HOW A LASER PRINTER FUNCTION
A laser printer is a high-quality, fast printer that uses a laser beam to create an image. The central part of the laser printer is its electrophotographic drum. The drum is a metal cylinder that is coated with a light-sensitive insulating material. When a beam of laser light strikes the drum, it becomes a conductor at the point where the light hits it. As the drum rotates, the laser beam draws an electrostatic image upon the drum, called the image. The undeveloped or latent image is passed by a supply of dry ink or toner that is attracted to it. The drum turns and brings this image in contact with the paper, which attracts the toner from the drum. The paper is passed through a fuser that is made up of hot rollers, which melts the toner into the paper.
Printing Process
The laser printer process involves six steps to print information onto a single sheet of paper.
Step 1: Cleaning
When an image has been deposited on the paper and the drum has separated from the paper, any remaining toner must be removed from the drum. A printer may have a blade that scrapes all excess toner from the drum. Some printers use an AC voltage on a wire that removes the charge from the drum surface and allows the excess toner to fall away from the drum. The excess toner is stored in a used toner container that is either emptied or discarded.
Step 2: Conditioning
This step involves removing the old latent image from the drum and conditioning the drum for a new latent image. Conditioning is done by placing a special wire, grid, or roller that receives a negative charge of approximately –600 volts DC uniformly across the surface of the drum. The charged wire or grid is called the primary corona. The roller is called a conditioning roller.
Step 3: Writing
The writing process involves scanning the photosensitive drum with the laser beam. Every portion of the drum that is exposed to the light has the surface charge reduced to about –100 volts DC. This electrical charge has a lower negative charge than the remainder of the drum. As the drum turns, an invisible latent image is created on the drum.
Step 4: Developing
In the developing phase, the toner is applied to the latent image on the drum. The toner is a negatively-charged combination of plastic and metal particles. A control blade holds the toner at a microscopic distance from the drum. The toner then moves from the control blade to the more positively-charged latent image on the drum.
Step 5: Transferring
In this step, the toner attached to the latent image is transferred to the paper. The transfer, or secondary corona, places a positive charge on the paper. Because the drum was charged negatively, the toner on the drum is attracted to the paper. The image is now on the paper and is held in place by the positive charge.
Step 6: Fusing
In this step, the toner is permanently fused to the paper. The printing paper is rolled between a heated roller and a pressure roller. As the paper moves through the heated roller and the pressure roller, the loose toner is melted and fused with the fibers in the paper. The paper is then moved to the output tray as a printed page.
The following mnemonic can help you memorize the order of the steps of the laser printing process: Continuous Care Will Delay Trouble Forever (Cleaning, Conditioning, Writing, Developing, Transferring, Fusing).
WARNING: The primary corona wire or grid, or the conditioning roller, can be very dangerous. The voltage runs as high as –6000 volts. Only certified technicians should work on the unit. Before working inside a laser printer, you should make sure that voltage is properly discharged.
Printing Process
The laser printer process involves six steps to print information onto a single sheet of paper.
Step 1: Cleaning
When an image has been deposited on the paper and the drum has separated from the paper, any remaining toner must be removed from the drum. A printer may have a blade that scrapes all excess toner from the drum. Some printers use an AC voltage on a wire that removes the charge from the drum surface and allows the excess toner to fall away from the drum. The excess toner is stored in a used toner container that is either emptied or discarded.
Step 2: Conditioning
This step involves removing the old latent image from the drum and conditioning the drum for a new latent image. Conditioning is done by placing a special wire, grid, or roller that receives a negative charge of approximately –600 volts DC uniformly across the surface of the drum. The charged wire or grid is called the primary corona. The roller is called a conditioning roller.
Step 3: Writing
The writing process involves scanning the photosensitive drum with the laser beam. Every portion of the drum that is exposed to the light has the surface charge reduced to about –100 volts DC. This electrical charge has a lower negative charge than the remainder of the drum. As the drum turns, an invisible latent image is created on the drum.
Step 4: Developing
In the developing phase, the toner is applied to the latent image on the drum. The toner is a negatively-charged combination of plastic and metal particles. A control blade holds the toner at a microscopic distance from the drum. The toner then moves from the control blade to the more positively-charged latent image on the drum.
Step 5: Transferring
In this step, the toner attached to the latent image is transferred to the paper. The transfer, or secondary corona, places a positive charge on the paper. Because the drum was charged negatively, the toner on the drum is attracted to the paper. The image is now on the paper and is held in place by the positive charge.
Step 6: Fusing
In this step, the toner is permanently fused to the paper. The printing paper is rolled between a heated roller and a pressure roller. As the paper moves through the heated roller and the pressure roller, the loose toner is melted and fused with the fibers in the paper. The paper is then moved to the output tray as a printed page.
The following mnemonic can help you memorize the order of the steps of the laser printing process: Continuous Care Will Delay Trouble Forever (Cleaning, Conditioning, Writing, Developing, Transferring, Fusing).
WARNING: The primary corona wire or grid, or the conditioning roller, can be very dangerous. The voltage runs as high as –6000 volts. Only certified technicians should work on the unit. Before working inside a laser printer, you should make sure that voltage is properly discharged.
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