Printers are commonly used output devices that produce
a hard copy of document stored in electronic form, i.e they
put information from computer on to paper.
There are various kinds of printers available today like
Impact printers, Bubble-jet printers, Laser printers, Thermal
2. Types of printers
2.1 Impact printers
Impact printers are among the old printing technologies,
which make use of inked ribbon to make an imprint on the
paper. Impact printers are considered noisy when compared
to other printers. The most commonly known impact printers
How Daisy-Wheel Printers work
i. Daisy-Wheel Printers
A Daisy-Wheel Printer works on the same principle as ball-head
typewriter. The daisy wheel printer consists of a disk made
of plastic or metal on which characters stand out along the
outer edge. The printer rotates the disk to print a character
until the desired letter is facing the paper, after which a
hammer called solenoid strikes forcing the character to hit
an ink ribbon making a mark of the character on the paper.
Their speed is rated by cps (number of characters per second).
Advantages and Disadvantages
The main disadvantage of this printer is that they make noise
when printing and these kind of printers cannot print graphics.
The advantage is that they are not expensive and can produce
ii. Dot-Matrix Printers
A typical dot-matrix printer is shown in the figure below.
It consists of a print head, sheet guide assembly, platen knob,
Fig.: Dot-matrix printer
Fig.: Continuous feed paper
The name Dot-Matrix refers to the mechanism the printer uses
to print characters on paper i.e., dots.
In this type of printer, it consists of a column of pins
on the printhead that form letters and numbers as the printhead
moves across the paper. The most recent dot matrix printers
are equipped with 24 pins
Figure: 8-pin dot-matrix print head with examples of printed
The pins, contained in the printhead, are about one inch
long and are driven by several hammers, which force each pin
into contact with the ink ribbon (and paper) at a certain time.
The force on these hammers comes from the magnetic pull of small
wire coils (solenoids), which are energized at a particular
time, depending on the character to be printed.
Most printers can print 80 columns, and 132 columns per line.
Advantages of Dot-matrix printers include the following:
They can print on multi-part stationary or carbon copies
Lower printing costs compared with Inkjet or Laser,
the reason being that dot-matrix printers use a ribbon and
rugged printing process.
These can withstand unclean or dusty environment whereas
Inkject or laser jet printers require clean environment
Suitable for traction fed paper or continuous paper
feed. Sometimes you may need to print an activity using
continuous paper feed. Inkjet and Laser printers use discrete
sheets of paper, and normally do not use continuous paper
Using these printers require negligible operator training.
These printers usually cost less (initial purchase cost
may be more, but running cost is negligible)
The main disadvantages of Dot-matrix printers are:
Dot-matrix printers are noisy but not as much as Daisy-wheel
The quality of print is not as good as laser and inkjet
These printers cannot be used for producing good quality
images or for photo printing.
These printers are slow compared with laser printers.
2.2 Solid-Ink Printers
Solid-Ink printers use ink in a waxy solid form than liquid
form which avoids problems like spillage. And these kinds of
printers print one line at a time and these printers are best
suitable for graphic companies that need true color at a price
lower than a color laser printer.
Advantages and Disadvantages
Advantages are good print quality, ease of use and generate
less waste and the disadvantages include more power consumption
and odour of wax
Solid ink printers are less sensitive to paper thickness
and paper fibers. This allows printing on a number of different
surfaces including recycled and handmade paper.
2.3 Thermal Printers
Thermal printers are of two kinds.
i. Direct Thermal printer
Direct Thermal printer use a heated printhead to burn dots
into the surface of special heat-sensitive paper. It is similar
to older fax machines. The disadvantage in this is that the
paper that is used gets darken early, thus making difficult
ii. Thermal wax-transfer printer
Thermal wax-transfer printers use a heat-sensitive-ribbon
instead of heat-sensitive paper. Thermal printhead melts wax-based
ink from the ribbon on to the paper. The disadvantages with
thermal transfer printers are that the heating and cooling of
the print head determines their speed which means that since
the printhead is extensively used, it has to be replaced often.
2.4 Inkjet Printers
Inkjet printers are those that place extremely small droplets
of ink onto paper to create an image. They use a reservoir of
aqueous ink, a pump and an ink nozzle to accomplish this. These
dots are extremely small and can have different colors combined
together to create photo-quality images. They essentially work
by shooting ink onto paper. Both inkjet and laser printers are
non-impact printers in the sense that they do not have mechanisms
that physically touch paper in order to create images. However,
unlike laser printers, inkjet printers use aqueous ink that
spontaneously colors the paper (unlike toner from laser printers
that has to be fused into the paper with a fuser).
Parts of a typical ink jet printer are shown in the figure
Edge guide - Helps load the paper straight. Adjust the
left edge guide so that it fits snugly to the width of your
Sheet feeder - Feeds a stack of paper automatically.
Paper support - Supports the paper loaded in the sheet
Feeder guard - Prevents objects placed on the document
cover from falling inside the printer when opening the document
Document cover - Open and close when you place a photo
Output tray - Receives ejected paper.
Output tray extension - Supports the ejected paper.
Scanner unit - Open and close when you replace an ink
On button - Turns the printer on and off.
i. Print head assembly
Print head :.The core component of the inkjet printer
is the print head that contains a series of nozzles that spray
dots of ink onto paper.There are two main mechanisms that generate
the spraying of ink from the nozzles. The first mechanism relies
on a thermal bubble. In these systems, current flows through
certain nozzles and heats up resistors near those nozzles. This
heat vaporizes some the ink and generates a bubble that expands.
As the bubble expands, ink is sprayed out of the nozzle. Then,
the current decreases, and the bubble pops, sucking more ink
from the cartridge to fill the empty space.
The other mechanism that inkjet printers rely on to spray
ink from their nozzles involves piezoelectric materials. These
materials change shape based on the electric field around them.
A transducer is placed at the base (top) of the nozzle. An electrical
stimulus excites the transducer so that it changes shape, causing
ink to spray out of the nozzle. When the stimulus stops, ink
from the reservoir flows back into the cartridge to fill the
Ink Catridges : These come in various combinations
such as separate black and color cartridges or even a cartridges
for each ink color.
Print head stepper motor : A stepper motor moves the
print head assembly (print head and ink cartridges) back and
forth across the paper
Belt : This 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 controlled.
ii. Paper feed assembly
Paper tray/feeder : This is actually a tray that you
load the paper into.
Rollers : These rollers pull the paper in from the
tray or feeder and advance the paper when the print head assembly
is ready for another pass.
Paper feed stepper motor : This powers the rollers
to move the paper in the exact increment needed to ensure a
continuous image is printed
Advantages and Disadvantages
The low cost and relatively high quality of prints that are
offered by the inkjet printer is suitable for most day-to-day
tasks and thus used in home and offices.
Inkjets have the advantage of practically no warm up time
and lower cost per page, no noise and the disadvantages are
ink cartridges are expensive. So if you're thinking of purchasing
an inexpensive inkjet printer, you may visit www.staples.com.
Inkjet printers can print on a variety of papers as they essentially
work by shooting printer ink on to the paper.
2.5 Laser printers
Laser printers are the fastest and most popular printers
on the market today. They produce extremely high quality images
- some near photo quality.
Main Principle of Laser Printer
The main principle in the working of laser printer is static
electricity i.e., they use electro photography, or an electrophotostatic
process, to form images on paper. The basis of the principles
involved here is the science of atoms - oppositely-charged atoms
are attracted to each other, so opposite static electricity
fields cling together.
Parts of a laser printer are
The basic parts that a laser printer consists of are toner
cartridges, photosensitive drum, erase lamp, primary corona,
transfer corona, fuser assembly. Each of these parts have a
very important role to play in the printing process.
How it works?
The drum is the main component in a laser printer and is
oftentimes located near the center. It is usually made of a
highly photoconductive material that can be charged or discharged
by light. The drum interfaces directly with the paper and places
the toner at the correct locations to produce the image.
The way that the drum works is that it is given an initial
charge to begin with. As the drum rotates in circles, the laser
shines upon certain areas of the drum. The parts of the
drum that get exposed to the laser experience a change in charge.
For example, in certain laser printers, the drum is initially
given strong negative electro-static charge and the laser causes
exposed areas to change from a negative to a positive electro-static
charge. In this way, the laser generates an electrostatic image
on the drum.
Then, the printer exposes the rotating drum to negatively
charged toner particles. The toner particles are attracted
to the positive areas of the drum that were exposed by the laser.
As a result, an electrostatic image is developed on the drum
surface that will get transferred to the paper at a later state..
Now, the paper is given a strong positive charge (much stronger
than that of the drum) and is slid beneath the drum. Since the
paper has a stronger positive charge than the drum, it takes
the toner off of the drum so that the pattern from the drum
is translated to the paper. Then, the paper goes through the
fuser and the toner particles are fused into the paper.
In brief, the steps involved in the working of a laser
printer are given below:
1. Paper feeding
The printer moves a sheet of paper from the proper tray onto
a series of rollers, through the imaging and fixing areas, and
to the output hopper.
2. Drum Cleaning and Charging
Any residual toner from past jobs is scraped from the printer's
photosensitive drum. A fine wire (the primary corona) produces
a negative electrical charge across the entire face of the drum.
The image is set in raster lines as a series of fine dots on
3. Imaging the Drum
The information from the raster-image processor is read from
memory and sent to the print engine, one line at a time. The
laser sets a positive charge in the areas of the image to be
filled with toner.
4. Transferring Toner to the Drum
A film of fine plastic power is placed on the toner transfer
roller, which is turning close to the photosensitive drum. This
toner is then attracted to the positively charged areas of the
5. Transferring Toner to the Paper
The corona wire places a positive electrical charge on the
paper as it moves close to the drum. The toner is attracted
to the page, forming an image.
6. Fusing the Toner
The page passes through a pair of rollers. The roller on
the side toward the toner that has been placed on the page is
heated just enough to melt the plastic toner particles onto
the page without smearing. The roller on the other side supplies
the needed pressure.
Advantages and Disadvantages
Laser printers have a number of advantages over the rival
inkjet technology. They produce much better quality black text
documents than inkjets, and they turn out more pages per minute
(100 to 200 pages per minute are typical) at a lower cost per
page than inkjets.
Laser printers are well known for their speed and they can
handle large volumes and another advantage is that they are
not messy as inkjet that is, there is no ink spillage as the
ink is created from powder and they can print on any type of
paper and the disadvantage is that laser printers are expensive.
Leading Manufacturers of Printers:
There are several reputed manufacturers if one intends purchase
a printer.They include:
HP (Hewlett Packard)
Xerox and others
For a comparative analysis of printers, please checkout comparison
shopping sites like pricegrabber.com, and nextag.com.