Paper sheet feeder. 4

[imcjoek]

I am having a difficult time finding a description of how the typical paper sheet feeder (in say, a printer, copier, fax-machine, etc) works. How do they prevent feeding multiple sheets if the stack sticks together? Clearly some printers do a much better job than others at this, so there must be some method to the design.

I'm surrounded by the damn things, but all my googling turns up is "Help me fix my paper jamming OfficeWhatever9000" and "Patent-Troll for paper feeding apparatus that probably doesn't work." I'm rapidly reaching the point where I'll need to sacrifice a printer to the curiosity gods.

I found this:
Link
Which, frankly, doesn't make a lick of sense to me. They are mum on what manner of sorcery makes this lower "friction roller" work. Why shouldn't it happily pass two sheets through? I'd guess they are trying to setup a shear action in the paper stack, but if the lower grip is too great, then the top roller merely slips and nothing feeds at all.

 

[drawoh]

imcjoek,

I have always been impressed by paper feeders, except for that of my Hewlett Packard printer. I am amazed that they work at all. Someone out there is very good at what they do.

--
JHG

 

[fegenbush]

The lower friction roller is not unlike a slip clutch. It will only provide a maximum torque before it slips. This torque relates to a linear force. If that linear force is greater than the frictional shear force between two sheets of paper, it strips the bottom sheet. If the linear force is less than the frictional shear, the second sheet is unaffected. I have seen systems that use a pad of material to create the friction instead of the slip clutch roller.

I do agree with drawoh, there is some person or group of persons that have this down cold. I am sure there are many factors involved in determining the frictional shear between different types of paper.

 

[MikeHalloran]

The friction roller you linked to, works by resisting the paper motion. I.e., it is anchored, not driven. A complementary driven roller is what causes the paper to move.

Traditional sheet printers use vacuum cups to grip the paper you want to move, and I think also to hold the paper you don't want to move.

I used to run a 3M copier that used a tiny roll of adhesive tape (no surprise given 3M's business), incrementally advanced from one roller to another, to pick up and feed the paper. It didn't double feed much, so there must have been some kind of retarding mechanism, but I don't remember seeing anything in particular.

In low-cost printers, yeah, it's black magic, and there's a huge commercial interest in keeping the exact details quiet.



Mike Halloran
Pembroke Pines, FL, USA

 

[FACS]

We manufacture friction feeders, and it's not black magic at all. It basic physics, Newton explains this in his first law.

If you need to familiarize yourself with Friction. Look at the basic inclined plane method of determining the frictional coefficient of materials.

Only on large printing presses, and some other automated machinery do we bother with vacuum cups. Vacuum systems are expensive and hard to maintain. The low cost printers and copy machines rely on friction, and friction alone.

We don't feed from the bottom, as the weight of the paper adds to the force on the intended sheet to be moved. We like to feed from the top.

Friction is dependent on the frictional coefficient of the surface and the force exerted on that surface. We are not exerting a force on the second sheet of paper, only the top. If we don't exert a force on the second sheet of paper, it will remain at rest.

The friction between two sheets of paper is very low. Therefore, one sheet moving across another is not enough to move the second sheet .... That is the fundamental basic of the system. That is the rule to remember. The black magic is the low coefficient of friction between the two sheets. It's not a secret, now you know.

Now, to move the top sheet, we use a friction roller or belt. Sometimes it's even plastic as in cheap printers that sometimes do not move anything at all, and leave a mark on your paper.

We put just a little force on that roller, and when we turn the roller, the friction of that roller will break the static friction of the paper on paper, and it will move. Speed has a little to do with it also... like when we pull a table cloth out from under a table full of china, which is all friction dependent.

The bottom sheet will not move, as the friction between sheets is weak, and not enough static friction is present. As soon as the static friction is broken, the sheet keeps moving and the chances of the second sheet moving is even less at this point. As you know, once an object starts to move on an incline plane, it keeps moving as the static friction is broken.

Too much force on the wheel will transfer some force to the second...or more .... sheets, and combined with what little friction there is..... more than one sheet may move. So here, the trick is to only press our friction wheel with enough force to make the first sheet move.

Researching "Friction Feeders" will give you more ideas than trying to search how printers work.

Charlie

http://www.facsco.com

 

[imcjoek]

"Friction feeder" appears to be a more profitable search term, yes.

What I find interesting about the "it's just simple friction" argument, is that some printers will happily feed less than ideal stacks of paper (Stuff with kinks, folds, texture).
While other printers won't feed a perfect ream unless the phase of the moon is right.

 

[FACS]

Yes, we make friction feeders for all kinds of things.
For example, when you want to put a coupon into a package on an automated packaging machine. The coupon is folded in several places.
But, we don't use just a friction wheel at that point. We use other methods, such as .... a friction wheel to push the coupon into a set of ribbons. The coupon is sandwiched between ribbons, and they move it along and drop it into the carton.

Folded and odd shaped things are actually easier to move. Air has no friction... if there is air between the sheets, then it's easy to move. Bumps, valleys, folds... these all have air.

Texture is actually easier to move as only the peaks of the surface touch. Less surface area, less friction. We use stainless steel with raised texture for the same purpose, to slide things around easier. Only half the surface area = half the friction.

A perfect ream of paper will perform better if you pre-break it.



Charlie

http://www.facsco.com

 

[SnTMan]

FACS, glad to hear you're not "bottom feeders"

I am pretty much amazed every time a document feeder on a copier on a works, and how well.

Regard,

Mike

 

[IRstuff]

OK, I need to ask forgiveness for a brief digression: What might be the cause of a printer to stop handling card stock, say 60 lb, when they used to work fine. My HPLJ5, Samsung CLP-310, both older, as well as a couple of newer ones, even when explicitly at a card stock paper thickness setting.

TTFN
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[FACS]

IRstuff,
I don't know the design but;
Card stock has a very low friction co. Especially if it is coated. It's dry and dusty.
There are two forces moving the card stock, the friction of the wheel or belt and the force.
It could be, as my first reaction: That the wheels or belt has gotten dirty and does not have enough friction to move the card.
Card stock is also dusty, over time, the dust will build up on the friction feeder. Maybe take it apart, and clean or replace the wheels or belt.

If that is not the problem, I would then suspect that the spring pressing the friction device against the card stock has worn, and is no longer providing force. Since card stock is slippery, compared to paper, it needs more force and friction.



Charlie

http://www.facsco.com

 

[IRstuff]

OK, thanks. I'll see if I can do anything to change that.

TTFN
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