Photocopier

Principle of operation

The vast majority of the photocopiers use the xerographic process which is a technique of electrophotography.

The photocopier consists of a metal cylinder named drum or photoconductor covered with a layer of material Semi-conducteur, Sélénium in the beginning. This semiconductor with the characteristic to be electrically resistant at the normal state but to become conducting when it is enlightened.

The first operation consists in positively charging the layer with semiconductor in static electricity. Then the image to be reproduced is projected via an objective and mirrors on the photosensitive drum. The clear zones of this image make surface semiconductor electrically neutral while making it possible the loads to disperse, these zones are not thus electrically charged. The following stage consists in applying the Toner: a very fine powder of Carbon black, negatively charged in electricity. This one will adhere to the drum only on the zones which are still positively charged (dark zones of the image). One then makes pass a sheet of paper against the drum. One reverses the electric charge of the sheet to allow the particles carbon to adhere to fibers paper. Then the sheet is heated definitively to fix the carbon powder which melts and is encrusted in fibers with paper.

To summarize:

electric loading of the drum;
exposure of the luminous image to the drum;
transfer of thundering on the nonexposed zones;
transfer of thundering, the drum towards paper;
fixing of thundering…. The drum is cleaned in preparation with the following copy.

The Printing S laser and numerical copiers use the same principle, but reversed. To thunder is in this case attracted by the parts of the drum which have summers lit by a laser beam whose power varies according to the intensity of each pixel.

Functionalities of the recent photocopiers

The recent photocopiers have all the characteristics of a Ordinateur: Processor, Hard drive, Modem, Email. They are usable like Imprimante S through the network.

It is also possible to use the photocopiers as scanner of documents in order to store a document under digital form either directly on the hard drive, or by transferring the data on a computer connected to the machine or to directly send the scan by the Internet or towards a solution of GED. It is also frequent that the connected photocopiers have a Interface Web making it possible to remotely parameterize or monitor the state of the machine, thus facilitating maintenance or the prevention for replacement of the consumable ones.

Evolution within the companies

The current trend aims at replacing in the companies the personal points of impressions (ink jet printer of ink or laser) by a platform of impression multifunction Bureautique making it possible to copy, print and fax the documents carried out. The goal of this change within the company is to reduce the loads related to the purchase of consumable for the printers.

The photocopier becomes then an element of the Data-processing network managed by the Administrateur network of the company or by an external person receiving benefits able to manage this kind of complex solutions

History

In 1938 Chester Carlson makes a demonstration of the process that a small American small firm decided to exploit commercially. The first xerographic copier (the 914 ) is marketed in 1959, after fourteen years of development. At the limit of the patent, at the beginning of the Années 1970 Xerox had become a multinational holding 95% of the market of the “duplicators”.

The general principle of the electrophotography however seems to be discovered by the physicist Jean-Jacques Trillat in 1935. It presented it to the company Kodak which declared the invention without commercial future. An article describing the general principle would have been published in a number of the review Science & life this same year.

Principal manufacturers of photocopiers

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