How does a printer get just one sheet of paper?

[Ethan]

Searching around google I mostly get results that look like, "why is my printer just printing half sheet…", and other troubleshooting pains.
But I'm genuinely curious how a printer is able to separate just one thin sheet of paper from a stack with incredible accuracy.

Anyone here have a better idea of how the feeder mechanism works (links/videos/etc would be great too)?

 

[JohnRoberts]

I have an old printer that isn't so accurate about doing that

generally it's a relative friction thing... you have a stack of paper and a feed wheel with thin rubber tire, like textured rubber band lightly presses on paper and grips it to feed it through the printer.

The friction between the rubber wheel and paper needs to grip stronger, than paper to paper friction so top sheet slides off the pile. Since the rubber feed wheel only touches the top page it should only feed one page at a time.

I get some double feeds and IIRC the last time I looked inside there were some broken or missing parts.

In guess if paper has static charge they may stick together, if feed is too fast there will be some suction between pages.

JR

 

[Ethan]

I have an old printer that isn't so accurate about doing that

generally it's a relative friction thing... you have a stack of paper and a feed wheel with thin rubber tire, like textured rubber band lightly presses on paper and grips it to feed it through the printer.

The friction between the rubber wheel and paper needs to grip stronger, than paper to paper friction so top sheet slides off the pile. Since the rubber feed wheel only touches the top page it should only feed one page at a time.

I get some double feeds and IIRC the last time I looked inside there were some broken or missing parts.

In guess if paper has static charge they may stick together, if feed is too fast there will be some suction between pages.

JR

I get the rubber wheel gripping the top sheet--more friction on top less on bottom, but I thought there might be some 'error checking' mechanism to validate that there is just one sheet. Perhaps an optical sensor with variable V output to detect one sheet (if 0-5V, say ~2.5V for 1 sheet and >3V for more than one sheet)?  Just guessing.
I recall with my old HP, it would sometimes pull back a paper feed when it detected more than one sheet was being loaded (it wasn't perfect, but amazingly reliable when considering the low rate of error).
I now wish I had kept that old printer so I could satisfy my curiosity.

 

[JohnRoberts]

There may be a few more parts... I can imagine the top rubber grip, and a second weaker friction surface working on the bottom side of the feed paper to stop a double feed, of course a triple page feed could still let two pass.

I suspect this is largely about tolerances and much work goes into high speed copy machines and printers.. not like the old pin feed printer pater.  Even the pin feed could jam and screw up...

JR

PS: I suspect the missing parts from my unreliable printer were from some past paper jam, where removing the severely jammed paper also damaged some useful internal parts.

 

[audiomixer]

did you think of checking patents? surely there must be one...
quick search didn't pan out right away, but I hadn't too much stamina....

- M

 

[sahib]

I have gone through a lot of printers and I have not seen any paper sensing mechanism in any of them. It just relies on the rubber feed disk.

But the most important aspect is the paper quality actually. Cheaper papers will not sheer clean when they are cut on the guillotine and will not separate properly. Then you'll have multiple feeds.

I have recently taken apart a brand new Dell printer that was dead on arrival. All I got is a damn handful of self tapping screws but nothing else. My guess is about 95% of it was all plastic. Incredible though when you think about it.

 

[PRR]

It is a LOT about the paper.

Copier paper is made very fussy. Surface finish is critical. Then they dust the paper (that dry-hand feeling you get when you load busy copiers/printers at work).

> some 'error checking'

Most paper-feeds will tolerate very thin and also card-stock. I think the range may be over 2:1 (but expressed in terms that make no sense outside the paper industry). So a simple thickness check (if even possible) would false-flag a lot.

> sometimes pull back a paper

I have seen that when paper "slipped". If the printer expects 11" paper, but paper is still coming at 11.5", either it's got the wrong stuff or the finger picked up one sheet and that dragged a second sheet.

I used to hand-feed a sheet printer (real printing: cold lead, ink roller, and a platten that would crush your hand). Even with hand sensitivity, misfeeds and blanks (double-feeds) were common. It is a LOT about the tight specs Xerox and others formulated for unattended copier paper. (I also recall earlier copiers that sucked roll-paper and cut it, but that jams other ways, and never looks so nice.)

 

[Andy Peters]

It is a LOT about the paper.

Copier paper is made very fussy. Surface finish is critical. Then they dust the paper (that dry-hand feeling you get when you load busy copiers/printers at work).

I used to think that "ink jet" paper was a bunch of hooey, but it really does work a lot better than standard copier paper in the Epson Workforce thing I have. Takes the ink well, dries without smudging, and it never double-feeds.

-a

 

[bruce0]

Mine doesn't!

 

[Kingston]

I have yet to use a reasonably modern copy/printer machine that didn't jam on something close to daily basis in normal (read: heavy) office use.

I would think it's pretty much core functionality to have the paper feed working perfectly reliably and these companies have had at least 30-40 years to get it designed to perfection. I have a sneaking suspicion this unreliability might be a part of some planned functionality, where said company is able to sell a mandatory support service.  :

There's something wrong with the printer business on a fundamental level. Low-end machines have internal hidden ink and copy counters that purposefully make the machine act as if it's need of a replacement part on regular intervals. Even if there's plenty of ink left. It's the same people designing the higher end office machines.

Not too far from the self-destruct timers you see designed in chinese powersupplies with electrolytics heat-glued to regulator heatsinks.

 

[shot]

I know that on the printing press they have vacuum suction mechanisms to lift the sheet of paper.
But don't know how it's done on home printers...

 

[pucho812]

there is a tiny little man inside ;D