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
). Such a print head has a number of print wires
) 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
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.