Impact printers are one of the earliest types of hard copy output devices used with computers. These printers, so named because of the physical impact they make with the printing surface, function by physically striking the surface to be printed, much like a traditional typewriter would do. The three primary types of impact printers are: dot matrix printers, which print one character at a time using an adjustable-pin print head; daisy wheel printers, which rotate a wheel containing every printable character to the appropriate position before striking the paper; and line printers, which print an entire line of text--rather than a single character--at a time.
Impact Printers Physically Hit The Paper
Impact Printers Use Magnets
To facilitate the high-speed impacts necessary to generate an impact print, printers use a small form of electromagnet to operate their movable print heads. Impact printers feature either a combination of pins that can move toward the print surface or, as is the case with a daisy wheel printer, a wheel that can spin to access the desired character. Dot matrix and line printers work with similar technology; when the printer receives data, a logic board on the printer interprets the data and generates a series of electrical impulses. These impulses travel to the print head, where an electromagnet converts them to physical movement of a print head; the print head moves a series of pins--ranging from 9 to 24 on a dot matrix printer and 9 to 24 pins per character on a line printer--toward the paper. Each of the pins creates a small dot on the paper that, when combined with the other dots generated by the print head, forms the shape of a letter. Daisy wheel printers use similar technology, but use the electromagnets to first spin a wheel to the appropriate printable character before sending the character toward the print surface.
Impact Printers Use Ribbon
Except in the case of sensitive carbon paper, the impact of a printer's pins are rarely sufficient to generate permanent, readable text on a printing surface. To augment the printing process and leave a more readily apparent mark on the paper, impact printers insert an ink-covered ribbon between the print head and the paper. When the print head touches the paper, the impact transfers a small amount of ink from the ribbon to the paper. This process helps ensure the document produced is readable for some time to come, though the ribbon itself is prone to being used up (especially in high-volume printing environments).
Impact Printers Are Becoming Obsolete
Impact printers work in a considerably different fashion from modern consumer-grade ink jet or laser printers. While an ink jet printer creates output by squirting tiny dots of ink onto paper and laser printers work by heating toner to be burned onto the paper, the need for impact printers to make physical contact with the paper makes them considerably louder and somewhat slower. The exception, however, are line printers; still in use in low-quality printing environments where noise is not a consideration (such as corporate billing centers), these printers produce a high volume of output very quickly and with only minimal maintenance.