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Filed under: Tensioning, Web Mechanics --- Tim Walker @ 10:20 AM

I just rec'd an amazing testimonial from Dr. J. Keith Good at OK-State U's Web Handling Research Center (WHRC). Can you believe motor controlled machine with a 6000:1 controllable speed range?

I created a little stir a few months back in asking whether torque control is EVER the right choice for closed-loop tension control. I didn't think it was, mostly due to the natural torque losses of speed reducers getting in the way of good torque transmission.

Pete Werner, formerly of Rockwell Automation, has been educating me on how torque control should be the first choice... and get rid of those speed reducers. Can we believe Pete? Well, I think YES. Read this testimonial from Dr. J. Keith Good, top researcher at the WHRC.
=====================================================
Tim,
Rockwell has done a superb job on our High Speed Web Line. It now has the Flex 700S phase II drives with the through axis Heidenhain encoders. This requires a special option board on the 700s to communicate with the encoder. I have no speed reduction in any form today, we are direct drive 1:1.

When our line was originally commissioned with Reliance's 1st generation VCI controllers cogging was a problem when running at low speed. In that day performance specs stated you should not run at less than 10% of full speed, thus we should not have hoped to have good speed and tension control until we reached 500 fpm. If the drive technology had not improved I was considering 2 speed gear boxes similar to Art's old solvent line to allow me to run at 50 fpm without cogging.

Today I'm running the same motors the line was commissioned with but with the new drives and encoders listed above. Tim I can run smoothly with no cogging at 1/2 fpm and if I had the guts I could go 5000 fpm. I don't because I still have some idlers that scare me at 3000 fpm. Also we commonly command zero fpm in our experiments. Tension and drives are fully on holding command tensions at zero velocity. We then transition to 10 or 50 fpm and the machine does so beautifully.
Thus I believe it is now possible to run at low speeds without cogging. I have yet to meet a zero backlash gearbox or right angle gearbox (no matter what their written specs are) so if you don't have to have them I'm all for eliminating them.

Best regards,
Keith (Dr. J. Keith Good, OSU)

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Maybe 10000:1 speed range, with a little guts? Whew.

BTW, I don't mean to make convertingblog.com a commercial promotion website, but I don't see a reason to leave out the brand name of products that are key part of a great solution story that help raise the knowledge of the entire converting community. I expect you can get similar results from non-Rockwell products and I encourage anyone to share their experiences here.

I happy to name brand name's on the good stories. I'll likely remove brand names where it is needed 'to protect the innocent.'

Filed under: Rollers, Traction --- Tim Walker @ 11:23 AM

Question:
I have a S-wrap configuration that is causing poor film quality because the delta T across the rolls is very high. The temperature varies because the chilled water is too cold. The water flow through the rolls is at a dribble to help the problem but the film heats the water causing the temp across the rolls to increase. Do you recommend chilled water, at what temp? or process water, normally 70 degF?
Michelle Perry
michelle.perry@amcor-Flexibles.com

Reply:
I'm note sure I understand the problem here.
Am I correct to assume the temperature variation is too high across the width of the rollers?
You state the water flow is at a dribble. Wouldn't a high flow rate reduce the temperature variation? At a dribble, it seems you are asking the web to control the roller temperature.

Regarding chilled or 70F water, the lower the temp, but more ability you have to fight the web heat transfer. Too low leads to the risk of dropping below the vapor temperature and forming condensation or sweating, but if you have a lot of heat from the web, this shouldn't be a problem until you stop the line.

tjw

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 10:32 AM

Two questions from Greg Martz of Martz Technologies
engineering@martztechnologies.com

Q1: Center Winding:
Diameter Calculator, or Ultra-sonic. Which is better and why?

Reply1:
The best answer is BOTH. By a diameter calculator, I assume you are talking about a tachometer ratio calculation using the spindle rpm, and the diameter + rpm of a non-slipping roller. The tach ratio diameter calculator is the most reliable approach, but it doesn't give you any information when the system is stopped. Therefore, the need for the ultrasonic sensor.
I wouldn't rely on the u/s sensor for the entire winding or unwinding process. They are too easily affected by outside influences, such as rapid air temperature or humidity changes and blockage from a web scraps.

By diameter calculator, you may have been thinking of the web thickness, core OD, and revolutions methods. I don't see this used as often, but if you know thickness (which may be a good question), then this works well, too.

Winders may not need the u/s sensor if you always start with a give core OD or start where you stopped (you may need to add a operator 'new core' button).

Q2: Center Winding:
Drive in Speed mode with a Torque Trim, or Drive in Speed mode with a speed trim?

Reply2:
How about torque mode with torque trim? This is what Pete Werner, formerly of Rockwell Automation, has been trying to make the case for. The classic or traditional design would have a speed reducer, therefore, you would run in speed mode with speed trim, since the motor has a large torque noisy drive train.

See today's post on torque control for more on the debate of torque vs speed mode tension control.

tjw

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 09:42 AM

Melissa from Cambridge Label stumped me with a simple question:

What is the most accurate proofing method available today?

I'm not in the loop on this technology enough to know.
If anyone has an answer. Please reply here or send a note to Melissa at melissa@cambridgelabel.com.

tjw

Filed under: Slitting, Cutting --- Tim Walker @ 09:36 AM

Question:
For tangential v. wrap shear slitting systems, how much wrap can you have before you are no longer considered tangential shear?

Our "tangential" web machines have a very small amount of wrap (~1 degree). We are contemplating some new machine designs, and it got me wondering,

Is the need for better web support typically the largest factor for switching to a wrap system?

Thanks in advance,

Jason Nelson, Toray
JNelson@toraycompam.com

Reply:
I think I better drum up Reiny Schable to chime in on this one.

I think one of the main benefits of tangential shear is to drive the top and bottom knives at the speed to get the best cut. This may be a bottom knife that is slightly faster than the web. Tangential shear also the web and knife to slip without significant friction and web tensioning. The wrap on tangential slitting is often nearly equal to the angle included by the chord length of engagement, so you aren't pulling the web up against the top knife or off the bottom knife until it has passed the entire overlap length.

Per your question on web support... Web support can be important in both wrap and tangential slitting. For tangential, you can get away with large gaps between bottom knives, but that doesn't mean you shouldn't consider supporting the web between knives.

tjw

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 09:21 AM

Question:
Has anyone modelled the effect of varying MD tension across the width on winding stresses? These are stresses created by previous spreading or steering devices, not a result of web thickness or bagginess variations. What do you think would happen?
Dilwyn Jones, Emral Ltd.
Dilwyn.Jones@physics.org

Reply:
My feeling is that the tensioning upstream of a winding roll, like any spreading device, is a temporary effect. The purpose, of course, is to eliminate wrinkling at winding. I expect once on the wound roll and away from the incoming span, the web would shift tension to conform to the shape of the roll. If the product was adhesive tape, then maybe the span tension would be locked into the layer.

Imagine a baggy edge web running into a nip. You can pull back on the baggy side with a misaligned roller or spreader and get it taut and into the nip wrinkle free, but the web comes out the other side of the nip still baggy. The same would happen in winding. You can get onto the wound roll, but a longer, low tension baggy lane will still have low tension.

Your thoughts?

tjw

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 09:21 AM

Question:
How good are winding models at predicting the diameter of wound rolls, for a given length, tension profile and lay-on force (The small variations from compression and air entrainment, of course!)?
Dilwyn Jones, Emral Ltd.
Dilwyn.Jones@physics.org

Reply (not exactly an answer):
I haven't seen this done.

Start with the easy case of a narrow, uniform thickness roll - I imagine that if you had the stack modulus data and modeled the roll pressure, you could map the web thickness on to the pressure model to get a thickness of each layer, total stack height, hence diameter.

The difficult case, as you've alluded to, is to incorporate thickness variations and entrained air. Some work along this line was presented at the last IWEB, Dr. Keith Good and xxx, but they were looking more at stresses, not stains and diameters.

What would you do with this info?
And what are your thought on this topic? Do tell.

tjw

Filed under: Winding, Unwinding, Roll Defects --- Tim Walker @ 08:10 AM

Question:
Does running a web through a 'z' pattern of rollers reduce tension variances? The 'z' pattern in question is made up of 4 rollers located immediately after the unwind.
Peter Krasucki
pkrasucki@rdspecialties.com

Answer:
Yes, to some degree, especially is the web had good friction on the roller (doesn't slip) and the rollers have modest to high inertia.

You can imagine a stopped web with stopped rollers. If you jerk on the web at the unwind and the web doesn't slip on the roller and the rollers don't turn, then NO tension shock would pass over the rollers.

A running web is different from this scenario. The tension or strain of the web travels with it. For a running web, if you change the unwind brake setting, the tension from the unwind to the next drive point will nominally go to the new level. So low frequency tesnion changes will pass through the system.

The benefit, if significant, will be in calming high frequency tension variations, where high frequency is relative to the span lengths (or the time to travel the span length). In some regards, longer spans will do more for tension noise attenuation than the rollers.

tjw

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 09:38 PM

A few months back, I made post asking 'Is motor torque control EVER the right?' This was a post based on my experience with several converting controls engineers.

Pete Werner, formerly of Rockwell Automation, posted his comments on this and made a strong case of torque-based motor control should be the first choice. This is quite a contrast from what I've seen over the last 20 years.

Since then, Pete has continued to educate me on this topic. Pete made an interesting presentation at the AWEB conference last month. He makes some good points about how speed regulation and dancer rollers the popular choice, but these are devices invented to solve problem many years ago.

Why does speed-based tension control continue to dominate converting applications?

Probably several reasons. First, controls engineers have learn this and know it works. Speed is easy to understand.

Why use speed reducers (gearboxes)?

Supplier like to boast speed accuracy. Controls engineers like using speed reducers to reduce motor size and increase efficiency. But you shouldn't be thinking about energy or motor costs when your goal is good tension control. Yes, eliminating the speed reduce increase motor size and cost (both torque related), but you save some of that back by not buy a gearbox. The most important motive should be good (or great) tension control.

I always had it drilled into me that you want a motor to run using its full operating speed range. If the motor has 0.01 percent speed accuracy, this is 0.2 rpm variation over 2000 rpms. If you run the motor at 100 rpm with no speed reducer, you're asking for 0.2 percent speed variations. Why would you do that?

This is the wrong question. Motor are not inherently speed devices. They are torque generators. Torque output divided by the mechanical leverage of radius creates tension. Why care about speed accuracy at all?
These are great questions.

I like Pete's question where he says 'You don't usually consider putting a speed reducer on a braked or clutched application, why do it on a motor?'

Today's drives call for new answers. I get the feeling Pete would like to eliminate 90 percent of the speed reducer (gearboxes) and dancer roller in the converting industry.

Let me know your thoughts or experiences regarding speed or torque motor control and when dancer rollers can be eliminated.

tjw

Filed under: General Business Topics --- Tim Walker @ 09:31 AM

If you've googled web handling and converting topics, such as wrinkling, winding, tension control, you'll find two guys popping up again and again. You're reading one of them now (moi...tjwalker, tjwa inc.) and the other is Dr. David Roisum of Finishing Technologies.

Dave has been an independent consultant a few more years than I have and his Beloit and Kimberly-Clark days give him much more paper industry experience than I'll ever have (I'm more of a film guy).

Dave has been more than gratious as I left 3M and became an independent consultant. The web handling areas is a 'big pond' with more than enough room for two fish.

Dave and I run into each other often (that sounds like it hurts). It's good to compare notes with a fellow consultant. I always read his stuff...and you should, too.

I write a monthly column for Paper, Film, and Foil Converter - WEB LINES.
Dave writes a montly column for Converting magazine - WEB WORKS.

I'm in the blogging game (you're reading it now).
Dave is also in the blog-o-sphere, via AIMCAL.
www.webhandlingblog.com

Enjoy. I hope we aren't giving away too many free answers. We both got families to feed (and hobbies to support).