Xerography

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Xerography
1. In this a electrostatic charge (around 600V) is passed of the surface of the drum by as a corona discharge which is controlled by a control grid. The electrostatic charge is generated from a narrow wire. A negative charge is put on the wire which ionizes the area in between the wire and conductor which repel the electrons to the conductor. The polarity is chosen to suit the purpose positive or negative process.

2. The document which then needs to be copied is illuminated by lamps which is either passed over a lens or scanned by a moving light and lens.
Where there is no image the drum will be illuminated and the charge will be dissipated elsewhere. The charge that stays on the drum after the exposure is called the latent image and is a negative of the original document.

3. The drum is then presented with a mixture of toner particles (powder) and reusable carrier particles. The carrier particles have this coating which when agitated generates a static charge which attracts the toner particles to coat them. By contact with the carrier each neutral toner particle has an electric charge of polarity opposite to the charge of the latent image on the drum. The charge attracts toner to form a visible image on the drum. To control the amount of toner transferred, a bias voltage is applied to the developer roller to counteract the attraction between toner and latent image.

The paper is then passed between the drum and the transfer corona which have polarity opposite to the charge on the toner. The toner image is then put on onto the paper by the combination of pressure and electrostatic attraction.

The image is then fixed there heat and pressure.
Definition - An electrostatic printing process for copying text or graphics wherebyareas on a sheet of paper corresponding to the image areas of theoriginal are sensitized with a charge of static electricity so that, whenpowdered with a toner carrying an opposite charge, only the cha -...
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