Thread: Laser Printer Operation

The printer receives the document in form of file. This file is generated by the application that actually issues the print command to the printer. This file is nothing but logical image of the document and such an image is quite essential to guide the printer for accurate printing. At initial stage of the printing, a light sensitive drum is given a positive charge with the help of a wire and the drum starts revolving. This wire is known as corona wire.

As the drum starts revolving, the printer shines a laser beam on the surface of drum to create some discharge points. In this way laser draws the letters and images to be printed as pattern of electrical charges. In order to draw the pattern on drum, the laser receives the page data (tiny dots that make up text and images) one horizontal line at a time. Also, the laser does not move the beam itself instead it emits the beam on a movable mirror. The mirror moves and shines the beam through series of lenses on the surface of the drum.



After the pattern is set, the printer coats the negatively charge surface of the drum with toner - a type of fine black powder. Since the toner is positively charged, it sticks only on negative discharged points on the drum. It is something like writing some words on the wall with glue and then rolling over some color powder on the words. The powder sticks to the glue-coated part of the wall and you end up with words written on the wall with powder.

With powder pattern attach, the drum rolls over the sheet of paper coming from paper tray. This paper sheet is positively charged. The positive charge is strong enough to attract the negatively charged toner particles from the drum. The toner particles leave the drum and go onto the paper. At this point, the Image is on the paper; however, the particles are held only by their opposite charge.

The printer passes the pages through the [user, a pair of heated rollers. As the paper passes through these rollers, the loose toner powder melts, fusing with the fibers in the paper. The fuser rolls the paper to the output tray and you have the finished page. The fuser also heats up the paper itself, which is why pages are always hot when they come out of a laser printer.

Lastly, the drum is cleaned to remove any toner particles left on its. Then the drum surface passes the discharge lamp. The bright light of the lamp exposes the entire surface of the drum, erasing the pattern of electric charges. Then corona wire reapplies the positive charge to the drum, making drum ready for next printing job.

Various manufacturers of laser printers categorize the working of laser printer that we just discused, in six steps. As a good technician, you must be familiar with these steps.

Conditioning: The drum is prepared for use and corona wire passes electric charge to the drum.

Writing: The laser beam and movable lens together write an image of document on the surface of drum. The image on the drum is nothing more than dots of electric charge and is invisible at this point.

Developing: During this step, the toner (fine black powder) is applied on the surfa'ce of the drum. The document image turns into black.

Transferring: The image transfers to the paper. The toner particles leave the drum and go onto the paper.

Fusing: The toner particles are melted on the surface of paper and attached permanently with the fibers of paper. This is done by passing the paper, with toner particles clinging to it, from fuser roller which applies heat and pressure on paper.

Cleaning: In this last step. toner is cleaned from the drum and then an erase or discharge lamp is focused on drum to neutralize any electric charge left on the drum.