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Photocopier

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A photocopier is a machine designed to make copies of documents or visual images. It can produce these copies onto paper or plastic film very quickly and cheaply. While many different technologies exist, most modern office machines use a process called xerography. This is a dry method that relies on electrostatic charges to function.

Xerographic photocopy process en
Xerographic photocopy process en

Because they are efficient, photocopiers are essential tools in business, education, and government sectors. Even as digital document storage grows, these machines remain widely used around the world.

To understand xerography, we must look at the specific steps of the mechanism. First, a cylindrical drum is given an electrostatic charge by a high-voltage wire. This wire is called a corona wire, or sometimes a charge roller is used. The drum is coated with a photoconductor, which is a semiconductor material. A photoconductor becomes conductive, or able to carry electricity, only when it is exposed to light.

Xerographic photocopy process en
Xerographic photocopy process en

This property is the foundation for how the image is formed.

Next, the machine performs the exposure step. A bright lamp illuminates the original document being copied. The white areas of the document reflect this light onto the surface of the photoconductive drum. When light hits the drum, those specific areas become conductive and discharge to the ground. However, the dark areas of the original document do not reflect much light. These dark areas remain negatively charged on the drum surface.

Once the charge pattern is set, the machine enters the developing stage. The machine applies toner, which is a fine powder, to the drum. This toner is positively charged. Because opposite charges attract, the positive toner sticks to the negatively charged areas of the drum. This is similar to how a balloon with a static charge can pick up small bits of paper.

Xerographic photocopy process en
Xerographic photocopy process en

This creates a visible image made of powder on the drum.

After the image is developed, the transfer and fusing steps occur. The toner image is moved from the drum onto a piece of paper. This works because the paper carries an even greater negative charge than the drum. Finally, the toner must be permanently attached to the page. The machine uses rollers that apply both heat and pressure to melt the toner. This process, called fusing, bonds the powder to the paper fibers so the image does not rub off.

The history of this invention began with Chester Carlson. Carlson was a patent attorney in New York who found copying papers to be a tedious and painful task. He began experimenting with photoconductivity in his own kitchen. In 1938, he applied for a patent for his "electrophotography" process. His first successful test used a zinc plate covered in sulfur. He used a microscope slide to create a mirror image of the words "10-22-38 Astoria."

Xerographic photocopy process en
Xerographic photocopy process en

Despite his success, Carlson struggled to find support for his idea. Between 1939 and 1944, over 20 companies rejected him. Large corporations like IBM and General Electric did not believe there was a market for copiers. Eventually, the Battelle Memorial Institute helped him refine the process. In 1947, the Haloid Corporation licensed the technology. They felt "electrophotography" was too difficult to remember, so they chose the term xerography. This name comes from Greek roots meaning "dry writing."

Fuji Xerox Document Centre 505 and Taiwan Xerox Walk-In 120D at ROC National Central Library 20101211
Fuji Xerox Document Centre 505 and Taiwan Xerox Walk-In 120D at ROC National Central Library 20101211

In 1949, the company introduced the Model A, the first xerographic copier. Haloid later became the Xerox Corporation in 1961. The company became so successful that people began using the word "xeroxing" as a verb. This made the brand a generic trademark in North America, though the company has fought to protect its name. Xerography was much more affordable than older methods. For example, in 1969, a Verifax print cost $0.15, while a Xerox print cost only $0.03.

Fuji Xerox Document Centre 505 and Taiwan Xerox Walk-In 120D at ROC National Central Library 20101211
Fuji Xerox Document Centre 505 and Taiwan Xerox Walk-In 120D at ROC National Central Library 20101211

Modern machines have evolved into highly complex devices. Many are now multi-function printers that combine copying, faxing, scanning, and printing. Digital technology has replaced older analog systems in many models. Digital copiers act as integrated scanners and laser printers. They offer features like automatic digital collation, which saves time. A digital copier can scan a page once and then print it many times automatically.

DADF (Canon IR6000)
DADF (Canon IR6000)

Some machines also include an ADF, or Duplex Automatic Document Feeder, to handle many pages at once.

DADF (Canon IR6000)
DADF (Canon IR6000)
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File:Fuji Xerox Document Centre 505 and Taiwan Xerox Walk-In 120D at ROC National Central Library 20101211.jpg
Fuji Xerox Document Centre 505 and Taiwan...
File:DADF (Canon IR6000).JPG
DADF (Canon IR6000).JPG
File:Xerographic photocopy process en.svg
Xerographic photocopy process en.svg
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