• Choose a category
• All
• Classic-Fiction

The printer must also be electrically cleaned. One or more erase lamps bombard the surface of the drum with the appropriate wavelengths of light, causing the surface particles to discharge into the grounded drum. After the cleaning process, the drum should be completely free of toner and have a neutral charge.

Charge the Drum

To make the drum receptive to new images, it must be charged (Figure 22-13). Using the primary corona wire, a uniform negative charge is applied to the entire surface of the drum (usually between ~600 and ~1000 volts).

Write and Develop the Image

A laser is used to write a positive image on the surface of the drum. Every particle on the drum hit by the laser releases most of its negative charge into the drum. Those particles with a lesser negative charge are positively charged relative to the toner particles and attracts them, creating a developed image (Figure 22-14).

Figure 22-13 Charging the drum with a uniform negative charge

Figure 22-14 Writing the image and applying the toner

Transfer the Image

The printer must transfer the image from the drum onto the paper. The transfer corona gives the paper a positive charge; then the negatively charged toner particles leap from the drum to the paper. At this point, the particles are merely resting on the paper and must still be permanently fused to the paper.

Fuse the Image

The particles have been attracted to the paper because of the paper’s positive charge, but if the process stopped here, the toner particles would fall off the page as soon as you lift it. Because the toner particles are mostly composed of plastic, they can be melted to the page. Two rollers—a heated roller coated in a nonstick material and a pressure roller—melt the toner to the paper, permanently affixing it.

* * *

CAUTION The heated roller produces enough heat to melt some types of plastic media, particularly overhead transparency materials. This could damage your laser printer (and void your warranty), so make sure you’re printing on transparencies designed for laser printers!

Finally, a static charge eliminator removes the paper’s positive charge (Figure 22-15). Once the page is complete, the printer ejects the printed copy and the process begins again with the physical and electrical cleaning of the printer.

Figure 22-15 Transferring the image to the paper and fusing the final image

* * *

NOTE Color laser printers use four different colors of toner (cyan, magenta, yellow, and black) to create their printouts. Most models put each page through four different passes, adding one color at each pass to create the needed results, while others place all the colors onto a special belt and then transfer them to the page in one pass. In some cases, the printer uses four separate toner cartridges and four lasers for the four toner colors, and in others the printer simply lays down one color after the other on the same drum, cleaning after each of four passes per page.

The Electronic Side of the Process

When you click the Print button in an application, several things happen. First, the CPU processes your request and sends a print job to an area of memory called the print spooler. The print spooler enables you to queue up multiple print jobs that the printer will handle sequentially. Next, Windows sends the first print job to the printer. That’s your first potential bottleneck—if it’s a big job, the OS has to dole out a piece at a time and you’ll see the little printer icon in the notification area at the bottom right of your screen. Once the printer icon goes away, you know the print queue is empty—all jobs have gone to the printer.

Once the printer receives some or all of a print job, the hardware of the printer takes over and processes the image. That’s your second potential bottleneck and has multiple components.

Raster Images

Impact printers transfer data to the printer one character or one line at a time, whereas laser printers transfer entire pages at a time to the printer. A laser printer generates a raster