How does a laser printer work?

When browsing a store such as www.internetink.com in search of consumables for your printer, you may be struck by the fact that, depending on the sort of printer you have, the consumables vary significantly in price and quantity.

The reason for this is straightforward and is owing to the two prevailing printer technologies.  The ‘ink’ used in a laser printer is entirely different to that used in an inkjet one, since the insides of a laser printer, and the principles by which one operates, are entirely different to those of an inkjet one.  But exactly how does a laser printer work?

Laser printers typically work in six stages, all of which take place in a fraction of a second. This process is not exactly the same for every variety of laser printer; some, for example, will use rollers where others use exposed wires, called ‘coronas’.  The principles, however, are largely identical.

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Clean

The first stage of the printing process is the clean.  The inside of a laser printer will typically contain several rollers, or drums, through which paper will pass.  The most important, and typically largest, of these drums is the photosensitive drum.  In some printers it is the only drum.

Before it can be used, however, the drum must be cleaned, both electrically and physically.  This is important in order to prevent black residue from appearing on the page.  The drum is very delicate; if care is not taken with the cleaning, then it can be scratched – and the result will be a permanent mark on every printed page.

The electrical cleaning is performed by a lamp, which will soak the drum in light which removes any residual static charge.

Charge

The next phase involve the charging of the photosensitive drum.  The entire surface of the drum is applied with a uniform, negative charge.  In some printers, this charging is done with a wire called the corona wire.  In other, newer printers, it is done by another roller called the charge roller.

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Expose

An image can now be created.  This is done using a laser, which impacts the drum, negatively charging the areas it strikes.  The laser does its work extremely quickly, striking the drum many millions of times per second.  The result is an image created from varyingly charged particles.

Develop

Following this, the roller will pass near another roller which applied toner.  Negatively charged particles of toner will be attracted to the areas of the paper which have been struck with a laser, and so an image made from electricity will become one made from toner.

Transfer

Once the image has been created on the drum, it must be transferred to the paper.  The transfer corona – or roller – will apply a positive charge to the paper.  Negatively charged particles of toner, which have formed the image on the drum, will immediately jump across to the paper.  The printing process is now almost complete.

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Fuse

Now the images and words have been created on the page.  The work of the printer is not quite done, however.  Were the print process to end here, then the toner would simply fall off the paper as soon as its charge is altered.

Something must be done to prevent this from happening, and to make the printing process permanent.  The final stage of the printer ensures this.  The paper finally passes through two tightly-packed rollers, which fuse the toner to the page with a combination of heat and pressure.

It should be noted that the heat and pressure generated here is sufficient to melt some forms of plastic media – such as transparent slides used in overhead projector machines.  It is therefore not advisable to try to print onto such media using a laser printer – attempting to do so could cause irreparable damage to the printer, and void its warranty.

Static-decharge

The printing is now complete.  But one final finishing touch remains; the paper itself must be free of static charge.  This is done by passing the paper over a special device known as a static charge eliminator, typically situated near to the printer’s out tray.

What about colour?

This is all very well and good for monochrome printers.  But how do colour laser printers achieve their results?  The answer is very straightforward.  In the vast majority of cases, colour laser printers work in precisely the same way, except that there will be four passes for every printed page, to apply cyan, magenta, yellow and black toner.

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