High Area Coverage Mode; Admix Mode; Led Light Quantity Control Of Holder Assy Ctd - Brother HL-4000CN Service Manual

7.4.3

High area coverage mode

A continuous printing of the image of area coverage exceeding the toner dispense
capability causes the toner density in the developer to be lowered.
The high area coverage mode extends the next page feed and dispenses the toner
during this time, if the toner dispense time reached the specified value during a
continuous printing.
7.4.4

Admix mode

Even the high area coverage mode may not be able to cope with the reduction of toner
density in the developer. Also, if the machine used in high humidity environment is
relocated to the place in low humidity environment, the reference value of toner density is
different in respective environments, thus causing large discrepancy between measured
value by holder ASSY CTD and reference value of toner density.
The admix mode dispenses the toner immediately to prevent the reduction of toner
density, if the patch density result measured by the holder ASSY CTD is far lower than
the reference value when the patches for toner density control are generated.
7.4.5

LED light quantity control of holder ASSY CTD

The holder ASSY CTD is a reflection type density sensor that radiates the light to an
objective from the LED in the sensor and detects the reflected light from the objective to
output electric signal according to the light quantity. For exact density measurement, the
sensor output value (reflected light quantity) must be the specified value when no toner is
put on the transfer roll cartridge as an objective. The reflected light quantity varies
depending on the transfer roll cartridge surface condition or dirty condition of holder
ASSY CTD surface. The light quantity emitted from the LED is controlled so that the
reflected light quantity satisfies the specified value.
This control is made in two ways; one to set the light quantity so that the reflected light
quantity satisfies the specified value, and one to adjust the subsequent light quantity to be
within the tolerance.
1) Light quantity setting
The reflected light quantity may vary largely, if the transfer roll cartridge unit ASSY
was replaced or the holder ASSY CTD was cleaned. Assuming this fact, the light
quantity is set when the power is turned on, or the front cover is opened and closed.
The light quantity of LED is increased gradually, and the set value is fixed when the
output of holder ASSY CTD exceeds the specified value. At this time, if the output of
holder ASSY CTD does not reach the specified value even though the light quantity
is increased to the upper limit, the controller judges the sensor as dirty. Also, the
controller judges the sensor as faulty in the event of extremely high output.
2) Light quantity adjustment
At the execution of ADC, the light quantity adjustment is made immediately before
the patches for toner density control are generated.
The light is emitted from the LED with current setting of light quantity to check if the
output value of the holder ASSY CTD is within the specified range. If the output value
is low, the light quantity is increased by the specified amount at the next ADC, or if
high, the light quantity is reduced at the next ADC.
At this time, if the output value is less than the first lower limit, the controller judges
the sensor as dirty and outputs the warning. Further, if less than the second lower
limit, the controller judges the sensor as faulty and stops the printing.
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