Ink Cartridge Components And Their Main Roles; Disc Valve S; Disc Valve D; Sensor Arm - Brother MFC640CW Service Manual

Ink cartridge components and their main roles

- Disc valve S

A plastic needle in the refill base opens this valve to supply air to the ink cartridge. Removing
the ink cartridge closes this valve to prevent leakage due to ink backflow.

- Disc valve D

A plastic needle in the refill base opens this valve to allow ink to flow out of the ink cartridge.
Removing the ink cartridge closes this valve to prevent leakage.

- Sensor arm

This arm indicates the amount of ink remaining. Certain positions cut the light beam to the ink
cartridge sensor on the ink cartridge PCB inside the ink refill assembly.
Filled with ink
Ink cartridge
sensor
These ink cartridges are single-use affairs. There is no provision for refilling them. The design
reduces environment load by using no metals and only burnable materials yielding no toxic
substances.
Ink near-empty detection
The ink refill assembly has four ink cartridge sensors (photosensors of transparent type) that
monitor the ink levels with sensor arms inside the ink cartridges.
Attached to one end of the sensor arm is a float. When there is ink in the cartridge, buoyancy lifts
the float, rotating the sensor arm about a pivot near the center of the arm to block the light beam to
the sensor, indicating that there is ink. As the ink level in the ink cartridge drops, however, the float
falls, eventually moving the sensor arm out of the beam.
Light hitting the sensor is the signal that ink is running low ("Ink near-empty"), activating a
firmware counter tracking ink usage during ink-jet printing, purges, and other operations. When
this counter reaches a predetermined limit, the firmware considers the "ink empty" and prompts the
use to replace it.
Removing an ink cartridge from its slot also causes light to hit the corresponding sensor. The
firmware differentiates this from the above "running low" situation by interpreting any intervening
activation of the scanner open sensor as indicating that the user has opened the scanner to remove
that ink cartridge, so considers the "ink empty".
Ink near empty No ink cartridge loaded
Sensor
actuator
3-20
Confidential