Xerox Phaser 6280, Service Manual

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2-54 Phaser 6280 Color Laser Printer Service Manual
Theory of Operation
4. The drum charging voltage, developing DC voltage, and the Laser Unit
beam intensity are adjusted for each color according to the detected
patch density.
Toner Density Control
Toner density must be kept constant to attain stable printing. The control
system for this purpose is called toner density control.
1. PCDC (Pixel Count Dispense Control)
The amount of toner to be consumed in the developing process is
calculated by counting the video signals entered to the Laser Unit. The
amount of the toner to be consumed is calculated by the toner dispensing
time. The toner motor is driven for the calculated toner dispensing time
when supplying the toner to the Developer.
2. ADC (Auto Density Control)
The patches of respective colors (Yellow, Magenta, Cyan, and Black) for
the toner density control are generated under a specified potential
condition, and transferred on the Belt. The ADC Sensor measures this
density, and the measured value is compared with reference value. If the
toner density is low, the toner dispense quantity is increased at the next
printing, or if the toner density is higher, the toner dispense quantity is
reduced at the next printing. The toner dispense quantity is calculated by
the toner dispense time. This calculation is made for each color.
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.
Paper Feeding
Length of One Turn of Belt
Toner Patch
Potential Control Patch Density