-- Specifying a Servo for Motor for Pinch rollers --

And get off your pc and go outside
I hear it’s snowing there


hey, my honey and I went for a long walk on and around Zoo Road in Durand Eastman Park today. With a mask.



Lake Ontario was gorgeous; I really have to restore our Rhodes Bantam ...



;)
 
We put accumulators upstream of winders quite often. As JRW said, if the process is relatively slow (<200 FPM or so) , if the material is extremely sensitive to the results of wrinkles at the core and if the customer is OK with manual transfers then an accumulator is often a cheaper and more reliable way to approach the problem than a continuous transfer style winder.

Keith
 
if that's the setup then it simple the unwind rolls should follow the pinch rolls by a fixed ratio both would have the same surface speed = web speed
Just some things to watch out for.
the problem you may have is as the roll gets smaller the weight on the unwind rolls get less and the friction between the source roll and the unwind rolls is less the could slip and could cause the web tension between the unwinder and pinch rolls to increase
 
if that's the setup then it simple the unwind rolls should follow the pinch rolls by a fixed ratio both would have the same surface speed = web speed
Just some things to watch out for.
the problem you may have is as the roll gets smaller the weight on the unwind rolls get less and the friction between the source roll and the unwind rolls is less the could slip and could cause the web tension between the unwinder and pinch rolls to increase


Thanks. Another issue I'm aware of, is as the roll get's smaller, the ratio between the pinch and the roll has to change. I may counter this with a high low distance sensor.

The question I have is how do I size the roll motor? I can get the speed, but the torque required is what I'm unsure of, since it's on bearings and shouldn't take much to spin it.

Am I thinking about it wrong? Is it just the normal toque required, but just good coefficient of friction?
 
both sets of rolls need to run at the same surface speed that's not going to change with the roll diameter what I think you are seeing is the lower friction from the smaller roll / less weight = less friction = more slip
one thing that may help is if the unwinder rolls were coated the friction grip material
smaller roll also equals less torque required
as for sizing the motor required I fall back to a mechanical engineer for that and whatever they recommend add about 25% I would rather have more power the I need then come up short
 
Thanks. Another issue I'm aware of, is as the roll get's smaller, the ratio between the pinch and the roll has to change. I may counter this with a high low distance sensor.

The question I have is how do I size the roll motor? I can get the speed, but the torque required is what I'm unsure of, since it's on bearings and shouldn't take much to spin it.

Am I thinking about it wrong? Is it just the normal toque required, but just good coefficient of friction?


For sizing the motor it sounds like the key thing will be speed and acceleration. How fast do you need to get the roller to full speed? If you do use a servo your max speed might be 3500 RPM as an example, so if you only need a 1000RPM roller (note you get a natural reduction due to the roller being a smaller dia than the film) you can put a 3:1 gearbox no dramas.

If you can tolerate a 3-5 second acceleration time then the required torque will be tiny. Maybe less than 1nm or so. Something like a AB TLP 70mm circle might do the trick.

There are calculators you can use for single mass rotating on its axis, then what ever torque you come up with you can reduce by the ratios of the rollers, and then the gear box. This could help: https://www.engineersedge.com/motors/calculator/accelerating_torque_force_solid.htm
 
For sizing the motor it sounds like the key thing will be speed and acceleration. How fast do you need to get the roller to full speed? If you do use a servo your max speed might be 3500 RPM as an example, so if you only need a 1000RPM roller (note you get a natural reduction due to the roller being a smaller dia than the film) you can put a 3:1 gearbox no dramas.

If you can tolerate a 3-5 second acceleration time then the required torque will be tiny. Maybe less than 1nm or so. Something like a AB TLP 70mm circle might do the trick.

There are calculators you can use for single mass rotating on its axis, then what ever torque you come up with you can reduce by the ratios of the rollers, and then the gear box. This could help: https://www.engineersedge.com/motors/calculator/accelerating_torque_force_solid.htm



That is very helpful. I made this calculator adding in addition to what that website had there.

Will someone look this over and let me know if it seems accurate? I'm more concerned about the sprocket combo thing I added at the bottom.


Thanks for the help!
 
I think you are way high on your calculated torque. It looks to me like you are using the pull roll RPM in the product roll torque calculation. When I hand calculate this I come up with more like 0.23 lb-ft. And then you need to apply the roll diameter difference scaling to see what that means to the pull roll. Once you apply that ratio you end up closer to 0.085 lb-ft.

This has got to be some pretty fluffy stuff. A 4ft diameter roll weighing only 30lb isn't none too dense.

Keith
 
I think you are way high on your calculated torque. It looks to me like you are using the pull roll RPM in the product roll torque calculation. When I hand calculate this I come up with more like 0.23 lb-ft. And then you need to apply the roll diameter difference scaling to see what that means to the pull roll. Once you apply that ratio you end up closer to 0.085 lb-ft.

This has got to be some pretty fluffy stuff. A 4ft diameter roll weighing only 30lb isn't none too dense.

Keith

Thanks I'm looking at it now. The size on there was probably too much. I was thinking Diameter when I was typing in the Radius box.

In the mean time, I downloaded Allen Bradley's Motion Analyzer and it is very nice.


Thank you for taking the time to check it. I appreciate it.
 

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