2 ] Features - Brother MFC620CN Service Manual

[ 2 ] Features
A distinct feature of this machine is the use of ink supply tubes between the ink cartridges and the
head/carriage unit. Relieving the head/carriage unit of the task of carrying heavy ink cartridges
back and forth across the page, the approach generally adopted by other ink-jet printers, offers the
following advantages.
- Smaller unit size--lower height, in particular
- Lower power consumption
- Lower noise levels
During print operation, the ink-jet mechanism inside the head/carriage unit sprays ink droplets from
the head nozzles. The loss of this ink from the head produces a negative pressure that replenishes
the head with ink from the ink tank through the supply tubes.
Note, however, that the above ink flow is only possible when the ink supply tubes are full of ink.
The factory therefore primes the ink supply path by applying strong suction to the head nozzles
with the maintenance unit to suck both air and ink through the ink supply tubes.
Leaving too long interval between this priming and actual use, however, risks air bubbles,
increased viscosity, and other quality issues with the ink in the supply tubes. Before using this
machine for the first time, therefore, the user must totally replace the ink supply path contents with
fresh ink using an initial purge, a repeat of this priming operation. The cartridges that ship with the
machine contain just that amount of ink extra over the ones sold as consumables.
When the machine is on standby, a constant negative pressure (which is produced according to the
difference in height between the head/carriage unit and ink cartridges) is applied to the rear of the
head/carriage unit, thus preventing ink from leading out of those nozzles.
NOTE: The above applies only as long as this machine rests on a horizontal surface. Standing this
machine on end or even just tilting it backwards with the print head uncapped risks overcoming this
slight negative pressure preventing ink leakage from the head nozzles.
Piezoelectric ceramic actuators inside the print head convert this ink to droplets sprayed onto the
paper. For further details, see "[ 3 ] Head/carriage unit" below.
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