Types of Impact Printers

Impact printers outnumbered inkjet and laser printers until the 1990s. An impact printer produces a printed character by striking a moulded letter made of plastic or metal against paper via an inked ribbon. In commercial data processing, personal desktop printing, and early forms of word processing, impact printing was widely used. Because the impressions were strong enough to penetrate several layers of paper, the method was ideal for multipart forms used in business and government.

Dot Matrix
The print head of a dot matrix printer projects the tips of nine wires, forming a vertical column of dots. An electronic mechanism pushes the wires out with precision timing as the print head scans a page. The wire tips make contact with a ribbon, which makes horizontal patterns of dots that form letters, numerals, lines, and other characters. The mechanism can produce simple graphics such as line drawings and bar codes because the printer can control the placement of individual dots. Dot matrix printers make a shrill buzzing noise; they are not suitable for quiet environments unless they have a sound-deadening case.

Chain
A chain printer is made up of a series of metal characters and numbers that are arranged in a continuous loop, similar to the blade of a chainsaw. A row of hammers strikes the characters as they move around the chain behind the paper. The chain mechanism can print several hundred lines per minute, which is faster than a dot matrix. Because it is more complicated mechanically, the chain printer is also more expensive than a dot matrix printer. Its character set is limited to whatever is on the chain; graphics created with a chain printer are at best crude. A chain printer, like a dot matrix printer, is somewhat noisy.

Daisy Wheel
Daisy wheel printers are roughly the size of a typewriter and were used as early typewriter substitutes. The print mechanism employs a collection of moulded characters arranged around the circumference of a circle; each letter is attached to the end of a thin metal or plastic stalk, resembling the petals of a daisy. A mechanism moves the daisy wheel across the page, causing the wheel to rotate and move the appropriate letters into place as an electric hammer strikes the character. The daisy wheels were designed by printer manufacturers to be replaceable; by changing the wheel, you could print with characters from different fonts. Daisy wheel printers are quieter than other types of impact printers, though some clatter is still produced.

Drum
Drum printers and chain printers share features and print at high speeds. Raised characters have been formed into the surface of a metal drum the size of a baker’s rolling pin. Electric hammers strike the paper as it rotates, forcing it against a ribbon that sits between the paper and the drum. The print drum is quieter than a chain because it makes no noise as it rotates, as opposed to the clatter that a chain makes as it spins. It prints only the characters on the drum, just like the chain printer.