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Xerography is a photocopying technology that uses light and an electrical charge to copy images onto paper. It was invented in 1937 and is now found in printers, fax machines, and copiers. The process involves a photoconductive material, a corona unit, a beam of light, toner, and a transfer corona. Xerography was invented by Chester Carlson and was successfully transformed into commercial products by Xerox in 1959. Today, many companies and products use xerography, with newer machines capable of creating high-quality black and white or color images.
Xerography is a photocopying technology that uses light and an electrical charge to copy images onto another sheet of paper. When it was invented in 1937, the process, then known as electrophotography, required a lot of manual attention to operate and generated very little interest. Today, however, xerography is easy to use and found in printers, fax machines, and copiers that can be found in nearly any office.
Modern photocopiers are automated so the user simply inserts the image he wants to copy, closes the lid, presses “start” and waits for a copy to be made. Inside, however, a complex process is taking place. Most xerography machines have a cylindrical plate, ribbon, or drum coated with a photoconductive material such as amorphous selenium. Photoconductors are substances that become more electrically charged when exposed to light. A mechanism in the copier called the corona unit uniformly applies a positive or negative charge to the drum.
A beam of light is then projected onto the image being copied. The image reflects light off the drum, casting more light from the whiter parts of the image and no light through the darker parts. This creates a reverse image on the drum, with the whiter parts composed of particles excited by exposure to light and the darker parts composed of less excited particles. This is called latent image.
A mixture of toner and medium is then applied to the drum. The support particles have an opposite charge to the excited particles, or the area exposed to light, in the latent image. Toner, a powder that provides color in the xerography machine, sticks to the substrate particles, where the dark parts of the original image would be. A card is then placed between the drum and a charged plate called a transfer corona. Using a thermal roller and the electrical attraction of the transfer corona, the toner is lifted from the drum and pressed into the paper, creating the photocopied image.
Xerography was first invented by Chester Carlson, a patent attorney who lives with his family in Queens, New York. He and his assistant, Otto Kornei, developed the first rudimentary xerography machine by manually applying the electrostatic charge, light, powder and pressure needed to make a photocopy. When they finally succeeded, however, it took Carlson another ten years to garner corporate interest. In 1944, Carlson secured a deal with Haloid, now known as Xerox, which successfully transformed xerography into useful and commercial products. The product was a huge success after it was released as an automatic office copier in 1959.
Today many other companies and products use xerography. The technology is used in both laser and LED printers as well as fax machines, more commonly known as fax machines. The product may have a ribbon or platen instead of a drum and often uses organic photoconductors (OPC) instead of the amorphous selenium originally used by Xerox. Depending on the age and make of the machine, it may only be good for black and white printed writing and basic images. Newer machines, however, can create complex high-quality black and white or color images.
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