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How Printers Work – WYSIWYG

WYSIWYG – what’s that?! Well, you pronounce it "whiz-e-wig", and it’s an acronym used in the image duplication industry. It stands for What You See Is What You Get. What it refers to is the principle of perfect reproduction – you want to be able to reproduce exactly what you print or copy. This has always been the goal of printing technologists – to get the perfect reproduction.

And how does that work, you say? That’s what we’re going to describe to you here. We’ll leave out the complicated technology and explain to you in simple layman’s terms just how printers work. Copy?

A tale of two technologies

There are two distinct printing technologies – laser and inkjet. Both of these incorporate non-impact printing. Actually, there is a third one – dot matrix – but that’s not used as much today – mostly for draft-quality printing. All these technologies have one thing in common – the printed image is created by a series of dots. The difference is the method by which these dots are created. First, we’ll look briefly at how dot matrix printers work.

A dot matrix printer is an impact printer in which each character is formed by a wire or pin striking a ribbon saturated with ink against the paper, much like a typewriter. (If you don’t know what a typewriter is, ask your parents.) The print resolution, or quality, of a dot matrix printer is determined by the number of pins used to form the characters. The typical number of pins is 9, 18 or 24, with 24 being the common number today.

Dot matrix and laser printers use the principles of electrophotography, which we’ll explain in more detail below. Inside a dot matrix printer, there’s a printhead; inside the printhead there’s a large permanent magnet. This magnet exerts a force on the pins, drawing them close to the surface of the magnet. A spring on the print wire tries to force the pin away from the magnet. The print wire is wrapped with a coil of wire that makes it an electromagnet. When power is applied to the coil, the resulting opposing magnetic field neutralizes the permanent magnet’s field and allows the spring to force the pin forward to strike the ribbon. This action repeated produces your printed page.

Laser printers – built for speed

Laser printers are the fastest and most popular printers on the market today. They produce extremely high quality images – some near photo quality. Let’s take a closer look at how they do that.

As we mentioned, laser printers use electrophotography, or an electrophotostatic process to form images on paper. The basis of the principles involved here is the science of atoms – oppositely-charged atoms are attracted to each other, so opposite static electricity fields cling together. It’s hard to imagine that this has anything to do with printing, but in actuality, this is precisely what makes laser printers work.

Inside the laser printer is a drum, or photoreceptor. It’s made of high photoconductive material that’s discharged by light photons. Initially, the drum is given a positive charge by a wire with an electrical current running through it called the charge corona wire. As the drum revolves, a tiny laser beam is shone across the surface to discharge certain points. These discharged points are ultimately what determine the images that’ll be printed.

After the laser sets the pattern, the printer coats the drum with positively charged toner, a fine, black powder. Since it has a positive charge, the toner clings to the negatively-discharged areas of the drum. Now you have a powder pattern on the drum, which then rolls over a sheet of paper, which has already been given a negative charge by the transfer corona wire. This charge is stronger than the negative charge of the electrostatic image, so the paper can pull the toner powder away. Since the paper is moving at the same speed as the drum, the paper picks up the image pattern exactly. Then the paper is immediately discharged by the detac corona wire so it doesn’t stick to the drum.

Finally, the paper is passed through the fuser, a pair of heated rollers, thereby melting the loose toner powder and fusing it with the fibers in the paper. The fuser rolls the paper to the output tray, and your page is printed.

After depositing toner on the paper, the drum surface passes the discharge lamp, which exposes the entire photoreceptor surface, erasing the electrical charge. The drum surface then passes the charge corona wire, which reapplies the positive charge. Now you’re ready for your next page.

Inkjet printers – let us spray

Inkjet printers literally spray liquid ink through a miniature nozzle similar to your garden hose nozzle. These printers are very quiet and are moderately priced. And the print quality rivals that of a laser printer. Here’s how they do that.

The printhead contains 4 cartridges of different colored ink: cyan (blue), magenta, yellow and black (CMYK). It moves along a bar from one side of the paper to the other, writing as it goes. The formatting information and data sent to it activates the chambers of the ink cartridges.

When the designated nozzle is selected, an electrical pulse flows through thin resistors in the ink chambers that form the character to be printed. The resistor is heated and used to heat a thin layer of ink in each selected chamber, causing the ink to boil or expand to form a bubble of vapor.

This expansion causes pressure on the ink, which pushes it through the nozzle onto the paper. Your page is printed.

Don’t sweat the complicated stuff – just print your page

So now you know how printers work. Once you understand the principle of electrophotography, you’ll have a basic knowledge of the inner workings of not only printers, but photocopiers and fax machines as well. Isn’t it amazing how such a complex system can be made to sound so simple? That’s the purpose of these articles. So as we said, don’t sweat it – just put your paper in the printer and print your image. And if everything’s working ok – WYSIWYG!

About The Author

Gareth Marples is a successful freelance writer providing valuable tips and advice for consumers purchasing Panasonic ink cartridges, lexmark ink cartridges and hp printer cartridges. His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.

This article on "How Printers Work" reprinted with permission.

© 2004 - Net Guides Publishing, Inc.

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