Photocopying machines have made our life a lot simpler.
Let’s start from what you are already knowing or have seen while the machine is in action.
You open up the top lid.
You put the paper (to copy) upside down on a glass surface.
You then close the lid and press the start button.
A intense light beam scans the entire image from one end to other.
After few seconds, you see, your copy coming out from another end.
Perfect! Here is what happens after step 4.
The intense light that falls on the image, gets reflected, passes through the lenses and falls on a photosensitive drum as shown below.
These lenses ( or/and) mirrors helps in magnifying and de-magnify the image. Note that the resolution of an image cannot be altered.
What is photo sensitive drum? Apart from being the reason for the name of the machine, this has got important function. The drum (or belt in come cases) is a metal roller with a covering of a photo conductive material.
This photo conductive material has a property of conducting electricity only in some conditions and not in other. Yes! it is a semi-conductor, generally selenium based. This material has a property to act as an insulator in dark areas, while when photons fall on it, it kicks the electrons to flow. Keep this fact in your head for a while.
Now all those areas of your sheet, which is white, will reflect the light on this material, while the printed letters being black, will not. The drum itself is charged positively and the lightened up area of the drum which emitted electrons, neutralises the charge.
So now you have the following result. All those areas of sheet which didn’t reflect light, left positive charge on the drum, while the rest of the areas are neutral.
For a black color A (with white background), This (sort of) thing forms on the roller, Here the black represents the neutralised areas and white represents the areas which are positively charged.
The drum while revolving gets coated with a layer of toner particles. Toner is like a dry ink. It is negatively charged plastic based powder.
You can easily guess now, the positively charged prints, attract the negatively charged toner particles and adhere it.
Finally a blank sheet of positively charged paper is passed over the roller and the toner particles gets attached to it. In the final step, the sheet is warmed – to melt the toner particles, and pressed – to make sure the particles remains there, through the rollers and comes out as the final product. You might have felt that the copy that comes out from the machine is warmer. Now you know the reason!
The entire process of photocopying though takes less than half a minute because of the entire thing seamlessly synchronized.
For color photo copy – In this the process occurs in layers. First, one color is applied, then next and so on. Four separate units that create and develop one by one: cyan, yellow magenta and black images. The superposition of these powder images produces full-colour documents.
Some Unknown facts:
The inventor of photocopying machine Chester Carlson, was turned down by more than 20 companies including the mighty IBM and General Electric, who believed no one needed such product!!
In fact Chester Carlson had to spend more than 6 years convincing companies of the utility of such thing. Later Haloid Corporation (later became Xerox) saw the potential of this and promoted it.
Xerox came from Xerography meaning “Dry writing”. The toner is dry powders and hence the name. The name change was a part of a marketing tactics.
Many photocopiers inserts some “barely visible” dots on the copied paper. This is to differentiate from the original one. Forensic people know more on this.
The world’s fastest photocopier developed for office use is the Riso ORPHIS X9050. This machine is capable of making over 200 copies per minute.