Misplaced Pages

This is an old revision of this page, as edited by AAAAA (talk | contribs) at 05:33, 30 January 2005 (→Dot matrix printers today: Adding info about dot matrix printers used today, TallyGenicom, etc.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A dot matrix printer or impact matrix printer normally refers to a type of computer printer with a print-head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter, 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 or "pin", which uses the power of a tiny electromagnet or solenoid to drive it forward. Generally the print head prints one line of text at a time. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.

Early dot matrix printers

The LA30 was a 30 character/second dot matrix printer produced by Digital Equipment Corporation of Maynard, Massachusetts. It printed 80 columns of uppercase-only 5x7 dot matrix characters across a unique-sized paper. The printhead was driven by a stepper motor and the paper was advanced by a somewhat-unreliable and definitely noisy solenoid ratchet drive. The LA30 was available with both a parallel interface and a serial interface, however, the serial LA30 required the use of fill characters during the carriage-return operation.

The LA30 was followed by the LA36 which achieved far greater commercial success, becoming for a time the architypical dot matrix computer terminal. The LA36 used the same printhead as the LA30 but could print on forms of any width up to 132 columns of mixed-case output on standard computer green bar fanfold paper. The carriage was moved by a much-more-capable servo drive using a dc motor and an optical encoder/tachometer. The paper was moved by a stepper motor. The LA36 was only available with a serial interface but unlike the earlier LA30, no fill characters were required. This was possible because, while the printer never communicated at faster than 30 characters per second, the mechanism was actually capable of printing at 60 characters per second. During the carriage return period, characters were buffered for subsequent printing at 60 characters per second during a catch-up period. The two-tone buzz produced by 60 character-per-second catch-up printing followed by 30 character-per-second ordinary printing was a distinctive feature of the LA36.

Digital then broadened the basic LA36 line onto a wide variety of dot matrix printers including:

• LA180 -- 180 c/s line printer
• LS120 -- 120 c/s terminal
• LA120 -- 120 c/s advanced terminal
• LA34 -- Cost-reduced terminal
• LA38

Meanwhile, Centronics (then of Hudson, New Hampshire) was reselling a printer mechanism produced by Brother Industries, Ltd. of Japan. Unlike Digital, Centronics concentrated on the low-end line printer marketplace with their distinctive units. In the process, they designed the electrical interface that was to become standard on most dot matrix printers (indeed, most printers in general) until it started to be replaced by the Universal Serial Bus (USB) in the late 90s.

Dot matrix features

Certain models produce double-wide or bold characters by printing each vertical slice of a character twice. They can also produce higher resolutions by moving the print head more slowly while keeping the same "dot rate". They can also produce graphics by printing dots, one horizontal character-high stripe of pixels at a time. (Because of the particular 1-of-64 printable-character encoding used by Digital, Digital referred to these dot columns as "sixels".) Though most dot matrix printers print in black and white, a few produce colour by making extra passes, shifting a multi-color striped ink ribbon between passes.

Dot matrix printers today

Dot matrix printers used to be considered inexpensive, and until the 1990s the most common form of printer used with PCs. (Since then, the prices of dot matrix printers have stayed roughly stable, while the prices of inkjet and laser printers have fallen profoundly.) The groundbreaking model that drove their initial popularity in the consumer market was the Epson MX-80. However, they were notorious in homes and offices for their loud buzzing sound when printing (finally softened in some later models), and for unattractive, spotty printouts unless the user paid extra for a fancy-printing program such as Bradford or, later, Windows 3.1. Using these programs slowed the printer down greatly.

Dot matrix impact printers remain in occasional use in devices such as cash registers, ATM printouts and in industry where a carbon copy is required although thermal printing has largely supplanted them even in these applications. However, some companies still produce Serial and Line printers, such as TallyGenicom. Impact printers are used because of their low cost per page.

Nearly all inkjet, bubblejet, thermal printers, and laser printers use a dot matrix to describe each character or graphic. In common parlance these are seldom called dot-matrix printers, to avoid confusion with dot matrix impact printers.

• Computer printers
• Impact printers
• DEC hardware
• Human-computer interaction