Xerox Phaser 6128 MFP, Service Manual

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Phaser 6128MFP Service Manual 2-35
Theory of Operation
High Area Coverage Mode
A continuous printing of any image of area coverage exceeding the toner dispense
capability causes the toner density in the Developer to be lowered.
The High Area Coverage Mode postpones the next page feed and dispenses extra
toner during this time, if the toner dispense time reaches the specified value
during a continuous printing.
Admix Mode
The Admix Mode dispenses toner immediately to prevent the reduction of toner
density, whenever the value of the toner density control patch measured by the
ADC Sensor falls far below the standard value, by dispensing extra toner. If the
toner density level cannot be recovered after this operation, it is determined that
toner has run out.
ADC Sensor Control Function
The ADC Sensor is a reflection type sensor that radiates light from its LED onto the
target and detects the reflected light at its photoreceptor and outputs electric
signals responsive to the amount of the detected light.
To ensure an accurate patch density measurement, the surface of the ADC sensor
is cleaned to remove soil due to toner, etc., and the light amount adjustment is
made so that the reflected light amount satisfies the prescribed value, when
creating the patch for potential control and toner density control.
Color Registration Control
The printer uses a tandem electro-photographic system with Organic Photo
Conductor (OPC) Drums and direct transfer by the transfer belt. Because the
images are formed on the individual Drums of the respective colors and then
overlapped to form one image, a color shift may occur. The color registration
control calculates how much the registration is shifted, and adjusts the Laser Unit
write timing.
The scan control adjusts all four colors in the process direction.
The color registration control is made from a change in inside temperature and the
print count at the execution of the process control. This control is outlined as
follows:
1. With no toner on the transfer belt, the output value of the ADC Sensor is
measured to determine the threshold value.
2. The patches for color registration control are generated on the Belt. These
patches are composed of 10 mm lines of K, C, K, M, K, and Y in this order by
the amount of four dispense counts, led by a black trigger.