Brother FAX-921 - Manual (Page 29)

III - 16
2.4 Sensors and Actuators
This equipment has five photosensors and two mechanical switches as described below.
Sensor name Type Located on
Document front sensor Photosensor Control panel PCB ASSY
Document rear sensor Photosensor (PI2) Main PCB
Paper-edge sensor Photosensor (PH1) Sensor PCB
Paper ejection sensor Photosensor (PH2) Sensor PCB
Ribbon sensor Photosensor (PI1) Main PCB
Cover sensor Mechanical switch (SW1) Main PCB
Hook switch sensor* Mechanical switch (SW1) Hook switch PCB
• Document front sensor which detects the presence of documents.
• Document rear sensor which detects the leading and trailing edges of pages to tell the control
circuitry when the leading edge of a new page has reached the starting position and when the
scan for that page is over.
• Paper-edge sensor which detects the leading and trailing edges of paper and the presence of
paper as well as detecting whether the paper front cover is closed.
• Paper ejection sensor which detects whether a paper jam has occurred.
• Ribbon sensor which detects whether the ink ribbon is loaded.
These photosensors are a photointerrupter consisting of a light-emitting diode and a light-sensitive
transistor. Each of them has an actuator separately arranged (see the following pages) except that
the paper-edge sensor has two actuators for sensing the paper and the paper front cover. When
an actuator is not activated, its black end lies in the path of light issued from the light-emitting diode
and interrupts its light so that the emitted light does not enter the light-sensitive transistor. If a
document, paper, or ribbon comes in so as to activate the actuator, the actuator's black end goes
out of the light path and the emitted light enters the light-sensitive transistor. This way, the sensor
detects the presence of documents, paper, or ink ribbon.
• Cover sensor which detects whether the recording paper cover ASSY is closed.
• Hook switch sensor* which detects whether the handset is placed on the handset mount.
The cover sensor has an actuator ASSY (consisting of two actuators and a spring). If you open the
recording paper cover ASSY, the actuator ASSY pops up to release the sensor.
* Not provided on the FAX-910.