DESCRIPTION
20509 Issue 7 Jan 2018 2-7
PRINT HEAD
Ink jet printing does not require contact with the print surface. It is therefore
particularly suitable for printing on rough, irregular, soft or other "difficult"
surfaces.
Macrojet 2 is a valve jet printer. Ink is maintained under pressure behind a
closed nozzle or valve. When the valve is opened for a short time, ink
emerges as a drop and is propelled by the pressure towards the print
surface or substrate. Drops are, therefore, only produced as required in
what is known as Drop-on-Demand printing.
Macrojet 2 print heads have either 7 or 16 nozzles producing a line of drops
called a stroke on the print surface. As the print surface moves past the
head, successive strokes containing different combinations of ink drops
build up the character in the form of a dot matrix. This is best understood
by studying the illustration below.
A dot matrix is specified by the number of dots in a stroke and the number
of strokes making up a single character (for example, the illustration shows
a 7x5 matrix).
The Macrojet print head has, at the front, a nozzle plate with either 7 or 16
nozzles. Ink is supplied under pressure to a manifold behind the nozzle
plate. A plunger, fitted with a rubber slug on its tip, is held against each
nozzle by a spring. The plunger is connected by a wire to a metal slug
sitting part of the way into a solenoid. When the solenoid is energised, the
slug is pulled into the centre of the solenoid. This pulls back the plunger,
opening the nozzle. When the solenoid is de-energised, the spring pushes
the plunger back to close the nozzle.
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