III-44
7.4.1 Potential control
To attain stable printing image density, the drum charging voltage and the developing DC
voltage are adjusted according to the developing capability of each color carrier that
varies momentarily. The adjusted drum charging voltage and the developing DC voltage
are fed back to keep the printing image density constant.
The potential control is made immediately before the start of printing, if either of the
following conditions is satisfied:
• At the first printing after the power on
• When cumulative print count after the power on exceeds 16
• When a cleaning cycle is executed during continuous printing
The outline of control is as follows.
1) The sensor HUM TEMP (temperature and humidity sensor) detects the
temperature and humidity, and sets target values of drum charging voltage and
developing DC voltage.
2) The patches of respective colors (yellow, magenta, cyan, and black) for the
potential control are generated and transferred on the transfer roll cartridge. (For
the shape of patches, see the following figure.)
Y
M
C
K
About 11mm
About 57mm
About 12mm
About 3mm
Fig.3-45
3) The holder ASSY CTD (density sensor) detects the density of the area on
transfer roll cartridge where no toner is present and the density of patches.
4) The density measured in step 3) is compared with target value set in step 1) to
change the drum charging voltage and the developing DC voltage for each color
according to a difference.
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