Printing technology
Printers are routinely classified by the technology they employ; numerous such technologies have been developed over the years. The choice of engine has a substantial effect on what jobs a printer is suitable for, as different technologies are capable of different levels of image or 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.
A second 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 liquid ink 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.
[2] 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.
[edit] Modern print technology
The following printing technologies are routinely found in modern printers:
[edit] Toner-based printers
Main article:
Laser printerA
laser printer rapidly produces high quality text and graphics. As with digital photocopiers and multifunction printers (MFPs), laser printers employ a
xerographic printing process but differ from analog photocopiers in that the image is produced by the direct scanning of a
laser beam across the printer's
photoreceptor.
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.
[edit] 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 used by consumers.
[edit] 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
energy consumption and long warm-up times from a cold state. Also, some users complain that the resulting prints are difficult to write on, as 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, it is also available by various Xerox concessionaires
[1].
[3] Previously,
solid ink printers were manufactured by
Tektronix, but Tek sold the printing business to Xerox in 2001.
[edit] 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.
[edit] Inkless printers
[edit] 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; these coloured sheets are not required in black-and-white output. One example is the ZINK technology.
[edit] 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]
[edit] 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 services.
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.
[edit] 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.
[edit] 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 form 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.
[edit] 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.
[edit] 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.
[edit] Line printers
Main article:
Line printer, 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, also called
line matrix 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, such as 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, better known as
line matrix 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, label or other item.
Printronix and
TallyGenicom are among the leading manufacturers today.
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. The legacy of line printers lives on in many computer
operating systems, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.
[edit] 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.
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]
[edit] Other printers
A number of other sorts of printers are important for historical reasons, or for special purpose uses:
[edit] Printing mode
The data received by a printer may be:
Some printers can process all three types of data, others not.
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.
[edit] 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 color, 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 prints made from
photographic film. Many can be used on a
standalone basis without a computer, using a
memory card or
USB connector.
[edit] 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 their 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]
[edit] 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 as well standardised as
toner yields. Usually pages per minute refers to sparse monochrome office documents, rather than dense pictures which usually print much more slowly, especially colour images. PPM are most of the time referring to
A4 paper in Europe and
letter paper in the United States, resulting in a 5-10% difference
