Photocopier

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. This motivated him to conduct experiments with photo conductivity. 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 failed because the process was still underdeveloped. At the time, multiple copies were most commonly made at the point of document origination, using carbon paper or manual 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 General Electric—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.[2]

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 1949, Xerox Corporation introduced the first xerographic copier called the Model A.[3] Defeating computer leader IBM,[4] 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.

In the early 1950s, Radio Corporation of America (RCA) 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.

Before 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 US$0.15 in 1969, while a Xerox print could be made for $0.03 including paper and labor. The coin-operated Photostat machines still found in some public libraries in the late 1960s made letter-size copies for $0.25 each, at a time when the minimum wage for a US worker was $1.65 per hour; the Xerox machines that replaced them typically charged $0.10.

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.

DADF or Duplex Automatic Document feeder - Canon IR6000

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 use plain (untreated) office paper;
• to implement duplex (or two-sided) printing;
• to scan several pages automatically with an ADF; and,
• eventually, to sort and/or staple output.

Schematic overview of the xerographic photocopying process (step 1-4)

Part of a series on the
History of printing
Woodblock printing 200 Movable type 1040 Printing press c. 1440 Etching c. 1515 Mezzotint 1642 Aquatint 1772 Lithography 1796 Chromolithography 1837 Rotary press 1843 Hectograph 1860 Offset printing 1875 Hot metal typesetting 1884 Mimeograph 1885 Photostat and rectigraph 1907 Screen printing 1911 Spirit duplicator 1923 Dot matrix printing 1925 Xerography 1938 Spark printing 1940 Phototypesetting 1949 Inkjet printing 1950 Dye-sublimation 1957 Laser printing 1969 Thermal printing c. 1972 Solid ink printing 1972 3D printing 1986 Digital printing 1991

1. Charging: cylindrical drum is electrostatically charged by 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.[5]
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 become conductive and therefore discharge to the ground. The area of the drum not exposed to light (those areas that correspond to black portions of the original document) remains negatively charged.
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 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 that has an even greater negative charge than the drum has.
5. Fusing: The toner is melted and bonded to the paper by heat and pressure rollers.

A negative photocopy inverts the colors of the document when creating a photocopy, resulting in letters that appear white on a black background instead of black on a white background. Negative photocopies of old or faded documents sometimes produce documents that have better focus and are easier to read and study.

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 copying for certain specified 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.

To counter the risk of people using color copiers to create counterfeit copies of paper currency, some countries have incorporated anti-counterfeiting technologies into their currency. These 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.

Color copying also raises concerns regarding the copying and/or forging of other documents as well, such as driver's licenses and university degrees and transcripts. Some driver's licenses are made with embedded holograms so that a police officer can detect a fake copy. Some university and college transcripts have special anti-copying watermarks in the background. If a copy is made, the watermarks will become highly visible, which allows the recipient to determine that they have a copy rather than a genuine original transcript.

Exposure to ultraviolet light 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.[6] 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.[6]

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.[7][8]

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.[9]

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.[10][11] The Electronic Frontier Foundation (EFF) has investigated this issue[12] 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.[13] The EFF also reports that the US government has asked these companies to implement such a tracking scheme, so that counterfeiting can be traced. The EFF has filed a Freedom of Information Act request in order to look into privacy implications of this tracking.[14]

• List of duplicating processes
• Heliography
• Reprography
• Risograph
• Scanography
• Thermochromatic ink
• Thermofax
• Xerox art
• Gestetner

Wikimedia Commons has media related to Photocopiers.

• R. Schaffert: Electrophotography. Focal Press, 1975
• Owen, David (August 2004). 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. New York: Simon & Schuster. ISBN 0-7432-5117-2.