10.05.2019 Photocopiers

Artwork courtesy of U.S. Patent and Trademark Office: Chester Carlson’s 

original photocopier from his patent granted on Sept. 12, 1944.

This week we had some issues with one of the copiers at the news office and it brought up some questions about how copiers work, and why sometimes they don’t. The photocopier has been around for longer than you might believe. Chester Carlson used his kitchen for “electrophotography” experiments, and in 1938, applied to patent the process. He used a zinc plate covered with sulfur to produce the first photocopy.

Carlson attempted to sell his patent to 20 different companies from 1939-1944, before Battelle Memorial institute assisted him in refining the process. In 1947, Haloid Corporation obtained the first license to develop, produce, and market a copying machine based on this technology. Haloid felt the word “electrophotography” was too complicated and hard to remember. They changed the term to xerography with was Greek for “dry writing.” The new machines were called “Xerox Machines” and in 1948, the word “Xerox” was trademarked. Haloid eventually changed its name to Xerox Corporation.

Enough about the history, now let’s get into how this thing works. Xerography works off basic principles of light and electricity. The first thing you must understand to grasp how photocopiers work is, “Light is a kind of electricity.” Light is just an electromagnetic wave traveling through space. Inside a photocopier is a device that allows current to flow through it when light shines on it. This device is called a photoconductor and it is used to capture the pattern of the light as a pattern of static electricity. Areas that are light will get an electrical charge and dark areas will get a no charge, making an electrical copy of the page.

The numbers in this section refer to the numbers in the drawing. Suppose you are trying to copy a page of this newspaper. If you shine an extremely bright light (52) at the paper (90), at the perfect angle, you will create a shadow of the paper on another object (41). In the case of a photocopier, that shadow is created on a photoconductive drum (41). The drum is then sprinkled with powdered ink which sticks to the charged areas on the drum. A piece of blank paper is pressed against the drum, transferring the ink powder to the paper (76). The paper now has a copy of the original document.

There is one more step in the process. The powdered ink must be bonded to the paper. This happens with combined heat and pressure in the fuser unit (72) of the copier. Sometimes the still warm copy comes out of the copier with enough static electric charge still on it that it will stick to your shirt, or the wall.  A very interesting thing happens when a fuser unit fails on a copier. You will see a perfect copy come out of the paper tray, and as soon as you pick it up, all the ink falls off onto the floor as powder. 

If you are looking for a full explanation of how the process works, you can read Carlson’s full patent; though technical in nature, it is fairly easy to understand. You can find his patent at https://patents.google.com/patent/US2297691.