine "smoothness" much better. It increased the "top end" of those steel belt spool production lines, the winder can now far out run the upstream slitters and cutters.

We did have two really high speed slitters for spiral overlay stock for z-rated tires. That machine had drives built for web handling with frequency signal from one to the other, and onboard ratio detection control, you put in the engineering values (like core diameter) and inches per encoder rev, and the two drives and slaved off the master with this simple one page sheet of info. I think we had a Siemens DC set up with nice built in ratio settings for winding in the big stuff in another department, making 4000lb rolls of steel belt and ply stock at 400 feet per minute.

I overhauled one with MaxPak DC drives and motors and it was also making ... picture rolls of thick black gum rubber tape with nylon backing, 1 inch wide, 3 feet in diameter on 3" cores from 42" wide rolled stock, with two takeoff shafts. This machien could probably hit 500 fpm with all new mandrels blades and chucks.

That type of performance calls for duty spec'd drives.

 

[gschwab]

Take a look at this
http://www.qcontrol.com/SP/AN/ApplicationExamples.html

 

[JRW]

What he doesnt have is the drive in the middle (like your link shows)
That's why I'm so interested in this thread

 

[Stuntman]

Update

Well the project has been pretty successful so far.

I have the machine running and unwind/rewinding up to 500fpm and holding tension at roughly +/-2 lbs. This 2 lbs swing is what I am reading directly from the load cell so its raw. Looking at the trend if i sampled and averaged it we would be very close maybe +/- 0.5 lbs The rolls being wound are nice and tight.

I have the unwind setting the speed of the web and I have the rewind setting the tension.

I give both the unwind and rewind a speed set point to follow for its given diameter. I then process the tension through a PI loop and scale my PI output of 0-100% to .8-1.2 and multiply that by rewind speed set point. So the speed of the rewind can be increased or decreased by 20% of the speed set point.

What I have noticed is as web speed gets faster the PI loop needs to be dialed back. If I leave the same PI settings for say 500fpm during start up the loops takes 5-10 seconds from the time you press the start button until the tension is following the set point. There is a few ways to go about solving this and I am not sure what the best way is. Anyway I kind of busy right now so that is all I have to say.

 

[JRW]

So did you complete this job?
Through a complete roll build how did the tension look?
Problems?

 

[Stuntman]

Yes, I did complete the job. I was really surprised with how well it controlled tension. I am able to hold tension at about +/- .5-lb of setpoint. I have load cells on on both the unwind and wind but only the wind load cells are being used for control. I did add measurement sensors on both the wind and unwind for roll diameter. Basically the Unwind sets the fpm and the wind controls the tension. I am using an S7-1200 with et200s distributed IO controlling 2 micromaster 440? drives using analog and discrete signals. The PID is in the PLC The hard part was at extremely low speeds when stopping and starting.

 

[dimigav]

Hello, I have a question. I work in a winder-unwinder application.
I use an S7-1200 plc with a WP231 weighting module. I measure the speed of the main machine with an encoder (20-80m/min). I also measure the Winder diameter (10-100cm) with a laser device in order to synchronize the two systems. With a loadcell connected to WP231 module I can take the tension of the fabric (I need tension between 2-20kg). With PID block inside the plc I trim (max 20%) the calculated speed of the Winder to keep tension steady.
Now, after many tests I saw instability on the tension. If I ask 5kg the actual tension moved between 4.6-5.5kg. I must say that I use the pre-tuning and fine-tuning functions pid_compact block.

Is that changes of tension acceptable, or I must tune the system more??

Thanks!!!

 

[Stuntman]

How does the finished roll look to you? If it looks good I would say it is acceptable. If the roll does not look good i would perform another fine tuning. If the roll after that is still bad, i would say something is not sized or scaled properly. Whether be a motor,gearbox, or output scaling within the PLC. Another thing i would consider is the sample rate of the loadcell by the PLC.

 

[PLC]

It's a small world. I heard the customer in Arkansas was looking at changing that machine because the control wasn't quite right