speed winder vs. torque winder 1

[PaulBr]

We are designing slitter-rewinder machine. This machine will be used to unwind various narrow (up to 17" wide) web materials like paper or films, slit them these materials to multiple streams and rewind these multiple streams on the individual cores. Example is the web with 5-6 rows of printed labels across is converted to 5-6 individual rolls which have only one label across.
Rewind shaft of the machine is driven by the motor and VFD. Until now in these types of application we configured drive in closed loop speed mode with external PID closed loop of tension. Tension feed back was coming from load cell. Signal from tension PID loop was trimming speed reference of the drive to achieve desired tension and produce good quality rolls. Max tension that machine is capable of is 20lb.
At this new machine someone is suggesting to configure rewind drive in torque mode still with tension feed back from the load cell, saying that in torque mode we'll have better tension control.
I've read in few places that both speed mode and torque mode of the drive are successfully used in winder applications. But I couldn't find comparison of these two methods, their advantages and disadvantages, and recommendations when to use one or another.
Does anyone have some sources of information on this subject?
Thank you

PaulBr.

 

[Skogsgurra]

There are several deep-probing articles on that theme. Google "winder tension control" to see a few. Further searches on the Rockwell, ABB and Siemens sites will fill in the details.

As a rule of thumb, Torque Control with a web tension feed-back is preferable in most cases where good tension control is needed when high speeds (500 - 2000 m/min) and fast ramp up/down is needed. What speed are you running? The control structure is simple and acceleration/deceleration inertia compensation is straigh-forward. The commissioning takes an experienced (and somewhat mathematically inclined) engineer. Fault-finding and maintenace may be a problem if the guy that commissioned the machine isn't available.

A simple dacer roll is adequate in many cases. It is simple and accurate.

I would not recommend a pure speed control with superimposed tension control. It is almost impossible to get a good tension control out of it since the tension controller has to have a very low P and long integration time and sometimes minimal (a few percent) influence on speed.



Gunnar Englund

http://www.gke.org

 

[PaulBr]

This machine is running at various speeds up to 900 feet per minute or 300 m/min.
Did I understand you correctly that when drive is in torque mode we would use two cascaded control loops: torque loop and tension loop. When drive is in speed mode we are having three contol loops: torque loop, speed loop, and tension loop. Because tension loop is the most outer loop, we are limited in our proportional gain.
Please correct me if I am wrong if drive is configured in torque mode we need to accurately predict required torque.
Where required torque is equal tension torque + inertia compensation torque + friction loses torque. Because this is slitting application, amount of friction loses unknown and will depend on type of web material, quality of slitting knives, number of slitting streams. Do you think we still will be able to have control tension well?
Would you please post few links that you feel are good in describing this topic.

Thank you

PaulBr

 

[Skogsgurra]

The tension control works directly on the limitation of the speed controller, so you actually has tension controller output coupled directly to motor/brake torque setpoint.

Yes, you need to predict torque - especially if you have short ramp times. Three hundred m/min is a rather low speed. So you can probably use a simpler tension control. It all depends on your web - if it is stiff or springy and what your tension quality requirements are. I guess that a simple dancer is adequate in your case.

Slitting action is usually very dependent on web tension and the walls of the rolls are, too.

I had a very good tutorial in English. It was by Siemens and is probably to find on their site. Look for products/drives and application notes.

Gunnar Englund

http://www.gke.org

 

[PaulBr]

"It all depends on your web - if it is stiff or springy and what your tension quality requirements are."

This is the key. We are not end user, we are OEM. We know that our customers will use different material. But we need to rewind "good" roll(have good tension control) with any type of material from thick papers with pressure sensitive labels to thin shrinking material like biopropilen.

I'll check Siemens web site.

Thanks,

PaulBr

 

[Skogsgurra]

OEM, huh?

Then you need a "sexy" solution. And dancers never are. So you should try indirect tension control. Once adjusted for the web/fabric/sheet it usually keeps tension within 10 or 15 percent over speed and diameter. Most customers run just one (or only a few) qualities so it should be possible to adjust for those during commissioning. And, with a good instruction manual, customers can do the adjustments themselves.

You need a "diameter servo" (old word for what it used to look like, it is a simple comparator/counter today) for unwind and wind and possibly individual tension controllers for the winders. It seems that you have at least one point where linear speed is controlled. So data for the diameter servo is available.

Your power requirements seem to be in the 500 W range for web tension at highest speed. So you will probably have around 2000 watts plus slitter power for the whole machine. That makes a purely electric solution relatively expensive. (Control is a large part of the package).

If I am mistaken with regard to power (more power needed), then the balance between drives and control will look better moneywise.

Gunnar Englund

http://www.gke.org

 

[PaulBr]

Existing design Machine itself is two motor two drive machine. One motor / drive is moving draw roll at constant speed and determine surface web speed.
Second motor is turning rewind shaft. Rewind shaft drive "knowing" surface speed of the web is able to calculate roll diameter and required rotational speed of rewind shaft. We are using load cell as tension feedback device. Output of tension PID loop is trimming speed reference of the rewind drive.
New design is trying to improve BOM (supplier change) and also improve performance of existing design.

PaulBr

 

[Skogsgurra]

No tension control on winders then? A lot easier to get a good result.

Where is the improvment potential the greatest - as you see it?

Gunnar Englund

http://www.gke.org

 

[Compositepro]

On a slitter you must rewind several stips simultaneously and maitain controlled tension on all of them. You can't do that with one control loop on one motor. If you must handle a variety of materials with varying stretch and compressability then the only method I know that will work is to overdrive the winding shaft(s) in speed cotrol and use slip clutches at each core. Of course, individual motors for each strip is also possible but seldon desireable.

I've operated many different designs and seen how material properties and mechanical precision interact to affect winding quality.

One issue that I have never really figured out is that most materials will wind best into straight rolls using 100% taper tension (constant torque) because every layer in the roll stays at the tension it was wound at as the roll diameter builds. Winding at constant tension often results in telescoped rolls due to the roll tightening as diameter increases. However, in most applications the roll is unwound at constant tension and telescoping occurs at unwnd. Often the simplest (but not desireable) solution is to use side plates on unwind.

 

[Skogsgurra]

That's a very valuable piece of information.

I really haven't done much work on smaller machines like this. So I am biased to think a couple of hundred kW for the unwind and wind. In those machines you have a very precise friction, acceleration and windage compensation. There is also a settable diameter dependent winding torque to avoid the accumulated pressure from external layers crushing the core. I guess that the Siemens papers I mentioned before are overkill for the smaller machines. Sounds like a real challenge to find a good and economical solution for those smaller machines. And interesting.

Gunnar Englund

http://www.gke.org

 

[ozmosis]

Paul
Siemens has a programme called "Converting Toolbox".

http://www.automation.siemens.com/mc/converting/en/e81d55fc-3897-43ab-9f1c-778fb67adeb7/index.aspx

It not only allows you to simulate and develop ideas "offline" but once decided, you can basically use the code you have developed in the actual programming of the system. The link shows a bit of info on the concept and a few references. The toolbox also allows you to swap between dancer control, closed loop tension (using torque or speed control) without having to commit to hardware.
It sounds like you are in the US so I would strongly advise you consult with a technical specialist on this application; you can get hold of one via this link:

http://www.sea.siemens.com/motioncontrol/default.html

 

[PaulBr]

Where is the improvment potential the greatest - as you see it?

We already have machine which I've described in previous posts. As far as size it is two motors 3HP each. This machine is performing OK, and customers like it.
This project is driven mostly by needs of BOM consolidation and using the same parts across all organization. We are changing supplier of electrical controls.
From the power and control view we will port existing solution on the new hardware base. Alone these lines we are trying farther improve existing design.
For example some of our customers need to operate this machine at lower tension setting because materials are stretching or they need "soft" wound rolls. We would like to improve machine performance at lower tension setting therefore I am investigating option of configuring rewind drive as torque winder.

One issue that I have never really figured out is that most materials will wind best into straight rolls using 100% taper tension (constant torque) because every layer in the roll stays at the tension it was wound at as the roll diameter builds. Winding at constant tension often results in telescoped rolls due to the roll tightening as diameter increases. However, in most applications the roll is unwound at constant tension and telescoping occurs at unwnd. Often the simplest (but not desireable) solution is to use side plates on unwind.

One of the features of our machine is tapered tension, where tension setpoint is function of wound roll diameter. On the unwind end we are controlling tension by controling braking torque proportional to unwind roll diameter.
I've checked web site with "Converting Toolbox". It looks pretty, but I am not sure if we'll be allowed to buy it.
PaulBr.

 

[Skogsgurra]

That's a very interesting piece of support! But I couldn't make any "own" settings. Is this for sale or do you download it? Or didn't I understand how to?

Gunnar Englund

http://www.gke.org

 

[ozmosis]

As I understand it, the software is for sale. It is not functional on-line (other than the odd demo button to show a few rollers moving around) via the links shown but in discussions with the local Siemens Motion Control PM (Production Machine) people you should find out more info on getting hold of it. I think it is fairly new as the local MC guys I spoke to here in the UK didn't know too much about it other than it was a tool coming out of Germany.

 

[automatic2]

the largest problem with controlling extensible substrates is the mass of the rewound / unwind rolls.

the second problem is not completely a tension problem, but the problem of extensibility imparted into the unwind roll at previous manufacturing processes. This affects the repeat quality of imprints, which in turn hampers end use equipment.

In manufacturing and printing of plastic substrates for the food / beverage industries, we turned our attention several times to the concept of having the print repeat contribute to the trim of rewinders.

Our most productive winders for high quality work where surface rewind, tension unwind. Although we did not close the loop, we sampled print repeat consistency between the two stages and made some interesting observations.

I no longer work in that industry, but am sure that closing the loop would improve processing on end use.

 

[jjohan]

In a former job, I worked with this type of application. First, forget the load cell and use a small dancer.

Use the dancer to regulate your tension.
The position of the dancer will provide a reference for your takeup (P control).

The system will operate as follows:

1 - Payoff system will start releasing product.

2 - Dancer will move down and maintain web tension

3 - Down movement will provide ref to takeup and will start takeup winding.

4 - P control to maintain the dancer at the center position will basically run the takeup at the speed the material is being fed into the system.

As the system accellerates, the dancer will tend to run a bit below the center point until full speed is reached. As the system decels, the dancer will be a bit above the center point. You will need to adjust the accel and decel rates to avoid maxing out the dancer.

The company I worked for is still in business and may even be able to help you.

http://www.Windakusa.com.

The system that most closely matches your application is a small tension control rewind system for optical fiber cable.

J