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OKI and the Changing Times

Part 14: Venturing into Optoelectronics with LED Printers

LEDs (light emitting diodes) have drawn increasing attention for the potential of its technology to help save energy and fight global warming. They have become more familiar in recent years in applications ranging from lighting to TVs. OKI began research on LEDs in 1965. In 1981, OKI unveiled the world's first page printer to use LEDs as its light source.

Foundations of LED printer development

LEDs are semiconductor elements that emit light on the application of a voltage in the forward direction. Printers incorporating LEDs as their light source are distinctly unique products, products with which the OKI name has become near-synonymous. The foundations for these products go back 46 years to 1965, when a lone researcher was sent to study LED technologies under Professor Junichi Nishizawa at Tohoku University. Subsequently, OKI came to dominate the market with facsimile incorporating thermal printers (printing thermally onto paper media), becoming a leader in the field of printer head technologies. At the same time, OKI turned its sights to developing LED printer heads to increase product differentiation from the competition.

First-generation LED array head

In 1977, OKI began work on developing LED array heads in a joint research project with Nippon Telegraph and Telephone Public Corporation's Yokosuka Electrical Communication Laboratory. The technology for producing LED arrays at that time was in its infancy. Manufacturing yield rates for LED chips were poor; they needed to be improved by an order of magnitude to achieve commercial feasibility.

The major initial problem was light source inconsistencies caused by differences in crystal density in the light emitting components. While the ideal solution would have been to eliminate semiconductor wafer defects, this was not possible given the technologies available at the time. The research team arrived at the following hypothesis: It should be possible to produce LED array heads with minimal light source variations, even with a certain amount of defects, provided that the defects were scattered uniformly. The research team proved this initial hypothesis in 1979, two years after beginning initial development, unveiling an electrophotographic printer incorporating an LED array light source and capable of printing 20 A4 pages per minute.

Full-scale entry into LED printer market

popular in the DTP market (launched 1991)

In 1981, OKI developed the OPP6100, the world's first page printer using a first-generation LED array head as its light source. This printer printed using a magnetic single-component system with pressure-fixed toner. The product was highly energy efficient for its time, an important factor in the era immediately following an oil crisis. While the OPP6100 was little more than a proof-of-concept device, its performance resulted in authorization for external sales, allowing OKI to develop its proprietary printer design. In 1983, the company announced a successor model, the high-speed OPP6220 B4-size desktop printer offering print speeds of 20 PPM(*1) (A4 horizontal). This became the world's first practical mass-produced LED printer.

OKI launched an OEM program for this product in the following year for overseas system manufacturers, a course of action that gave OKI the opportunity to gain expertise in refining its products. With continuing improvements over the years, OKI developed a series of distinctive printers that would become best-sellers, including the MICROLINE 4w, the world's smallest page printer and one of the first to incorporate eco-friendly technologies, and the MICROLINE 905PSII, the world's first printer to incorporate a 1200 dpi LED head.

  • *1:PPM

    Page per printer. The number of pages a printer prints per minute.

The challenge: Color LED printers

With steady improvements in the performance and cost of personal computers, the 1990s saw growing demand for color printing. OKI, too, was keen to develop compact color printers based on LEDs.

Schematic diagram of tandem
printing process

The first challenge in developing color printers was to select printing methods. Possible choices included four-cycle printing and tandem printing. Selected after careful consideration, the tandem printing process deploys four-color imaging units arranged in a line along the paper feed direction to overlay colors directly onto the paper as it passes through the printer. This gives print speeds identical to monochrome printing and four times faster than the four-cycle process. This decision was based in part on the future goal of high-speed color printing.

Development began with the creation of a prototype that used four monochrome printer imaging units. The development team faced a vast number of issues, including the different characteristics of different color toners, the extremely narrow fixing area due to the overlaying of toners on the paper, and the need to select suitable materials for the transfer carriage belt, being manufactured for the very first time. OKI persevered. In 1998, it launched the MICROLINE 8c color printer, the first A4-size printer to use tandem printing technologies.

This achievement was followed by a steady stream of improvements. A major turning point came in 2006 with the development of Epi Film Bonding technology. This world's-first feat made it possible to bond materials with differing properties, eventually leading to the successful commercialization of innovative LED printing heads. OKI's LED printers are the fruits of OKI's DNA, which holds OKI's deeply-held commitment to innovation. OKI continues to lead the field in LED technology innovations in Japan and worldwide.

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