Photocopier
Introduction
A photocopier is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process that uses electrostatic charges on a light-sensitive photoreceptor to first attract and then transfer toner particles (a powder) onto paper in the form of an image. Heat, pressure or a combination of both is then used to fuse the toner onto the paper. (Copiers can also use other technologies such as ink jet, but xerography is standard for office copying.)
History
The concept of the photocopier was first introduced by Chester Floyd Carlson, a patent attorney and part-time researcher and inventor. His job at the patent office in New York required him to make a large number of copies of important papers. Carlson, who was arthritic, found this to be a painful and tedious process. This motivated him to conduct experiments with photoconductivity. Carlson used his kitchen for his "electrophotography" experiments, and in 1938, he applied for a patent for the process. He made the first "photocopy" using a zinc plate covered with sulfur. The words "10-22-38 Astoria" were written on a microscope slide, which was placed on top of more sulfur and under a bright light. After the slide was removed, a mirror image of the words remained. Carlson tried to sell his invention to some companies, but failed because the process was still underdeveloped. At the time, multiple copies were most commonly made at the point of document origination, using carbon paper or manual duplicating machines, and people did not see the need for an electronic machine. Between 1939 and 1944, Carlson was turned down by over 20 companies, including IBM and GE, neither of which believed there was a significant market for copiers.
Technology
The xerographic process, which was invented by Chester Carlson in 1938 and developed and commercialized by the Xerox Corporation, is widely used to produce high-quality text and graphic images on paper. The process, which is used in both analog and digital photocopiers, involves six steps:
- Charging: The photoconductive surface of the drum is given a positive electrostatic charge.
- Exposure: The original document is scanned and a light image of it is projected onto the drum, discharging certain areas of the surface to form an electrostatic latent (invisible) image on the drum surface.
- Developing: The latent image is developed by applying negatively charged toner particles onto the drum surface, which are attracted to the positively charged latent image on the drum.
- Transfer: The toner image on the drum surface is transferred onto a piece of paper by applying a charge to the paper from behind, which attracts the toner particles to the paper.
- Fusing: The toner image on the paper is fused by heat and pressure to make it adhere permanently.
- Cleaning and recharging: The drum surface is cleaned of residual toner and recharged in preparation for another print cycle.
Modern Photocopiers
Modern photocopiers may also include features such as: - Printing: Many photocopiers are now capable of printing from a computer too, essentially acting as a high-volume laser printer. - Scanning: Some models can scan a document to a file on a computer or network, or to an email address. - Faxing: Some models can send a fax of a scanned document. - Finishing: Some models can staple, hole punch and even bind documents together.
Environmental Impact
Photocopiers can have a significant impact on the environment. The production of toner and paper, as well as the electricity used by the machine, all contribute to environmental degradation. In addition, the waste produced by discarded toner cartridges and old machines can also be harmful. Many companies are now offering more environmentally friendly options, such as recycled paper and toner, energy-saving features, and recycling programs for old machines and cartridges.
See Also
- Xerography - Chester Carlson - Laser Printer - Fax Machine