Informational

[Music] We don't want to install the sensor too far away or in the next span. This is mainly for control system purposes and stability. When the web guide makes a corrective action, that action is not seen at the sensor immediately. So, if you're running really fast, you might get away with moving these sensors a little further down.

But if you're running slow, whenever this web guide moves here, you would see that motion, if the sensor is as close to the exit roller as possible. If you install it here or here, especially when the web stops and there is a small error, the web guide would keep moving and that might cause the web to break or have unintended consequences. So, we don't want to have the sensor further away or in next span. And we don't even we don't also want to have a scenario where you have an angle that is not 90°.

If you have a 90° wrap, you have twist. As soon as you introduce something which is deviating more from the 90°, you start creating bending in the web. So these kind of bending is going to act as under steering the web. It's going to cause bending that's going to under steer the web and it also causes distortions and guiding stability.

So we don't really want to have any of these conditions. On the contrary, if you have a span exit span that is spread out like this, this is going to over steer the web. It's the bending effect that is causing that and we really don't want to do that. So ideal scenario would be to have a 90°ree wrap in and out.

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So in terms of edge guiding, most of you are familiar with this. We have a web guide and an edge sensor to provide feedback for the web guide mechanism. Last month we talked about the guiding principles and fundamentals of it. But essentially in most machines in edgeguiding kind of an application you position the sensor either on the operator side or on the drive side drive or the gear side and then the web is guided to the middle of the sensor position and the sensor is positioned along the cross machine direction so that the alignment provides the required justification of the web.

The main thing with this kind of a system is that it works well for most cases and for maybe majority of the applications there's no issue with it. The main issue comes when we have to change the web width. Whenever there is a product change over and you do a web width change the sensor has to be repositioned. As we get narrower, the sensor has to be moved to a different location.

That location of the sensor has to be justified based on the process requirement. In these examples, the sensors were moved so that the web center line position is always the same irrespective of the web width. But in certain other applications, it may be necessary to justify along the operator side or maybe along the drive side. So that is the only thing someone has to do in terms of product change over is to move the sensor.

But moving the sensor creates opportunities for operator errors and this can have other consequences with the web guiding performance.

[Music] So in terms of installation, we want to make sure that we have a 90° wrap at the entry and exit of the roller. And then there are considerations on the span length at the entry and exit. Usually you can get away with half a web width. We recommend about one to two web widths if possible.

If you have a stiffer web like metals, you might need a longer entry and exit span. We want to locate the sensor as close as possible. This is true for any web guide. It doesn't matter if it's a displacement guide, unwind guide, rewind guide, any web guide.

We want to have the sensor as close as possible hitting the span where the guiding action takes place. The recommendation is to be within the first half of the exit span. And then how long this span really depends upon how much correction you're looking for. Typically these carriages are allowed to pivot only about 5 to 10°.

If you want larger correction then you can make these fans longer. The main thing is that you need to make sure that the plane of motion of the carriage is perpendicular to the entry and exit span so that you can create a pure twist on these spans. And then as long as these rollers are moving in tandem or parallel to each other, then you will have the desired effect. They don't have to be on the same carriage.

They can be on different carriages as long as we are able to move them parallel to each other. You can even have a process here. You don't really have to have just two rollers. You can have multiple rollers.

So, it provides a lot of flexibility here. The guiding action is actually happening in the exit span. We don't want to install the sensor too far away or in the next span. This is mainly for control system purposes.

and stability. When the web guide makes a corrective action, that action is not seen at the sensor immediately. So, if you're running really fast, you might get away with moving these sensors a little farther down. But if you're running slow, whenever this web guide moves here, you would see that motion if the sensor is as close to the exit roller as possible.

If you install it here or here, especially when the web stops and there is a small error, the web guide would keep moving and that might cause the web to break or have unintended consequences. So, we don't want to have the sensor farther away or in an expand. And we don't even we don't also want to have a scenario where you have an angle that is not 90°. If you have a 90° wrap, you have twist.

As soon as you introduce something which is deviating more from the 90° you start creating bending in the web. So these kind of bending is going to act as under steering the web. It's going to cause bending that's going to under steer the web and it also causes distortions and guide instability. So we don't really want to have any of these conditions.

On the contrary, if you have a span exit span that is spread out like this, this is going to over steer the web, it's the bending effect that is causing that. And we really don't want to do that. So, ideal scenario would be to have a 90° wrap in and out. [Music]

Now moving over to intermediate web guides, we have a displacement web guide. This is another type of one of the most commonly used web guide that you're going to see and we would recommend this as the first choice for any web guiding application. One of the main reasons for that is it actually displaces the web. And in this web guide, it's not bending the web.

The reason why it's not bending the web is you have this entry span and a 90° wrap. And then you have the plane of the carriage right here. When this carriage pivots, the pivot point is shown here, but that's a mistake. It should have been right at the edge of right here.

So when this carriage rotates, pivots about the pivot point at this point right there, these two rollers are actually moving in tandem. So there's no bending in this region. In these fans, since they are perpendicular, that motion is a pure twist. So really there is no bending in this kind of a web guide.

If the web guide is designed properly, then these web guides can have one one ratio in the sense that if you move the web guide one unit, then the web will actually move one unit. That's why we call them a perfect web guide. I do see a question here that says, would you agree that an offset pivot guide acts on a different principle other than normal entry? That is correct.

Because these two rollers are parallel to each other. There is no bending in the span. The entry and the exit rollers are perpendicular or the wrap angle are perpendicular. This span is perpendicular to the plane of motion of the web guide.

They are going to be in twist. So there's no bending. And when there's no bending, there's no normal entry coming into picture there. The twist is an important design part.

And this would be our first choice for us in terms of applying it in any webg guiding situation.

So let's dive into detail about different components of the web guide. First we'll start off with guide structures and look at how guide structures are with different types of web guides that we saw. So first and foremost we have the unwind web guide structure. In this case you have a parent roll feeding the web into your machine.

This role is on a shifting stand or a base supported by linear bearings. An actuator connects the moving stand with the fixed base and then there's a sensor here that is looking at the position of the web. The main objective of an unwind web guide is to ensure that the web fed into the process is at the desired location. Because of that, you have a sensor fixed to a machine frame actually moves in and out of the monitor.

It's going to go in and out. And the feedback from the sensor is used to make this unwind guide move in and out so that it can position at the right location. One thing I wanted to point out is that there is a shifting idler. When I say shifting idler, it means that this idler is attached to this moving base.

The main reason why we do that is that if we put a sensor right here, it is not an ideal location just because of the fact that when the diameter of this roller changes, you're going to have the web plane go in and out. And if that happens, that's going to affect your guiding. Typically, you would see a shifting idler. It doesn't have to be one.

It can be multiple. It could also be a whole frame with a lot of rollers. We need to put the sensor just downstream of the last shifting idler and the sensor is fixed to the machine frame so we can guide the web. So those are the main things with an unwind guide.

Now when we look at rewind guide rewind even though we call it as a guiding it's not actually guiding the web it's chasing the web. The main thing unique about this is that in a rewind system you have a sensor attached to the rewind frame. All of the things in terms of the carriage it's exactly the same. You have a sensor that is attached to the rewind stand so that when the rewind moves, the sensor also moves and then you have a fixed idler.

Rewind is not really guiding the web. It's actually chasing the web. And the main reason why we do that is that we need to maintain the relative position of the web and the rewind roll. If we put the sensor on a fixed frame and look at this rewind roll, then we would not know the relative position between those two.

That's the main reason why we attach this sensor onto the moving rewind stand gives us indirectly the position of the rewind stand. And the objective is to make sure that we move the rewind stand so that the middle of the sensor or the guide point of the sensor matches the location of the web. Like I mentioned, it's not really guiding the web. We are chasing the web so that the rewind roll would be at the right location to get the web bound properly.

So just to summarize about these two terminal guides, we can look at what are the things that we need to have a good rewind or unwind guiding system. First of all, in terms of design, we need to make sure that the mechanical structure and rigidity and stiffness are designed properly. We are moving a big mass and depending upon the type of web may be metals it may be thousands of pounds multiple thousands of pounds that we are trying to move and we need to make sure that the structure is rigid enough so that we can avoid any mechanical resonance the natural frequency of the structure should be at least 3 to four times the operating frequency of the control system. The other thing we need to consider especially with these kind of guides is that we need to size the actuator properly.

When we talk about sizing the actuator what we are talking about is it should have enough thrust so that it can push the mass. It has enough thrust to overcome the static friction and provide the desired acceleration to reject the disturbances or errors that may be there. Just like the mechanical structure rigidity, we need to also make sure that the actuator coupling and the actuator stiffness are all accounted for. Any play in the actuator coupling is going to reduce the stiffness of the overall system.

That's going to destabilize your system. In terms of installation consideration, the main thing that we want to look for in these type of guides is the location of the sensor with respect to the moving stand. Either it's fixed to the machine frame or it's moving with the carriage. That's the main thing.

These web guides are simple. That's one of the advantages of these web guides. And these web guides really do not have to take advantage of the normal entry roll because all the rollers are parallel to each other. So there's not going to be any misalignment in them.

So there's going to be less amount of stresses on the web. The disadvantages with these kind of web guides. Well, first of all, you need a high thrust actuator, especially when you have larger mass to move and it's not cost effective. If you really want good performance from a web guide, if you want to reject a high frequency disturbance, then this may not be a good choice for us.

[Music]

[Music] Normal entry is a web approaching a roller will always align itself perpendicular to the axis of rotation of the roller. As you see in this video right here, let me restart that. As soon as the roller on the left has a misalignment, the web started to track and move in such a way that it will approach the roller on the left perpendicular to the axis of the rotation. This is the fundamental principle used in most of the intermediate web guides that we're going to see.

What's happening here is that the web is essentially behaving like a beam and the angular displacement on this left hand side is bending the beam and it's causing the beam to bend and that's what is causing the web to track to this side. There are lots of dynamics involved in this process. how fast the web moves, how much does it move, all of those depends upon the transport conditions, the what type of web it is, what kind of traction you have and things like that. And obviously the static behavior is that um at steady state once this angle is set, how much is it going to move?

Are we going to see any movement on this side? As you can notice when this web moved the upstream roller, the web was still there. It was maintaining there because it was able to have enough traction so that the lateral forces or the moment that is acting there was not able to make the web move. And whenever we have a motion like this, bending occurs, bending in term means that there are stresses developed in the web.

So you're going to have a tight side and a slack side and they're going to be a tension profile here. So these are important to understand for a successful webg guiding application or execution of a web guide. [Music]

In terms of a basic web guiding system, we are mainly dealing with four main items apart from the web. One is the guide structure or mechanism. This is the device that is actually making contact with the web and that's the one that is need to be moved or it moves the web. There are different types of guide structures that we will go through.

The other component of a web guiding system is an actuator. So actuator is something that takes an electrical signal and converts that into physical motion so that it moves the guide structure so that the web can be located at the desired location. The third and one of the most important components of a web guiding system is a sensor. The sensor is the device that provides the feedback.

The sensor is the one that tells us where the web is inferring the position and then that signal is sent to a controller. The controller is mainly the intelligence or the brains that takes that sensor signal and computes the corrective action required. So the actuator can move the guide mechanism to the the location where we can get the desired web position. Again, another schematic of how the components of the web guides are.

Web is a part of the web guiding system. And then you have the mechanism. There's an actuator inside the mechanism. The sensor gets the position feedback of where the web is, sends that information to the controller.

controller then computes an error and it sends the command to the actuator so that the mechanism can be moved to position the web at the right location. This is a closed loop feedback control system that is a main part of a web guiding system.

[Music] So why do we need web guiding? Well, there are mainly four reasons why we need web guiding. First and foremost is that materials are not perfect. You might have a poorly wound roll that is not wound properly or deliberately wound roll with an oscillation on it.

And when you are trying to feed it into your rollto-roll machine, you need to guide it so that it aligns with your process. Some materials may have thickness variation like gauge band variation either during coating or forming processes especially with paper mills. Different gauge papers may track or slide differently. Splices when joining two rolls of web might be a step change or an angular misalignment.

Some materials have a natural curvature called camber. So when the materials are not perfect, that's going to have the web nist track in your machine. It could also be due to machine itself. So either you have machines with out of round rollers like a crown concave or a convexed roller.

Whenever you have a variation in the diameter of the roller, that's a problem. Or the rollers are not aligned properly with respect to each other. That could also cause the webs to misrack. You might also have tension control issues.

If you don't have enough tension, you don't have traction, then that's going to be an issue. Whenever you have acceleration or deceleration, that might also cause the web to misrack. It could also be due to processes. For example, if you have a coding process and you have uneven coding across the width of the web, that's going to cause issues with tracking.

And also some processes where you could have air intrained between the web and the roller that would cause the web to lose fraction and mistract. That could also be an issue. That's why we need web guiding. Finally, operators mainly when they are splicing the web or when they are putting a new parent roll into their roll-to-roll machine, they may not center it or put it at the right location.

That might also cause an issue and might need web guiding. So web guides are necessary at different locations of the machine because you might need alignment at different parts of the machine. That's the main thing with web guiding. You have to put a web guide in front of any process that requires web alignment.

Just to give you an example, let's say you are laminating something and you have two layers of web coming in to this lamination process. At this point you would need a web guide so that you can align this layer and this layer with respect to each other. The guides that are used within the machine are called intermediate guides or they are intermediate to the machine and the guides that are used at the entry and exit of the machines are called as terminal guides. So we're going to look at all of these in detail but that gives you an idea of why we need web guides and where we need web guides.

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In terms of location, when you have a web guide that is located at the entry and exit of the machine, they are called terminal web guides. There are lots of names for these and some of the common names are shifting stand, shifting base, shifting side lay or roll positioning stands. If you're in the metals industry, it might be uncoil or recoil. In other industries, it might be called payoff and tension reel.

Specifically, in these presentations, we call them unwind guide is something that is at the uh entry of your roll throughroll machine while a rewind guide is at the winder or the exit of a roll to roll machine. These are some of the terms used for terminal guides. In terms of intermediate guides, these are the web guides used within the process within the machine. There are multiple types of web guides.

The most common one is called an offset pivot guide. Other names for offset pivot guides are displacement guides, positive displacement guide, pivot frame, or table guide. The second most commonly used intermediate web guide is a remotely pivoted guide. That's a technical term term but most commonly it's called as steering guide or a steering roller or a swivel roller.

And then there are other less common web guides like end pivoted guide or center pivoted guide and then even turn bars are all available. We'll take a deeper look at all of these different kinds as we go along. Most of these web guides work on a basic fundamental principle and that is what we call it as normal entry.

To get to the operator width screen from the home screen, we're going to press the tools icon, then the operator icon on the top right and then the width icon. This first page is the operator width home screen. The second page is an additional setup screen where you're able to do more setup related things.