Sensors; Sensor Types; Photo Sensors - Xerox Phaser 6300 Service Manual

Sensors

The printer contains sensors of various types that perform a variety of functions. One
group of sensors track the progress of the paper along the paper path, and detects if a
paper jam occurs. Other sensors detect the presence of the Toner Cartridges, stop
printer activity if a door is open (interlock), detect the presence and size of media in
the trays, and monitor the fusing temperature.

Sensor Types

The types of sensors used vary with function. In general, there are three types in use:

Photo Sensors

Two types of photo sensors are used, photo-reflective and photo-receptive. Photo-
reflective sensors use light reflected back from an object to detect its presence. Photo-
receptive sensors use an actuator or the object itself to block the light path to detect an
object or condition.
Photo-reflective sensors have the light emitter and light receiver aligned on a single
surface. Output of the photo-receptor is High (> +4.5 V) when light is being reflected
back and Low (< +.3 V) when it isn't. Photo-receptive sensors consist of a LED in one
arm of a U-shaped holder, and a photo-transistor in the other arm. When the sensing
area is vacant, nothing is between the arms of the sensor, light falls on the photo-
receptor sending the signal High. If the light is interrupted, the photo-transistor goes
Low.
Microswitches
Microswitches are used primarily as paper size sensors and cover interlocks. They are
in a normally open state, and close when actuated. A bank of microswitches is used to
detect paper size in the universal trays. Microswitches also employ hooks or catches
for retention in the bracket or frame.
Thermistors
Thermistors have a known value of resistance whose value varies with temperature.
Used primarily in the Fuser for temperature sensing.
2-18 Phaser 6300/6350 Color Laser Printer Service Manual