Sensors; Sensor Types - Fuji Xerox Phaser 5500 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 detect if a
paper jam occurs. Other sensors detect the presence of the Drum Cartridge, stop
printer activity if a door is open (interlock), 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. The figure below shows a typical photo-receptive sensor with the Hooks
(catches) used to secure the sensor to its bracket.
Hooks
Hook
Sensor Bracket
Microswitches
Microswitches are used primarily as cover interlocks in the printer. 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. The figure illustrates a typical microswitch.
Theory of Operation 2-11