No matter where you are reading this article from, you most
likely have a printer nearby. And there's a very good chance
that it is an inkjet printer. Since their introduction
in the latter half of the 1980s, inkjet printers have grown in
popularity and performance while dropping significantly in
An inexpensive color inkjet printer made by
An inkjet printer is any printer that places
extremely small droplets of ink onto paper to create an image.
If you ever look at a piece of paper that has come out of an
inkjet printer, you know that:
The dots are extremely small (usually between 50 and 60
microns in diameter), so small that they are tinier than the
diameter of a human hair (70 microns)!
The dots are positioned very precisely, with resolutions
of up to 1440x720 dots per inch (dpi).
The dots can have different colors combined together to
create photo-quality images.
In this edition of HowStuffWorks,
you will learn about the various parts of an inkjet printer
and how these parts work together to create an image. You will
also learn about the ink cartridges and the special paper some
inkjet printers use.
First, let's take a quick look at the various printer
Impact vs. Non-impact There are several
major printer technologies available. These technologies can
be broken down into two main categories with several types in
Impact - These printers have a mechanism that
touches the paper in order to create an image. There are two
main impact technologies:
Dot matrix printers use a series of small pins
to strike a ribbon coated with ink, causing the ink to
transfer to the paper at the point of impact.
Character printers are basically computerized
typewriters. They have a ball or series of bars with
actual characters (letters and numbers) embossed on the
surface. The appropriate character is struck against the
ink ribbon, transferring the character's image to the
paper. Character printers are fast and sharp for basic
text, but very limited for other use.
Non-impact - These printers do not touch the
paper when creating an image. Inkjet printers are part of
this group, which includes:
Inkjet printers, which are described in this
article, use a series of nozzles to spray drops of ink
directly on the paper.
Laser printers, covered in-depth in How
Laser Printers Work, use dry ink (toner), static
electricity, and heat to place and bond the ink onto the
A Hewlett Packard LaserJet
Solid ink printers contain sticks of wax-like
ink that are melted and applied to the paper. The ink then
hardens in place.
printers have a long roll of transparent film that
resembles sheets of red-, blue-, yellow- and gray-colored
cellophane stuck together end to end. Embedded in this
film are solid dyes corresponding to the four basic colors
used in printing: cyan, magenta, yellow and black (CMYK).
The print head uses a heating element that varies in
temperature, depending on the amount of a particular color
that needs to be applied. The dyes vaporize and permeate
the glossy surface of the paper before they return to
solid form. The printer does a complete pass over the
paper for each of the basic colors, gradually building the
Thermal wax printers are something of a hybrid
of dye-sublimation and solid ink technologies. They use a
ribbon with alternating CMYK color bands. The ribbon
passes in front of a print head that has a series of tiny
heated pins. The pins cause the wax to melt and adhere to
the paper, where it hardens in place.
Thermal autochrome printers have the color in
the paper instead of in the printer. There are three
layers (cyan, magenta and yellow) in the paper, and each
layer is activated by the application of a specific amount
of heat. The print head has a heating element that can
vary in temperature. The print head passes over the paper
three times, providing the appropriate temperature for
each color layer as needed.
Out of all of these incredible technologies, inkjet
printers are by far the most popular. In fact, the only
technology that comes close today is laser printers.
So, let's take a closer look at what's inside an inkjet
Inside an Inkjet Printer Parts of a typical
inkjet printer include:
Print head assembly
Print head - The core of an inkjet printer, the
print head contains a series of nozzles that are used to
spray drops of ink.
The print head
Ink cartridges - Depending on the manufacturer
and model of the printer, ink cartridges come in various
combinations, such as separate black and color cartridges,
color and black in a single cartridge or even a cartridge
for each ink color. The cartridges of some inkjet printers
include the print head itself.
Print head stepper motor - A stepper
motor moves the print head assembly (print head and
ink cartridges) back and forth across the paper. Some
printers have another stepper motor to park the
print head assembly when the printer is not in use.
Parking means that the print head assembly is restricted
from accidentally moving, like a parking
brake on a car.
Stepper motors like this one control the
movement of most parts of an inkjet
Belt - A belt is used to attach the print head
assembly to the stepper motor.
Stabilizer bar - The print head assembly uses a
stabilizer bar to ensure that movement is precise and
Here you can see the stabilizer bar and
Paper feed assembly
Paper tray/feeder - Most inkjet printers have a
tray that you load the paper into. Some printers dispense
with the standard tray for a feeder instead. The
feeder typically snaps open at an angle on the back of the
printer, allowing you to place paper in it. Feeders
generally do not hold as much paper as a traditional paper
Rollers - A set of rollers pull the paper in
from the tray or feeder and advance the paper when the
print head assembly is ready for another pass.
The rollers move the paper through the
Paper feed stepper motor - This stepper motor
powers the rollers to move the paper in the exact
increment needed to ensure a continuous image is printed.
Power supply - While earlier printers often had
an external transformer,
most printers sold today use a standard power
supply that is incorporated into the printer itself.
Control circuitry - A small but sophisticated
amount of circuitry is built into the printer to control all
the mechanical aspects of operation, as well as decode the
information sent to the printer from the computer.
The mechanical operation of the printer is
controlled by a small circuit board containing a
Interface port(s) - The parallel
port is still used by many printers, but most newer
printers use the USB port. A
few printers connect using a serial
port or small computer system interface (SCSI) port.
While USB taking over, many printers still
use a parallel
Heat vs. Vibration Different types of inkjet
printers form their droplets of ink in different ways. There
are two main inkjet technologies currently used by printer
View of the nozzles on a thermal bubble
Thermal bubble - Used by manufacturers such as Canon
Packard, this method is commonly referred to as
bubble jet. In a thermal inkjet printer, tiny
resistors create heat, and this heat vaporizes ink to create
a bubble. As the bubble expands, some of the ink is pushed
out of a nozzle onto the paper. When the bubble "pops"
(collapses), a vacuum is created. This pulls more ink into
the print head from the cartridge. A typical bubble jet
print head has 300 or 600 tiny nozzles, and all of them can
fire a droplet simultaneously.
Click the button to see how a thermal bubble
inkjet printer works.
Piezoelectric - Patented
by Epson, this technology uses piezo crystals. A
crystal is located at the back of the ink reservoir of each
nozzle. The crystal receives a tiny electric charge that
causes it to vibrate. When the crystal vibrates inward, it
forces a tiny amount of ink out of the nozzle. When it
vibrates out, it pulls some more ink into the reservoir to
replace the ink sprayed out.
Click on the button to see how a piezoelectric
inkjet printer works.
Let's walk through the printing process to see just what
Click "OK" to Print When you click on a
button to print, there is a sequence of events that take
The software application you are using sends the data to
be printed to the printer driver.
The driver translates the data into a format that the
printer can understand and checks to see that the printer is
online and available to print.
The data is sent by the driver from the computer to the
printer via the connection interface (parallel,
The printer receives the data from the computer. It
stores a certain amount of data in a buffer.
The buffer can range from 512 KB random access memory (RAM) to 16
MB RAM, depending on the model. Buffers are useful because
they allow the computer to finish with the printing process
quickly, instead of having to wait for the actual page to
print. A large buffer can hold a complex document or several
If the printer has been idle for a period of time, it
will normally go through a short clean cycle to make sure
that the print head(s) are clean. Once the clean cycle is
complete, the printer is ready to begin printing.
The control circuitry activates the paper feed stepper
motor. This engages the rollers, which feed a sheet of paper
from the paper tray/feeder into the printer. A small trigger
mechanism in the tray/feeder is depressed when there is
paper in the tray or feeder. If the trigger is not
depressed, the printer lights up the "Out of Paper" LED and
sends an alert to the computer.
Once the paper is fed into the printer and positioned at
the start of the page, the print head stepper motor uses the
belt to move the print head assembly across the page. The
motor pauses for the merest fraction of a second each time
that the print head sprays dots of ink on the page and then
moves a tiny bit before stopping again. This stepping
happens so fast that it seems like a continuous motion.
Multiple dots are made at each stop. It sprays the CMYK
colors in precise amounts to make any other color
At the end of each complete pass, the paper feed stepper
motor advances the paper a fraction of an inch. Depending on
the inkjet model, the print head is reset to the beginning
side of the page, or, in most cases, simply reverses
direction and begins to move back across the page as it
This process continues until the page is printed. The
time it takes to print a page can vary widely from printer
to printer. It will also vary based on the complexity of the
page and size of any images on the page. For example, a
printer may be able to print 16 pages per minute
(PPM) of black text but take a couple of minutes to print
one, full-color, page-sized image.
Once the printing is complete, the print head is parked.
The paper feed stepper motor spins the rollers to finish
pushing the completed page into the output tray. Most
printers today use inks that are very fast-drying, so that
you can immediately pick up the sheet without smudging it.
In the next section, you will learn a little more about the
ink cartridges and the paper used.
Paper and Ink Inkjet printers are fairly
inexpensive. They cost less than a typical black-and-white
laser printer, and much less than a color laser printer. In
fact, quite a few of the manufacturers sell some of their
printers at a loss. Quite often, you can find the printer on
sale for less than you would pay for a set of the ink
This printer sells for less than
would they do this? Because they count on the supplies you
purchase to provide their profit. This is very similar to the
way the video
game business works. The hardware is sold at or below
cost. Once you buy a particular brand of hardware, then you
must buy the other products that work with that hardware. In
other words, you can't buy a printer from Manufacturer A and
ink cartridges from Manufacturer B. They will not work
A typical color ink cartridge: This
cartridge has cyan, magenta and yellow inks in separate
way that they have reduced costs is by incorporating much of
the actual print head into the cartridge itself. The
manufacturers believe that since the print head is the part of
the printer that is most likely to wear out, replacing it
every time you replace the cartridge increases the life of the
The paper you use on an inkjet printer greatly determines
the quality of the image. Standard copier paper works, but
doesn't provide as crisp and bright an image as paper made for
an inkjet printer. There are two main factors that affect
The brightness of a paper is normally determined by
how rough the surface of the paper is. A course or rough paper
will scatter light in
several directions, whereas a smooth paper will reflect more
of the light back in the same direction. This makes the paper
appear brighter, which in turn makes any image on the paper
appear brighter. You can see this yourself by comparing a
photo in a newspaper with a photo in a magazine. The smooth
paper of the magazine page reflects light back to your eye
much better than the rough texture of the newspaper. Any paper
that is listed as being bright is generally a
The other key factor in image quality is absorption.
When the ink is sprayed onto the paper, it should stay in a
tight, symmetrical dot. The ink should not be absorbed too
much into the paper. If that happens, the dot will begin to
feather. This means that it will spread out in an
irregular fashion to cover a slightly larger area than the
printer expects it to. The result is an page that looks
somewhat fuzzy, particularly at the edges of objects and text.
Imagine that the dot on the left is on coated
paper and the dot on the right is on low-grade copier
paper. Notice how irregular and larger the right dot is
compared to the left
As stated, feathering is caused by the paper absorbing the
ink. To combat this, high-quality inkjet paper is
coated with a waxy film that keeps the ink on the
surface of the paper. Coated paper normally yields a
dramatically better print than other paper. The low absorption
of coated paper is key to the high resolution capabilities of
many of today's inkjet printers. For example, a typical Epson
inkjet printer can print at a resolution of up to 720x720 dpi
on standard paper. With coated paper, the resolution increases
to 1440x720 dpi. The reason is that the printer can actually
shift the paper slightly and add a second row of dots for
every normal row, knowing that the image will not feather and
cause the dots to blur together.
Inkjet printers are capable of printing on a variety of
media. Commercial inkjet printers sometimes spray directly on
an item like the label on a beer
bottle. For consumer use, there are a number of specialty
papers, ranging from adhesive-backed labels or stickers to
business cards and brochures. You can even get iron-on
transfers that allow you to create an image and put it on a
T-shirt! One thing is for certain, inkjet printers definitely
provide an easy and affordable way to unleash your creativity.
the expense of inkjet cartridges, a huge business has
grown around the idea of refilling them. For most
people, refilling makes good sense, but there are a few
things to be aware of:
Make sure the refill kit is for your printer
model. As you learned in the previous section,
different printers use different technologies for
putting the ink on the paper. If the wrong type of ink
is used, it can degrade the output or possibly damage
the printer. While some commercial inkjets use
oil-based inks, virtually all desktop inkjets for home
or office use have water-based ink. The exact ink
composition varies greatly between manufacturers. For
example, thermal bubble inkjets need ink that is
stable at higher temperatures then piezoelectric
Most manufacturers require that you use only their
approved ink. Refill kits normally will void your
While you can refill cartridges, be very careful
of the ones that have the print head built into the
cartridge. You do not want to refill these more than
two or three times, or the print head will begin to
deteriorate and could damage your printer.
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