Brother MFC 685CW - Color Inkjet - All-in-One, Service Manual

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3-44
Confidential
3.2.3 Sensors and Actuators
This machine uses the following sensors and thermistors.
Sensor Name Sensor Type Location
Document front sensor
* 1
Photosensor
Document rear sensor *
1
Photosensor
In the ADF unit
* 1
Scanner/ink cartridge cover sensor Photosensor On the cover sensor PCB
Paper width sensor (media sensor) Photosensor
Head thermistor Thermistor
CR encoder sensor Photosensor
On the carriage PCB
Registration sensor Photosensor On the registration sensor PCB
PF encoder sensor Photosensor On the PF encoder PCB
Purge cam switch Mechanical switch On the maintenance unit
Ink cartridge sensors (four) Photosensor
Casing internal temperature thermistor Thermistor
On the ink cartridge PCB inside
the ink refill assembly
Hook switch *
2
Photosensor
On the hook switch PCB *
2
in
the lower cover
*
1
For models with ADF
* 2
For models with handset
• 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/ink cartridge cover sensor detects whether the scanner cover (scanner unit) and the
ink cartridge cover are properly closed.
• The paper width (media) sensor detects the size of recording paper. With this sensor signal, the
controller prevents the print head from printing on the outside of paper in borderless printing. It
also protects the platen from no-paper printing when a paper jam occurs, preventing stains on the
platen and the back side of paper.
• 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. If the controller detects a head's travel speed error, it interprets the error state as a paper
jam and stops the operation.
• The registration sensor detects the leading and trailing edges of paper for use in determining print
start and end timings and detecting paper jams.
• 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 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.