Photocopiers look complex, but they work on two very basic elements of science.
A drum that is coated with a special coating is at the center of every photocopier. The bright light shines over the paper, and white areas are positively charged while black parts remain negatively charged. The drum draws the toner and binds it to the paper, forming an impression of ink.
Xerography
The technology behind most copies today is known as xerography. It’s a dry process made using electrostatic charge. Basically, it works by giving opposite electrical static charges to the “ink” (a black powder known as toner) followed by applying heat to get them to stick to the paper.
Chester Carlson invented the xerographic method in his own home laboratory in 1938. It changed the way we work, making it possible to produce large numbers of copies. Carlson’s invention was initially rejected by large corporations however he was able to transform it into one of the biggest office innovations of the 20th century.
The piece of paper that will be photocopied is illuminated by a bright light. In a photocopier, the sheet of paper to be copied is illuminated with the very intense light. The printed or marked parts don’t bounce the light back. The electrons that are near the surface of drums with photoconductive properties are absorbed, leaving an image that is not visible to the paper.
Then, the toner gets charged negatively. The ‘inks’ pass through an electric field generated through corona cables. The negatively charged toner is drawn by the electric shadow of the photoconductor belt. It then forms an inked copy of the original document. The paper from the other side of the conveyor belt then gets a positive charge through an incline, and this attracts the toner with a positively charged charge. The toner and paper are then fused with high heat. The result is that the copy the appearance of a permanent copy.
Photocopying technology
Thue may photocopy hcm print documents on papers using the power of electricity, instead of ink. This charge is generated through a rotating drum which contains a reservoir containing black powder, also known as toner. Toner and the drum both have opposite electrical charges. They draw each other. The drum is coated by a specific chemical that can absorb the toner particles and then deposit the toner particles on a clean piece of paper.
The document that you want to copy can be placed in an opening on the top of the machine. A bright light scans over the document, searching for areas of black. The light from the scanner reflects off these dark areas and creates an “electrical shadow” of the page.
The photoconductor is a cylinder that has a photo-conductive coating over it. A laser in a printer or a scanning device in scanners gives the drum an overall positive electric charge. The drum is also exposed to a reservoir of carbon toner particles that have a negative charge. The toner is glued to the exposed parts of the drum, which are then heated and then fused to the paper going through the copy machine. The paper that is copied still has a little bit of static electricity on it that can result in the paper sticking where it shouldn’t, and create jams. That’s why it is important to clean the paper surface of the copier frequently.
Photocopier components
The most obvious photocopier components are the glass tray in which you can place your documents and the lamp that casts light on it as well as the drum, which is the conveyor belt that rotates in a photo-conductive special material. Early copiers used a photoconductor made of selenium, however later models used selenium telluride. The substance converts light into electricity, by removing electrons from photo-conductive atoms. When you illuminate the original document more light will bounce off of the unprinted white areas than the inked black areas. This creates an electrical shadow.
The document is then scanned by the optical scanner which produces an electronic image which the RIP transmits to the printer section of the photocopier. The printing section is also responsible for generating the static electricity, and it uses the same process as an analog photocopier to create each line of text on the document. The document is printed by the drum using heat to set the ink.
You’ve probably seen static electricity in the past. It’s what you get when you put a balloon in your clothes and then stick it on the wall. Another scientific trick is the capacity of some materials to become more conductive upon absorbing light (photoconductivity). This is how xerography works and is what makes many modern photocopiers the dependable and efficient machines they are.
Electrophotography
The key to the process of photocopying is the electrostatic charge that is formed on the drum or other surface. This charge comes from corona wires that are exposed to high voltage in order to create an electrical field between the drum and paper. The negative charge on the paper attract the positively charged toner particles and create an image on the paper.
The basic operating principle behind all digital copiers and laser printers is known as electrophotography (or xerography). Chester Carlson invented the process in 1937 and collaborated together with Battelle Memorial Institute on developing it into a device to be used in commercial settings. He created Haloid Corporation, which eventually changed its name to Xerox Corporation in 1961.
Electrophotography is based on two fundamental phenomena: objects with opposing electrical charge attract, and that certain materials become better conductors of electricity after exposure to light. Carlson created a process of six steps to transfer images from one surface to another using these phenomena.
The document is then exposed to the photoreceptor. This is usually an especial drum that is covered with a semiconductor which only conducts in an upward direction. After placing the document on top of a photoreceptor, a bright light will be shone on it. The light is reflected off of the white parts of the document, and is then is transmitted through mirrors to illuminate the dark portions. The light reflected is then transmitted through the photoreceptor, which discharges the electric charge into the illuminated areas. Latent images are patterns of electrical charges that appear on a photoreceptor.