Photocopiers...How they work.

How Photocopiers Work – A Clear Picture

Thu, 03/16/2000 - 07:17 — Arlene Martell

The purpose of photocopiers is to create a clear picture – a picture that’s an exact duplicate of the original. Look at the word – photocopy. Photo – picture of. Copy – duplicate. So, as we said, a photocopy is a duplicate of the original picture. But how could an exact copy be created? What kind of technology would it involve? Would it surprise you that the technology behind photocopying is based on two natural phenomena?

The amazing thing about how photocopiers work is the nature of these phenomena. These principles are:

1. Materials of opposite electrical charges attract, and
2. Some materials become better conductors of electricity when exposed to light.

When Chester F. Carlson applied these principles to his work – to find an alternative method of duplicating for the myriad of reports he had to produce – the result was the basis of today’s photocopier, printer and fax machine technology.

The basic principles of photocopying

Chester Carlson’s experiments followed a simple process:

1. A photoconductive surface is given a positive electrical charge.
2. The photoconductive surface is then exposed to the image of a document.
3. The electrical charge dissipates in the exposed areas.
4. Negatively-charged powder that’s spread over the surface sticks to the positively-charged areas through electrostatic attraction.
5. A piece of paper is placed over the powder image and given a positive charge.
6. The negatively-charged powder is attracted to the paper as it’s separated from the photoconductor.
7. Heat fuses the powder image to the paper, producing a copy of the original image.

Today’s copiers follow these principles

Carlson’s electrophotographic process, through much experimentation, has been greatly improved. Modern-day copiers are much advanced from the original model first put out by Xerox in 1948. Let’s look at the electrophotographic process, after it was developed into what we know of today as the photocopier.

• Inside every copier is a light-sensitive surface called a photoreceptor, consisting of a thin layer of photoconductive material that’s applied to a flexible belt or drum. This drum can be charged with a form of static electricity.
• Also inside the copier is toner, a very fine black powder. The drum, when it’s charged with static electricity, can attract the toner particles.
• The drum can be selectively charged; that is, selected parts of it can be charged, thereby attracting toner to only those parts that are charged.
• The sheet of paper gets charged with static electricity and it pulls the toner off the drum.
• The toner is heat sensitive, so the loose toner particles are attached, or fused, to the paper with heat as soon as they come off the drum.

How do you like your copy?

So let’s put all these principles together and see exactly what happens after you put your original on the platen (glass) and close the lid.

After you close the lid, the first thing you see is that bright light passing over your original. This is a similar process to light being let in by a camera lens, projecting the image onto a photoreceptive surface. In the case of the photocopier, the photoreceptive surface is the drum.

The dark, or printed, areas on the original don’t reflect light, and that produces a positive electrical charge. Since positive charges attract, they pull toner, which carries a negative charge, from the toner cartridge, only to the areas that carry a positive charge – the printed areas. From there, heat is applied (which is why your copies are so hot), which fuses the particles of toner to the blank sheet of paper, thereby reproducing your original.

That’s simply it! You get your copy exactly as you want it – exactly what you tell the photocopier to give you.

What about all those parts?

Don’t you wonder how all those moving parts come together at exactly the right time to give you your copy? Let’s see if we can see inside the photocopier to find out what happens when you press that “Start” button.

The first part that comes into play is the corona wire. Its job is to lay down a positively-charged layer of ions on the drum. Then, simultaneously, the light comes on, and the drum begins to rotate. The light reflects off mirrors onto the drum, with the dark areas absorbing the light.

The drum is made out of aluminum, which is a great conductor of electricity. And that makes it the ideal material, because the next step in the process is the addition of an electrical charge, or voltage. And the next part that comes into play is the rollers, which are covered with toner. The toner is pressed onto the roller.

Then the corona wire is activated again, giving the sheet of paper that’ll ultimately be your copy, a positive charge. The sheet of paper then picks up the toner from the drum, and is then sent to the fuser. The fuser consists of heated rollers that melt the toner onto the page.

The copied page is then sent to the collection tray and, voila! You have your photocopy.

The principles of electrophotography are used in many machines today

All this from the dreams and the efforts of one man – Chester F. Carlson – the creator of xerography. Xerography is a unique process that depends on chemical, electrical, mechanical and software know-how. Besides photocopiers, this process is also used in printers and fax machines. The rapid and economical digital printing process most used today produces either one print or hundreds of identical prints in black and white or color. More importantly, the capability of xerography enables on-demand printing of complete documents such as brochures and books. Such on-demand printing can save time, reduce costs, and eliminate document obsolescence, overruns and warehousing.

So you can see, there are many reasons to gain a good knowledge and understanding of electrophotography and its subsequent technology, xerography. If you know what’s going on with your copier, you’ll be able to get the maximum use of its features and benefits. And with that, you’re left with a clear picture.