Electrostatics

Copy Machine

The History Behind It All

Most copy machines nowadays use an electrostatic process called Xerography, a word founded from the Greek words Xeros for dry and Graphos for writing, therefore meaning "Dry Writing". 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 the Xerox Corporation.


They Are Everywhere We Go

If you walk into almost any business office, you'll probably find a photocopier with a line of people waiting to use it. For most businesses, small or large, the copier has become standard equipment, much like having a desk and chair to work with. Photocopiers have gradually increased in accessibility and grown into businesses worldwide.

How It Works

A selenium-coated aluminum drum sprayed with a positive from points on a device called a corotron. Selenium has an interest property, in that it's a photo conductor. Selenium is an insulator when in the dark and a conductor when exposed to light.

In the first stage of the xerography, the conducting aluminum drum is grounded so that a negative charge is induced under the thin layer of positively charged selenium. In the second stage, the surface of the drum is exposed to the image of what is to be copied. Where the image is light, the selenium becomes conducting, and the positive charge is becomes neutral. In dark areas, the positive charge remains, and so the image transfers to the drum.


The third stage takes dry black powder, called toner, and sprays it with a negative charge so that it will be attracted to the positive areas of the drum. Then, a blank piece of paper is given a greater positive charge than on the drum so that it will pull the toner from the drum.


Finally, the paper and electrostatically hold the toner that is passed through heated pressure rollers, which melt and permanently attach the toner within the fibers of the paper.

Works Cited

"Applications of Electrostatics." Connexions. Openstax College, Web. 13 Feb. 2013. <http://cnx.org/content/m42329/latest/?collection=col11406/latest>.


"How does a photocopier work?." Scientific American. Dan A. Hays, Web. 13 Feb. 2013. <http://www.scientificamerican.com/article.cfm?id=how-does-a-photocopier-wo>.


"How Photocopiers Work." HowStuffWorks. Ann Meeker-O'Connell, Web. 13 Feb. 2013. <http://www.howstuffworks.com/photocopier.htm>.


"Chester Carlson and Xerography." Xerox. n.d. Web. 14 Feb. 2013. <http://www.xerox.com/innovation/chester-carlson-xerography/enus.html>.


"How does a Photocopier work?." Falcon. n.d. Web. 14 Feb. 2013. <http://www.falcon.co.uk/how-does-a-photocopier-work.html>.