Laser printer

From Free net encyclopedia

Image:Apple LaserWriter Pro 630.jpg 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 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 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 43 th tApple 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.

As with most electronic devices, the cost of laser printers has fallen markedly over the years. In 1985 the HP LaserJet sold for $2995.00 and weighed a hefty 71 pounds. The Apple LaserWriter (which shipped with a more powerful processor and the Postscript page description language) cost almost $7000.00. Today a comparable laser printer that boasts more memory, a higher print speed and duplexing capability can be had for about $300.00. A bare-bones laser printer costs less than $100.00.

The three major advantages of laser printers over inkjets are sharper text, lower cost per page and much faster print speed, since the entire page is imaged at one time, while an inkjet typically prints a page one narrow strip at a time.

1 How it works
2 Secret marks
3 See also
4 External links

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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. DC current drives a system that writes light onto the drum surface by using a laser and mirrors, thus developing a latent image on the drum's surface. 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, thus transferring the image. The paper passes through a fuser assembly, which, having rollers that provide 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 (see LED printer). The toner is essentially ink or lampblack and also includes either wax or plastic, so that when the paper passes through the fuser assembly, the particles of toner will melt. The paper may or may not be oppositely charged. The fuser can be an infrared oven, a heated roller, or (on some very fast, expensive printers) a xenon flash lamp. Color laser printers add colored toner (typically but not always cyan, yellow, and magenta -- see CMYK) in three additional steps or passes.

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, including the graphic-intensity of the job being processed. The fastest models can print over 200 monochrome pages per minute (12,000 pages per hour). The fastest color laser printers can print over 60 pages per minute (3600 pages per hour). Very high-speed laser printers are used for mass mailings of personalized documents, such as credit card or utility bills.

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.

A duplexing printer (one that prints on both sides of the paper) can halve paper costs and reduce filing volumes and floor weight. Formerly only available on high-end printers, duplexers are now common on mid-range office printers, though not all printers can accommodate a duplexing unit. Duplexing can also result in slower printing throughput, because of the more complicated paper path.

Many printers have a toner-conservation mode or economode, which can be substantially more economical at the price of 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 a high degree of accuracy.

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Secret marks

Image:Printermarkrp.jpg

Modern color laser printers mark printouts by a nearly invisible dot raster, for the purpose of identification. The dots are yellow and about 0.1 mm in size, with a raster of about 1 mm. This is purportedly the result of a deal between the US government and printer manufacturers to help track counterfeiters.

The dots encode the printing date, time, and printer serial number in binary-coded decimal on every sheet of paper printed, which allows pieces of paper to be traced by the manufacturer to identify the place of purchase, and sometimes the buyer. Some are concerned that this is a threat to the privacy and anonymity of those who print.

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