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Xerox

 In 1937, the process called Xerography was invented by American Law student Chester Carlson. Carlson had invented a copying process based on electrostatic energy. Xerography became commercially available in 1950 by Xerox Corporation. Xerography comes from the Greek for “dry writing”.


Chester Carlson had been frustrated with the slow mimeograph machine and the cost of photography and that lead him to inventing a new way of copying. He invented an electrostatic process that reproduced words on a page in just minutes. Carlson had a hard time finding investors in his new invention. He was turned down by IBM and U. S. Army Signal Corps, it took him eight years to find investor, which was the Haloid Company later to become the Xerox Corporation.


Chester Carlson was both a research engineer and a patent attorney. He filed a patent application in April, 1939, stating, “I knew I had a very big tiger by the tail”. The Xerox Corporation trademarked the name “Xerox” and has protected the name carefully.


Working

A copier works because of one basic physical principle: opposite charges attract.


As a kid, you probably played with Static electricity and balloons. On a dry winter day, you can rub a balloon on your sweater and create enough Static electricity in the balloon to create a noticeable force. For example, a balloon charged with Static electricity will attract small bits of paper or particles of suger very easily. A copier uses a similar process. Inside a copier there is a special drum. The drum acts a lot like balloon — you can charge it with a form of Static electricity. Inside the copier there is also a very fine black powder known as toner. The drum, charged with Static electricity, can attract the toner particles. There are three things about the drum and the toner that let a copier perform it’s magic. The drum can be selectively charged, so that only parts of it attract toner.

Copier

In a copier, you make an “image” in Static electricity on the surface of the drum. Where the original sheet of paper is black, you create Static electricity on the drum. Where it is white. What you want is for the white areas of the original sheet of paper do not attract toner. The way this selectivity is accomplished in a copier is with light — this is why it’s called photocopier! Somehow the toner has ato get onto the drum and then onto a sheet of paper. The drum selectively attracts toner. Then the sheet of paper gets charged with Static electricity and it pulls the toner off the drum. The toner is heat sensitive, so the loose toner particles are attracted (fused) to the paper with heat as soon as they come off the drum. The drum, or belt, is made out of photoconductive material.


Here are the actual steps involved in making a photocopy: The surface of the drum is charged. An intense beam of light moves across the paper that you have placed on the copier’s glass surface. Light is reflected from white areas of the paper and strikes the drum below. Wherever a photon of light hits, electron is emitted from the photoconductive atoms in the drum and neutralizes the positive charges above. Dark areas on the original do not reflect light onto the drum, leaving regions of positive charges on the drums surface.

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