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40930701TH DRAFT Vesion 24 /
2.3.2 Electro-photographic process
The electro-photographic processing is outlined below. Figure 2-5 shows the electro-photo-
graphic printing process.
1 Charging
The surface of the image drum is uniformly charged with negative charges by applying a
negative voltage to the charge roller.
2 Exposure
Light emitted from the LED head irradiates the negatively charged surface of the image drum.
The surface potential of the irradiated part of the image drum surface is lowered, so that an
electrostatic latent image associated with the print image is formed.
3 Developing and toner recovery
When the negatively charged toner is brought into contact with the image drum, it is attracted
to the electrostatic latent image by static electricity, making the image visible.
At the same time, the residual toner on the image drum is attracted to the developing roller
by static electricity.
4 Transfer
When paper is placed over the image drum surface and a positive charge, opposite in polarity
to the toner, is applied to the reverse side of the paper from the transfer roller, the toner is
attracted by the positive charge and is transferred to the paper. As a result, the toner image
formed on the image drum is transferred to the paper.
5 Temporary cleaning
Residual toner that remains on the image drum without being transferred is made uniform
by the cleaning roller and is temporarily attracted to the cleaning roller by static electricity.
6 Fusing
The toner image transferred to the paper is fused under heat and pressure.
Figure 2-6 shows an electro-photographc process timing chart.