How does your laser printer work?

Have you ever wondered how you can print text with a beam of light? It sounds impossible but it’s exactly how a laser printer works when it makes a permanent copy of data from your computer onto a piece of paper. Over the last few years, lasers have become one of the most important tools we use. They are used in several different areas of work, including medicine. We tend to think of lasers as incredibly powerful light beams that can slice through blocks of metal or blast enemy spaceships to pieces, thanks to sci-fi and spy movies. Tiny lasers are useful in a much more humdrum way, they can read sounds or video clips from CD and DVD s. They are also vital parts of laser toner printers!

Let’s take a look at how your laser printer works.

A compact laser printer doesn’t look all that different to your average inkjet printer, but it puts ink on to the paper in a completely different way. An inkjet printer uses heat to squirt droplets of wet ink from hot syringe like tubes, while a laser printer uses static electricity to transfer a dry ink power called toner. Laser printers are very similar to photocopiers and use the same basic technology.

When you print something, your computer sends a large stream of electronic data to your laser printer. An electronic circuit in the printer figures out what all this data means and what it needs to look like on the page. It makes a laser beam scan back and forth across a drum inside the printer, building up a pattern of static electricity. The static electricity attracts powdered ink called toner onto the paper.  Finally, a fuser unit bonds the toner to the paper.

Below is a step by step guide of how a laser printer works.

1. Millions of bytes of data stream into the printer from your computer.

2. An electronic circuit in the printer figures out how to print this data so it looks correct on the page.

3. The electronic circuit activates the corona wire. This is a high voltage wire that gives a static electric charge to anything close by.

4. The corona wire charges up the photoreceptor drum so the drum gains a positive charge spread uniformly across its surface.

5. At the same time, the circuit activates the laser to make it draw the image of the page onto the drum. The laser beam doesn’t actually move, it bounces off a moving mirror that scans it over the drum. When the laser beam hits the drum, it erases the positive charge that was there and creates an area of negative charge instead. Gradually, an image of the entire page builds up on the drum, where the page should be white, there are areas with a positive charge and where the page should be black there are areas with a negative charge.

6. An ink roller which touches the photoreceptor drum coats it with tiny particles of powdered ink (toner). The toner has been given an electrical charge, so it sticks to the parts of the photoreceptor drum that have a negative charge. No ink is attracted to the parts of the drum that have a positive charge. An inked image of the page builds up on the drum.

7. A sheet of paper from the hopper on the other side of the printer feeds up towards the drum. As it moves along, the paper is given a strong electrical charge by another corona wire.

8. When the paper moves near the drum, its strong charge attracts the charged toner particles away from the drum. The image is transferred from the drum onto the paper but, for the moment, the toner particles are just resting lightly on the paper’s surface.

9. The inked paper passes through two hot rollers (the fuser unit). The heat and pressure from the rollers fuse the toner particles permanently into the fibres of the paper.

10. The printout emerges from the side of the copier. Thanks to the fuser unit, the paper is still warm. It’s literally hot off the press.