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A laser printer is a common type of computer printer that produces high quality printing, and is able to produce both text and graphics.
The process is very similar to the type of dry process photocopier first produced by Xerox. Indeed, the first laser printer was created by Xerox researcher Gary Starkweather by modifying a Xerox copier in 1971. Laser printing eventually became a multibillion-dollar business for Xerox.
The first commercial implementation of a laser printer was the IBM model 3800 in 1976, used for high-volume printing of documents such as invoices and mailing labels. It is often cited in technology writing as "taking up a whole room," implying that it was a primitive version of the later familiar device used with a personal computer; however, while large, it was designed for an entirely different purpose. Many 3800s are still in use.
The first laser printer designed for use with an individual computer was released with the Xerox Star 8010 in 1977; however, although it was highly innovative the Star was an expensive system that was only purchased by a small number of laboratories and institutions. After personal computers became more widespread, the first laser printer intended for a mass market was the HP Laserjet 8ppm, released in 1984, which used a Canon Inc. developed engine controlled by HP developed software. The HP Laserjet printer was quickly followed by other laser printers from Brother Industries, IBM, and others.
Most noteworthy, however, was the role the laser printer played in popularizing desktop publishing with the introduction of the Apple LaserWriter for the Apple Macintosh, along with Aldus PageMaker software, in 1985. With these products, users could create documents that would previously have required professional typesetting.
How it works
An electric charge is first projected onto a revolving drum by a corona wire (in older printers) or a primary charge roller. The drum has a surface of a special plastic or garnet. Electronics drive a system that writes light onto the drum. The light causes the electrostatic charge to leak from the exposed parts of the drum. The surface of the drum passes through a bath of very fine particles of dry plastic powder, or toner. The charged parts of the drum electrostatically attract the particles of powder. The drum then deposits the powder on a piece of paper. The paper passes through a fuser, which, with heat and pressure, bonds the plastic powder to the paper. The temperature of the fuser can rise up to 200 degrees Celsius during printing.
Each of these steps has numerous technical choices. One of the more interesting choices is that some "laser" printers actually use a linear array of light-emitting diodes to write the light on the drum. The toner is essentially ink and also includes either wax or plastic. The chemical composition of the toner is plastic-based or wax-based so that, when the paper passes through the fuser assembly, the particles of toner will melt. The paper can be oppositely charged, or not. The fuser can be an infrared oven, a heated roller, or (on some very fast, expensive printers) a xenon strobe.
The slowest printers of this type print about four pages per minute (ppm), and are relatively inexpensive. Printer speed can vary widely, however, and depends on many factors. The fastest print mass mailings (commonly for utilities) at several thousand pages per minute.
The cost of this technology depends on a combination of costs of paper, toner replacement, and drum replacement, as well as the replacement of other consumables such as the fuser assembly and transfer assembly. Often printers with soft plastic drums can have a very high cost of ownership that does not become apparent until the drum requires replacement.
One helpful trait is that in very high volume offices, a duplexing printer (one that prints on both sides of the paper) can halve paper costs, and reduce filing volumes and floor weight as well. Not all laser printers, however, can accommodate a duplexing unit. Duplexing can also result in slower printing speeds, because of the more complicated paper path.
Many printers have a toner-conservation mode, which can be substantially more economical at the price of only slightly lower contrast.
Aside from these components, typical maintenance is to vacuum the mechanism, and eventually clean or replace the paper-handling rollers. The rollers have a thick rubber coating which eventually become covered with slippery paper dust and suffer wear. They can usually be cleaned with a damp lint-free rag and there are chemical solutions that can help restore the traction of the rubber.
A Raster Image Processor (RIP) chip is used in laser printers to communicate raster images to a laser.
The Warm Up is the process that a laser printer goes through when power is initially applied to the printer.
Lasers are used because they generate a coherent beam of light for high degree of accuracy.
Secret marks
Small yellow dots on white paper, generated by a color laser printer (scale: 0.1mm).
Modern color laser printers mark printouts by a nearly invisible dot raster, for the purpose of identification. The dots encode the printing date and printer ID [1].
The dots are yellow and about 0.1mm in size, with a raster of about 1 mm.
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