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| Photocopier |
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| Then term 'Xerography'; the use of Photoelectric phenomena to transfer an image from one sheet of paper to another comes from the Greek words for "dry" and "writing". |
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| Dry copying is based on the principle that materials with opposite electrical charges attract one another and that some materials conduct electricity better after exposure to light. In the basic xerography process a photoconductive surface receives a positive electrical charge. An image is then exposed on the surface, because the illuminated sections (the non-image areas) becomes more conductive, their charge displaces. Negatively charged powder spread over the surface adheres through electrostatic attraction to the positively charged image area. A piece of paper is then given a positive charge and placed over the surface, where it attracts the negatively charged powder. Finally, heat fuses the image etched in powder to the paper. |
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| Working |
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| Photocopier moves a document from the handler to the glass plate, where the pattern of the image is projected by lamps, mirrors and lenses onto a photoreceptor belt (or drum). The electrostatic charge on the belt fades in areas receiving light from the projected image. Magnetic rollers brush the belt with dry ink (toner), which because of its static charge clings to the image area on the belt. A sheet of paper approaching the belt is also given a static charge sufficiently strong to draw the image pattern in the toner away from the belt. Rollers then apply heat and pressure to fuse the toner image into place. For color copying a multi-step process is used, which scans the image through color filters and then applies separate tones for magenta, cyan, yellow and black. |
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