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My award winning and trademarked Web101 short courses in Web Handling, Convertingand Windingthat have been taken by 5,000 students will be held June 18-21 in Milwaukee.  They are hosted by AIMCAL’s Converting School.  As a bonus feature, noted web machine builder Faustelwill be hosting an open house on June 18 to see real machines on their lab and shop floors.  If that schedule does not fit your own, you can take the same material as video-on-demand through AIMCAL’s Converting School Online.  If neither fits your schedule, you can always learn the hard way.

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Processor Power

Yellow Submarine Original Artwork copyright 2012

When I started my career in drive control and automation, I tried hard to do the most with the least processor power and the least memory. I learned which data types used the least memory and executed the quickest. We all knew that no one could possibly use or need 64K of memory.

That policy of conserving processor resources saved a lot of cost in most cases (excluding the cost of extra engineering). Several times I ran out of memory. On one project I had less than 300 bytes available on a 32K system. Way too close for comfort!

Often I have wondered if drive system performance would be improved with a faster scan time. One time the processor for a high performance coater drive had a scan time of 45msec. I got funding to upgrade the processor to one with 6 times the performance. On that occasion, the improved scan time (45 msec down to 9 msec) did not provide any improvement in tension regulator response. But it did not hurt!

Today memory chips are inexpensive, but memory modules for control systems still cost thousands per Megabyte. I am not advocating spending an extra $10K per system on memory. I do advocate purchasing enough processor and memory for the application with a minimum of 20 to 40% extra capacity.

I also recommend taking a bit of time to optimize programs to save processor time and memory. This can result in tighter code easier to read and understand. However, taking the programming to an ultimate saving in memory and processor time results in such complexity that even the original programmer cannot debug or modify the program several years later.

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Web handling is the science of moving a web as quickly and reliably as possible.  But where did that science come from?  Who studied the web processes in order to develop hypothesis about their behavior? Who ran trials to validate their hypothesis?  Who identified the mathematical relationships that describe the behavior of webs?  John Shelton is the first person who identified what we now refer to as web handling in his seminal 1967 Master’s thesis. Who was his advisor?  Karl Reid.  Do you know who Karl Reid is?  Have you ever heard of Oklahoma State’s Web Handling Research Center?

The WHRC is an Industry / University Cooperative Research Center that was first established in 1986.  They are the only center of its type in the world.  They have been focused on expanding the knowledge base in web handling and transferring that information to their industrial sponsors and others that are concerned about web handling.

How did the WHRC come about you may ask?  John Shelton worked at Fife Corporation.  His manager was Bruce Feiertag.  John wanted to pursue a master’s degree in Mechanical Engineering to better understand the products that Fife made.  Bruce sponsored him to do so.  John’s thesis advisor was Karl Reid.  John with Karl’s guidance identified the first and second laws of web handling.  The idea for the WHRC came about when Bruce Feiertag told Karl that there was a great need in industry to study this new field.  Bruce provided a list of companies who would be interested.  John wrote the basis for what this new center would study.  Karl Reid led the effort to establish the WHRC as a National Science Foundation Center (I/UCRC). 

At the time Karl was the department head of OSU’s School of Mechanical and Aerospace Engineering.  He later became the Dean of the College of Engineering, Architecture and Technology. He served in that role for more than 25 years.  During this tenure Karl nurtured the growth of the WHRC.  He brought faculty into the WHRC such as Keith Good, Prabhakar Pagilla and Ron Markum to drive the technology to new heights.  Karl began the rich tradition to host the first International Web Handling Conference “IWEB” in 1991.  In two months the 15th IWEB will be held on June 10-13, 2019. Who will be leading the conference? Karl Reid.

I have the rich honor to say that I know Karl Reid and have benefitted greatly from what he has provided to industry.  If you have the opportunity to participate at IWEB 15 please make a point to shake Karl’s hand and thank him for his tireless efforts.

Neal Michal - neal@convertingexpert.com

 

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Torque Boost

Yellow Submarine Original Artwork copyright 2012

Often the Torque Hold function provides adequate tension during most of the index, but may not provide enough tension for a good clean cut. The knife may require a very taut web if the web is stretchy. In this case, Torque Boost is required.

Torque Boost is used instead of Tension Boost, because the turret spindle is not running n tension control during an index. The spindle is running in Torque Hold mode. A boost in torque will create a boost in tension.

For some stretchy products like polyethylene stretch wrap, a 300% torque boost may be required to provide a clean cut. Torque boost will tighten the web, but will also cause the web width to shrink (neck in). Torque boost should be applied as late as possible just before the knife cut. Torque boost will end when torque hold mode ends – at the cut or a web break.

Torque boost should be used only if the product calls for it. The lowest level of boost that will perform satisfactorily should be used. Downsides of torque boost are the outside layers of your roll will be wound with a high tension and the product width will shrink.

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When Should I Change Out My Roller?

The simple answer is: you must use economics to answer this or any other general question of product quality as it relates to maintenance that is not totally crystal clear.  Here you would find the minima of the sum of the costs of changing a roller, which you know all too well, plus the costs of NOT changing a roller, which you likely do not know as well.  The costs of NOT changing a roll are the incremental increases in waste, delay and customer complaint with regard to trying to squeeze more running time before taking the machine down for repairs.  Since you know the costs of changing well and the costs of NOT changing NOT very well, you will, as a rule, run too long or way too long and cost your company needlessly in extra waste, delay and customer complaint.  Bottom line: know your defects and know economics and do the work to best serve the bottom line.

https://www.youtube.com/watch?v=itmJD7lN7yE

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Torque Hold

Yellow Submarine Original Artwork copyright 2012

Many events happen during a turret winder index that make it very difficult to control tension. An old, but practical, technique for surviving an index is to put the outgoing spindle into Torque Hold mode.

Torque Hold is a drive function that memorizes the torque at a particular instant, and then runs the motor at that constant torque value. For the outgoing spindle drive on a turret winder, the torque is measured and memorized just after tension boost is applied, but before the layon roller or the turret are permitted to move.

Theoretically, the outgoing spindle will maintain or hold tension during the index if its torque is held at the last known good value. As the web path changes because the layon roller is moving or the turret is rotating, the speed of the spindle will vary appropriately, but still maintain tension.

Torque Hold mode is ended with the knife cut. After the knife cut, the outgoing spindle is no longer in control of the web and should be stopped. Torque Hold mode should also be ended if a web break occurs. If the spindle drive remains in torque hold mode after a web break, the spindle will accelerate without limit creating a hazardous overspeed condition with a large roll.

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What is the Best Cover Hardness?

 

 

The simple answer is: it depends.  Covers can be foam soft to ‘bone’ hard (fiber-epoxy laminates used in highly loaded paper calendaring rollers) to no cover at all.  More than anything else, process lineal nip load (N/m or PLI) and peak pressure under the nip (Mpa or psi) determine what cover options will survive.  Here a laminator nip may be 10-100X the load of a winder nip and a calender nip can be 10X higher still.  So, you need to know your process application well to make the first cull of cover options that can survive.  The second cull will be for any cover temperature and chemistry limitations.  Once you have the shorter list of cover hardnesses and chemistries, the answer may become simpler.  The softest cover (that still does the process work) that you can afford to maintain in good condition.  That is because the softer cover provides more ‘forgiveness’ to variations in web, cover and roller.  Thus, for many applications it is simply a tradeoff between life (ongoing costs) and quality (uniformity of nip).

https://www.youtube.com/watch?v=_R2Iidv33Y8

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Yellow Submarine Original Artwork copyright 2012

While not the only cause, it is well known that tension variations cause a web to move in the cross-machine direction. The web displacement or movement can be in either direction, to the operator size or to the back side. With many webs, the displacement can cause severe problems.

Some of the problems I have seen are listed. On coaters, the coating may build up at the edges of the web. If the web moves, it's edge will cross over the buildup and break.

If the web is slit, the slitting may cut off any evidence of web wandering. However, if the web is printed, laminated or embossed prior to slitting, the displacement may damage the product. I once worked with a construction product with bubbles. Web displacement caused the slit to cut the bubbles, rather than on the flat track between bubbles.

Not all web displacement problems are caused by tension variations. An easy method to determine whether tension variations are the source of the problem is to determine if the displacement happens only when speed is changed. An additional test is to see if a change in tension setpoint causes the displacement while running at a steady speed.

If tension variations cause web displacement, check for mechanical problems such as roller alignment. The drive will probably require improvements in tension regulator tuning.

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What is the best winder curve/taper?

 

 

The simple answer to this quite common question is “it depends largely on the defect(s) you are trying to avoid.”  If you have no tightness related defects.  Nothing need be done.  If you have a tight defect, then back off.  If you have a loose defect, then crank it up.  However, that presumes you know your defects very well.  For example, there are 3 kinds of core crush, two are tight defects and one is a loose defect.  There are six kinds of telescopes, some are tight, some are loose and one is a taper defect.  So, your choice of curve or taper would then depend on which specific typeof core crush and which specific typeof telescope you have on a specific wound roll.  Also note that you can have tight and loose defects in the same roll, same set of rolls or under the same winder settings. In short, the best winder curve depends on how well you understand your specific defect mix and the limitations of your web and winding machine.

https://www.youtube.com/watch?v=vmfHxfvlsOg

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Tension Boost

Yellow Submarine Original Artwork copyright 2012

One of the drive tools available for turret winder applications is tension boost. This function is different than torque boost.

Tension boost is not always required. It may be required if the winder includes a layon roller or rider roller. The layon roller is removed for the turret index and thus the wound in tension is reduced. Boosting the tension can reduce wound roll defects due to the loss of the layon roller.

The timing for tension boost on the outgoing roll is important. The tension should be automatically increased just before (~0.5 second) the layon roll lifts. The boost should remain active the entire time the layon roll is lifted. In fact, so many actions occur during the index, that it may make sense to maintain tension boost until the knife cut is complete. After the knife cut, tension drops to zero on the outgoing roll. Tension control including tension boost should be disabled while the outgoing roll is stopped.

Tension boost may also be required on the incoming roll to provide a tightly wound start at the core. If tension boost is used for the incoming roll, the boost should be ramped off over several seconds rather than simply removed.

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How to Communicate Via Video

190307 = How to Communicate Via Video 

Video is the most powerful way to communicate many types of messages whether it be for instruction or persuasion.  Yet, it is almost absent in our web industries.  Here I show how you can do industrial video without spending thousands of hours in school or tens of thousands of dollars on contractors.

Step 0 - Communication - https://www.youtube.com/watch?v=9HMEDhQyg1U

Step 1 - Videography - https://www.youtube.com/watch?v=m9__0VF92e4

Step 2 – Video Editing - https://www.youtube.com/watch?v=37gmNtCZpKU

Step 3 – Video Platforms and SEO - https://www.youtube.com/watch?v=_Dhd5Z6yASo

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Virtual Computers

Yellow Submarine Original Artwork copyright 2012

Many older drive systems rely on programming tools that will only run on older operating systems. The drive program may run only on an old DOS or Windows operating system. Newer operating systems on modern computers simply laugh when you try to install the drive program.

One way of keeping these old programs operating is to purchase second hand old computers as needed.

The new method is to install virtual computer software on a modern. The virtual computer looks like just one more window on the computer screen. However, inside this window you can install any older operating system and the drive software.

Virtual computers may allow you to keep your existing drive systems maintained for many more years. There still remain many problems in getting Virtual machines running correctly without freezing or crashing. You may require help from your IT department.

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Just over one month until the must-attend ICE-USA tradeshow.  I wouldn’t miss it.  In fact, can’t.  I will be busy giving short courses on rewinder department productivity will be one of a small stable of Ask The Experts.  The link below gives information on how to sign up for a 15 minute block for advice from some of the smartest converting people on the planet.  Sign up now because I was completely booked until the last afternoon at the last tradeshow.  https://www.ice-x-usa.com/ask-the-experts

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Remote Access

Today most companies expect remote access troubleshooting from suppliers of drive systems. Remote access software over the internet and using Virtual Private Networks (VPN) or web-based remote access provide very useful connectivity.

Technically remote access can be performed two ways.

A customer’s server (on or off-site) can provide a connection point to the drive system which the drive supplier can use to connect to the drive system and make changes independent of the customer’s maintenance personnel. IT departments often prefer this method, but it makes maintenance leery.

Alternately the customer’s maintenance computer can be set up to run the maintenance program and share the screen, keyboard, and mouse over the internet. Maintenance sees everything the supplier is doing. Maintenance is often more comfortable with this method, but IT becomes very leery.

In either case, the supplier can see anything the computer can see. The screen update rate is quite reasonable, almost like being right on site. That includes seeing numbers changing quickly and reading trend charts on the screen.

The supplier cannot see what is happening to the line, or feel any vibration, or listen for unusual noises, or smell smoke, or know what the operator will do next. Until the computer knows more about the state of the web line, remote changes should not be made without live communications with personnel on site.

Remote access is very good, but not as good as being on site.

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How to Size Nearly Everything

We continue the discussion of ‘nominal’ from the previous post with an example load cell application.  Sizing loads cells is easy provided that someone takes the time to do some simple trigonometry and engineering statics calculations.

1)  'Best' is not the goal

2)  'Good enough' is the goal

By good enough I mean that the load cell system should be able to measure/resolve less than 5% of the lowest tension you ever expect to run.  While wrapping more (or getting a better load cell) and getting to 1% of the lowest tension might seemlike it is better, it will give you no better practical results.  Thus, if the simpler Option A is good enough, then that is what you want.  However, if even Option B with the higher wrap angle is not good enough, you must re-iterate on the design.  With light weight webs you may need to do more.  You could, for example, use 180 degree wraps (pulling up) and light weight carbon fiber roller to get the tare weight down and thus get a smaller more sensitive load cell.

This is not only how we size load cells, but also how we size brakes, motors, cylinders, sensors and much much more.

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Permanent Magnet Motors

Yellow Submarine Original Artwork copyright 2012

Permanent Magnet (PM) motors stators are very similar to synchronous or induction motor stators. The rotor is made of a shaft with a sandwich of steel layers (laminations) or alternately with a solid casting. The rotor is permanently magnetized, usually with rare earth magnets.

The PM produces flux and torque without the cost of magnetizing current.

The stator needs 3 phase poles with copper windings. If there are 2 poles, the motor will turn at exactly 3600 RPM (3000 RPM) at 60H (50 Hz). A 4 pole motor will rotate at exactly 1800 RPM. A 6 pole motor will rotate at exactly 1200 RPM.

PM motors produce torque only when they are turning at exactly synchronous speed. Slipping a pole due to torque overload is a serious problem which must trip the motor. The trick is in starting a PM motor since it has no torque until it gets to synch speed. Special PM variable speed drives or servo drives are used with PM motors. Many servo systems use PM motors and drives. PM motors are expected to become more common, unless a shortage of rare earth magnets make them prohibitively expensive.

Warning – PM motors are always on, even when the drive is turned off. Rotating the shaft by hand or by pulling on the web will generate current at the stator and motor leads back to the drive. Lockout/Tagout should include locking the shaft.

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NASA Nominal and Web Handling Design

 

 

NASA, aerospace companies and many other organizations make regular use of the concept of nominal to achieve some truly dazzling results.  In lay person’s terms, it means within preset parameters or, more simply, good enough.  In economic terms, it is the optimum or lowest cost solution between too little diligence and too much diligence.  Thus, while NASA regularly threads the needle with some truly amazing billiard shot paths to planets, they do all of this without paralyzing perfectionism [1].  Yes, they do miss a few deadlines and sometimes they totally miss a planet.  But these are due to unanticipated snags of a truly first of a kind project.  They are not due to improving things that are not broken, nor seek performance beyond nominal.

So, what has this to do with web handling?  It has to do with over-engineering components, which though uncommon, does happen.  As an example, roller alignment that avoids wrinkling and other web damage may be good enough.  A load cell that can resolve 10% of the lightest tension to be run may be good enough. Drive systems that can hold tensions during steady state to better than 5% may also be good enough.

[1] https://www.nasa.gov/sites/default/files/atoms/files/nasa_systems_engineering_handbook_0.pdf

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Synchronous Motors

Yellow Submarine Original Artwork copyright 2012

Synchronous motors stators are very similar to induction motor stators. The rotor is made of a shaft with a sandwich of steel layers (laminations) or alternately with a solid casting. The rotor requires a winding which must be excited with dc current. The rotor current or excitation electro-magnetizes the rotor.

Rotor excitation current can be achieved with normal brushes or on larger motors with a brushless exciter. The brushless exciter consists of an extra small generator on the shaft with a rectifier.

The stator needs 3 phase poles with copper windings. If there are 2 poles, the motor will turn at exactly 3600 RPM (3000 RPM) at 60H (50 Hz). A 4 pole motor will rotate at exactly 1800 RPM. A 6 pole motor will rotate at exactly 1200 RPM.

Synchronous motors produce torque only when they are turning at exactly synchronous speed. Slipping a pole due to torque overload is a serious problem which must trip the motor. The trick is in starting a synchronous motor since it has no torque until it gets to synch speed. For across the line starts, the rotor is shorted. This make the rotor act essentially like the rotor in an induction motor. Induced rotor current then produces torque proportional to slip and the motor accelerates. Once the speed is close to synch speed, the field excitation is applied and the motor snaps into synchronous speed.

Variable speed drives must be specified for operation with synchronous motors. Except for some servo drives, few synchronous motors are used for variable speed operation. Note that Permanent Magnet (PM) motors are a special class of synchronous motor and are becoming widespread in web handling applications.

Advanced users:

A large synchronous motor can have its rotor current over-excited to produce vars (Volt-Ampere Reactive) which can correct the plant electrical power factor and reduce utility charges due to poor power factor.

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