Detect Supply Mode - Ricoh FT4220 Service Training Manual

6. TONER DENSITY DETECTION AND SUPPLY
6.1

DETECT SUPPLY MODE

Sensor
Pattern
ON OFF ON
A B C
RAM Clear
1 2 3 4 5
Toner Density Detection
1st
The CPU checks toner density by directly sensing the image density every 10
copy cycles (every 5 copies for the color development unit). If the RAM is
cleared (SP99), or a new RAM is installed, the CPU checks the image
density at the beginning of the first copy cycle.
During the check cycles, the sensor pattern is exposed prior to exposure of
the original. After the sensor pattern is developed, its reflectivity is checked
by the image density sensor (a photosensor). The CPU notes the reflectivity.
If the reflected light is too strong, indicating a too low toner density condition,
toner is added to the development unit.
The toner is not added all at once. The CPU energizes the toner supply
clutch for the proper amount of time to add a selected amount of toner over
the next 10 cycles.
When a color development unit is used, the CPU automatically selects fixed
toner supply mode.
STM
Original Lead Edge
Original
OFF
Leading Edge Erase
D E
6 7 8 9 10 11
Detection
Toner Supply Clutch ON
2-36
ID Sensor
Pattern
12 13 14 20
Toner Density Detection
2nd
Low Toner Density
Toner Supply Timing
Toner Add
Detection
(10 times)
Development
Bias
21 22
Toner Density
Detection
3rd
FT4220/4222