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Chapter 6 Principles of Operation
6-363
7.4.2 Toner Density Control
The toner density must be kept constant to attain stable printing image. To keep the toner density constant,
the toner should be dispensed exactly by the quantity consumed for the printing. This system is the PCDC.
However, the system with only the PCDC generates a difference from target toner density, thus requiring
the system to correct this error. This is the toner density control by the SENSOR ADC ASSY. These two
control systems are altogether called the toner density control.
1) PCDC (Pixel Count Dispense Control)
The toner quantity consumed in the developing process is calculated by counting the video signals
entered to the ROS ASSY. The video signal counting is made by the charging and discharging of the
capacitor in the CR circuit arranged in parallel to the video signal line. The consumed toner quantity is
calculated by the toner dispense time. The Toner Motor in the HOLDER TCRU ASSY is driven by the
amount of calculated toner dispense time to supply the toner into 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 BTR. The SENSOR ADC ASSY
measures this density. The measured value is compared with reference value, and if the toner density is
low, the toner dispense quantity is increased at the next printing, or if the toner density is high, 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.
ADC is made after the completion of printing, if either of the following conditions is satisfied:
• When cumulative print count after the power on exceeds 16
• When a cleaning cycle is executed during continuous printing
3) Example of toner dispensation
The Toner Motor revolves for the duration of the specified time per 1-time dispensation. The toner
dispense time in 1) and 2) above is calculated with the number of revolutions of Toner Motor. In the
following description, this is called the dispense count.
The dispense count calculated by the ADC is cancelled in the subsequent 8 prints.
If 16 dispense counts were calculated as a lack of toner by the ADC, the toner is dispensed additionally
to the dispense count calculated by the PCDC by 2 counts (16(8=2) in the subsequent 8 prints.
Or, if 16 dispense counts were calculated as an excess of toner by the ADC, the toner is dispensed by
subtracting from the dispense count calculated by the PCDC in the subsequent 8 prints. If the excess
amount cannot be subtracted in 8 prints, the remainder is subtracted in 9 and subsequent prints.
Total dispense counts
Correction amount by ADC +16
Dispense counts by PCDC
Correction amount by ADC -8
Total dispense counts
2 3 1 2 0 0 1 2 3 2
Even allotment in first 8 prints
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