YOKOHAMA: About 25 years ago, a new type of page-printing process using an LED (light-emitting diode) was developed, which promised to make office printers smaller, quieter, more reliable and less expensive than laser printers.
LED technology uses the same fundamental electrostatic (an electrical charge is built up on an insulated object) method as the laser ROS (raster output scanner) systems of applying toner to paper.
But instead of the complex series of lenses, rotating mirrors and scanning systems employed in laser printers, the LED printhead is solid-state, meaning no moving parts. The LED bar pulse-flashes across the entire page width and creates the image on the print drum as it moves down.
This method is not only mechanically simpler and less expensive to manufacture, but is also much more compact than a laser-printing system.
But five years after it was introduced, the LED system still hadn’t made much of an impact on the market or on users because its simplicity was also its downfall.
Due to the fixed horizontal position and maximum 600dpi resolution of the LED system, along with its varying light intensity, the printed results were often disappointing compared to laser-printer outputs.
LED printed pages frequently featured blurry type, jagged edges on images, fuzzy halftones and mis-registered colour reproduction.
To make matters worse, if individual LEDs failed in the device, the entire printhead had to be replaced by the manufacturer.
Print quality, especially in terms of resolution and reliability, became the LED system’s primary disadvantage, and led to the laser printer’s dominant position in the marketplace today.
A new take
Fuji Xerox working with partner Nippon Electric Glass Co Ltd — a manufacturer of specialty glass, such as glass tubing and CRTs (cathode-ray tubes) — finally found the solution to the problem, in the form of self-scanning integrated circuitry and optical technology.
The “brain” behind the entire self-scanning LED or SLED printhead process is a proprietary integrated application specific circuit (or ASIC) driver chip.
This high-performance driver precisely controls the intensity and timing of the 14,592 dots of light (LEDs) in each printhead to enable uniform printing.
Also, SLED has another advantage — with each LED array now able to pack up 1,200 diodes per inch — it is able to surpass the 600dpi resolution limitation of the early printers.
Now, having achieved 2,400dpi resolution, SLED printers have much finer print quality that’s equivalent to, and often better than, comparable laser-printers.
In recognising its contribution to the advancement of electrophotographic technology, the Fuji Xerox’s SLED printhead received the Technology Award from the Imaging Society of Japan last year. — ZAM KARIM
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