Xerography

Xerography (or Electrophotography) is a photocopying technique developed by Chester Carlson in 1938 and patented on October 6, 1942. He received United States Patent number 2,297,691 for his invention.

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Xerography is used in most photocopying machines and in laser and LED printers.

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Step 1. Charging

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Electostatic charges are uniformly distributed over the surface of a drum or belt by a scorotron, or bias charge roller.

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Step 2. Exposure

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The document to be copied is passed over a lens, at exactly the same speed that the drum turns, and a light is flashed at the document. In a laser or LED printer, a thin beam is modulated by the controller. Where there is text or image on the document, light will not penetrate to the drum; the opposite is true where there is no image. The light that penetrates neutralizes the charge on the drum, but only where there is no image. The resulting charge that remains on the drum is called the 'latent' image and is a positive of the original document.

Photocopying: Photocopying is a process which makes paper copies of documents and other visual images quickly and cheaply. It was introduced by Xerox in the 1960s, and over the following 20 years it gradually replaced copies made by carbon paper, mimeograph machines and other duplicating machines. The prevalence ...

Chester Carlson: Chester F. Carlson (February 8, 1906 - September 19, 1968) was an American physicist and inventor born in Seattle, Washington. He invented electrophotography(Xerox), the process of instant copying. A hard worker, he persisted in his quest, meeting disappointment and failure for many years before fin...

1938: 1938 was a common year starting on Saturday (link will take you to calendar)....