Laser printers are complex machines but are not really that hard to understand. This node will describe the basic process by which a laser produces printed images.
The underlying principle in laser printers is the electrophotographic process (EP) which uses a combination of static electricity and laser technologies to create printed images on paper. To set up the explanation, I'll need to go over the components of a laser printer.
- Laser
- The laser does not "burn" an image onto the paper, nor does it melt toner onto the paper, it simply "draws" an image onto a photosensitive drum by giving it an opposite charge where it wants toner to attract to.
- Photosensitive drum
- The photosensitive drum is like the motherboard of a PC; it pulls everything together to make it work. However it should be noted that unlike a motherboard the drum is not one of the biggest components, in fact its diameter usually is an inch or tighter. Obviously this means that for a single page to be completed the whole process must be repeated several times. It is written on by the laser system, applied toner to, transfers the toner to the paper, and then is erased through a grounding wire and it starts all over.
- Toner cartridge
- The toner cartridge contains the toner, duh. When the electrically charged drum rolls past the toner cartridge, the toner, which is electrically charged (charged negatively if the drum is charged negatively and positive if the drum is positively charged), is attracted towards the electrically opposite "image" which the laser created on the drum.
- Transfer corona
- The transfer corona applies an electrically opposite charge to the paper so that it attracts the toner from the drum. After the toner transfers to the paper another corona removes the static charge from the paper so that it doesn't stick to other printer components, or your hand or something.
- Fuser
- The fuser is a pair of Teflon coated rollers. At least one of these, the top one, is heated. The heat melts the plastic in the toner and the rollers smash the toner to the paper, thus creating a fusing effect.
- Erase lamp
- The Erase lamp, are you ready for this, erases. It causes all charges from the photosensitive drum to drain out through the drums ground so that another image can be applied.
- Primary corona
- The primary corona is a wire that is closely positioned to the drum. It carries a very high voltage creating an electrical field (corona), which charges the drum.
Now that we know what is what and what it does. Lets do a run through of the print process.
- Charging:
The printer's power supply, supplies power to the primary corona wire which in turn charges up the drum.
- Writing:
The laser is aimed at a moving mirror which directs the laser through different lenses onto the photosensitive drum. Where ever the laser strikes the drum the charge is reversed, thus creating the electrophotographic image.
- Developing:
The toner cartridge opens up so that the electrostatically charged toner particles can be attracted to the drum where the laser struck.
- Transferring:
While the paper is rolled passed the drum, it receives a charge from the transfer corona wire, so that it can attract the electrically charged toner.
- Fusing:
When it is on its way out of the printer the paper is heated and rolled by the fusing rollers so that the image stays on the page.
- Cleaning:
When the print is complete an electrically neutral rubber blade cleans off any excess toner on the drum and deposits it into a reservoir which occasionally needs cleaning. The erase lamp is booted up and all remaining charges on the drum escape through the printers ground.
So there you have it, the basic process by which your laser printer produces a monochrome image. It amazes me because when you get into high-end laser printers, which can get up and around 1000 ppm, everything is moving faster than a silver toaster on ice. A color laser printer is very much the same except that the process is repeated each time for each of the primary colors cyan, magenta, yellow and black.
source used: www.smartcertifydirect.com