Laser printing
Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively charged cylinder called a "drum" to define a differentially charged image.[1] The drum then selectively collects electrically charged powdered ink (toner), and transfers the image to paper, which is then heated to permanently fuse the text, imagery, or both, to the paper. As with digital photocopiers, laser printers employ a xerographic printing process. 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.
"Silentwriter" redirects here. For the Apple Thermo printer sometimes called SilentWriter, see Apple Silentype.The laser printer was invented at Xerox PARC in the 1970s. Laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and many others. Over the decades, quality and speed have increased as prices have decreased, and the once cutting-edge printing devices are now ubiquitous.
In the 1960s, the Xerox Corporation held a dominant position in the photocopier market.[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. After transferring to the recently formed Palo Alto Research Center (Xerox PARC) in 1971, Starkweather adapted a Xerox 7000 copier to make SLOT (Scanned Laser Output Terminal). 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.[3][4][5]
Laser printers brought exceptionally fast and high-quality text printing in multiple fonts on a page, to the business and home markets. No other commonly available printer during this era could also offer this combination of features.
Performance[edit]
As with most electronic devices, the cost of laser printers has decreased significantly over the years. In 1984, the HP LaserJet sold for $3500,[21] had trouble with even small, low-resolution graphics, and weighed 32 kg (71 lb). By the late 1990s, monochrome laser printers had become inexpensive enough for home-office use, having displaced other printing technologies, although color inkjet printers (see below) still had advantages in photo quality reproduction. As of 2016, low-end monochrome laser printers can sell for less than $75, and while these printers tend to lack onboard processing and rely on the host computer to generate a raster image, they nonetheless outperform the 1984 LaserJet in nearly all situations.
Laser printer speed can vary widely, 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 100 pages per minute (6000 pages per hour). 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.[22]
The cost of this technology depends on a combination of factors, including the cost of paper, toner, drum replacement, as well as the replacement of other items 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.
Duplex printing (printing on both sides of the paper) can halve paper costs and reduce filing volumes, albeit at a slower page-printing speed because of the longer paper path. 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.
In a commercial environment such as an office, it is becoming increasingly common for businesses to use external software that increases the performance and efficiency of laser printers in the workplace. The software can be used to set rules dictating how employees interact with printers, such as setting limits on how many pages can be printed per day, limiting usage of color ink, and flagging jobs that appear to be wasteful.[23]
Safety hazards, health risks, and precautions[edit]
Toner clean-up[edit]
Toner particles are formulated to have electrostatic properties and can develop static electric charges when they rub against other particles, objects, or the interiors of transport systems and vacuum hoses. Static discharge from charged toner particles can ignite combustible particles in a vacuum cleaner bag or cause a small dust explosion if sufficient toner is airborne. Toner particles are so fine that they are poorly filtered by conventional household vacuum cleaner filter bags and blow through the motor or back into the room.
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. These specialized tools are called "ESD-safe" (Electrostatic Discharge-safe) or "toner vacuums".
Ozone hazards[edit]
As a normal part of the printing process, the high voltages inside the printer can produce a corona discharge that generates a small amount of ionized oxygen and nitrogen, which react to form ozone and nitrogen oxides. In larger commercial printers and copiers, an activated carbon filter in the air exhaust stream breaks down these noxious gases to prevent pollution of the office environment.
However, some ozone escapes the filtering process in commercial printers, and ozone filters are not used at all in most smaller home printers. 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. A potential health hazard is theoretically possible in extreme cases.[33]