Dot matrix printing


Dot matrix printing, sometimes called impact matrix printing, is a computer printing process in which ink is applied to a surface using a relatively low-resolution dot matrix for layout. Dot matrix printers are a type of impact printer that prints using a fixed number of pins or wires and typically use a print head that moves back and forth or in an up-and-down motion on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper. They were also known as serial dot matrix printers. Unlike typewriters or line printers that use a similar print mechanism, a dot matrix printer can print arbitrary patterns and not just specific characters.
The perceived quality of dot matrix printers depends on the vertical and horizontal resolution and the ability of the printer to overlap adjacent dots. 9-pin and 24-pin are common; this specifies the number of pins in a specific vertically aligned space. With 24-pin printers, the horizontal movement can slightly overlap dots, producing visually superior output, usually at the cost of speed.
Dot matrix printing is typically distinguished from non-impact methods, such as inkjet, thermal, or laser printing, which also use a bitmap to represent the printed work. These other technologies can support higher dot resolutions and print more quickly, with less noise. Unlike other technologies, impact printers can print on multi-part forms, allowing multiple copies to be made simultaneously, often on paper of different colors. They can also employ endless printing using continuous paper that is fanfolded and perforated so that pages can be easily torn from each other.

History

In 1925, Rudolf Hell invented the Hellschreiber, an early facsimile-like dot matrixbased teletypewriter device, patented in 1929.
Between 1952 and 1954 Fritz Karl Preikschat filed five patent applications for his so-called "PKT printer", a dot matrix teletypewriter built between 1954 and 1956 in Germany. Like the earlier Hellschreiber, it still used electromechanical means of coding and decoding, but it used a start-stop method rather than synchronous transmission for communication. In 1956, while he was employed at Telefonbau und Normalzeit GmbH, the device was offered to the Deutsche Bundespost, which did not show interest.
When Preikschat emigrated to the US in 1957 he sold the rights to utilize the applications in any country to TuN. The prototype was also shown to General Mills in 1957. An improved transistorized design became the basis for a portable dot matrix facsimile machine, which was prototyped and evaluated for military use by Boeing around 1966–1967.
File:Epson MX-80.jpg|left|thumb|An Epson MX-80, a classic model that remained in use for many years. IBM sold it as their IBM 5152.
In 1968, the Japanese manufacturer OKI introduced its first serial impact dot matrix printer, the OKI Wiredot. The printer supported a character generator for 128 characters with a print matrix of 7 × 5. It was aimed at governmental, financial, scientific and educational markets. For this achievement, OKI received an award from the Information Processing Society of Japan in 2013.
In 1970 Digital Equipment Corporation introduced an impact dot matrix printer, the LA30, as did Centronics : the Centronics 101. The search for a reliable printer mechanism led it to develop a relationship with Brother Industries, Ltd of Japan, and the sale of Centronics-badged Brother printer mechanisms equipped with a Centronics print head and Centronics electronics. Unlike Digital, Centronics concentrated on the low-end line printer marketplace with their distinctive units. 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 in the late 1990s.
DEC was a major vendor, albeit with a focus on use with their PDP minicomputer line. Their LA30 30 character/second dot matrix printer, the first of many, was introduced in 1970. In the mid-1980s, dot-matrix printers were dropping in price, and began to outsell daisywheel printers, due to their higher speed and versatility. The Apple ImageWriter was a popular consumer dot matrix printer in the 1980s until the mid-1990s.
In the 1970s and 1980s, dot matrix impact printers were generally considered the best combination of cost and versatility, and until the 1990s were by far the most common form of printer used with personal and home computers.
Increased pincount of the printhead from 7, 8, 9 or 12 pins to 18, 24, 27, or 36 permitted superior print quality, which was necessary for success in Asian markets to print legible CJKV characters. Epson's 24-pin LQ-series rose to become the new de facto standard, at 24/180 inch. 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. Although the text quality of a 24-pin was still visibly inferior to a true letter-quality printer such as a daisy wheel or laser printer, print quality was greatly superior to a 9-pin printer. As manufacturing costs declined, 24-pin printers gradually replaced 9-pin printers.
By the dawn of the 1990s, inkjet printers became more common as PC printers.

Design

Dot matrix printing uses a print head that moves back-and-forth, or in an up-and-down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter. 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.
Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers. Facing the ribbon and the paper is a small guide plate named ribbon mask holder or protector, sometimes also called butterfly for its typical shape. It is pierced with holes to serve as guides for the pins. The plate may be made of hard plastic or an artificial jewel such as sapphire or ruby.
The portion of the printer that contains the pin is called the print head. When running the printer, it generally prints one line of text at a time. The printer head is attached to a metal bar that ensures correct alignment, but horizontal positioning is controlled by a band that attaches to sprockets on two wheels at each side which is then driven with an electric motor. This band may be made of stainless steel, phosphor bronze or beryllium copper alloys, nylon or various synthetic materials with a twisted nylon core to prevent stretching. 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.
Because the printing involves mechanical pressure, dot matrix printers can create carbon copies and carbonless copies.
Although nearly all inkjet, thermal, and laser printers also print closely spaced dots rather than continuous lines or characters, it is not customary to call them dot matrix printers.
Dot matrix printers have one of the lowest printing costs per page.
They are able to use fanfold continuous paper with tractor holes.
Dot matrix printers create noise when the pins or typeface strike the ribbon to the paper, and sound-damping enclosures may have to be used in quiet environments.
They can only print lower-resolution graphics, with limited color performance, limited quality, and lower speeds compared to non-impact printers.

Variations

The common serial dot matrix printers use a horizontally moving print head. The print head can be thought of featuring a single vertical column of seven or more pins approximately the height of a character box. In reality, the pins are arranged in up to four vertically or/and horizontally slightly displaced columns in order to increase the dot density and print speed through interleaving without causing the pins to jam. Thereby, up to 48 pins can be used to form the characters of a line while the print head moves horizontally. The printing speed of serial dot matrix printers with moving heads varies from 30 to 1550 characters per second.
In a considerably different configuration, so called line dot matrix printers or line matrix printers use a fixed print head almost as wide as the paper path utilizing a horizontal line of thousands of pins for printing. Sometimes two horizontally slightly displaced rows are used to improve the effective dot density through interleaving. While still line-oriented, these printers for the professional heavy-duty market effectively print a whole line at once while the paper moves forward below the print head. Line matrix printers are capable of printing much more than 1000 cps, resulting in a throughput of up to 800 pages per hour.
A variation on the dot matrix printer was the cross hammer dot printer, patented by Seikosha in 1982. The smooth cylindrical roller of a conventional printer was replaced by a spinning, fluted cylinder. The print head was a simple hammer, with a vertical projecting edge, operated by an electromagnet. Where the vertical edge of the hammer intersected the horizontal flute of the cylinder, compressing the paper and ribbon between them, a single dot was marked on the paper. Characters were built up of multiple dots.

Manufacturers and models

DEC

Unlike the LA30's 80-column, uppercase-only 5 x 7 dot matrix, DEC's product line grew. New models included:
  • LA36 : supported upper and lower case, with up to 132 columns of text
  • LA34: a lower-cost alternative to the LA36
  • LA38: an LA34 with more features
  • LA180: 180 CPS
  • LS120: 120 CPS
  • LA120: 180 CPS
  • LA12: a portable terminal – the DECwriter Correspondent