Sensors - Xerox Phaser 4620 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 is not. 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.
sensor with the hooks (catches) used to secure the sensor to its bracket.
Figure 1 Photo Sensor
Revision - Xerox Internal Use Only
Phaser 4600/4620 Printer Service Manual
Figure 1 shows a typical photo-receptive
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. Figure 2 illustrates a typical microswitch.
Figure 2 Door interlock switch
Thermistors have a known value of resistance whose value varies with temperature. Used pri-
marily in the Fuser for temperature sensing.
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Principles of Operation
Sensors