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Laser printer is a common type of computer printer that produces
high quality printing and is able to print both text and graphics. It
works on laser beam technology to print on paper.
The process is very similar to the type used in a photocopier. Infact, first
laser printer was created by modifying a photocopy machine!!!
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| Advantages of Laser Printers: |
| Laser printers are bought today for their: |
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Speed |
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Precision |
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Long Term Economy |
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| The advantages of Laser Printers over InkJet Printers are: |
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1.
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It can draw more precisely than an inkjet, without spilling any
excess ink. Lasers use toner* instead of ink.
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2.
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Laser Printers produce much better quality black text documents
than inkjets
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3.
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Laser Printers are designed more for the long haul - that is, they turn out
more pages per month at a lower cost per page than inkjets.
So, if it's an office workhorse that's required, the laser printer may be the
best option.
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4.
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Laser Printers handle envelopes, card and other
non-regular media, better than inkjets. This is a major factor of importance to
both the home and business segments.
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| Anatomy of a Laser Printer |
| Laser has mainly four subparts:
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Paper feeder Unit- Feeds the paper into the print
mechanism. Main constituents are tray, paper take-up roll and paper take-up
switch.
Processing Unit- Main constituents are toner, developer and drum.
*Toner is an electrically charged powder with two main ingredients: pigment and
plastic.The pigment provides the coloring that fills in the text and
images.This pigment is blended into plastic particles, so the toner will
melt when it passes through the heat of the fuser.
Developer supplies toner from the toner cartridge to the drum and ensures that
it is evenly spread.
Drum is the single largest part of the laser printer.
It is an aluminum cylinder coated with photosensitive material. This
receives the latent image of the document and then transfers it onto the
paper.
Print Head Unit- The laser beam light emitted from the Print Head is
used to create an electrostatic latent image on the surface of the Drum.
Fuser Unit- The toner image transferred onto the paper is securely
fixed to the paper.
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| Demystifying Laser's Printing
Process |
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In this article, we'll unravel the mystery behind the laser
printer, tracing a page's path from the characters on your computer screen to
printed letters on paper. The whole printing process can be broken down into
seven simple steps:
Step1: Data Transfer
First, the computer sends data to the printer. But it doesn't just barrel
ahead-it queries the output port to make sure a printer is attached and ready.
The printer sends a signal back indicating it is ready for data. Then, the
print job is sent and stored in the printer.
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Step 2: Drum Writing
The printer conditions the drum to receive the image by applying a uniform
negative charge of -600v to its surface. The data in the printer's memory is
then written onto the drum using a laser. Rather than writing on it with ink or
toner, however, it writes by shining a very precise laser on the photosensitive
drum in certain spots, changing the electrical charge in those spots. This
image isthe negative of the print image. These neutralized spots will be the
areas where toner adheres to the drum later in the process and then transfers
onto the paper.
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The printer photoconductor drum rotates very accurately to build
one horizontal line at a time. The smaller the rotation, the higher the
resolution down the page - the step rotation on a modern laser printer is
typically 1/600th of an inch, giving a 600 dpi vertical resolution rating.
Similarly, the faster the laser beam is switched on and off, the higher the
resolution across the page.
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Step 3: Paper feed
Now it's time for the paper to join in. Feed rollers draw the paper into the
printer from the paper tray. Registration rollers hold the paper until it's
time for it to be released, making sure that the top of the paper feeds in
exactly at the moment when the laser image of the page that's on the drum
rotates past it.
Sensors are kept across the path of the paper which keep sending signals to the
Printed Circuit Board about the entry of paper in various parts of the printer.
The printer knows how long it should take for the paper to move from one sensor
to the next, and if the paper is delayed, the printer gives you a paper jam
message
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Step 4: Toner pickup
Steps 4 and 5 occur more or less simultaneously:
As the paper is being drawn in, the toner is being applied to the drum. The
toner cartridge contains a rotating, magnetic, metal-developing cylinder, a
toner reservoir, and a height control mechanism that limits the amount of toner
the cylinder can pick up at a time. Development is done by spreading the toner
over the surface of the photoconductor drum. The toner carries an opposite
charge to that of the charge on the photoconductor drum. Thus the toner adheres
only to the charged areas on the photoconductor, thus making the latent image
visible
Printer View
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Step 5: Transfer of developed image onto the paper
At this point, the image exists on the drum, complete with toner. If you could
look inside the printer as it operates (you can't, by the way, because of the
safety features in place) and stop the drum from rotating for a moment, you
could see the page on the drum, just as it is to be printed.
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As the paper feeds into the printer, the transfer corona applies
a +600v (positive) charge to the paper. The sheet of paper now comes into
contact with the drum, fed in by a set of rollers. This charge on the paper is
stronger than the negative / positive charge of the electrostatic image
(depending on the printer maker), so the paper magnetically attracts the toner
powder. As it completes it's rotation it lifts the toner from the drum, thereby
transferring the image to the paper. Charged areas of the drum don't attract
toner and result in white areas on the paper.
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Step 6: Fusing the toner
The image is now on the paper, but it's not secure there; it's just loose toner
held in place by gravity and a weak electrostatic charge. For permanent
application, it must be fused. Fusing is basically melting the toner's plastic
particles so they stick, or fuse, to the fibers in the paper.
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The fuser roller is a nonstick cylinder with a high-powered lamp
inside it that heats the paper to around 330 to 355 degrees Fahrenheit. As the
paper passes by it, the toner melts. This is the reason why the printouts from
a laser printer are slightly warm.
Typically, the drum rotates thrice for every page of A4 print,
since the length of the A4 page is thrice of the circumference of the drum.
The final part of the fusing assembly is the pressure roller. It's a rubber
roller that presses against the fuser roller; the paper feeds between it and
the fuser roller on its way through the printer.
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Step 7: Drum Preparation
In preparation for printing, the drum must be cleaned to remove any traces of
previous pages. First, a rubber blade wipes the excess toner from the drum, and
then discharge lamps electrostatically cleans it by neutralizing residual
electrical charges on it. Now the drum is ready to receive the data for the
next print.
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Making the right Choice
One buys laser printer because it offers several advantages over other printers
(refer first page). Because there is much differentiation within the laser
printer market, so in order to realize these advantages it becomes extremely
necessary that the right choice is made. Asking the right questions can help
you make the right decision.
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Q) What's the resolution?
If you are going to be using your laser printer for text, then 600x600
resolution is usually sufficient. Otherwise, go for at least 1200x1200.
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Q) Is it fast enough?
Because one of the reasons to get a laser printer is speed, take a close look
at the page per minute (ppm) speeds. A home laser printer should be capable of
at least 15-20ppm; more expensive printers can get a lot faster.
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Q) Separate toner and drum?
Some laser printers have separate toner and drum units; others include them in
one disposable part. The advantage to having separate units is that you save
money: Toner will run out way before you have to replace the drum unit.
However, it's a lot easier to replace an all-in-one combination. Your call.
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Q) Check paper sizes and weights.
Different printers come with different paper tray sizes. Some can only handle
upto 8.5x11-inch paper or A4 paper. This is fine if that is what you are mostly
going to print on, but if you need to print on legal or ledger paper, make sure
the printer can accommodate them.
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Q) Can you network it?
If you're planning to share your laser printer with others, then make sure that
it is network-capable. Some of the low-cost home units can only be used by a
single computer.
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Q) What will be the maintenance costs?
Compare prices of consumable items such as toner cartridges and replacement
drums. Compare warranties and service contracts.
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