What Is a Laser Printer Drum Unit?

Laser printers are fast and precise. They do not use ink and are often cheaper per page than prints from ink jet printers. Older laser printers are usually black and white, but many modern laser printers offer color printing. One of the main components of a laser printer is the printer drum unit.

The Drum

A drum unit contains an electrically charged drum. This charge is created either using a corona wire or a separate charged roller.

The Laser

A mechanism in the drum unit rotates the drum. As it is rotating, a laser is used to "paint" the letters or image on the drum by shining the laser light on certain points. When the laser strikes a point, the electricity on that point is discharged, thus changing its polarity. On positively charged drums, the letters and images are then negatively charged. On negatively charged drums, the letters and images are positively charged.

Attracting the Toner

The drum unit attracts toner via electrostatic attraction, also known as static electricity. If the drum is positively charged, the toner particles are also positive. If the drum is negatively charged, the toner particles are charged negatively. The charge on the toner particles causes them to be attracted to the oppositely charged places on the drum, thus creating letters and other content to be printed. As the drum rotates, the letters "painted" on the drum attract toner.

Transferring the Toner to the Paper

Just before the paper rotates under the drum, it is given an opposite charge to the toner charge. This causes the paper to attract the toner from the drum, thus transferring the letters from the drum to the paper.

Fusing the Toner

Once the letters and image have transferred to the paper, the static charge on the paper is discharged and the paper is rolled through heated rollers to melt the toner into the page and create the final print.