It is an impact printer in which, the printhead contains a row of pins (short hard wire). These pins trigger in patterns to form letters and numbers as the printhead moves across the paper. The moving portion of the printer is called the print head, and when running the printer generally prints one line of text at a time. Early printers had 9-pin and now 24-pin printers are used. They can be highly durable.
Features – Their image quality is poor compared to other printers and the default quality is draft quality which is good text prints. But with advancements 9-pin printhead upgraded to 17-pin and 24-pin thus print quality improved to near letter quality (NLQ) which is similar to typewriter output. They are noisy and their print speed is fast (typically in the range of 36 to 72cps) and some can print to a page per second. They can use multipart forms and are suitable for text printing.
Print process – The pins in the printhead are wrapped with coils of wire and are held by a combination of a small magnet and a spring. To use a specific pin, the printer controller sends a signal to the printhead, which energizes the wires around the print wire of specific print pin and then the print pin is repelled against the ink ribbon and making a dot on the paper. The arrangement of the dots in columns and rows creates the letters and numbers on the page.
As shown in the image above, paper is fed to the printer by paper feed roller and moved before the print head with the help of paper drive roller and other feed rollers. Paper presence or exit is sensed with the help of paper exit sensor present in the back. Platen or platen is pressed against paper to cause an impression by the print head.