Brother DCP-6690CW, Service Manual, Page: 66 / 506

3-12 Confidential
[ 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.
- Lower power consumption
- Lower noise levels
- Lower vibration
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, this machine automatically replaces the ink supply path
contents with fresh ink using an initial purge, a repeat of this priming operation.
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 print head, 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.