When we discuss the principles of operation for any device (not just printers), we are referring to the way that they work. In the case of printers, it is useful to be aware of the quality and cost of the final output to allow us to make a choice of which to use for a particular purpose.
Laser printers make use of a powder containing magnetic material called toner. The printed output is created by fusing this toner to the paper using the following steps (these steps relate to the numbers shown in the animation above):
- Paper is taken from the tray using a roller
- The drum (shown in yellow) is given a negative charge all over
- The laser uses a mirror to direct a beam onto the roller inverting the charge in the areas to be printed (forming a negative of the document)
- The drum is coated with toner which has a positive charge. The toner is then repelled where the negative charge remains
- The paper is moved using rollers & the drum rolls over the paper, transferring toner onto it
- The paper is then fed through the fuser (two heated rollers) melting the toner onto the paper.
(Some printers use a positively charged drum and negatively charged toner. The important thing to remember is that the charges are always opposite.)
And if you’ve ever wondered why the paper from a laser printer is hot, it’s not the laser – it’s the fuser!