Dot matrix printing
With 24-pin printers, the horizontal movement can slightly overlap dots, producing visually superior output (near letter-quality or NLQ), usually at the cost of speed.
Unlike other technologies, impact printers can print on multi-part forms, allowing multiple copies to be made simultaneously, often on paper of different colors.
Between 1952 and 1954 Fritz Karl Preikschat filed five patent applications[7][8] for his so-called "PKT printer",[6] a dot matrix teletypewriter built between 1954 and 1956 in Germany.
[6] In 1956, while he was employed at Telefonbau und Normalzeit GmbH (TuN, later called Tenovis), the device was offered to the Deutsche Bundespost (German Post Office), which did not show interest.
An improved transistorized design[6] became the basis for a portable dot matrix facsimile machine, which was prototyped and evaluated for military use by Boeing around 1966–1967.
In the process, they designed the parallel electrical interface that was to become standard on most printers until it began to be replaced by the Universal Serial Bus (USB) in the late 1990s.
Not only could a 24-pin printer lay down a denser dot-pattern in a single pass, it could simultaneously cover a larger area and print more quickly.
However, unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced.
Actual position can be found out either by dead count using a stepper motor, rotary encoder attached to one wheel, or a transparent plastic band with markings that is read by an optical sensor on the printer head (common on inkjets).
Dot matrix printers create noise when the pins or typeface strike the ribbon to the paper,[28] and sound-damping enclosures may have to be used in quiet environments.
[32] The print head can be thought of featuring a single vertical column of seven or more pins approximately the height of a character box.
The printing speed of serial dot matrix printers with moving heads varies from 30[34] to 1550 characters per second (cps).
[41] The carriage was moved by a much-more-capable servo drive using a DC electric motor and an optical encoder / tachometer.
In 1985, The New York Times described the use of "near letter-quality, or NLQ" as "just a neat little bit of hype"[3] but acknowledged that they "really show their stuff in the area of fonts, print enhancements and graphics."
In 1985, PC Magazine wrote "for the average personal computer user dot matrix remains the most workable choice".
Early impact printers (including the MX) were notoriously loud during operation, a result of the hammer-like mechanism in the print head.
In office applications, output quality was a serious issue, as the dot-matrix text's readability would rapidly degrade with each photocopy generation.
General strategies were: Some newer dot-matrix impact printers could reproduce bitmap images via "dot-addressable" capability.
In 1981, Epson offered a retrofit EPROM kit called Graftrax to add this to many early MX series printers.
Banners and signs produced with software that used this ability, such as Broderbund's Print Shop, became ubiquitous in offices and schools throughout the 1980s.
Proportional-spaced fonts allowed the printer to imitate the non-uniform character widths of a typesetter, and also darker printouts.
When Hewlett-Packard's US patent 4578687 expired on steam-propelled photolithographically produced ink-jet heads in 2004, the inkjet mechanism became available to the printer industry.
For example, dot matrix impact printers are still used at bank tellers and auto repair shops, and other applications where use of tractor feed paper is desirable such as data logging and aviation.
Most of these printers now come with USB interfaces as a standard feature to facilitate connections to modern computers without legacy ports.
