photocopy n : a photographic copy of written or printed or graphic work v : reproduce by xerography [syn: run off, xerox] [also: photocopied]

English

Noun

1. A copy made using a photocopier

Translations

Verb

1. to make a copy using a photocopier

Translations

A photocopier (or copier) is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat. (Copiers can also use other output technologies such as ink jet, but xerography is standard for office copying.)

Xerographic office photocopying was introduced by Xerox in the 1960s, and over the following 20 years it gradually replaced copies made by Verifax, Photostat, carbon paper, mimeograph machines, and other duplicating machines. The prevalence of its use is one of the factors that prevented the development of the paperless office heralded early in the digital revolution.

Photocopying is widely used in business, education, and government. There have been many predictions that photocopiers will eventually become obsolete as information workers continue to increase their digital document creation and distribution, and rely less on distributing actual pieces of paper. However, photocopiers are undeniably more convenient than computers for the very common task of creating a copy of a piece of paper.

How a photocopier works (using xerography)

1. Charging: The surface of a cylindrical drum is electrostatically charged by either a high voltage wire called a corona wire or a charge roller. The drum has a coating of a photoconductive material. A photoconductor is a semiconductor that becomes conductive when exposed to light.
2. Exposure: A bright lamp illuminates the original document, and the white areas of the original document reflect the light onto the surface of the photoconductive drum. The areas of the drum that are exposed to light (those areas that correspond to white areas of the original document) become conductive and therefore discharge to ground. The area of the drum not exposed to light (those areas that correspond to black portions of the original document) remain negatively charged. The result is a latent electrical image on the surface of the drum. (In digital machines, the original document is scanned and digitized and a laser is employed to discharge the drum in a similar fashion)
3. Developing: The toner is positively charged. When it is applied to the drum to develop the image, it is attracted and sticks to the areas that are negatively charged (black areas), just as paper sticks to a toy balloon with a static charge.
4. Transfer: The resulting toner image on the surface of the drum is transferred from the drum onto a piece of paper with a higher negative charge than the drum.
5. Fusing: The toner is melted and bonded to the paper by heat and pressure rollers.
6. Cleaning: The drum is wiped clean with a rubber blade and completely discharged by light.

This example is of a negatively charged drum and paper, and positively charged toner as is common in todays digital copiers. Some copiers, mostly older analog copiers, employ a positively charged drum and paper, and negatively charged toner.

Invention and development

In 1937 Bulgarian physicist Georgi Nadjakov found that, when placed into an electric field and exposed to light, some dielectrics acquire permanent electric polarization in the exposed areashttp://www.issp.bas.bg/lab/ephi/Museum/acad_GNadjakov/GN11-page5.html. That polarization persists in the dark and is destroyed in light. Chester Carlson, the inventor of photocopying, was originally a patent attorney, as well as a part-time researcher and inventor. His job at the patent office in New York required him to make a large number of copies of important papers. Carlson, who was arthritic, found this to be a painful and tedious process. As a result, he was motivated to conduct experiments with photoconductivity. Carlson used his kitchen for his "electrophotography" experiments, and, in 1938, he applied for a patent for the process. He made the first "photocopy" using a zinc plate covered with sulfur. The words "10-22-38 Astoria" were written on a microscope slide, which was placed on top of more sulfur and under a bright light. After the slide was removed, a mirror image of the words remained. Carlson tried to sell his invention to some companies, but, because the process was still underdeveloped, he failed. At the time, multiple copies were made using carbon paper or duplicating machines, and people did not see the need for an electronic machine. Between 1939 and 1944, Carlson was turned down by over 20 companies, including IBM and GE, neither of which believed there was a significant market for copiers.

In 1944, the Battelle Memorial Institute, a non-profit organization in Columbus, Ohio, contracted with Carlson to refine his new process. Over the next five years, the institute conducted experiments to improve the process of electrophotography. In 1947, Haloid Corporation (a small New York-based manufacturer and seller of photographic paper) approached Battelle to obtain a license to develop and market a copying machine based on this technology.

Haloid felt that the word "electrophotography" was too complicated and did not have good recall value. After consulting a professor of classical language at Ohio State University, Haloid and Carlson changed the name of the process to "Xerography," which was derived from Greek words that meant "dry writing." Haloid called the new copier machines "Xerox Machines" and, in 1948, the word Xerox was trademarked. Haloid eventually changed its name to Xerox Corporation.

In the early 1950s, RCA (Radio Corporation of America) introduced a variation on the process called Electrofax, whereby images are formed directly on specially coated paper and rendered with a toner dispersed in a liquid.

During the 1960s and through the 1980s, Savin Corporation developed and sold a line of liquid-toner copiers that implemented a technology based on patents held by the company.

In 1949, Xerox Corporation introduced the first xerographic copier called the Model A. Xerox became so successful that, in North America, photocopying came to be popularly known as "xeroxing." Xerox has actively fought to prevent "Xerox" from becoming a genericized trademark. While the word "Xerox" has appeared in some dictionaries as a synonym for photocopying, Xerox Corporation typically requests that such entries be modified, and that people not use the term "Xerox" in this way. "Photostat" is an outdated term for a photocopy. Some languages include hybrid terms, such as the widely used Polish term kserokopia ("xerocopy"), even though relatively few photocopiers are of the Xerox brand.

Prior to the widespread adoption of xerographic copiers, photo-direct copies produced by machines such as Kodak's Verifax were used. A primary obstacle associated with the pre-xerographic copying technologies was the high cost of supplies: a Verifax print required supplies costing USD $0.15 in 1969, while a Xerox print could be made for USD $0.03 including paper and labor. At that time, Thermofax photocopying machines in libraries could make letter-sized copies for USD $0.25 or more (at a time when the minimum wage for a US worker was USD $1.65).

Xerographic copier manufacturers took advantage of a high perceived-value of the 1960s and early 1970s, and marketed paper that was "specially designed" for xerographic output. By the end of the 1970s, paper producers made xerographic "runability" one of the requirements for most of their office paper brands.

Some devices sold as photocopiers have replaced the drum-based process with inkjet or transfer film technology.

Among the key advantages of photocopiers over earlier copying technologies are their ability to do the following:

• to use plain (untreated) office paper
• to implement duplex (or two-sided) printing
• to sort and/or staple output

Color photocopiers

Colored toner became available in the 1950s, although full-color copiers were not commercially available until 3M released the Color-in-Color copier in 1968, which used a dye sublimation process rather than conventional electrostatic technology. The first electrostatic color copier was released by Canon in 1973.

Color photocopying is a concern to governments, as it makes counterfeiting currency easier to accomplish. Some countries have introduced anti-counterfeiting technologies into their currency specifically to make it harder to use a color photocopier for counterfeiting. These technologies include watermarks, microprinting, holograms, tiny security strips made of plastic (or other material), and ink that appears to change color as the currency is viewed at an angle. Some photocopying machines contain special software that can prevent copying currency that contains a special pattern.

Digital technology

In recent years, all new photocopiers have adopted digital technology, thus replacing the older analog technology. With digital copying, the copier effectively consists of an integrated scanner and laser printer. This design has several advantages, such as automatic image quality enhancement and the ability to "build jobs" (that is, to scan page images independently of the process of printing them). Some digital copiers can function as high-speed scanners; such models typically offer the ability to send documents via email or to make them available on file servers.

A great advantage of digital copier technology is "automatic digital collation." When copying a set of twenty pages twenty times, for example, a digital copier scans each page only once then uses the stored information to produce twenty sets. In an analog copier, either each page is scanned twenty times (a total of 400 scans), making one set at a time, or twenty separate output trays are used for the twenty sets.

Low-end copiers also use digital technology, but they tend to consist of a standard PC scanner coupled to an inkjet or low-end laser printer, both of which are far slower than their counterparts in high-end copiers. However, low-end scanner inkjets can provide color copying at a far lower cost than can a traditional color copier. The cost of electronics is such that combined scanner-printers sometimes have built-in fax machines. (See Multifunction printer.)

Copyright issues

Photocopying material that is subject to copyright (such as books or scientific papers) is subject to restrictions in most countries. This is common practice, as the cost of purchasing a book for the sake of one article or a few pages can be excessive. The principle of fair use (in the United States) or fair dealing (in other Berne Convention countries) allows this type of copying for research purposes.

In certain countries, such as Canada, some universities pay royalties from each photocopy made at university copy machines and copy centers to copyright collectives out of the revenues from the photocopying, and these collectives distribute resulting funds to various scholarly publishers. In the United States, photocopied compilations of articles, handouts, graphics, and other information called readers are often required texts for college classes. Either the instructor or the copy center is responsible for clearing copyright for every article in the reader, and attribution information must be clearly included in the reader.

Health issues

Ultraviolet exposure is a concern. In the early days of photocopiers, the sensitizing light source was filtered green to match the optimal sensitivity of the photoconductive surface. This filtering conveniently removed all ultraviolet http://aic.stanford.edu/sg/bpg/annual/v08/bp08-05.html#note17. Currently, a variety of light sources are used. As glass transmits ultraviolet rays between 325 and 400 nanometers, copiers with ultraviolet-producing lights such as fluorescent, tungsten halogen, or xenon flash expose documents to some ultraviolet http://aic.stanford.edu/sg/bpg/annual/v08/bp08-05.html#note18.

Concerns about emissions from photocopy machines have been expressed by some in connection with the use of selenium and emissions of ozone and fumes from heated toner http://www.lhc.org.uk/members/pubs/factsht/76fact.pdf http://www.nasuwt.org.uk/Templates/Internal.asp?NodeID=71671&ParentNodeID=43086. These concerns, however, can be a result of misunderstanding or exaggeration http://www.safety.ed.ac.uk/resources/General/printers.shtm

Forensic identification

Similar to forensic identification of typewriters, computer printers and copiers can be traced by imperfections in their output. The mechanical tolerances of the toner and paper feed mechanisms cause banding, which can reveal information about the individual device's mechanical properties. It is often possible to identify the manufacturer and brand, and, in some cases, the individual printer can be identified from a set of known printers by comparing their outputs. http://news.uns.purdue.edu/UNS/html4ever/2004/041011.Delp.forensics.html http://dsc.discovery.com/news/briefs/20041011/printer.html

Some high-quality color printers and copiers steganographically embed their identification code into the printed pages, as fine and almost invisible patterns of yellow dots. Some sources identify Xerox and Canon as companies doing this http://www.pcworld.com/news/article/0,aid,118664,00.asp http://www.pcworld.idg.com.au/index.php/id;1002274598. The Electronic Frontier Foundation (EFF) has investigatedhttp://www.eff.org/Privacy/printers/ this issue and documented how the Xerox DocuColor printer's serial number, as well as the date and time of the printout, are encoded in a repeating 8×15 dot pattern in the yellow channel. EFF is working to reverse engineer additional printers. The US government has been reported to have asked these companies to implement such a tracking scheme, so that counterfeiting can be traced.

Current copier brands

• Canon

• Gestetner, owned by Ricoh
• Hewlett Packard
• Konica Minolta
• Kyocera Mita, including its Copystar brand
• Lanier, owned by Ricoh
• Océ. including its Océ Imagistics brand
• Oki Electric Industry, OKI Printing Solutions brand
• Panasonic
• Rex-Rotary, owned by Ricoh
• Ricoh
• Savin, owned by Ricoh
• Sharp
• Toshiba
• Xerox / Fuji Xerox partnered companies with non-overlapping marketing areas

Further reading

• R. Schaffert: Electrophotography. Focal Press, 1975
• Copies in Seconds : How a Lone Inventor and an Unknown Company Created the Biggest Communication Breakthrough Since Gutenberg: Chester Carlson and the Birth of the Xerox Machine

See also

• Duplicating machines
• List of duplicating processes
• Multifunctional copier
• Negative photocopy
• Printing
• Risograph

External links

• Detailed description and simulation of the electrophotographic print process
• How a colour copier works

Ditto copy, Photostat, Xerox, Xerox copy, blowup, blueprint, contact print, contact printing, cyanotype, enlargement, glossy, hectograph copy, hologram, impress, impression, lantern slide, matte, microcopy, microprint, mimeograph copy, negative, offprint, photograph, photogravure, photostatic copy, positive, print, projection printing, proof, reprint, semi-matte, slide, stat, transparency