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

Hey,

I'm having trouble thinking about this one...

If I have a roll (20lbs), sitting on a roller with bearings and it takes very little to cause it to roll (like a wheel or something). How would I go about calculating the force required to unroll it?


There will be two pinch rollers pulling the material, so I wasn't sure about the physics behind it since while being pulled, it is on bearings and rolling freely.

Do I need just enough force to move the pinch rollers?
or
Do I need to look at the mass of the product rolling as if it were moving the entire thing?





Thanks!

How aggressively are you accelerating? Is the roll just going to completely free-wheel? If so, how are you going to keep it from dumping it's contents on the floor when you stop?

Keith

why use a high priced servo when a vector VFD can do it at a better price

kamenges said:

How aggressively are you accelerating? Is the roll just going to completely free-wheel? If so, how are you going to keep it from dumping it's contents on the floor when you stop?

Keith

Click to expand...

Great point.

We spoke about designing a brake system to stop it or even adding a second servo to the roll itself and have them move sequentially.

all of that can be done with a Flux Vector VFD
drive on each roll synced together
controlled acc and dcc breaking all doable and already been done

The big question is still how aggressively are you accelerating? drbitboy points to the concern, albeit a little circumspectly. If the acceleration is very low or this is intended to be a constant speed application you have much less to worry about than if you intend to accelerate this very quickly.

GaryS, it depends on the size and available platform. At 1HP and below I could price a Beckhoff servo system that would come in less than an induction motor system in most control platforms. Once you get above 1HP it tends to go the other way. With a 20lb roll just siting on a set of bearings I can't imagine this will be all that big.

Keith

kamenges said:

The big question is still how aggressively are you accelerating? drbitboy points to the concern, albeit a little circumspectly. If the acceleration is very low or this is intended to be a constant speed application you have much less to worry about than if you intend to accelerate this very quickly.

GaryS, it depends on the size and available platform. At 1HP and below I could price a Beckhoff servo system that would come in less than an induction motor system in most control platforms. Once you get above 1HP it tends to go the other way. With a 20lb roll just siting on a set of bearings I can't imagine this will be all that big.

Keith

Click to expand...

Sorry I didn't answer that. Yes, it will be accelerating rather quickly.

It's a 50mm diameter roller and needs to index 150mm every 6 seconds. Out of that 6 seconds, I need to spend around 2 seconds actually driving the material through the pinch rollers. I need the other 4 seconds for other operations. This 2 seconds will include accel and decel.

So it is a rather high speed application.


So I'm guessing I need to look at what it takes to accelerate the mass (Rollers and material) and then what it takes to stop both of them. Rolling resistance is pretty much negligible.

Any tips outside of this?

Yes, as I see it, accel/decel will be your biggest concern. That also means product roll control will be a big concern. If it spins as freely as you say you can't just give it a yank and let it go. How you choose to control the product roll will likely have an effect on your pinch roll drive sizing.

Keith

Also
Will the material distort or “neck” in if pulled too hard from the pinch rollers?

JRW said:

Also
Will the material distort or “neck” in if pulled too hard from the pinch rollers?

Click to expand...

That will also be a concern. It is a thin plastic film. I'm starting to think I will just have 2 servos. One will be the pinch feeding it out and the other will rotate the roll.

I was trying to avoid this because then the rolling speed will change as the roll gets smaller and smaller.

It will allow me to start and stop the roll allot easier.

Can you design a small surface driven unwind? This will decrease the required size of the unwind motor and takes away the concern of speed change.

Keith

scenario's

expanding on Keith's response...
These scenario's are generally what I see
Thoughts?

JRW said:

expanding on Keith's response...
These scenario's are generally what I see
Thoughts?

Click to expand...

So the surface unwind motor is controlled based on the (filtered?) dancer position, and runs about at 150mm per 6s?


The pinch rollers' motor does the 150m per 2s, then holds for 4s, pulling against the dancer?


And the dancer supplies constant tension? Is that with an air cylinder, or weights, or similar?


Could the dancer pull in any direction? up, down, horizontal?

We are not getting the whole picture on this there is way too much missing
I thought you were unwinding through the pinch rolls but the drawing dose not support that
The dancer does not control the tension on the web it only measures the web tension and supplies feedback to the tension controller usually a drive of some kind. You also need something to work with for tension usually pinch rolls but it could b a take up reel.
In that case the pinch rolls would run at a constant speed or they would be used to pull the tension .
When you talk about the pinch rolls speeding and slowing down it sounds like a flying shear where you cut a web into sheets of either a fixed or varying length in those the pinch point must be travelling at the exact same speed as the web while the roll rotation must slow down or speed up to accommodate the length.
To maintain tension you must use center wind you would not be able to maintain tension on a surface wind the friction on would not consistent enough to do it.
I would like to see the whole picture of the system that would give us a better chance to help you