2-18 Phaser 6300/6350/6360 Color Laser Printer Service ManualTheory of OperationSensorsThe printer contains sensors of various types that perform a variety offunctions. One group of sensors track the progress of the paper along thepaper path, and detects if a paper jam occurs. Other sensors detect thepresence 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 thefusing temperature.Sensor TypesThe types of sensors used vary with function. In general, there are three typesin use:Photo SensorsTwo types of photo sensors are used, photo-reflective and photo-receptive.Photo-reflective sensors use light reflected back from an object to detect itspresence. Photo-receptive sensors use an actuator or the object itself to blockthe light path to detect an object or condition.Photo-reflective sensors have the light emitter and light receiver aligned on asingle surface. Output of the photo-receptor is High (> +4.5 V) when light isbeing reflected back and Low (< +.3 V) when it isn’t. Photo-receptive sensorsconsist of a LED in one arm of a U-shaped holder, and a photo-transistor inthe other arm. When the sensing area is vacant, nothing is between the armsof the sensor, light falls on the photo-receptor sending the signal High. If thelight is interrupted, the photo-transistor goes Low.MicroswitchesMicroswitches are used primarily as paper size sensors and cover interlocks.They are in a normally open state, and close when actuated. A bank ofmicroswitches is used to detect paper size in the universal trays.Microswitches also employ hooks or catches for retention in the bracket orframe.ThermistorsThermistors have a known value of resistance whose value varies withtemperature. Used primarily in the Fuser for temperature sensing.
