Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and medium-quality photos) by repeatedly sending laser rays back and forth through a negatively charged cylinder called "drum" to determine differential charged images. The drum then selectively collects the electrically charged toner (toner) powder, and transfers the image to paper, which is then heated to permanently combine text, image, or both. Like digital copiers, laser printers use the xerographic printing process. However, laser printing differs from analog copiers because the images are generated by a direct scan of the media between the photoreceptor of the printer. This allows laser printing to copy images faster than most copiers.
Invented at Xerox PARC in the 1970s, laser printers were introduced to offices and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and many others. For decades, quality and speed have improved as prices have fallen, and the most sophisticated printing devices are now ubiquitous.
Video Laser printing
History
In the 1960s, Xerox Company held a dominant position in the photocopier market. In 1969, Gary Starkweather, who worked in the Xerox product development department, had the idea of ​​using laser light to "draw" what images would be copied directly to the drum of the photocopier. After transferring to the newly formed Palo Alto Research Center (Xerox PARC) in 1971, Starkweather adapted the Xerox 7000 copier to make SLOT (Scan Laser Output Terminal). In 1972, Starkweather worked with Butler Lampson and Ronald Rider to add control systems and character generators, resulting in a printer called EARS (Ethernet, Alto Research character generator, scanned laser output terminal) - which later became the Xerox 9700 laser printer.
The first commercial implementation of laser printers was the IBM 3800 in 1976. It was designed for data centers, where line printers were replaced with mainframe computers. The IBM 3800 is used for high-volume printing on continuous stationery, and reaches speeds of 215 pages per minute (ppm), at a resolution of 240 dpi per inch (dpi). More than 8,000 printers are sold. The Xerox 9700 was brought into the market in 1977. Unlike the IBM 3800, Xerox 9700 is not targeted to replace certain existing printers; however, it does have limited support for font loading. The Xerox 9700 excels in printing high value documents on cut-sheet paper with a variety of content (eg insurance policies).
In 1979, inspired by the commercial success of Xerox 9700, Canon's Japanese camera and optics company Canon developed a cheap laser printer, Canon LBP-10. Canon then began working on a much better printing press, Canon CX, resulting in an LBP-CX printer. Having no experience in selling to computer users, Canon sought partnerships with three Silicon Valley companies: Diablo Data Systems (which rejected the offer), Hewlett-Packard (HP), and Apple Computer.
The first laser printer designed for office use reached the market in 1981: Xerox Star 8010. The system uses unmatched desktop metaphors in commercial sales, up to Apple Macintosh. Although innovative, Star workstation is a very expensive system ( US $ 17,000 ), only a small percentage of targeted businesses and institutions.
The first laser printer devoted to mass-market sales was HP LaserJet, released in 1984; it uses a Canon CX engine, controlled by HP software. LaserJet is quickly followed by printers from Brother Industries, IBM, and others. The first generation machine has a large photosensitive drum, a larger circle than the length of paper loaded. After a faster recovery coating is developed, the drum can touch the paper several times in the track, and therefore smaller in diameter.
In 1985, Apple introduced LaserWriter (also based on the Canon CX engine), but used the newly released PostScript page description language. Up to this point, each manufacturer uses his own page description language, making supporting software complicated and costly. PostScript allows the use of text, fonts, graphics, images, and colors that are largely independent of brand or printer resolution. PageMaker, written by Aldus for Macintosh and LaserWriter, was also released in 1985 and the combination became very popular for desktop publishing. Laser printers bring very fast and high-quality text printing in various fonts on the page, to business and consumer markets. No other printers are generally available during this era that can also offer a combination of these features.
Maps Laser printing
Printing process
A laser beam (typically, aluminum gallium arsenide (AlGaAs) semiconductor laser) projects a drawing page to be printed onto a drum containing selenium, selenium-coated, spinning, cylindrical (or, more commonly in the next version, a drum called organic photoconductors made from N-vinylcarbazole, organic monomer). Photoconductivity allows the filled electrons to fall from the area exposed to light. The ink powder particles (toner) are then electrostatically attracted to the area charged to the drum that has not been given a laser beam. The drum then transfers the image to paper (which is passed through the machine) with direct contact. Finally the paper is passed to the finisher, which uses a strong heat to instantly put the toner/image onto the paper.
There are usually seven steps involved in the process:
Raster image processing
Documents to be printed are encoded in a page description language such as PostScript, Printer Command Language (PCL), or Open XML Paper Specification (OpenXPS). Raster image processors convert page descriptions into bitmaps stored in the printer's raster memory. Each horizontal strip of dots on the page is known as a raster or scanning line.
Laser printing is different from other printing technologies because each page is always displayed in one nonstop process in the middle while other technologies such as inkjet can pause every few lines. To avoid the underrun buffer (where the laser reaches a point on the page before it has a point to draw there), the laser printer usually requires enough raster memory to hold a bitmap image of the entire page.
Memory requirements increase with square point by inch, so 600 dpi requires at least 4 megabytes for monochrome, and 16 megabytes for color (still at 600 dpi). For full graphical output using the page description language, it takes at least 1 megabyte of memory to store all the letter/A4 size monochrome pages at 300 dpi. At 300 dpi, there are 90,000 dots per square inch (300 dots per linear inch). Ordinary paper measuring 8.5 ÃÆ'â € "11 has a 0.25 inch (6.4 mm) margin, reducing the print area to 8.0 x 10.5 inches (200 mm × 270 mm), or 84 square inches. 84 sq/in ÃÆ'â € "90,000 dots per sq/in = 7,560,000 dots. 1 megabyte = 1,048,576 bytes, or 8,388,608 bits, large enough to hold an entire page at 300 dpi, leaving about 100 kilobytes for use by raster image processors.
In color printers, each of the four CMYK toner layers is stored as a separate bitmap, and all four layers are usually preprocessed before printing begins, so a minimum of 4 megabytes is required for full color letter pages at 300 dpi.
During the 1980s, memory chips were still very expensive, which is why the entry-level laser printers of that era always came with the suggested four-digit retail price in US dollars. Memory prices then fall, and 1200 dpi printers have been widely available in the consumer market since 2008. Electrophotographic plate makers 2400 dpi, basically laser printers that print on plastic sheets, are also available.
Charging
In older printers, the corona wire is positioned parallel to the drum or, in newer printers, the main charge roller, projecting electrostatic charges to the photoreceptor (if not called a photo conductor unit), a rotating photovoltaic drum or sensor capable of holding an electrostatic charge on its surface when in the dark.
AC bias voltage is applied to the main charge roller to remove the remaining charge from the previous image. The roll will also apply a DC bias on the drum surface to ensure a uniform negative potential.
A number of patents describe a photosensitive drum layer as a silicone sandwich with a photo loading layer, a leakage barrier layer, and a surface layer. One version uses amorphous silicon containing hydrogen as the light receiving layer, Boron nitride as a leakage barrier layer, as well as a doping silicone surface layer, especially silicon with oxygen or nitrogen which at sufficient concentration resembles engine silicon nitride.
Exposing
A laser printer uses a laser because the laser is able to form highly focused, precise, and intense light beams, especially at short distances within the printer. The laser is aimed at a rotating polygonal mirror that directs light through the lens system and mirrors to the photoreceptor drum, writing pixels at speeds up to 65 million times per second. The drum keeps spinning during sweeping, and the angle of sweeping strokes is very little to compensate for this movement. The flow of raster data stored in printer memory quickly turns the laser on and off while sweeping.
The laser light neutralizes (or flips) the charge on the surface of the drum, leaving a negative image of static electricity on the surface of the drum that will expel the negatively charged toner particles. The area on the laser-struck drum, however, temporarily has no charge, and the toner pressed against the drum by the toner-coated development roller in the next step moves from the rubber surface of the roll to the uncharged portion of the drum surface.
Some non-laser printers (LED printers) use an array of light-emitting diodes that extend the width of the page to produce an image, rather than using a laser. "Uncover" is also known as "writing" in some documentation.
Develop
The surface with the latent image is exposed to toner that has been applied in a 15-micron thick layer to the developer roll. Toner consists of fine particles of dry plastic powder mixed with carbon black or dye. The toner particles are given a negative charge inside the toner cartridge, and when they appear to the developer drum they are electrostatically attracted to the photoreceptor's latent image (the area on the surface of the drum being hit by the laser). Because negative charges repel each other, the negatively charged toner particles will not stick to the drum where the negative charge (given earlier by the charge roll) remains.
Transfer
A piece of paper is then rolled up under the photoreceptor drum, which has been coated with a toner particle pattern in the exact spot where the laser hit it just moments before. Toner particles have a very weak appeal on both the drum and the paper, but the bond on the drum is weaker and the transfer of particles once again, this time from the surface of the drum to the surface of the paper. Some machines also use a positively charged "displacement roller" on the back side of the paper to help pull the negatively charged toner from the photoreceptor drum onto the paper.
Fusing
The paper passes through the rollers in the assembly fuser, where temperatures of up to 427 ° C (801 ° F) and pressure are used to permanently bind toner to paper. One roller is usually a vacuum tube (hot roller) and the other is a supported rubber roller (pressure roll). The radiant heat is suspended in the center of a vacuum tube, and its infrared energy uniformly heats the roller from within. For proper binding of the toner, the fuser roll must heat evenly.
Some printers use very thin flexible metal foil rollers, so that less heated thermal mass and smelter can reach faster operating temperatures. If the paper moves through the fuser more slowly, there is more roller contact time for the toner to melt, and the fuser can operate at a lower temperature. Smaller and cheaper laser printers usually print slowly, because of this energy-efficient design, compared to large high-speed printers where paper moves faster through high temperature fusers with very short contact times.
Cleanup and recharging
When the drum completes the revolution, it is confronted with a neutral soft plastic blade that cleans the toner residue from the photoreceptor drum and stores it into the waste reservoir. A charge roller then reassembled a uniform negative charge on the surface of the clean drum now, ready to be hit again by the laser.
Continuous printing
Once the raster generation is complete, all the steps of the printing process can occur one after another in sequence. This allows the use of very small and compact units, where the photoreceptor is charged, rotates a few degrees and scanned, rotates a few more degrees and is developed, and so on. The entire process can be completed before the drum completes a revolution.
Different printers apply these steps in different ways. The LED printer uses a linear array of light-emitting diodes to "write" the light on the drum. Toner is based on wax or plastic, so when the paper passes through the fuser assembly, the toner particles melt. The paper may or may not be charged in the opposite way. The fuser may be an infrared oven, a heat-pressure roller, or (on some very fast and expensive printers) xenon flash. The heating process performed by the laser printer when power is initially applied to the printer mainly consists of heating the fuser element.
Malfunction
The mechanism inside the laser printer is somewhat complicated and, once broken, is often impossible to repair. The drum is an especially important component: it should not be allowed to be exposed to ambient light for more than a few hours, since it is this light that causes it to lose its charge and will eventually wear out. Anything that interferes with laser surgery like a torn piece of paper can prevent the laser from releasing some parts of the drum, causing the area to appear as a white vertical line. If the neutral eraser knife fails to remove the residual toner from the surface of the drum, the toner may be circulating on the drum for a second time, causing a stain on the printed page with each revolution. If the charge roller becomes damaged or lacks sufficient power, it may not be sufficient to charge the negative charge of the drum surface, allowing the drum to take excess toner on the next revolution of the developer's scroll and causing repetitive but dim pictures from previous revolutions to appear on the page.
If the toner doctor blade does not ensure that a smooth and even toner layer is applied to the developer's roll, the printout may have white stripes of this in places where the blade has scraped too much toner. Or if the blade loads too much of the toner to stay on the developer roll, the toner particles may loose as the roll spins, settles on the paper underneath, and becomes attached to the paper during the melting process. This will result in general page embedding in wide vertical stripes with very soft edges.
If the fuser roll does not reach a sufficiently high temperature or if the environmental humidity is too high, the toner will not merge properly into the paper and may peel after printing. If the fuser is overheated, the plastic components of the toner may lubricate, causing the printed text to look wet or blurry, or may cause the melt toner to seep through the paper to the rear side.
Different manufacturers claim that their toner cartridges are specifically developed for their printers, and that other toner formulations may not conform to the original specifications in the event of a tendency to receive a negative charge, to move to the photoreceptor drum removal area of ​​the developer roll, to fuse precisely onto the paper , or to get out of the drum cleanly in every revolution.
Performance
Like most electronic devices, the cost of laser printers has dropped markedly over the years. In 1984, HP LaserJet sold for $ 3500, had problems with small graphics, low resolution, and weighs 32 kg (Â £ 71). Starting in 2016, low-end monochrome laser printers can be sold for less than $ 75. These printers tend to be less on onboard processing and rely on host computers to produce raster images, but outperform LaserJet 1984 in almost all situations.
The speed of a laser printer can vary greatly, and depends on many factors, including the graphic intensity of the work being processed. The fastest model can print more than 200 monochrome pages per minute (12,000 pages per hour). The fastest color laser printer can print more than 100 pages per minute (6000 pages per hour). Very high speed laser printers are used for bulk personal document submissions, such as credit cards or utility bills, and compete with lithography in some commercial applications.
The cost of this technology depends on a combination of factors, including the cost of paper, toner, replacement of drums, and replacement of other items such as fuser assembly and transfer assembly. Often printers with soft plastic drums can have very high cost of ownership that does not become real until drums require replacement.
Duplex printing (printing on both sides of the paper) can reduce half the cost of paper and reduce the volume of archiving. Previously only available on high-end printers, duplexer is now common in middle-class office printers, although not all printers can accommodate duplexing units. Duplex can also provide a slower page printing speed, due to longer paper paths.
In commercial environments such as offices, it is increasingly common for companies to use external software that improves the performance and efficiency of laser printers in the workplace. The software can be used to define rules that determine how employees interact with the printer, such as setting limits on how many pages can be printed per day, limiting the use of color ink, and marking jobs that seem useless.
Color laser printer
Color laser printers use color toner (dry ink), usually cyan, magenta, yellow, and black (CMYK). While monochrome printers only use one assembly of a laser scanner, color printers often have two or more.
Color printing adds to the complexity of the printing process because very small errors known as registration errors can occur between printing each color, causing unwanted, blurred, or light/dark color fringing along the edges of the colored area. To allow for high registration accuracy, some color laser printers use large rotating belts called "transfer belts". The transfer belt passes in front of all toner cartridges and each layer of toner is appropriately applied to the belt. The combined layers are then applied to the paper in one uniform step.
Color printers typically have higher per page costs than monochrome printers (although they only print monochrome pages only).
Comparison of business models with inkjet printers
Manufacturers use similar business models for cheap color laser printers and inkjet printers: printers are sold at bargain prices while toners and replacement inks are relatively expensive. Color laser printers are much faster than inkjet printers and their operating costs per page are usually slightly less. Color laser print quality is limited by its resolution (typically 600-1200 dpi) and its use is only of four color toners. They often have difficulty printing large areas with the same color gradations or fine. Inkjet printers designed for photo printing can produce much higher quality color images.
In-depth comparison of inkjet and laser printers shows that laser printers are an ideal choice for high-quality high-volume printers, while inkjet printers tend to focus on large format printers and household units. Laser printers offer more precise tagging and deep mono-chromatic colors, but tend to be more expensive than traditional inkjet printers.
Anti-counterfeit marks
Many modern color laser printers mark the printouts with almost invisible point raster, for tracking purposes. The dots are yellow and about 0.1 mm (0.0039 in) in size, with raster about 1 mm (0.039 inches). This is supposedly the result of an agreement between the US government and printer manufacturers to help track counterfeiters. Points encode data such as printer date, time, and serial number in binary-coded decimal on every printed sheet of paper, allowing the piece of paper to be tracked by the manufacturer to identify the place of purchase, and sometimes the buyer.
Digital rights advocacy groups such as the Electronic Frontier Foundation are concerned about the privacy erosion and anonymity of those who print.
Smart chip in toner cartridge
Similar to inkjet printers, the toner cartridge may contain a smart chip that reduces the number of pages it can print (reducing the amount of ink or toner that can be used in cartridges sometimes only 50%), in an effort to increase sales of toner cartridges. In addition to being more expensive for consumers, this technique also increases waste, and thereby increases the pressure on the environment. For this toner cartridge (such as inkjet cartridges), reset devices can be used to override the limits set by the smart chip. Also, for some printers, an online walk-through has been posted to demonstrate how to use all the ink in the cartridges. These chips do not provide benefits to the end consumer - all laser printers initially use optical mechanisms to assess the amount of toner remaining in the cartridge rather than using chips to calculate the number of pages printed electronically, and chip functions only as an alternative method to reduce the life of the cartridge.
Safety hazards, health risks and precautions
Toner cleanup
Toner particles are formulated to have electrostatic properties and can develop static electricity charges as they rub against other particles, objects, or interior transport systems and vacuum hoses. The static release of charged toner particles can trigger flammable particles in a vacuum bag or create a small dust explosion if sufficient toner is in the air. The toner particles are so fine that they are not filtered properly by conventional household vacuum filters and blow through the motor or back into the room.
If toner is spilled onto a laser printer, a special type of vacuum cleaner with an electrically conductive hose and high efficiency filter (HEPA) may be required for effective cleaning. These special tools are called "ESD-safe" (Electrostatic Discharge-safe) or "toner vacuums".
Ozone Dangers
As a normal part of the printing process, high voltage inside the printer can produce corona releases that produce small amounts of ionized oxygen and nitrogen, which react to form ozone and nitrogen oxides. In larger commercial and copier printers, activated carbon filters in the exhaust streams break down these harmful gases to prevent pollution of the office environment.
However, some ozone escapes the screening process in commercial printers, and ozone filters are not used at all in most of the smaller consumer printers. When laser printers or copiers are operated for long periods of time in a small space, poor ventilation, these gases can build up to a level where ozone odor or irritation may be noticed. The potential to create a theoretical health hazard may be in extreme cases.
Respiratory health risks
According to a 2012 study conducted in Queensland, Australia, some printers emit sub-micrometer particles that may be associated with respiratory diseases. Of the 63 printers evaluated in the Queensland University of Technology study, 17 of the strongest emitters were made by HP and one by Toshiba. The population of the machines studied, however, are only machines that already exist in the building and thus are biased towards certain manufacturers. The authors note that particle emissions vary substantially even among the same engine models. According to Professor Morawska of Queensland University of Technology, one printer emits particles as much as a burned cigarette:
The health effects of inhaling ultrafine particles depend on the particle composition, but the results can range from respiratory irritation to more severe illnesses such as cardiovascular or cancer problems.
Muhle et al. (1991) reported that responses to inhaled inhaled toner, pigmented plastic dust with carbon black, titanium dioxide and silica were also similar qualitatively to titanium dioxide and diesel exhaust.
In December 2011, Australian Working Australia's Safe Work Australia reviewed existing research and concluded that "no epidemiological studies directly link laser laser emissions with adverse health outcomes" and that some assessments conclude that "the risk of direct toxicity and effects health consequences of laser printer emission exposure can be ignored ". The study also observed that, since emissions have been shown to be volatile or semi-volatile organic compounds, it is logical to expect health effects that may be more related to the chemical properties of aerosols than to the physical characteristics of particulates because they are unlikely remain as 'particulates' after they come into contact with the respiratory tissues.
Air transport ban
After the 2010 cargo plane bomb plot, in which the delivery of laser printers with toner cartridges containing explosives was found on separate cargo planes, the US Transportation Security Administration banned passengers from carrying toner or ink cartridges weighing more than 1 pound (0.45 kg) on ​​flights enter, both the built-in baggage and checked baggage. PC Magazine notes that the ban will not affect most travelers, as the majority of cartridges do not exceed illegal weights.
See also
- Carton engineering
- Daisy wheel printer
- Automation of documents
- The dot matrix printer
- Printer sublimation dye
- LED Printer
- List of printer companies
- Solid ink
- Steganography
- Thermal printers
- Winprinter
References
External links
- Howstuffworks "How Laser Print Works"
- Detailed description, modeling and simulation of electrophotographic printing process (technical: 7.2 MB)
- How Laser Printers Work Video
- The Evolution of Color Laser Printers
- Q. Why is not there a CD or DVD laser printer?
Source of the article : Wikipedia
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