Laser printing
Laser printing differs from traditional xerography as implemented in analog photocopiers in that in the latter, the image is formed by reflecting light off an existing document onto the exposed drum.
Laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and many others.
[2] In 1969, Gary Starkweather, who worked in Xerox's product development department, had the idea of using a laser beam to "draw" an image of what was to be copied directly onto the copier drum.
In 1972, Starkweather worked with Butler Lampson and Ronald Rider to add a control system and character generator, resulting in a printer called EARS (Ethernet, Alto Research character generator, Scanned laser output terminal)—which later became the Xerox 9700 laser printer.
The IBM 3800 was used for high-volume printing on continuous stationery, and achieved speeds of 215 pages per minute (ppm), at a resolution of 240 dots per inch (dpi).
Unlike the IBM 3800, the Xerox 9700 was not targeted to replace any particular existing printers; however, it did have limited support for the loading of fonts.
The Xerox 9700 excelled at printing high-value documents on cut-sheet paper with varying content (e.g. insurance policies).
Once faster-recovery coatings were developed, the drums could touch the paper multiple times in a pass, and therefore be smaller in diameter.
PostScript allowed the use of text, fonts, graphics, images, and color largely independent of the printer's brand or resolution.
[5][6] Laser printers brought exceptionally fast and high-quality text printing in multiple fonts on a page, to the business and home markets.
[citation needed] A laser beam projects an image of the page to be printed onto an electrically charged, photoconductive, rotating, cylindrical drum.
1 megabyte = 1,048,576 bytes, or 8,388,608 bits, which is just large enough to hold the entire page at 300 dpi, leaving about 100 kilobytes to spare for use by the raster image processor.
During the 1980s, memory chips were still very expensive, which is why entry-level laser printers in that era always came with four-digit suggested retail prices in US dollars.
The primitive microprocessors in early personal computers were so underpowered and insufficient for graphics work that attached laser printers usually had more onboard processing power.
[13] Memory prices later decreased significantly, while rapid improvements in the performance of PCs and peripheral cables (most importantly, SCSI) enabled the development of low-end laser printers which offload rasterization to the sending PC.
Toner consists of fine particles of dry plastic powder mixed with carbon black or coloring agents.
A sheet of paper is then rolled under the photoreceptor drum, which has been coated with a pattern of toner particles in the exact places where the laser struck it moments before.
Some printers use a very thin flexible metal foil roller, so there is less thermal mass to be heated and the fuser can more quickly reach operating temperature.
The fuser can be an infrared oven, a heated pressure roller, or (on some very fast, expensive printers) a xenon flash lamp.
Different manufacturers claim that their toners are specifically developed for their printers and that other toner formulations may not match the original specifications in terms of either tendency to accept a negative charge, to move to the discharged areas of the photoreceptor drum from the developer roll, to fuse appropriately to the paper, or to come off the drum cleanly in each revolution.
Laser printer speed can vary widely, and depends on many factors, including the graphic intensity of the job being processed.
Very high-speed laser printers are used for mass mailings of personalized documents, such as credit card or utility bills, and are competing with lithography in some commercial applications.
Digital-rights advocacy groups such as the Electronic Frontier Foundation are concerned about this erosion of the privacy and anonymity of those who print.
If toner spills into the laser printer, a special type of vacuum cleaner with an electrically conductive hose and a high-efficiency (HEPA) filter may be needed for effective cleaning.
In larger commercial printers and copiers, an activated carbon filter in the air exhaust stream breaks down[citation needed] these noxious gases to prevent pollution of the office environment.
When a laser printer or copier is operated for a long period of time in a small, poorly ventilated space, these gases can build up to levels at which the odor of ozone or irritation may be noticed.
[35] According to a 2012 study conducted in Queensland, Australia, some printers emit sub-micrometer particles which some suspect may be associated with respiratory diseases.
According to Professor Morawska of the Queensland University of Technology, one printer emitted as many particles as a burning cigarette:[37][38] The health effects from inhaling ultrafine particles depend on particle composition, but the results can range from respiratory irritation to more severe illness such as cardiovascular problems or cancer.In December 2011, the Australian government agency Safe Work Australia reviewed existing research and concluded that "no epidemiology studies directly associating laser printer emissions with adverse health outcomes were located" and that several assessments conclude that "risk of direct toxicity and health effects from exposure to laser printer emissions is negligible".
[39] The German Social Accident Insurance has commissioned a human study project to examine the effects on health resulting from exposure to toner dusts and from photocopying and printing cycles.
[41] After the 2010 cargo plane bomb plot, in which shipments of laser printers with explosive-filled toner cartridges were discovered on separate cargo airplanes, the US Transportation Security Administration prohibited pass-through passengers from carrying toner or ink cartridges weighing over 1 pound (0.45 kg) on inbound flights, in both carry-on and checked luggage.
