Electrophotography
Electrophotography is a photocopying process that was invented in 1938 by Chester Carlson. He was awarded a patent for the process in 1942. This process was later called xerography, which means this process uses no liquid chemicals. The main process this is used in is photocopying. For more information, please search for the word electrophotography on Wikipedia.
The main element used in photocopying is called a drum. A cylinder made of metal is attached to rotate on a horizontal axis. These drums rotate at the same speed as the paper output. One revolution of the drum involves the following seven steps.
The first step is called charging. It is when an electrostatic charge is evenly distributed on the drum. Polarity is then used to choose the positive or negative process.
The second step is called exposure. This is when the document to be copied is illuminated and scanned by a moving lens. The document’s image is projected onto the moving drum surface.
The third step is called development. In this stage, the drum is shown a mixture of toner and carrier particles. These two types of particles then join together to form visible images on the drum.
The fourth step of the process is called transfer. During this stage, paper is transported between the drum and the transfer corona. The toner image is transferred from the drum to the paper using pressure.
The fifth step of the process is called separation. This stage is where the electric charges left on the paper are neutralized. At this point, the paper separates from the drum and sometimes the paper does not have the completed image.
The sixth step of the process is called fixing. This is where the toner image is fixed permanently to the paper through the use of heat.
The seventh step is called cleaning. The drum surface is cleaned by a small brush that removes excess toner. At this point, the excess toner is either returned to the unit for reuse, or moved to a waste compartment for later removal, depending on the model.