How does a copier work?

You’ve probably used a photocopier lots of times; chances are you’re using it every day at your office. Perhaps you know a bit about various models, differences between various manufacturers or all the newest copier software developments, but do you know how the copier unit actually works? It’s a simple yet delicate and effective process that you might want to know about.

copier

The process of xerography was famously invented by Chester Carlson in 1938, and further perfected by the Xerox Corporation. It changed the way we handle and copy text as it could produce text and images on paper very fast and relatively cheap. Since Xerox came up with the first paper copiers, the term “Xerox machine” eventually started to denote even the photocopier machines my by other manufacturers, and people are often unaware that they are misusing Xerox’s trademark.

Chester Carlson

The inventor originally named the process electrophotography. It works thanks to two natural phenomena; materials of opposite electrical charges attract and certain materials, when exposed to light, become good conductors of electricity. By using these two phenomena Carlson designed a process consisting of six steps; a way to transfer an image from one surface to another. It begins with giving a photoconductive surface a positive electrical charge, and then exposing that surface to an image or a document. Since the sections which are illuminated (the blank, non-image areas of a paper) become more conductive, the charge will dissipate in the areas which are exposed. Then the negatively charged powder, which spread over the surface, will adhere to the positively charged area through electrostatic attractions; a sheet of paper is positively charged and placed over the powder image. The powder is attracted to the paper the moment it is separated from the photo conductor. The heat will then fuse the image to the paper and produce a copy of the original image.

Charge – Every laser printer or photocopier has a surface called the photoreceptor, which is light-sensitive and applied to a flexible drum or a belt. This surface consists of a very thin layer of  hotoconductive material. When kept in dark, the photoreceptor is insulating, but when exposed to light, it becomes conducting. This is done through adjacent wires which are charged with a high DC  voltage; this creates an electric field close to the wires, which causes the ionization of air molecules. As the ions of the same polarity as the voltage on the wires gather on the surface of the photoreceptor, an electric field is created.

This is why the process requires a source of light; it has to be powerful enough in order to boot electrons out of the photoconductive atoms. So, which wavelengths can do this? Most of the visible spectrum, actually, especially the green and the blue end, which have more than enough energy to initiate the process. Pioneers of this technology also avoided using UV light; although it had more than enough energy to create a photocopy, it may damage skin and eyes.

When the copier lamp is turned on, its movements inside the copier illuminate a single strip of a paper sheet at a time; the mirror which is attached to the lamp will direct the reflected light on the copier drum. Before the light reaches the drum, it will pass through a lens which allows copier users to focus on a copy of the image in a certain place; this is done so you can magnify or reduce the size of the original image/ document when you’re making a copy.

Expose – New digital copiers and printers use a scanning modulated laser or a LED image bar to expose the image to the photoreceptor. Old analogue models used the reflected light from an illuminated image, which was projected onto the receptor. Both methods selectively discharge the photoreceptor areas which are exposed to the light, which causes a reduction of the electric field, while the dark areas retain their charge.

Development – As you probably know, the pigmented powder used to develop an image is called toner. An amalgam of colorant and plastic resin, its tiny particles (between five micrometers in diameter) get mixed with magnetized carrier beads. The beads electrically charge the toner and transport it to the development part of the copier unit. There the toner particles get electrically charged, thanks to triboelectricity, or what is commonly known as static electricity. The electric field associated with the image’s charge will then exert a electrostatic force and adhere the charged toner to the image. When it comes to copying in color, there are usually four xerographic units which create black, yellow, magneta and cyan images separately, which are then positioned to form color copies.

Transfer – The image will then be transferred onto paper. The copier brings the paper close to the toner and applies an electric charge. The charge’s polarity must be opposite to that of the toner, and powerful enough to overpower the toner’s adhesion to the photoreceptor. Then the unit releases a second charge which will release the paper (with the image on it) from the photoreceptor.

Fusing – The toner is melted and sealed to the paper as the paper passes through a number of heated rollers. The roll will melt the toner, thus fusing it to the paper - with some help from the second roller, which applies pressure to ensure the toner is completely fused.

And finally, cleaning consists of removing the toner leftovers from the photocopier before the next cycle starts. This is necessary as the transfer of the toner from the receptor to a sheet of paper most often lefts some bits of toner behind. Virtually all modern copiers and printouts perform cleaning with a rotating brush cleaner.

Since Carlson made his first copy on October 22, 1938, the technology of photocopying has greatly evolved. The printers and copiers of today are a product of more than seventy years of constant perfectioning and exploring better ways to make a photocopy; and the best part is - this journey is far from over! Since photocopying is now an essential part of our lives, it is to be expected that the future will bring even more efficient ways and methods of photocopying.

 

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