A line matrix printer is a type of computer printer that is frequently used in office and accounting environments where a large amount of printing is required, taking advantage of the speed of line matrix printer technology. The mechanism a line matrix printer uses is similar to a dot matrix printer in that several dots are used to form completed letters or graphics, although hammers are used instead of small pins. The hammers print to a page by pressing against an ink ribbon similar to a typewriter ribbon, transferring the ink to the target page. Many printers have the capacity to hold wide sheets of continuous-feed paper that are more convenient for printing large reports, although the paper must be calibrated when initially fed into the machine and can cause problems if the paper shifts during printing. In addition to text and other standard print symbols, the printer is capable of producing graphics, although the mechanics of the system limit them to black and white images.
The way a line matrix printer works involves an array of small hammers that are set inside a device known as a shuttle. The shuttle is very wide, usually only a little smaller than the maximum paper width that the machine can accept. Magnets inside the shuttle lock each of the hammers in place, with the bottom of the hammer tensely loaded against a spring-like device. When a hammer needs to make a dot on a paper during printing, the hammer is released from the magnetic field and shoots forward until it strikes the paper. Once the mark has been made, the magnet is reactivated and the hammer returns to its locked position, ready to be fired again.
The wide shuttle of a line matrix printer does not sweep from one side of the page to the other as a dot matrix shuttle might do, but instead only moves a short distance, because it is almost as horizontally wide as a full page. The multiple hammers can fire, several at a time, to quickly create a line of dots. As each line is finished, the page automatically is fed upward by one row of dots and the printing resumes. Dots are used to form letters and symbols, and these same dots can be used to create black and white graphics on a page. The fact that a physical, impact printing method is used also means that forms that use carbon to make multiple copies can be used in a line matrix printer.