The extraordinary journey of an ordinary piece (of paper )
When
you push your laser printer ‘print’ button you trigger a sequence of events
that, together, partake of the magic. Technical descriptions can be boring. Why? Because
mechanical parts do not have a personality, they lack the spice that makes human events
interesting. However, if you pretend for a moment that mechanical parts have a character
or even a gender, then even a machine comes to life. The mechanical parts are now actors
playing to perfection (we hope) a skillful act. Mechanically inclined readers, please
forgive the rest of us who must season our understanding with the pepper of our
imagination.
The play opens with the paper starting the journey from the paper tray and disappearing into the secret chambers of your laser printer. Meanwhile parts of the cartridge are very busy at work in an act of superb synchronization. The cartridge drum begins to rotate and is first cleaned mechanically and electrically. The drum is designed to receive electric charges. Its outer layers are coated with Organic Photoconductive Material (OPM), that is material whose electric characteristics are sensitive to light. The Eraser Lamp first cleans the drum of any existing electrostatic charge. The Wiper Blade, meantime, cleans the drum of any residual toner. When the cleaning is done, the Cartridge Corona Wire turns on and applies a uniform NEGATIVE charge to the surface of the drum, very much like a painter applies a ‘wash’ to the canvas.
Once the wash is applied the drum is ready to receive the image. The laser beam is reflected off a rotating mirror and translates the digital image on the computer into a sequence of on/off instructions (as many as 30,000 per second). Wherever the laser beam hits the drum surface, that area becomes electrostatically POSITIVE. The computer image is ‘electrostatically’ reproduced on the drum surface.
Enter the toner. The toner (a mixture of plastic, sand, and rust) is electrostatically charged. The Developer Roller, which has a magnet at its core, attracts and increases the NEGATIVE charge of the toner. The DOCTOR BLADE, located just above the roller surface, lets just the correct amount of toner reach the drum surface. The electrostatic image, as we saw, is POSITIVE, the toner is NEGATIVE. The two are irresistibly attracted to each other and a visible IMAGE is formed on the drum surface.
Meanwhile the paper passes under the cartridge and over the MACHINE CORONA WIRE. The corona wire applies a very strong POSITIVE charge to the paper, stronger than the positive charge that originally attracted the toner to the drum. What does the toner do then? Irresistibly attracted by the positively charged paper it leaves the drum. The image is finally on paper, but it is not over yet. Don’t sneeze. The powdery toner is lying precariously over the paper surface. You can see this when a paper jam occurs and you need to remove the paper before the image is ‘fixed’.
The final act sees the paper being fed through the fuser assembly (located underneath the felt green cover that usually says "Warning - High Temperature’). The paper passes through two rollers one of which is heated to 300º F by a high intensity lamp, the other provides the pressure. Heat and pressure melt the toner onto the paper. The fuser wand has an oiled felt that lubricates the rollers and cleans the top roller of dust and powder.
The paper journey is nearing the end. The printed paper emerges from the fuser assembly.
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