October 2012
8-9
ColorQube 8570/8870 Service Manual
Sensors, Printer Electronics
Theory of Operation
Xerox Internal Use Only - Revised, 3rd Revision
Sensor Types
The type 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 Sensors
Photo-reflective - Photo-reflective Sensors use light reflected back from an object to detect its
presence. 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 is not.
Photo-receptive - Photo-receptive Sensor uses an Actuator or the object itself to block the
light path to detect an object or condition. 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.
Temperature Sensors
The Temperature Sensors (Thermistors) have a known value of resistance whose value varies
with temperature. The Temperature Sensors are used primarily in the Drum, Preheater, and
Printhead for temperature sensing.
Printer Electronics
Electronics Module
Figure 1 Electronics Module
The Electronics Module includes the Main Controller Board, Power Control Board, and the
Power Supply.
Figure 2 Electronics Components
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