When you print something, your computer sends a vast stream of electronic data (typically a few megabytes or million characters) 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 onto the page a kind of powdered ink called toner. Finally, as in a photocopier, a fuser unit bonds the toner to the paper.
data
stream into the printer from your computer.electronic circuit
in the printer (effectively, a small computer in its own right) figures out how to print this data so it looks correct on the page.corona wire
. This is a high-voltage wire that gives a static electric charge to anything nearby.photoreceptor drum
so the drum gains a positive charge spread uniformly across its surface.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. Where 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; where the page should be black, there are areas of negative charge.ink roller
touching the photoreceptor drum coats it with tiny particles of powdered ink (toner). The toner has been given a positive electrical charge, so it sticks to the parts of the photoreceptor drum that have a negative charge (remember that opposite electrical charges attract in the same way that opposite poles of a magnet attract). 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.paper
from a hopper on the other side of the printer feeds up toward the drum. As it moves along, the paper is given a strong negative electrical charge by another corona wire.fuser unit
). The heat and pressure from the rollers fuse the toner particles permanently into the fibers of the paper.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!
Until the early 1980s, hardly anyone had a personal or office computer; the few people who did made "hardcopies" (printouts) with dot-matrix printers. These relatively slow machines made a characteristically horrible screeching noise because they used a grid of tiny metal needles, pressed against an inked ribbon, to form the shapes of letters, numbers, and symbols on the page. They printed each character individually, line by line, at a typical speed of about 80 characters (one line of text) per second, so a page would take about a minute to print. Although that sounds slow compared to modern laser printers, it was a lot faster than most people could bash out letters and reports with an old-style typewriter (the mechanical or electric keyboard-operated printing machines that were used in offices for writing letters before affordable computers made them obsolete). You still occasionally see bills and address labels printed by dot-matrix; you can always tell because the print is relatively crude and made up of very visible dots. In the mid-1980s, as computers became more popular with small businesses, people wanted machines that could produce letters and reports as quickly as dot-matrix printers but with the same kind of print quality they could get from old-fashioned typewriters. The door was open for laser printers!
Photo: Dotty characters like this are a tell-tale sign of a dot-matrix printer at work.
Fortunately, laser-printing technology was already on the way. The first laser printers had been developed in the late 1960s by Gary Starkweather of Xerox, who based his work on the photocopiers that had made Xerox such a successful corporation. By the mid-1970s, Xerox was producing a commercial laser printer—a modified photocopier with images drawn by a laser—called the Dover, which could knock off about 60 pages a minute (one per second) and sold for the stupendous sum of $300,000. By the late 1970s, big computer companies, including IBM, Hewlett-Packard, and Canon, were competing to develop affordable laser printers, though the machines they came up with were roughly 2–3 times bigger than modern ones—about the same size as very large photocopiers.
Two machines were responsible for making laser printers into mass-market items. One was the LaserJet, released by Hewlett-Packard (HP) in 1984 at a relatively affordable $3495. The other, Apple's LaserWriter, originally cost almost twice as much ($6995) when it was launched the following year to accompany the Apple Macintosh computer. Even so, it had a huge impact: the Macintosh was very easy to use and, with relatively inexpensive desktop-publishing software and a laser printer, it meant almost anyone could turn out books, magazines, and anything and everything else you could print onto paper. Xerox might have developed the technology, but it was HP and Apple who sold it to the world!
Dipping into the archives of the US Patent and Trademark Office, I've found one of Gary Starkweather's original laser-printer designs, patented on June 7, 1977. To make it easier to follow, I've colored it in and annotated it more simply than the technical drawing in the original patent (if you wish, you can find the full details filed under US Patent 4027961: Copier/Raster Scan Apparatus).
What we have is essentially a laser scanning unit (colored blue) sitting on top of a fairly conventional, large office photocopier (colored red). In Starkweather's design, the laser scanner slides on and off the glass window of the photocopier (the place where you would normally put your documents, face down), so the same machine can be used as either a laser printer or a copier—anticipating all-in-one office machines by about 20–25 years.
Artwork: Gary Starkweather's orginal laser printer design from US Patent 4027961: Copier/Raster Scan Apparatus, courtesy of US Patent and Trademark Office.
I used to share an office with someone who refused to share our office with a laser printer; we had to move our machine into a closet and keep the door shut tight. This kind of worry is far from rare, but is it simply superstition? As we saw up above, laser printers use a type of solid ink called toner, which can be a source of dusty, fine particulates (remember that sooty particulates, released by such things as car tailpipes, are one of the more worrying ingredients in urban air pollution). One recent study found some printers emit nearly 10 billion particles per printed page (although it's important to note that the type and quantity of particle emissions vary widely from model to model). They also produce volatile organic compounds (VOCs) and a gas called ozone (a very reactive type of oxygen with the chemical formula O3), which is toxic and, at high enough concentrations, produces a variety of health impacts. Thankfully, ozone is transformed into ordinary oxygen (O2) relatively quickly inside buildings.
Chart: According to one study, just under half (40 percent) of laser printers emit sub-micron particles (so PM1 particulates and smaller). Of these, just under a third (27 percent) were high emitters. Drawn using data from Particle emission characteristics of office printers by C. He et al, Environ Sci Technol, 2007.
Do printers and copiers present any risk to our health? A few scientific studies have been done; although the results are mixed, they do seem to suggest it's worth taking simple precautions, such as placing your printer well away from your workstation, if you use it a great deal, and ensuring good ventilation. You should also take great care when changing toner cartridges or handling empty ones. But keep things in perspective. According to a 2020 study by Jianwei Gu et al in the journal Indoor Air: "The health risk from exposure to LPD [laser printing device]-emitted particles is small compared with the health risk from exposure to ambient particles." In other words, everyday outdoor air pollution presents a bigger risk. You'll find a list of recent studies in the further reading below.
Please do NOT copy our articles onto blogs and other websites
Articles from this website are registered at the US Copyright Office. Copying or otherwise using registered works without permission, removing this or other copyright notices, and/or infringing related rights could make you liable to severe civil or criminal penalties.
Text copyright © Chris Woodford 2007, 2022. All rights reserved. Full copyright notice and terms of use.
Please rate or give feedback on this page and I will make a donation to WaterAid.
If you've enjoyed this website, please kindly tell your friends about us on your favorite social sites.
Press CTRL + D to bookmark this page for later, or email the link to a friend.
Woodford, Chris. (2007/2022) Laser printers. Retrieved from https://www.explainthatstuff.com/laserprinters.html. [Accessed (Insert date here)]
For more information warehouse printer, please get in touch with us!