This article includes a list of references, but its sources remain toner secret key because it has insufficient inline citations. Chodowiecki Basedow Tafel 21 c Z.
Xerography or electrophotography is a dry photocopying technique. Its fundamental principle was invented by American physicist Chester Carlson and based on Hungarian physicist Pál Selényi’s publications. The technique was originally called electrophotography. Carlson’s innovation combined electrostatic printing with photography, unlike the dry electrostatic printing process invented by Georg Christoph Lichtenberg in 1778. By using a cylinder to carry the photosensor, automatic processing was enabled. In 1960, the automatic photocopier was created and many millions have been built since. The same process is used in microform printers and computer output laser or LED printers.
The end-to-end dimension is the width of print to be produced plus a generous tolerance. The steps of the process are described below as applied on a cylinder, as in a photocopier. Some variants are described within the text. Every step of the process has design variants. The physics of the xerographic process are discussed at length in a book. A negative charge is placed on the wire, which will ionize the space between the wire and conductor, so electrons will be repelled and pushed away onto the conductor. The conductor is set on top of a conducting surface, kept at ground potential.
The polarity is chosen to suit the positive or negative process. Positive process is used for producing black on white copies. This is to economize on the use of laser light by the «blackwriting» or «write to black» exposure method. Alternatively, the image may be exposed using a xenon strobe onto the surface of the moving drum or belt, fast enough to render a perfect latent image. Additional lenses, with different focal lengths or zooming lenses are utilized to enlarge or reduce the image. The scanning system, though, must change its scanner speed to adapt to elements or reductions. A drum is inferior to a belt in the sense that although it is simpler than a belt, it must be buffered gradually in parts rolling on the drum.
As a result, the belt is more efficient to use one exposure to make a direct passage. In a laser or LED printer, modulated light is projected onto the drum surface to create the latent image. The modulated light is used only to create the positive image, hence the term «blackwriting». Where a negative image is required, as when printing from a microform negative, then the toner has the same polarity as the corona in step 1. Electrostatic lines of force drive the toner particles away from the latent image towards the uncharged area, which is the area exposed from the negative.