How Do Laser Printers Work.txt
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Step 1 - Cleaning
During the first stage of the image formation process, a photosensitive drum's surface is prepared to hold an image through a physical and electrical cleaning process. Before a new image is formed on the drum, leftover toner from the previous image must be removed. This is accomplished by a rubber-cleaning blade which scrapes toner off the drum into a debris cavity. The drum is also electrostatically cleaned by erase lamps which illuminate the drum's photosensitive material to neutralize any electrical charges that remain on the drum.
Step 2 - Condition
After the photosensitive drum has been physically and electrically cleaned, it must be conditioned. The conditioning process consists of the application of a uniform negative charge on the surface of the photosensitive drum by the primary corona wire. A high negative voltage is applied to the primary corona wire by the high voltage power supply. Negative charges from the wire migrate to the surface of the drum. The primary corona grid is positioned between the primary corona and the drum's surface to regulate the voltage applied to the drum so that a uniform negative charge is applied.
Step 3 - Write
After rotating past the conditioning station, the drum has a uniform high negative charge on its surface. At the writing station, a sweeping laser beam is used to discharge this potential in selected areas by focusing laser light on selected portions of the photosensitive drum. This creates what is known as an electrostatic image. This image is later developed into a visible image. Portions of the drum not exposed to the laser still have a high negative charge.
Step 4 - Develop
At the developing station, the invisible electrostatic image is developed into a visible image on the photosensitive drum when toner from a developer cylinder is transferred to discharged areas on the drum. The toner particles acquire a negative charge from the developer cylinder which is connected a negative DC power supply. This electrostatic charge causes the toner particles to be attracted to the areas of the drum which have been exposed to the laser light and repelled to the areas not exposed. An AC potential is applied to the developer cylinder to assist the attraction of the toner from the developer cylinder to the photosensitive drum. (Particles are -200 Volts to -500 Volts)
Step 5 - Transfer
At the transfer station, the toner image on the photosensitive drum is transferred to the paper. A corona wire is positioned behind the paper so that the paper, which is traveling the same speed as the drum's surface is rotating, contacts the drum. This corona produces a positive charge on the paper. Because the positive charges on the paper are stronger, they pull the negatively charged toner particles off the drum and on to the paper. As the paper and drum advance, a row of metal teeth with a high negative charge called the static charge eliminator weakens the attractive force between the negatively charged drum and the positively charged paper. This helps separate the photosensitive drum and paper.
Step 6 - Fuse
Until the paper reaches the fusing station the toner is held on the paper only by gravity and weak electrostatic forces. At the fusing station, toner is melted and forced into the paper by pressure and heat of the fusing roller to produce a permanent image. The heat of the fusing roller is maintained by a high intensity lamp inside the fusing roller. At this point the finished print is ejected and the process is restarted from stage one.
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