There are several printer technologies used in today's home, office and banking printers.
Dot matrix printers, known also as
impact printers, represent the oldest printing technology, are still the widespread today, grace of it's best
cost per page ratio. Dot matrix printers are divided on two main groups:
serial dot matrix printers and
line dot matrix printers (or simply
line printers).
In serial dot matrix printers the characters are formed by the
print head (or
printhead). Such a print head has a number of
print wires (
pins) arranged in vertical columns and electro-magnetic mechanism able to shoot these wires.
There are two main printhead technologies - in the first one electromagnetic field shoots the print head's wire. In the second one, the so called permanent magnet printheads, a spring shoots the printhead wire and the magnetic field just holds the spring in stressed and ready to shoot position. When the electromagnetic field equalizes the magnetic field, the spring is released to shoot the wire. Both print head mechanisms are shown in action at the picture bellow.
Dot matrix printer head mechanisms in action:
Classical printhead mechanism is showed from the left side. The permanent magnet printer head mechanism you may see at right.
In general the permanent magnet printheads are faster and are used in
heavy-duty printers. Some of the most popular print
heads of this type are:
Epson DFX,
IBM 4226,
Fujitsu 5600 and 6400, and all Oki print heads.
How the serial dot matrix printers work?
As the printer head moves in horizontal direction, the printhead controller sends electrical signals which forces the appropriate wires to strike against the inked
ribbon, making
dots on the paper and forming the desired characters.
The most commonly used printer heads has 9 print wires in one column (
9-pin printheads) or 24 print wires in two columns (
24-pin printheads), for better print quality. In some heavy-duty dot matrix printers there are also used 18 wire print heads (
18-pin printheads) which have 2 columns, 9 wires in each.
The
printing process of a 9-pin printer head is shown at the picture bellow:
Serial 9-pin dot matrix printer in action
The distance between wires in column may give us the vertical
printing resolution. For example: 9 wire print head with distance 0.35 mm between adjacent wires will result in 25.4/0.35=72.5
dots/inch (
dots per inch DPI) vertical printing resolution for one pass printed line of characters. 24 wire print heads has 2 columns - 12 wires in each, with a vertical displacement of ½ step. So if the distance between adjacent wires is 0.21 mm, then one column will print with 25.4/0.21=120.9 dots/inch (DPI) vertical resolution, but since the second column print between the dots printed from the first one, the overall vertical resolution will be
240 DPI. Please note that the first
laser printers released on the market had the same resolution.
