Table 4-1 Laser-Printing Process

Step	Details of Each Step	Mnemonic
1.	Processing	The printer receives page, font, text, and graph-	Proper
		ics data from the printer driver and creates a page
		image.
2.	Conditioning	Puts uniform charge of –600 VDC. This phase is	Californian
		also called charging.
3.	Exposing (formerly	Laser traces the image on the charged drum and	Elephants
referred to as Writing)	changes the voltage to –100 VDC in those areas
		the laser touched.
4.	Developing	Negatively charged toner is applied to the drum	Dance
		and sticks to the areas with altered voltage.

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Table 4-1 Continued

Step	Details of Each Step	Mnemonic
5.	Transferring	The secondary corona wire or roller charges the	The
		paper. The toner is statically attracted to the paper.
6.	Fusing	Rollers melt the toner and embed it into the paper.	Fandango
7.	Cleaning	The drum is cleaned by a wiper or in some cases	Cleverly
		an electrical charge can drop excess toner from
		the drum.

 

 

Some all-in-one (multifunction) printer/scanner/copier devices use laser-printer engines and are configured for printing the same way as a printer is.

 

Figure 4-1 provides an “inside” view of a typical monochrome laser printer and its components.

 

 

Paper feed direction

Paper path

 

 

	Fold-down
	output tray

2 3

 

 

 

5

 

6

 

 

Pickup rollers

 

Figure 4-1 A typical monochrome laser printer’s components.

 

 

A color laser printer works in a somewhat similar fashion, but uses four toner cartridges and a transfer belt to transfer toner (see Figure 4-2).

Chapter 4: Printers 83

 

Paper path	Cleaning
unit
Fusing rollers	Waste toner

Toner particles

 

OPC Belt

 

Transfer
roller
Imaging drum	Erase lamp		Laser
Paper pickup				Cleaning	Charger	Laser mirror
			blade
Paper in paper tray

 

Figure 4-2 A typical color laser printer’s components.

 

 

Keep in mind that laser printers are page printers; the entire page must fit into the printer’s mem-ory. Laser printers can use page-compression techniques to help complex pages (graphics, many fonts) to fit into the printer’s memory, but if printing a page produces an error, you can typically reduce the resolution of graphics on the page through the printer properties sheet’s Advanced Options dialog (see Figure 4-3).

 

 

Figure 4-3 Reducing graphics resolution to enable a complex page to print.

84 CompTIA A+ Quick Reference

 

Inkjet

 

Inkjet printers include either thermal or piezoelectric nozzles:

 

Thermal nozzles boil the ink and jets of steamed ink shoot onto the paper. Thermal inkjet printers’ ink cartridges also include the print head.

 

Piezoelectric nozzles energize crystals that vibrate and control ink flow. Piezoelectric noz-zles are built in to the printer and the ink cartridges snap into the built-in print heads.

 

Both types of inkjet printers use at least four ink colors: Cyan, Magenta, Yellow, and blacK (hence the initials CMYK for this color model). Some printers optimized for photo printing add additional color inks or might have interchangeable blank inks for text and black-and-white photo printing.

 

The inkjet print process is as follows:

 

1. A feed mechanism loads paper into the printer by means of a roller.

2. The print head moves into position by means of a carriage bar across the width of the paper and a belt that moves the print head along the carriage.

3. Under command from the printer driver, ink is deposited on the paper to create letters and shapes as the paper is moved through the printer.

4. If the printer contains a duplexer and the print job calls for two-sided printing, the paper is reversed and the print job continues on the reverse side.

5. The paper is ejected.

 

Figure 4-4 shows typical components of an inkjet printer optimized for photo and text printing.

 

Because a printed line or shape might require several passes of the print head, it is important to properly align the print head. Some printers perform this task automatically when the ink cartridg-es are replaced, whereas others can perform this task on demand.

 

To deal with clogged inkjet nozzles, it is sometimes necessary to run a self-cleaning utility. Both the alignment and the self-cleaning utilities are usually found in menus in the printer properties sheet. Figure 4-5 illustrates a typical maintenance menu with these and other options.

 

Most all-in-one (multifunction) printer/scanner/copier devices use inkjet printer engines and are configured for printing the same way as a printer is.

Chapter 4: Printers 85

 

1. Dust cover

2. LCD instruction panel

 

3. Control panel

 

4. Printhead drive belt

 

5. Output tray

 

6. Ink cartridges

 

7. Flash memory card reader

 

 

Figure 4-4 A typical inkjet printer with its cover open.

 

 

Figure 4-5 This printer’s maintenance menu offers options for print head cleaning, alignment, andchecking ink levels.

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Thermal

 

Thermal printers are used most often on point-of-sale systems to print receipts and other inex-pensive continuous feed outputs, such as those produced by EKGs, label makers, and old fax machines. Most thermal-print paper is roll paper, but a few portable printers for PCs use sheet-fed thermal paper. The print process works like this:

 

1. A feed mechanism loads paper into the printer.

2. The heating element heats the paper to form letters and shapes.

3. The paper is ejected.

 

Some older printers use a thermal-transfer method that uses plain paper and thermal ribbons to print. In this variation, the printer uses a print head and a ribbon instead of a full-width heating element.

 

Figure 4-6 illustrates direct-thermal and thermal-transfer printing technologies.

 

Printed areas on media	Thermal printhead
				Heat-sensitive media

Wax/resin

^Ribbon transfer material

 

Wax/resin transfer material transferred to media surface

 

Media

 

Figure 4-6 Direct-thermal (top) and thermal-transfer (bottom) printing technologies.

 

Impact Printer

 

Impact printers are primarily used for reporting, warehousing, and some types of point-of-sale use today. The print process for a dot-matrix printer (its rival, the daisy-wheel printer, is long obsolete) works this way:

Chapter 4: Printers 87

 

1. A tractor-feed mechanism pulls (or pushes) paper into place from the rear or bottom of the printer. Some printers can use single sheets of paper, but this usage is rare today.

2. A carriage and band mechanism is used to position the print head.

3. A series of fine wires in the print head (9-pin, 18-pin, and 24-pin) are fired by a solenoid to create letters and shapes that are transferred by a printer ribbon to the paper.

4. The feed mechanism pulls the paper through until it can be torn off.

 

Impact printers are measured in CPS, not PPM. Near letter quality (NLQ) is the best quality a dot-matrix printer can have. Impact printers can use carbon copy paper because the impact travels through to the carbon copies beneath the original paper.

 

Figure 4-7 illustrates a typical wide-carriage dot-matrix impact printer.

 

1. Rear cover (top cover removed, not shown)

2. Paper supports for tractor-feed paper path

3. Platen for using single sheets of paper

4. Manual paper advance knob

5. Paper bail lifter

 

6. Paper bail

 

7. Timing/drive belt

 

8. Printhead signal control cable

9. Printhead with heat sink

 

10. Ribbon holder

 

11. Printhead support rod

 

12. Head gap adjustment

 

13. Tractor/friction-feed selector lever

14. Tractor feed

 

Figure 4-7 Components of a typical dot-matrix impact printer; although this example is a wide-carriage model, printers that use standard-width paper are similar.