The A+ Certification & PC Repair Handbook (Charles River Media Networking/Security)

A dot matrix printer is a form of impact printer whose technology closely resembles that of a typewriter. They have survived based on their ability to print multiple-part forms and because of their paper-feeding capabilities. It is common to find dot matrix printers in stores, doctors’ offices, banks, and any other location where multiple-part paper forms and receipts are needed.

Dot matrix printers contain their own print buffer. This buffer is a storage location for the information to be printed after it is sent from the CPU. After the information has been sent to the dot matrix print buffer, the printer’s processor calculates the best approach to printing the lines and characters needed, and makes adjustments to the paper feeders if necessary.

The dot matrix printer has a magnetic print head that contains either 9 or 24 pins. A 24-pin print head is used to print letter-quality pages. A 9-pin print head is used for draft quality. Each of the pins on the print head has its own solenoid, spring, and coil. A dot matrix printer uses a series of dots per inch (dpi) to form an image, symbol, character, or number. When the printer processor receives enough information from the print buffer to begin printing, a signal is sent to the magnetic print head. A combination of events takes place, and the pins attached to the print head hit an ink ribbon, which is held in place by a platen, that is between the pins and the paper. After the pin has applied its dot, it is pulled back, and the next pin applies its dot. This process repeats until a character is complete. All of this happens very quickly. The friction caused by the constant movement of the print head can make it get extremely hot. When working on a dot matrix printer, never touch the print head until it has time to cool down. Dot matrix printer speeds are measured in printed Characters Per Second (cps). Characters-per-second speeds differ based on print quality and manufacturer. Dot matrix printers are capable of up to 500 cps.

Dot matrix printers use either a pressure roller or tractor-feed method of pulling continuous-form paper through the printer one line at a time. The continuous use of a dot matrix printer without proper maintenance can cause the tractor-feed rollers and platen to become misaligned. This commonly results in ink fading as it is applied from left to right or uneven lines of output across the paper. Lack of proper maintenance can also result in constant paper jams. Use a can of compressed air regularly to spray out any loose particles around the tractor rollers. Rubber-cleaning solutions should be used to clean the tractor belts and rollers.

Ink-jet printers are a very popular type of printer, and are used in many homes and small businesses. Ink-jet technology is typically faster than dot matrix, but not as fast as the average laser printer. Its main benefits are its affordability and ease of maintenance compared to laser printer technology.

Ink-jet printers use a type of print head that houses many tiny nozzles, sometimes referred to as jets. These jets spray or drop fast-drying ink into a condensed area to form the tiny dots that make up a character. A thermal resistor actually heats up the ink until it expands and is eventually forced out of the print nozzle in the form of a bubble or droplet. The ink bubble is then sprayed or dropped onto paper. The ink droplets can tend to smear or splatter when they hit the paper, which causes the dot created on the paper to become somewhat distorted. To refine this process, the thermal resistor bubble-creation process was replaced with piezoelectric crystal. The piezoelectric process uses crystals that react to electric charge. When charged, a crystal draws or pulls ink from an ink storage unit held above the crystal. In simple terms, the piezoelectric process can cut or refine the exact amount of ink needed to refine the dot placed on paper. This reduces the smudging effect of traditional ink-jet technology and provides better printer resolution. In fact, this process allows resolutions greater than 1440 dpi.

Ink-jet printers accept paper one sheet at a time. This process, called single-sheet form feed, involves pulling paper into the printer with rollers. The paper is aligned under a print mechanism that moves across the paper to apply an image.

If sheets of paper connected into one long sheet are placed in printer guides with plastic teeth, the printer is said to be a continuous form-feed printer. Ink-jet printers use single-sheet form feed technology. Dot matrix printers use the continuous form-feed process.