Oki Microline (Okidata ML)

What the Oki Microline was

Microline — styled Okidata ML in the United States — is the brand name that Oki Electric Industry Company, Ltd. of Tokyo gave to its serial impact dot matrix (SIDM) printers. Oki describes the line as a family of low-cost, compact printers built as output devices for the personal computers that were only just reaching the market at the end of the 1970s, and the brand went on to be sold worldwide for receipts, forms and everyday business documents. In North America the printers were distributed by Okidata, Oki's US sales company, which is why the same machines are commonly cited under both the "Oki Microline" and "Okidata ML" names.

How the Microline printed

The Microline is a serial impact dot matrix printer: a wire dot print head travels across the page and strikes an inked ribbon to build characters and images out of patterns of dots, the same basic principle covered in the general account of dot-matrix printing. Oki's distinguishing engineering was the print head itself. Rather than the "clapper" mechanism used by rivals, Oki adopted a spring-charging head, in which a wire welded to a spring is held back by a magnet and then released so the spring drives the wire against the ribbon. Oki credits this design — later refined with an ultra-hard wire and carbon-black ribbons — with the higher speed, printing force and durability behind the Microline's reputation as a "printer that never breaks down."

The first model: the ML80 (1979)

According to Oki's own history, the Microline was born from a September 1978 agreement to supply low-cost printers to the US firm Tandy/Radio Shack. Oki's engineers developed a compact wire dot head and finished the resulting printer around that year's New Year holiday, after which the head of the Technical Department carried it to the United States. That machine, the ML (Microline) 80, is described by Oki as "the very first Microline model"; it used a 7-pin wire dot head and went on sale in 1979. The same engine was also fitted in Oki's own if800 model 120 personal computer. The line was soon changed from the 7-pin head to a 9-pin head, which Oki credits with its strong subsequent sales.

Old Microline and New Microline

In 1981 Oki launched the ML82A (A4) and ML83A (A3), the models later remembered as the "Old Microline" and prized for a build so solid it was nicknamed "tank-tough." It was during this period that the brand's spring-charging impact head matured, and Oki gold-plated an ML92 to commemorate one million Microline printers manufactured. In 1984 Oki introduced the ML182/192 and ML183/193 — the "New Microline" — which added a self-running head carriage and a re-inking system, cut the parts count by roughly half, and were among Oki's first products to use a custom LSI, surface-mount assembly and robotized production lines in Fukushima (for export) and Takasaki (for the domestic market).

The 300, 500 and 300R series

In 1987 Oki shipped the "300 series": the 9-pin ML320/ML321 as budget models and the 24-pin ML390/ML391 for higher print quality. Oki reports that, contrary to Okidata's US forecasts, the 9-pin ML320/ML321 became the best seller, while the 24-pin models found their strongest market among value-added resellers. The 500 series (ML520/521 and ML590/591), released in 1992, added an "intelligent" print head that sensed media thickness and gaps to keep printing force uniform, and the 300R series followed in 1995 as a faster, lower-cost successor built partly at Oki plants in the UK and Thailand. Oki also produced an 18-pin ML200 colour series and, for kanji markets, a flat-bed printer it says it was the first company to produce.

Place in printing history

Oki frames the story of the Microline as, in effect, "the history of the wire dot head." When development began in 1978 the printer market was still dominated by type (daisy-wheel and cylinder) printers, and the compact, lightweight SIDM machines that followed helped open dot-matrix printing to personal-computer users. As inkjet and laser printers later displaced dot-matrix machines for general use, the Microline endured in niches that valued its reliability — point-of-sale receipts, banking and other business printing — where the ability to print multi-part (carbon-copy) forms, a general strength of impact dot-matrix printers, also kept such machines useful, and Oki notes it retained a large SIDM market share in North America. Examples such as the Microline 92 are preserved in museum collections including The Henry Ford and the Smithsonian's National Museum of American History.