How Everything Works
How Everything Works How Everything Works

Question 676

How is the xerographic copying process related to laser and led printers? - BG
The same basic printing process is used in both xerographic copiers and laser or led printers. In all cases, a charge image is formed on the surface of a photoconductor and this pattern of electric charge attracts a pattern of colored plastic powder. The powder is then transferred to paper and melted or pressed into the paper's surface to form a permanent print.

The main difference between a copier and a printer is in the source of light used to produce the charge image. In a copier, lenses and mirrors are used to form a real image of the original document on the surface of the photoconductor. Wherever light from the white portions of the document strikes the photoconductor, the photoconductor becomes an electric conductor and charge is able to move. The pattern of light then becomes a pattern of charge—a charge image.

In a printer, a laser or an array of light emitting diodes is used to form the pattern of light on the surface of the photoconductor. Wherever the light strikes the photoconductor, charge is again able to move about. Dot by dot or row by row, the charge image takes shape. The pattern of charge that's written on the surface of the photoconductor eventually becomes the printing itself.


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