Dell 3130cn - Color Laser Printer, Service Manual

Page: 775 / 854

6 – 51
Chapter 6 Principles of Operation
Version 1 2007.12.28
5.4.2 Toner Density Control
The toner density must be kept constant to attain stable printing image. The control system for this
purpose is called toner density control.
1) PCDC (Pixel Count Dispense Control)
The quantity of the toner to be consumed in the developing process is calculated by counting the
video signals entered to the PRINTHEAD. The quantity of the toner to be consumed is calculated by
the toner dispensing time. The toner motor is driven based on 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 specified potential condition, and transferred on the Belt. The ADC Sensor
measures this density. The measured value is compared with the reference value. If the toner
density is lower, 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.
5.4.3 High Area Coverage Mode
A continuous printing of any image of area coverage exceeding extra 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 the toner during this time,
if the toner dispense time reached the specified value during a continuous printing.
5.4.4 Admix Mode
This mode prevents the toner density from being lowered, whenever the value of the toner density
control patch measured by the ADC Sensor falls far below the standard value, by performing extra
toner dispensation. If the toner density level cannot be recovered even after this operation, it is judged
that the toner has run out.
5.4.5 ADC Sensor Adjustment
The ADC Sensor is a reflection type sensor that irradiates the 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 surfaces 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.