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Science & Tech.
Mahesh

31/10/23 06:50 AM IST

The act of photocopying

In News
  • Photocopying is a set of techniques with which to duplicate some content using, among other things, light.
Photocopying
  • photocopying is a set of techniques with which to duplicate some content using, among other things, light. However, the contemporary colloquial use of the word ‘photocopying’ refers almost exclusively to xerography.
  • Both the word ‘xerography’ and the name ‘Xerox’ come from the Greek root-word ‘xero’, meaning ‘dry’.
  • This is because xerography is a type of photocopying method whose process doesn’t involve messy liquid chemicals.
  • Xerographic machines are in ubiquitous use around the world today to quickly and cheaply reproduce printed material.
Working of Xerography
  • The first is the photoconductive surface – a surface coated with a photoconductive material. Such a material, when exposed to light, allows electrons to flow through it (i.e. conducts electricity) but blocks them when it’s dark.
  • This surface is negatively charged by placing a thin negatively charged wire with a high voltage next to it.
  • Then, the sheet of paper to be copied is illuminated with a bright light. The darker parts of the paper – where something is printed, i.e. – don’t reflect the light whereas the unmarked parts do.
  • This reflected light is carried by lenses and mirrors to fall on the photoconductive surface.
  • In the parts of the surface where light falls, the photoconducting material will become conductive and allow the electrons near its surface to dissipate downwards (into a grounding). So the parts that remain negatively charged at the end of this step will correspond to parts of the paper-to-be-copied (TBC) where something was printed.
  • Next, a powdery substance called toner is applied to the surface.
  • The toner is positively charged, so it will settle where negative charge persists on the surface.
  • The surface then transfers the pattern of toner on it to a sheet of paper. The paper has a stronger negative charge that causes the toner to jump.
  • Finally, the toner is heated so that it melts and fuses with the paper.
  • This is the paper that rolls out of the photocopying machine, the whole process having been completed in a few seconds
Invention of Xerography
  • Inspired by the work of the Hungarian engineer Paul Selenyi, an American attorney named Chester F. Carlson came up with a rudimentary version of xerography by 1938.
  • Seven years later, he sold his idea to a non-profit organisation called the Battelle Memorial Institute in Ohio, where researchers refined the technique.
  • A year later, in 1946, the small New York-based Haloid Photographic Company purchased a licence from Battelle to build a machine based on the technique.
  • The company trademarked the name for this machine as the “Xerox machine” in 1948 and availed the first model for sale in 1949.
Xerography Impact
  • Counterfeiting: In 2002, people discovered that Xerox machines refused to copy banknotes that included a particular marking – of five small rings positioned like stars in the Orion constellation. Similar markings have since been found on the banknotes of at least 35 national banks. A 2005 statement from the Reserve Bank of India, accompanying the release of new Rs 50 notes, called it the “Omron anti-photocopying feature”, suggesting that a Japanese corporation named Omron was responsible for designing the rings to prevent counterfeiters from duplicating or printing currency notes using xerographic machines.
  • Copyright and surveillance
Source- The Hindu

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