In computing, a printer is a peripheral
which produces a hard copy (permanent readable text and/or graphics) of
documents stored in electronic
form, usually on physical print media such as paper or transparencies.
Many printers are primarily used as local peripherals, and are attached
by a printer cable or, in most newer printers, a USB
cable to a computer which serves as a document source. Some printers,
commonly known as network
printers, have built-in network interfaces (typically wireless and/or
Ethernet), and can serve as a hardcopy device for any user on the
network. Individual printers are often designed to support both local
and network connected users at the same time. In addition, a few modern
printers can directly interface to electronic media such as memory
sticks or memory cards, or to image capture devices such as digital
cameras, scanners; some printers are combined with a scanners and/or fax
machines in a single unit, and can function as photocopiers. Printers
that include non-printing features are sometimes called Multifunction
printers (MFP), Multi-Function Devices (MFD), or All-In-One (AIO)
printers. Most MFPs include printing, scanning, and copying among their
features.
A Virtual printer is a piece of computer software whose user
interface and API resemble that of a printer driver, but which is not
connected with a physical computer printer.
Printers are designed for low-volume, short-turnaround print jobs;
requiring virtually no setup time to achieve a hard copy of a given
document. However, printers are generally slow devices (30 pages per
minute is considered fast; and many inexpensive consumer printers are
far slower than that), and the cost per page is actually relatively
high. However this is offset by the on-demand convenience and project
management costs being more controllable compared to an out-sourced
solution. The printing press naturally remains the machine of choice for
high-volume, professional publishing. However, as printers have
improved in quality and performance, many jobs which used to be done by
professional print shops are now done by users on local printers; see
desktop publishing. The world's first computer printer was a 19th
century mechanically driven apparatus invented by Charles Babbage for
his Difference Engine.[1]
Printing
technology
Printers are routinely classified by the underlying print technology
they employ; numerous such technologies have been developed over the
years. The choice of print engine has a substantial effect on what jobs a
printer is suitable for, as different technologies are capable of
different levels of image/text quality, print speed, low cost, noise; in
addition, some technologies are inappropriate for certain types of
physical media (such as carbon
paper or transparencies).
Another aspect of printer technology that is often forgotten is
resistance to alteration: liquid ink such as from an inkjet head or
fabric ribbon becomes absorbed by the paper fibers, so documents printed
with a liquid ink sublimation printer are more
difficult to alter than documents printed with toner or solid inks,
which do not penetrate below the paper surface.
Cheques should either be printed with liquid ink or on special
"cheque paper with toner anchorage".[1]
For similar reasons carbon film ribbons for IBM Selectric typewriters
bore labels warning against using them to type negotiable instruments
such as cheques. The machine-readable lower portion of a cheque,
however, must be printed using MICR
toner or ink. Banks and other clearing houses employ automation
equipment that relies on the magnetic flux from these specially printed
characters to function properly.
Modern print
technology
The following printing technologies are routinely found in modern
printers:
Toner-based
printers
Main article:
Laser
printer
Another toner based printer is the LED
printer which uses an array of LEDs
instead of a laser
to cause toner adhesion to the print drum.
Recent research has also indicated that Laser
printers emit potentially dangerous ultrafine
particles, possibly causing health problems associated with
respiration [1] and
cause pollution equivalent to cigarettes.[2]
The degree of particle emissions varies with age, model and design of
each printer but is generally proportional to the amount of toner
required. Furthermore, a well ventilated workspace would allow such
ultrafine particles to disperse thus reducing the health side effects.
Liquid inkjet
printers
Inkjet printers operate by propelling variably-sized droplets of
liquid or molten material (ink) onto almost any sized page. They are the
most common type of computer printer for the general consumer.
Solid ink
printers
Solid
Ink printers, also known as phase-change printers, are a
type of thermal
transfer printer. They use solid sticks of CMYK
Coloured ink (similar in consistency to candle wax), which are melted
and fed into a piezo crystal operated print-head. The printhead sprays
the ink on a rotating, oil coated drum. The paper then passes over the
print drum, at which time the image is transferred, or transfixed, to
the page.
Solid
ink printers are most commonly used as Colour office printers, and
are excellent at printing on transparencies and other non-porous media. Solid
ink printers can produce excellent results. Acquisition and
operating costs are similar to laser printers. Drawbacks of the
technology include high power consumption and long warm-up times from a
cold state.
Also, some users complain that the resulting prints are difficult to
write on (the wax tends to repel inks from pens),
and are difficult to feed through Automatic
Document Feeders, but these traits have been significantly reduced
in later models. In addition, this type of printer is only available
from one manufacturer, Xerox,
manufactured as part of their Xerox
Phaser office printer line is also available by various Xerox
concessionaires [2].[3]
Previously, solid
ink printers were manufactured by Tektronix,
but Tek sold the printing business to Xerox in 2001.
Dye-sublimation
printers
A dye-sublimation printer (or dye-sub printer) is a
printer which employs a printing process that uses heat to transfer dye
to a medium such as a plastic card, paper or canvas.
The process is usually to lay one Colour at a time using a ribbon that
has Colour panels. Dye-sub printers are intended primarily for
high-quality Colour applications, including Colour photography; and are
less well-suited for text. While once the province of high-end print
shops, dye-sublimation printers are now increasingly used as dedicated
consumer photo printers.
Inkless printers
Thermal printers
Thermal printers work by selectively heating regions of
special heat-sensitive paper. Monochrome thermal printers are used in
cash registers, ATMs,
gasoline
dispensers and some older inexpensive fax machines. Colours can be
achieved with special papers and different temperatures and heating
rates for different Colours. One example is the ZINK technology.
UV printers
Xerox
is working on an inkless printer which will use a special reusable
paper coated with a few micrometres of UV
light sensitive chemicals. The printer will use a special UV light
bar which will be able to write and erase the paper. As of early 2007
this technology is still in development and the text on the printed
pages can only last between 16–24 hours before fading.[4]
Obsolete and
special-purpose printing technologies
The following technologies are either obsolete, or limited to special
applications though most were, at one time, in widespread use.
Impact printers rely on a forcible
impact to transfer ink to the media, similar to the action of a typewriter.
All but the dot
matrix printer rely on the use of formed
characters, letterforms that represent each of the characters that
the printer was capable of printing. In addition, most of these printers
were limited to monochrome printing in a single typeface at one time,
although bolding and underlining of text could be done by overstriking,
that is, printing two or more impressions in the same character
position. Impact printers varieties include, Typewriter-derived
printers, Teletypewriter-derived printers, Daisy wheel printers, Dot
matrix printers and Line printers. Dot matrix printers remain in common
use in businesses where multi-part forms are printed, such as car rental
service counters. An overview of impact printing [5]
contains a detailed description of many of the technologies used.
Pen-based plotters were an alternate printing technology once
common in engineering and architectural firms. Pen-based plotters
rely on contact with the paper (but not impact, per se), and special
purpose pens that are mechanically run over the paper to create text and
images.
Typewriter-derived
printers
Several different computer printers were simply computer-controllable
versions of existing electric typewriters. The Friden
Flexowriter and IBM
Selectric typewriter were the most-common examples. The Flexowriter
printed with a conventional typebar mechanism while the Selectric used
IBM's well-known "golf ball" printing mechanism. In either case, the
letter form then struck a ribbon which was pressed against the paper,
printing one character at a time. The maximum speed of the Selectric
printer (the faster of the two) was 15.5 characters per second.
Teletypewriter-derived
printers
Main article:
TeleprinterThe common teleprinter
could easily be interfaced to the computer and became very popular
except for those computers manufactured by IBM.
Some models used a "typebox" that was positioned (in the X- and Y-axes)
by a mechanism and the selected letter from was struck by a hammer.
Others used a type cylinder in a similar way as the Selectric
typewriters used their type ball. In either case, the letter form then
struck a ribbon to print the letterform. Most teleprinters operated at
ten characters per second although a few achieved 15 CPS.
Daisy wheel
printers
Daisy-wheel printers operate in much the same fashion as a typewriter.
A hammer strikes a wheel with petals (the daisy wheel), each
petal containing a letter form at its tip. The letter form strikes a
ribbon of ink,
depositing the ink on the page and thus printing a character. By
rotating the daisy wheel, different characters are selected for
printing.
These printers were also referred to as letter-quality printers
because, during their heyday, they could produce text which was as
clear and crisp as a typewriter (though they were nowhere near the
quality of printing
presses). The fastest letter-quality printers printed at 30
characters per second.
Dot-matrix
printers
In the general sense many printers rely on a matrix
of pixels,
or dots,
that together form the larger image. However, the term dot
matrix printer is specifically used for impact printers that use a
matrix of small pins
to create precise dots. The advantage of dot-matrix over other impact
printers is that they can produce graphical
images in addition to text; however the text is generally of poorer
quality than impact printers that use letterforms (type).
A
Tandy
1000 HX with a Tandy DMP-133 dot-matrix printer.
Dot-matrix printers can be broadly divided into two major classes:
Dot matrix printers can either be character-based
or line-based (that is, a single horizontal series of pixels across the
page), referring to the configuration of the print head.
At one time, dot matrix printers were one of the more common types of
printers used for general use — such as for home and small office use.
Such printers would have either 9 or 24 pins on the print head. 24-pin
print heads were able to print at a higher quality. Once the price of
inkjet printers dropped to the point where they were competitive with
dot matrix printers, dot matrix printers began to fall out of favor for
general use.
Some dot matrix printers, such as the NEC P6300, can be upgraded to
print in Colour. This is achieved through the use of a four-Colour
ribbon mounted on a mechanism (provided in an upgrade kit that replaces
the standard black ribbon mechanism after installation) that raises and
lowers the ribbons as needed. Colour graphics are generally printed in
four passes at standard resolution, thus slowing down printing
considerably. As a result, Colour graphics can take up to four times
longer to print than standard monochrome graphics, or up to 8-16 times
as long at high resolution mode.
Dot matrix printers are still commonly used in low-cost, low-quality
applications like cash
registers, or in demanding, very high volume applications like invoice
printing. The fact that they use an impact printing method allows them
to be used to print multi-part documents using carbonless
copy paper (like sales invoices and credit card receipts), whereas
other printing methods are unusable with paper of this type. Dot-matrix
printers are now (as of 2005) rapidly being superseded even as receipt
printers.
Line printers
Main article:
Line
printerLine printers, as the name implies, print an entire line of
text at a time. Three principal designs existed. In drum printers,
a drum carries the entire character set of the printer repeated in each
column that is to be printed. In chain printers (also known as train
printers), the character set is arranged multiple times around a
chain that travels horizontally past the print line. In either case, to
print a line, precisely timed hammers strike against the back of the
paper at the exact moment that the correct character to be printed is
passing in front of the paper. The paper presses forward against a
ribbon which then presses against the character form and the impression
of the character form is printed onto the paper.
Comb printers represent the third major design. These printers
were a hybrid of dot matrix printing and line printing. In these
printers, a comb of hammers printed a portion of a row of pixels at one
time (for example, every eighth pixel). By shifting the comb back and
forth slightly, the entire pixel row could be printed (continuing the
example, in just eight cycles). The paper then advanced and the next
pixel row was printed. Because far less motion was involved than in a
conventional dot matrix printer, these printers were very fast compared
to dot matrix printers and were competitive in speed with
formed-character line printers while also being able to print dot-matrix
graphics.
Line printers were the fastest of all impact printers and were used
for bulk printing in large computer centres. They were virtually never
used with personal
computers and have now been replaced by high-speed laser printers.
Line printers, better known as linematrix printers are widely used in
the automotive, logistic and banking world for high speed and barcode
printing. They are known as robust and durable printers that have the
lowest price per page (form). Companies as Printronix Inc. and TallyGenicom are the leading
manufactures today.
The legacy of line printers lives on in many computer operating
systems, which use the abbreviations "lp", "lpr", or "LPT" to refer
to printers.
Pen-based
plotters
A plotter is a vector
graphics printing device which operates by moving a pen over the
surface of paper. Plotters have been used in applications such as computer-aided
design, though they are rarely used now and are being replaced with
wide-format conventional printers (which nowadays have sufficient
resolution to render high-quality vector graphics using a rasterized
print engine). It is commonplace to refer to such wide-format printers
as "plotters", even though such usage is technically incorrect. There
are two types of plotters, Flat Bed and Drum.
Sales
Since 2005, the world's top selling brand of inkjet
and laser
printers has been HP
which now has 46% of sales in inkjet
and 50.5% in laser printers.[6]
Other printers
A number of other sorts of printers are important for historical
reasons, or for special purpose uses:
Printing mode
The data received by a printer may be:
- a
string of characters
- a
bitmapped image
- a
vector image
Some printers can process all three types of data, others not.
- Character Printers (such as Daisy
wheel printers) can handle only plain text data or rather simple
point plots.
- Pen Plotters
typically process vector images. Inkjet based Plotters can adequately
reproduce all three.
- Modern printing technology, such as laser
printers and inkjet
printers, can adequately reproduce all three. This is especially
true of printers equipped with support for PostScript
and/or PCL;
which includes the vast majority of printers produced today.
Today it is common to print everything (even plain text) by sending
ready bitmapped images to the printer, because it allows better control
over formatting. Many printer
drivers do not use the text mode at all, even if the printer is
capable of it.
Monochrome, Colour and
photo printers
A monochrome
printer can only produce an image
consisting of one Colour,
usually black. A monochrome printer may also be able to produce various
tones of that Colour, such as a grey-scale.
A Colour printer can produce images of multiple Colours.
A photo
printer is a Colour printer that can produce images that mimic the Colour
range (gamut)
and resolution
of photographic
methods of printing. Many can be used autonomously
(without a computer), with a memory
card or USB
connector.
The
printer manufacturing business
Often the razor
and blades business model is applied. That is, a company may sell a
printer at cost, and make profits on the ink
cartridge, paper, or some other replacement
part. This has caused legal disputes regarding the right of
companies other than the printer manufacturer to sell compatible
ink cartridges. To protect the razor and blades business model several
manufacturers invest heavily in developing new cartridge technology and
patenting it.
Other manufacturers, in reaction to the challenges from using this
business model, choose to make more money on printers and less on the
ink, promoting the latter through their advertising campaigns. Finally,
this generates two clearly different proposals: "cheap printer —
expensive ink" or "expensive printer — cheap ink". Ultimately, the
consumer decision depends on their reference interest
rate or their time
preference. From an Economics
viewpoint, there is a clear trade-off
between cost per copy and cost of the printer[7].
Printing speed
The speed of early printers was measured in units of characters
per second. More modern printers are measured in pages per minute.
These measures are used primarily as a marketing tool, and are not well
standardised. Usually pages per minute refers to sparse monochrome
office documents, rather than dense pictures which usually print much
more slowly. PPM are most of the time referring to A4
paper in Europe and Letter
(paper size) paper in the US, resulting in a 5-10% difference.
See also
References