A laser printer is a printer for computers. It uses laser or LED-technology to get small particles of toner from a cartridge onto paper. Very often, this costs less to use than the ink of inkjet printers. Laser printers often print text more neatly than inkjet printers, but print photos less clearly. Printing on photo paper or coated paper designed for inkjet printers can damage the laser printer's drum and fuser unit.
Laser printing is a process which typically involves seven steps:
- Raster Image Processing: the processor inside the printer converts the data to be printed from its current file format, into a bitmap of the page to be printed - this is then stored in raster image memory.
- Charging: An electrostatic charge is then projected onto a revolving photosensitive drum inside the printer.
- Writing: A laser beam is directed at a rotating polygonal mirror, which redirects the beam onto the photosensitive drum. The rasterized data in memory is now read, and used to control whether the laser is on or off, as the beam sweeps across the drum - where the laser beam strikes the drum the charge is reversed, creating a latent electrical image on the surface. Some laser printers use an array of tiny LEDs instead of a sweeping laser beam.
- Developing: The surface of the drum is then exposed to negatively charged particles of toner, which are attracted to the areas where the laser wrote the latent electrical image. The toner will be repelled by the negative charge on areas of the drum where the laser beam did not strike, and hence remove the charge.
- Transferring: The drum is now rolled over paper, transferring the image from the drum to the paper (to aid in this process there is a positively charged roller behind the paper, which pulls the toner off the drum and onto the paper).
- Fusing: The paper is then passed through a fuser, where rollers provide heat and pressure to bond the toner to the paper.
- Cleaning: An electrically uncharged blade and a discharge lamp remove any toner and all the charge remaining on the drum (this will all happen in one revolution of the drum).