Today’s video is about printers.
I know, you’re probably filled with excitement at the mere mention of printers, but please
remain calm.
If you were to go shopping for a printer, you’ll almost certainly find yourself choosing
between an inkjet printer and a laser printer.
Or perhaps a 3D printer, but we’re not talking about those today.
Now, I won’t get into the many reasons that I don’t really like inkjet printers for
anything but photo printing because that’s not really the point of this video.
Instead, we’re going to talk about a subset of the laser printer
that seems to fly under the radar.
The LED printer.
Now, if you’ve never heard of this before I wouldn’t blame you.
Fundamentally LED printers are the same as a laser printer.
They still use powdered toner rather than liquid ink.
They use photosensitive drums to transfer toner to paper (along with corona wires and/or
other charge inducing or destroying doodads).
And a fuser melts this toner onto the paper, so a tall stack of freshly printed printouts
is nice and warm, just asking you to give it a hug.
But where they differ is in how the image is drawn on the drum.
And to understand why that’s important, let’s have a quick lesson into how laser
printing works and how it came about.
Laser printers are essentially an offshoot of the photocopier.
Using a process called xerography, which comes from the Greek for dry writing (and now you
know where Xerox got its name), analog photocopiers use a cylindrical drum coated in a photoconductive
material.
This material becomes conductive when exposed to light.
To duplicate the image, the drum is first charged by a corona wire, which produces a
high voltage and gives the drum a static charge.
The now negatively charged drum is rolled underneath a piece of paper to be copied,
where a lens focuses the image of the paper onto the drum, and a bright light source provides
illumination.
Because the photoconductive material will conduct electricity when exposed to light,
any bright areas become discharged, as a path to ground can now be completed.
Dark areas, where printing or handwriting exist on the original,
will remain negatively charged.
This drum is then rolled against a supply of powdered toner, which is positively charged.
This toner will thus want to stick to any areas of the drum that remained negatively
charged from the original exposure.
Now the drum has a coating of powdered toner in the same pattern as the writing or image
or whatever in the original document.
Next, another corona wire creates a stronger negative charge in the paper that is to receive
the toner, and this stronger charge will attract the toner off of the of drum and onto the paper.
And finally the paper, now covered in powder, goes through the fuser unit, which melts this
powder to the paper, and thus a stable photocopy is made.
Fast forward to the late 1960’s, and Gary Starkweather, an engineer from Xerox’s product
division, had the idea of using a laser beam to draw directly onto the imaging drum of
a photocopier.
With computer control, you could draw text and images directly on the drum with the laser,
thus turning it into a printer.
And that’s exactly what happened.
Using a laser diode, lenses, and a spinning mirror, laser printers draw onto the drum
in lines, and the laser is pulsed on and off to create the image.
The resolution of the printer is determined by the number of lines it can draw in a given
unit, in addition to the maximum number of times the laser can be pulsed on or off within
that line.
Often the resolution is measured in dots per inch, so a printer with 600 dpi will scan
the drum 600 times along the length of one inch, and the laser can pulse on and off 600
times within one inch of each line, meaning each square inch has 600 by 600 discrete points
that can be either on or off--that is, black or white.
Incidentally, this method of creating an image using lines of light is strikingly similar
to how analog television works.
I made a series on television if you’d like to check it out, but the pattern is called
a raster.
Raster scanning in laser printers requires that the entire image, in its full resolution,
be loaded into its memory before printing can commence,
as it has to be done in one shot.
It can’t start and stop like an inkjet printer, particularly because the fuser unit is liable
to burn some paper (or at least singe it a litte) if it were to suddenly stop mid-print.
So, laser printing works.
And it works really well!
But the actual laser mechanism is kinda big, and relying on a spinning thing to make the
image introduces more moving parts and complexity.
And that’s where the LED printer comes in.
When did it come in?
And who invented it?
I’m not sure.
It’s a weird footnote into the development of the laser printer, but Oki claims to have
made the world’s first LED printer in 1981.
It’s surprising how little info there seems to be about LED printers, though as we’ll
see, perhaps that’s to be expected.
What makes LED printers different?
Well, rather than use a scanning laser, LED printers use LEDs.
Shocking.
But in a unique way--this Brother HL-3040CN is a color LED printer.
If I lift on the lid, you’ll see these four bars here that kinda flip out of the way when
the lid’s all the way up.
There are four because this is a color printer--one each for cyan, magenta, yellow, and black
(more correctly referred to as key).
These bars are the key.
Each of these things is an array of tiny individual LEDs.
Each LED handles one column of pixels--or dots--on the page.
This printer has a resolution of 600 DPI, so along this entire bar there are roughly
5,000 LEDs.
If you look closely you’ll see a pattern of dots--these are lenses that focus the light
from multiple LEDs behind them onto the correct spot of the drum.
The LEDs themselves are so small as to be nearly invisible to the naked eye.
Below these assemblies lie individual drum and toner cartridges.
You can see that when the lid is closed, the LED bar sits right on top of the drums.
You’ll also find evidence of toner mishaps, but, ehhh.
So when this printer prints, rather than spinning a mirror and pulsing a laser on and off, each
LED simply pulses on its own.
As the print drum rotates, the LEDs will flash when they need to, and stay dark when they don’t.
There are many times as many light sources--in fact thousands of times--compared to a laser
printer, but the lack of a mechanical component, plus the direct physical alignment of the
LEDs with the drum, means that LED printers might be more reliable.
And they certainly are more compact.
Particularly with color printers.
Notice how this printer has each color of toner simply in a row.
Because there’s no need for a complicated optical system, this printer is essentially
just 4 printers lined up in one case.
And if I pull one of these out, you’ll see how small the toner and drum cartridges are.
Yes compared to an injket these are laughably big, but for a toner-based printer this is
actually pretty small.
This design also gives color LED printers a huge advantage compared to laser--speed.
To convert from black and white to color, this printer essentially just takes the printer
part, then Ctrl-C Ctrl-V’s it a few times.
The paper travels in a straight path as it gets black, yellow, magenta, and finally cyan toners.
Then it’s fused on its way out.
Color LED printers used to boast that their printing speeds were nearly the same between
color and black and white.
Many color laser printers, such as this one from Samsung, print at a fraction of their
black and white speeds, because when printing in color, the paper has to take a meandering
path through four printing assemblies.
With setups like this from Brother, it’s just boom boom boom boom, fuse the toner,
and we’re done.
Now, laser printers do still have their advantages over LED.
It’s easier to achieve a higher resolution when you have the benefit of motion, rather
than relying on smaller and smaller LEDs.
Plus, apparently LED printers can have less consistent images due to slight variations
between each LED.
I can’t say whether I’ve noticed that in person, but this paper from Xerox sure
is trying to convince me.
But here’s the kinda humorous bit.
I’m willing to wager that many “laser printers” available on the market are in
fact LED printers, but they’re just not so clearly labeled.
Poking around on Amazon I found plenty of printers that don’t have much of a difference
between their color and black and white speeds, and some printers like this Canon have the
toner arranged suspiciously similarly to this Brother printer.
And Brother is definitely still using LED printing technology, as evidenced by this
picture on this Amazon listing.
To their credit, they simply call it a “digital color printer” and it’s Amazon that’s
labeling it as “laser printer technology”.
Anyway, maybe this Canon is a real laser printer, and they’re just packaging the laser scanners
more efficiently so that the paper can pass in a straight line.
But there are still some color laser printers on the market that print fast in black and
white and at a leisurely pace for color.
The Samsung unit we looked at earlier prints at a respectable 19 pages per minute black
and white, but only 4 ppm color.
Not so “Xpress”, after all.
In any case, I think that it’s a shame how little is known about the LED printer.
Sure, on the surface, it’s just a laser printer.
An LED printer will produce near identical results, and behave in a near-identical fashion.
It’s still a drum and toner system--how the image gets to the drum is arguably trivial.
But I think it’s a clever way to handle it.
Thanks for watching this (for this channel anyway) quick video.
I’ve interrupted the series on the compact disc to bring you this video and we’ll be
resuming where we left off soon.
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