Laser printer and a drum?

There have been a number of incorrect statements regarding the internal
function of laser printers. I'm sure the best of intentions were the
motivation, but a number of factual errors in recent postings leave me
wishing to correct some notions.



Laser printers need a surface which is sensitive to light and which
changes static charge based upon exposure to light. The light source is
often a laser beam, or LEDs. Typically, this surface is coated on a
cylindrical drum made of aluminum, although some units use a transfer
belt which is a long film like belt which has a similar surface.

When the drum or belt is properly charged, the parts that will be
printing an image acquire a static charge which attracts the very finely
ground powder called toner. It clings to the surface of the drum of belt.

There are several different ways that the toner can be made available to
the drum surface. In some cases, the toner is presented at very close
proximity to the drum surface by a roller which is saturated in the
toner, in some cases, the toner contains very fine iron particles which
the toner is integrated with and this materials sticks to a magnetic
roller and the charge on the drum pulls in to the drum surface. In
older systems, the iron particles were a separate agent which the toner
coated and only the toner transfered to the drum surface, leaving the
iron particles behind where they were reused.

Typically, on newer laser printers, the drum is only about the diameter
of 1/4th of the paper length, so the drum surface is charged and toner
coated about 4 times to produce an image on one sheet of paper.

The way the toner gets transfered is a mixture of pressure and use of
static charges to transfer the toner powder from the drum to the paper
which passes directly in contact with the drum. Not all the toner comes
off, however, so a flexible wiper or squeegee removes the excess toner.
This may then go into a waste toner hopper, which is sometimes part of
the cartridge, or the toner may simply be recycled and mixed with the
rest of the unused toner.

Over time, the drum may lose some of it's light sensitivity, may get
damaged from bad paper feeds, bits of grit, poor toner quality, staples,
etc, may get worn from the continual wiping to clean it, etc. Some
companies do refurbish this drum by removing the old surface down to the
metal and applying a new light sensitive surface. Some companies
rebuild the cartridge and may replace the drum with a new manufactured
one, while they also refurb other components in the cartridge and then
refill it with toner.

In the final stage of printing, the paper, now containing the toner, is
passed through some more rollers, including a highly heated Teflon
coated one. This is called the fuser,a sit fuses or melts the toner
onto the paper surface. Some printers have a cartridge or wiper with
fuser oil on it or in it, so that the toner, as it melts, doesn't stick
to the heated roller or other components. Usually, this roller is
heated by a halogen lamp which sits inside the aluminum fuser cylinder.

With color laser printers, some have 4 drums and go through this process
4 times, usually placing each color in sequence onto the paper but only
doing one fusing process per page. However, some lay all the color
toners down on the transfer belt and then transfer that final image to
the paper before fusing. Those models usually have one transfer belt or
drum rather than one per color.

I hope this helps to clarify some of the internal operation of a laser
printer (photocopiers work similarly). As a disclaimer, I have
simplified things regarding issues like how the static charges are used
to get the image to the drum and then the paper.


Art


If you are interested in issues surrounding e-waste,
I invite you to enter the discussion at my blog:

http://e-trashtalk.spaces.live.com/

Joel wrote:
> Bob Eager <rde42@spamcop.net> wrote:
>
>>>>> There should be no toner in the Drum to refill, or it seems like
>>>> you
>>>>> are
>>>>> talking about the Toner Cartridge *not* the DRUM
>>>> Unless you're specifically talking about this particular model,
>>>> remember that in some cases the toner cartridge *includes* the drum.
>>> Yes, ALL laser printers have Toner Cartridge *inside* the Drum as
>> this
>>> is
>>> where the Drum get the toner print on paper.
>> Wrong.
>
> Then you must be almost right then <BG>

"Joel" <joel@nospam.com> wrote in message
news:trd2c5l4gcv6kudb9r2k03k87f69ajtr19@4ax.com...
> Bob Eager <rde42@spamcop.net> wrote:
>
>> >> > There should be no toner in the Drum to refill, or it seems like
>> >> you
>> >> > are
>> >> > talking about the Toner Cartridge *not* the DRUM
>> >>
>> >> Unless you're specifically talking about this particular model,
>> >> remember that in some cases the toner cartridge *includes* the drum.
>> >
>> > Yes, ALL laser printers have Toner Cartridge *inside* the Drum as
>> this
>> > is
>> > where the Drum get the toner print on paper.
>>
>> Wrong.
>
> Then you must be almost right then <BG>

The HP/ Canon (the originator) types - and 75% of all, have a toner hopper
with a magnetic roller which dispenses toner in a thin toner film. The
static image on the drum opposite has an attraction for the toner which it
pulls across the few mm gap to form the print image on the drum. These and
the fuser roller close to one end of the paper tray are constantly turning,
and the drum polarity changing as the paper has the toner heated to 350
degrees, and pressed into the paper.

How can you do duplex (two sided) printing without melting the toner on the
front of the page? The toner also polymerizes as it is fused, and won't melt
a second time at that temperature.

These technical marvels were first put together by Xerox in the 1970s, who
'only marketed the laser printer inside Xerox' according to one Xerox
propeller head. They also developed, but never originally marketed the
graphic user interface - the DNA of WP and desk top publishing.

Canon missed the boat by licensing the product to HP in the 1980s which
seized control of the market by the simple means of giving any software
developers, all their proprietary driver manuals and floppy diskettes for
free.

These are two little examples of why sales and marketing people make more
money than technical staff.