Image of a Xerox Copier

The copying process is called xerography (also called electrophotocopy) derived from a Greek word “xeros” and “graphos” which mean dry writing.


The main part of machine (heart) is a drum which is an aluminium cylinder (excellent conductor) coated with a layer of selenium (a photo conductor).


As selenium acts as insulator in the dark and as conductor in the light, therefore when a positive charge is sprinkled over the selenium, it remains there as long as selenium remains in dark. Now, if the drum is exposed to light, the electrons from aluminium pass through the conducting selenium because it conducts in light and neutralize the positive charge.

When the drum is exposed to an image of a document which is to be xerographed, the dark and light areas produce corresponding areas on the drum. The dark areas retain there positive charge, but light areas become conducting, lose there positive charge and become neutral.

Labelled Diagram or Xerographer

In this way a positive charge image of the document is set on the selenium surface. Then a special dry, black powder called toner is given a negative charge and spread over the drum, where it sticks to the positively charged areas. After all, the toner from the drum is transferred to the sheet of paper on which the image is to be photocopied. Heated pressure rollers then melt the toner into the paper and produce the permanent impression of the document.

Inventor of Xerography:

The process of xerography was invented by Chester Carlson in 1938 and developed and commercialized by the Xerox Corporation, is still widely used to produce high quality text and graphic results on paper.

We are giving this questionnaire to help you improve your skill level.

[Q1] What is a photo conductor???
[Q2] Why selenium is a better photo conductor???
[Q3] How could we improve the quality of a Xerox image???

Please submit answers to these questions in the comments..


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1 Comment

  1. This is very intersting blog.Metal Cans, Metal Closures & Steel Drums, and also complete packaging lines for powder, liquid & paste in rigid containers of Plant and Machinery are manufactured in Recon Machine Tools Pvt Ltd.Roller Coating Machinery.

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