Sensors And Actuators - Brother MFC640CW Service Manual

3.2.3 Sensors and Actuators

This machine uses the following sensors and thermistor.
Document front sensor
Document rear sensor
Scanner open sensor
Paper width sensor
Head thermistor
CR encoder sensor
PF encoder sensor
Registration sensor
Purge cam switch
Ink cartridge sensors (four)
Hook switch sensor (MFC640CW)
• The document front sensor detects whether there is a document in the ADF.
• The document rear sensor detects the leading and trailing edges of document pages, indicating to
the control circuitry the point at which to start reading and when page scanning is complete.
• The scanner open sensor detects whether the scanner cover (scanner unit) is properly closed.
• The paper width (media) sensor detects the right and left paper edges, as well as the paper width
in near-edge printing.
• The head thermistor detects the temperature of the print engine. According to the sensor
information, the controller adjusts the head driver to compensate for changes in ink viscosity.
• The carriage motor (CR) encoder sensor monitors the head/carriage unit's current position and
speed. An error in the head's travel speed usually indicates a paper jam.
• The paper feed motor (PF) encoder sensor monitors the PF roller rotation angle and speed for
use in optimizing paper feed amount and speed.
• The registration sensor detects the leading and trailing edges of paper for use in determining
registration timing and detecting paper jams.
• The purge cam switch detects the drive positions of the purge cam.
• There are four ink cartridge sensors, one for each color. The sensor actuator inside the ink
cartridge usually blocks the light path to indicate the presence of ink. When ink runs low (near-
empty), the arm moves out of the beam, activating the sensor. The same signal also indicates
whether there is an ink cartridge present.
• The hook switch sensor detects whether the handset is on the handset mount. (MFC640CW)
Sensor Name Sensor Type
Photosensor
Photosensor
Mechanical switch
Photosensor
Thermistor
Photosensor
Photosensor
Photosensor
Mechanical switch
Photosensor
Photosensor
3-37
Location
In the ADF unit
In the ADF unit
In the rubber keypad in the
control panel ASSY
On the carriage PCB
On the PF sensor PCB
On the maintenance unit
On the ink cartridge PCB
inside ink refill assembly
On the hook switch PCB in
the lower cover
Confidential