Ink Supply And Ink Jet Mechanism - Brother MFC4820C Service Manual

4.2.3.1

Ink supply and ink jet mechanism

The ink supply and ink jet mechanism is illustrated below. When the machine is first turned on
after shipment, it will carry out an initial purge in which the air pump & motor module and the
purge unit supply the print head unit with ink from the four ink cartridges (black, cyan, magenta,
and yellow) via the needle tubes.
When the machine is on standby, a constant negative pressure (which is produced according to the
difference in height between the print head unit and ink cartridges) is applied to the rear of the
print head unit. This is to keep the meniscus of ink (see the illustration below) in the head nozzles
(shown on page 4-14), thus preventing ink from leaking out of those nozzles. During an initial
purge or reset purge (refer to Section 4.2.3.3), however, the air pump & motor module applies a
positive pressure to the rear of the print head unit. Such pressure control is called "back-pressure
control."
NOTE: Since the negative pressure prevents the ink from leaking out of the print head unit, be
sure to place the machine in a horizontal position. If you place the machine upright or inclined
backwards with the print heads uncapped, ink may leak out of the nozzles.
Ink supplied to the print head unit will be jetted out through the head nozzles by the piezoelectric
ceramic actuators (refer to "[2] Structure of the print head unit" further on in this section). The ink
drops produced will be output as small dots on the paper.
Air pump &
motor module
Print head unit
Ink
Nozzle plate
Meniscus
(Free surface of ink which is
curved because of surface tension)
4 -1 2
Needle tubes
Ink cartridges