narrow web guides

[Music] So in terms of actuators, there are lots of terminology that is involved. Some of them are thrust or power, how fast the accelerator is, what is the correction speed, what is the acceleration, stroke length, mounting, what type of coupling we have and things like that. Actuators are pretty standard right now. It's not as important as installation of a web guide or the sensor, but it is an important part of a web guiding system.

The older actuators were either pneumatic or hydraulic. You had an hydraulic pump pumping a double acting cylinder and moving the web guide structure. These were more common in the 50s and up to about maybe '90s before the electronic electromechanical actuators started coming into the market. You could have pneumatic actuators or hydraulic actuators.

The hydraulic actuators have the advantage that it can provide high thrust and can shift large loads quickly. Even now in metals industry, hydraulic actuators are pretty common. You can see them. But the problems are that it's a problem with maintenance.

You need to balance the valves and stuff like that. Change the filters. They could cause leak and this could contaminate your product. And then the precision and accuracy that you can get with an electronic actuator or electric actuator is not something that you can expect in an hydraulic actuator.

So most web guides nowadays are going to use actuators like what these actuators usually have a motor that drives a belt pulley system. There's usually a lead screw, a ball screw or a roller screw that converts the rotary motion into linear motion at the end of the actuator. Some common terminologies that you would see with actuators are maximum current, voltage, power. Whenever we have something with a lead screw or a pitch, that's a common term.

What is the lead of the actuator? Pitch of the actuator. Gearing ratio. Backlash is another thing that you would commonly see with electric actuators, especially with low-end lead screw actuators.

Resolution. What is the smallest movement an actuator can produce? Back drive is a common terminology especially if you're installing a web guide that has to work against gravity. And then types of actuators you have inline and reverse parallel.

Some actuators have limit switches or end stops. And then type of motor used in the actuator. You would commonly see servo stepper brushed or brushless DC motor. So actuators are providing the driving force to the guide structure so that it can position the web.

In terms of thrust, the thrust is the amount of force exerted by the actuator to move the guide structure. And this thrust really depends upon as we saw before mass of the structure that we are trying to move, what is the friction there, how fast you want to move and sometimes gravity as well if you're acting against gravity. In terms of sizing actuators, these are some of the things you need to know to size an actuator properly. a web blind speed mainly because if you have a slow moving web the maximum disturbance frequency you can get depends upon the speed of transport of the web.

If you're moving at 100 ft per minute you might not need a high dynamic response while if you're moving at high speed you might need a much higher dynamic response. The dynamic response is related to the acceleration. Acceleration is related to the thrust. So that's why line speed becomes important.

Guide structure weight and roll weight. If you're trying to move a big mass, we need to know that what type of bearing you're using. So that what is the breakaway force that we need to overcome based on the coefficient of friction of the bearing and then what kind of disturbances we are trying to correct for. There is a correlation between the amount of disturbance that can propagate through a roll-to-roll machine that really depends upon the speed of the web.

The faster you go, higher frequency disturbances can go through. So the web acts as like a low pass filter and then the acceleration and then if you have to look at any gravitational effects. These are some of the key factors that are involved in properly sizing an actuator. But like I said, actuators are pretty straightforward nowadays.

Just need to have some basic questions answered and then we'll be good to go. [Music]

[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]

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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