Dot matrix printers, also known as line printers, are generally used in more industrial or stores environments where quality isn't necessarily top of the agenda. They are by far the most robust of printers and are able to print on multi-part or carbon copy stationery using pre-printed "tractor-feed" paper. This technology is typically very noisy although sound dampening cabinets are available for office installations.
How it works
A Dot Matrix image is made up of exactly that, a matrix of dots to create more often than not alphanumeric characters, to form words and numbers. Dot Matrix printheads typically come in 9, 18 or 24 pin versions. The higher the number of pins in a printhead, the higher the resolution or quality.
The image is formed by the pins or dots in the printhead being fired onto a ribbon impregnated with ink which in turn leaves a mark on the paper. The printhead moves horizontally along the paper, before feeding the paper up to move onto the next line, very similar to the way in which an old typewriter would work.
The image or text can be enhanced by placing dots closer together or by overlapping them, this is the same way that a laser printer enhances the printed image. The more dots you can lay down, the better the image will look to the human eye. The pins in the printhead are pushed onto the ribbon impregnated with ink, leaving a dot on the page.
Print head technologies
There are two ways to physically make the pin fire into the ribbon, the first uses an electromagnetic field to fire the pin. In the second one a magnet holds the pins in a ready position, and an electromagnetic field releases the pin for firing. As a rule, the permanent magnet print heads are faster as the pin is already in the ready position. They also tend to be used in more heavy duty printers.
As the print head moves across the page the print controller sends electric signals controlling which wires strike against the inked ribbon, to create the image on the page.
by Andy Leighton