Tuesday, June 6, 2017

The Laser Printing Process

There are many different kinds of printers on the market. In office environments, laser printers are by far the most numerous. Not only do they produce good quality printouts, but they are fast, which is important when you have people to please and deadlines to meet. Therefore, computer technicians have to be very familiar with how laser printers work so breakdowns can be fixed and Janet can get her TPS reports on time.

A laser printer follows a specific process when printing a sheet of paper. The process can be divided into seven steps.

1. Processing

In order to start printing, the printer has to first receive print data from a computer. The program the user is printing from (say, a word processor) has to first convert the document to some kind of format the printer understands. Many Windows applications use a system called GDI (graphical device interface), which is used in conjunction with the specific printer driver, to generate this print data.

The application then sends the print data to the print spooler, which is responsible for queuing up print jobs and sending them one at a time to the printer. Once the print job has been completely sent to the printer, it disappears from the print spooler (whether the printer is done printing it or not).

Note that, while it is possible to cancel a print job from the print spooler, this only stops the flow of information from the computer to the printer. For example, if the spooler sends half of the print job before you cancel it, the printer will print exactly that, even if the job is canceled before any pages came out of the printer. Therefore, you should also press the “stop” button on the printer itself to be sure the printing truly stops (do not pull out the paper tray, as this could jam the printer).

2. Charging

The rest of this process is centered around an important part of the printer called the drum. The drum is a cylinder shaped component which is used to transfer images onto the sheets of paper.  It does this using positive and negative electrical charges.

In the Charging step, the primary corona wire (or primary charge roller) gives the drum's surface a uniform negative electrical charge.

3. Exposing

A laser draws a positively charged image into the drum (hence the name, “laser printer”).

4. Developing

Negatively-charged toner particles attach themselves to the positively-charged parts of the drum the laser drew from the last step. "Toner" is the stuff that makes up the image on the piece of paper (it is a laser printer's “ink”).

5. Transferring

Here is where the actual piece of paper comes into play. The transfer corona (or transfer roller) applies a positive charge to a sheet of paper. Then, the negatively-charged toner particles on the drum attach themselves to the positively-charged paper. Voila! The toner has been “transferred” to the page.

6. Fusing

At this point, the toner is simply resting on top of the page like a layer of dust. In the Fusing step, the toner is melted onto the page using a heating element called the fuser (toner is mostly made of plastic). Hot Pockets! The page is now done!

7. Cleaning

Now that the page is done, the printer has to be “reset” for the next page. Notably, the drum must be cleaned. First, any residual toner is scraped off using a rubber cleaning blade. Then, erase lamps give the drum a neutral charge. Go back to step 2.

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