Sardar Patel University 2007 B.E Computer Science Computer peripherals (CP313)(Internal ) - Question Paper

Solution
Computer peripherals (CP313)


Q – one [A] discuss subsequent steps of Laser printer in briefly:
1) Writing of the image on the OPC drum
2) Developing image on the OPC drum

Answer:
Inside a laser printer the image formation process revolves around a photosensitive drum called Organic Photo Conductive (OPC) drum. The complete image formation process consists of the subsequent 6 steps:
a. cleaning of the OPC drum
b. conditioning of the OPC drum
c. Electro-statically writing the image onto the OPC drum
d. Developing the image on the OPC drum
e. Transferring of the image from OPC drum to the paper
f. Fusing the image on the paper

WRITING of the image on the OPC drum
? Drum is having uniform -600V potential on its surface by conditioning process.


? The laser beam makes the charge at that particular are where Laser strikes to discharge to the ground, the areas where Laser does not strike retains its -600V.
? The image created is called latent electrostatic image of the image to be printed.
? Laser beam is generated by Laser diode and this beam is focused and send to a scanning mirror, the scanning mirror sweeps the Laser beam across the entire width of the OPC drum
? A set of mirror and lenses are used to focus this scanning beam into any area on the drum’s surface which is rotated by 1/300th of an inch so that beam can write next line
? This provide 300 Dots per Inch of vertical and horizontal resolution called 300 X 300 dots per square inch (DPI) resolution
? Once the Drum is through the writing process, the portions of the drum not exposed to the Laser are at the -600 V potential placed there by the primary corona or the primary charging roller while those portions that are exposed by laser light have discharged to approximately -100 V

DEVELOPING of the image on the OPC drum
? To convert latent image generated by writing on OPC drum into a visible image the toner is transferred to the discharged areas of the drum
? The toner is a black plastic resin, powdery substance bound to iron particles.
? Fig 3-10
? The iron in the toner causes it to be attracted to the magnet inside the developing cylinder. As the cylinder rotates, the height-control blade limits the amount of toner on the cylinder to a uniform thickness
? The developing cylinder is connected to a negative power supply, this reason the toner particles to receive the negative charge from the cylinder.
? This negative electrostatic charge reason the toner to be attracted to the areas of the OPC drum which has been exposed to the Laser beam or those areas that contain the image to be printed. The toner particle is repelled by the other areas which are not exposed to the Laser beam.
? AC potential is also applied to the developer cylinder to decrease the attraction ranging from the toner particles and the magnet. DC potential can be adjusted by the print density sliding switch given on the printer

Earning:   Approval pending.