File:Copier-engineerguy.ogv

Bill uses power tools to take apart a photocopier. He shows how it works, and shares the story of its invention by Chester Carlson.

Transcript:This is one of my favorite piece of engineering. I want to show you how it works. I'm not quite sure how to take it apart, but I've got the manual to help me.

Its inventor, Chester Carlson demonstrated true innovation when he put together scientific phenomenon that no one before had ever related.

Carlson read patent after patent searching for ideas. He learned of electrostatics: things sticking together because of static electricity - and photoconductivity - that's light causing current to flow ... both of which are critical to the photocopier.

Alright. I now have the four key elements: There is an aluminum drum coated with amorphous silica; a wire, which is used to deliver a high voltage; a 265 watt halogen lamp; and the very last item is toner. Of course it is what is all over my hands and the floor back here. Now let me explain how these work.

It takes five steps to make a copy.

First the machine sensitizes this drum by raising this wire to a potential of 850 volts relative to the drum. This separates the air molecules between the wire and the drum into negative and positive ions, which in turns creates a charge separation on the drum. The insulated silica surface has a positive charge, the aluminum interior negative.

Second a very bright halogen lamp scans the image. Black areas don't reflect light, but white non-image areas do. When the light strikes the drum the silica surface becomes conductive and charge flows away leaving only a charged image.

Third, the machine wipes toner across the drum. Toner isn't ink. Its tiny particles made of plastic and carbon. Because it has a negative charge the toner sticks only to the positive image on the drum.

Fourth, the wire charges a piece of paper so it can attract the toner from the drum.