xerography Forming an image by the action of light on a specially coated charged plate; the latent image is developed with powders that adhere only to electrically charged areas
n 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. Xerography comes from the Greek for "dry writing".
A photo sensitive drum or other surface is charged with about 14 thousand volts. An image is projected onto the drum surface by means of lenses or a laser. The light causes the charge to dissipate wherever the light falls. Toner with a smaller charge of the same polarity comes into contact with the charged drum. The toner sticks to the drum where the charge has dissipated due to the potential difference between charges. ie the area where the light fell is negative relative to the positive chrge on the toner. The area where no light fell still has a positive charge so toner does not stick. The paper now gets fed between the drum and a negative charge of about 14 thousand volts. The toner is attracted to the opposite charge but gets caught by the paper that is in the way. The toner is now fused into the paper by means of hot / pressure rollers.