Xerox Phaser 6360, Service Manual, Page: 55 / 564

Phaser 6300/6350/6360 Color Laser Printer Service Manual 2-11
Theory of Operation
LED Light Density CTD (ADC) Control Sensor
The CTD (ADC) Sensor is a photo-reflective sensor that emits light from an
LED and detects the reflected light returning from the Transfer Roller. The
CTD (ADC) Sensor reference voltage (reflected light density) is established
when both the sensor and the Transfer Roller are clean and free of defects.
The light emitted from the LED is controlled so that the reflected light density
meets the reference value.
LED light emission control is implemented in two ways:
■
Sets the light density so that the light reflected satisfies a specific
value.
■ Adjusts the subsequent light density to be within a specific tolerance
value.
1. Light Density Setting
The reflected light density can vary greatly if the Transfer Roller has just been
replaced or the CTD (ADC) Sensor has just been cleaned, or is dusty with
waste toner. To compensate with this variance, the light density is reset each
time the power is turned on or a door is opened.
When the output of the CTD (ADC) Sensor does not meet the reference
value, the intensity of the LED light emissions are increased gradually and the
Light Density Setting is adjusted. If the light density is increased to the
maximum and output of the CTD (ADC) Sensor does not reach the reference
value, a warning message indicates the sensor is dirty. If the sensor output
remains above the reference value, a fatal error reports that the sensor is
faulty.
2. Light Density Adjustment
At the execution of Automatic Density Control, the Light Density Adjustment is
made just before the toner patches for toner density control are generated.
Light is emitted from the LED using the current Light Density Setting, to check
if the output value of the CTD (ADC) Sensor is within the specified range. If
the output value is low, light density is increased. If the output value is high,
light density is decreased.
If the output value is less than the first lower limit, a warning message
indicates the sensor is dirty. If the output value is less than the second lower
limit, a Fatal Error signals that the sensor is faulty and the printer stops
printing.