Laser Printers

Laser printers are the current favorite form of office printer. These printers work on principles similar to those of photocopiers. They also traditionally require a fair amount of computing power in the printer itself, although some recent models change this fact.

Basic Laser Printer Technology

Laser printing centers on the printer's drum, which is a light-sensitive cylinder. A laser printer imparts an electrostatic charge on the drum. When exposed to light, the drum's electrostatic charge changes. A laser and mirror assembly "paints" an image of the document to be printed on the drum, which simultaneously rotates. As the drum rotates, it's brought near a reservoir of toner, which is a static-sensitive plastic powder. The toner sticks to the drum in the areas that have been struck by the laser's light. Further rotation of the drum brings it into contact with paper, which has also been charged, so the toner is drawn from the drum onto the paper. The paper is then heated in a fuser assembly to a high-enough temperature to melt the toner, which quickly cools and sticks to the paper. Additional components then return the drum surface to its original state, and the process begins again. Figure 20.1 illustrates this process.

Chapter 20

Roller

Figure 20.1

A laser printer's innards use a number of precision components operating in concert to produce a legible image.

Roller

Figure 20.1

A laser printer's innards use a number of precision components operating in concert to produce a legible image.

A variant on the laser printer is the LED printer, which uses a bank of light emitting diodes (LEDs) in place of the laser and mirror shown in Figure 20.1. Aside from anything having to do with lasers, everything I write in this chapter about laser printers applies to LED printers, as well. In fact, many people refer to LED printers as laser printers, despite the fact that there's no laser in an LED printer. The term page printer is sometimes used to refer to both types of printer.

Most laser printers include the drum assembly in a sealed package along with the toner. Because the drum eventually wears out, this arrangement allows for easy replacement of the drum when the toner runs out. Other models have separate drum units and toner supplies. With these, the drum is typically designed to last longer, but it's more expensive than the drum/toner units of other models. When you compute the estimated operating costs of a laser printer, be sure to consider both the toner and (if it's separate) drum cartridges.

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