09/2007
8-11
Phaser 8860/8860MFP Service Manual
Image Output Terminal
Theory of Operation
Initial Issue
Sensors
The system 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 Ink Sticks, stop system activity if a door is
open (interlock), detect the presence and size of media, and monitor system temperatures.
Figure 5 Sensor Locations
Sensor Types
The types of sensors used vary with function. In general, there are three types in use:
• Photo Sensors
• Microswitches
• Temperature 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 when light is being reflected back and Low 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 are used primarily as paper size sensors and cover interlocks. They are in a nor-
mally 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.
Temperature Sensors (Thermistors) have a known value of resistance whose value varies with
temperature. Used primarily in the Drum and Printhead for temperature sensing.
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