Technical Description: Printhead
Issue 2
49
Part No. 306-0430-102
Construction
The printhead consists of a chassis on which are mounted the following components:
•
The nozzle assembly (
4
) which forms the ink into a stream of droplets as described below:
The jet valve (
17
) delivers ink from the ink system to the nozzle assembly.
The bleed valve (
18
) mounted on the heater module block is normally closed, only opening during
purging, flushing of the nozzle and start up and shutdown.
The bleed valve when energised removes air from the feed and return pipework and the nozzle when
being purged.
A vacuum is also applied through the bleed valve to the nozzle during a nozzle flush.
The ceramic transducer (
11
) is fed with a modulation signal. The transducer causes the nozzle assembly
to vibrate along its length so that the ink stream from the nozzle jet orifice is formed into individual
droplets.
The nozzle jet orifice (
12
) has a diameter of 60 microns.
•
The Light Emitting Diode (LED) (
13
) is located behind the charge electrode (
3
). The LED is strobed at the
modulation frequency so that the position of individual droplets can be observed with a magnifying glass
(x10 minimum). The charge electrode applies an electrical charge to each individual ink droplet. The charge
applied to the droplet is variable and affects the position of the droplet on the substrate.
•
The phase detector (
2
) senses the strength of the electrical charge applied to the ink droplets and adjusts
the charge pulse timing accordingly.
•
The ground potential deflector electrode (
1
) and the high voltage deflector electrode (
14
) are parallel
rectangular plates. The deflector electrodes generate a constant electrostatic field through which the
electrically charged ink droplets pass. The charged ink droplets are deflected by the electrodes, the amount
of deflection is dependent on the charge applied to the ink droplet.
•
The gutter (
15
) is the return path for ink droplets which are not used for printing. The gutter delivers the ink
back to the ink system.
•
The front cover (
16
) is secured to the printhead by a knurled screw (
6
). The front cover protects the
printhead components. Removal of the cover is sensed by the printer via the cover switch (
5
). When the
cover is removed the voltage to the deflector electrodes is turned off.
•
The rear cover (
7
) protects the printhead internal electrical wiring and ink system tubing.
•
The umbilical (
9
) contains the electrical wiring and ink system tubing from the printer.
•
The head heater (
8
) maintains the temperature of the ink; it consists of a heating element and a temperature
sensor.
•
The jet valve (
17
) is mounted on the heater module block. It is open while printing and during the flushing
cycle, but closes when the printer stops to prevent leakage from the nozzle.
•
The gutter detect (
10
) senses when ink is present in the gutter. It’s ink feed tubes are metallic and a signal
is fed to one of them. A signal return lead is connected to the other. When ink (which is conductive) is
present, the signal passes through it to the return lead. The gutter detect signal is then fed, via the umbilical,
to the I/O board in the electronics system.
A wiring diagram for the printhead electrical and ink systems is shown in Figure 19.
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