Gestetner A294 Service Manual page 95

V Detection
T
The toner density in the developer is detected once every copy cycle, after the
trailing edge of the image passes the development roller.
If the reading from the TD sensor becomes abnormal during a copy job, the
machine holds the GAIN factor constant to allow toner supply to vary with only the
pixel count for the rest of the copy job. Then at the end of the job, SC340 is
generated and the machine must be repaired.
If the TD sensor needs to be replaced and none is available, the toner supply
mode can be set to image pixel count mode using SP2-208.
Image Pixel Count
For each copy, the CPU adds up the value of each pixel and converts the sum to a
value between 0 and 255. (The value would be 255 if the page was all black.)
Gain Determination
GAIN is another factor in the toner supply clutch on time calculation. Its value can
be 0, 1, 1.5, 2, 3, or 4. It is calculated either using V
being used, or every copy using "V
(see Sensor Control Mode – Overview for more on TD and ID sensor control).
ID Sensor Control
V /V
SP SG
≤ 3/40
≤ 9/100
≤ 21/200
≤ 1/8
≤ 4/25
≤ 41/200
≤ 1/2
> 1/2
Toner Supply Clutch On Time Calculation
The toner supply clutch on time for each copy is decided using the following
formula: (GAIN x Image pixel count x 0.7mg/cm
When GAIN is "0", the above 50 ms is set to "0".
The toner supply rate can be changed using SP2-209.
Image Pixel Count Control
This mode should only be use as a temporary countermeasure while waiting for
replacement parts, such as a TD sensor. This mode controls the toner supply using
the same formula for the toner supply clutch on time. However, the GAIN value is
fixed at 0.7.
SM
CÓPIA NÃO CONTROLADA
– V
T REF
a = V
GAIN
0
0.00 ≤ a < 0.02
0
0.02 ≤ a < 0.08
1
0.08 ≤ a < 0.14
1.5
0.14 ≤ a
2
3
4
1
2-45
CÓPIA NÃO CONTROLADA
/V if ID sensor control is
SP SG
" if TD sensor control is being used
TD Sensor Control
GAIN
– V
T REF
a < 0.00
0
1
2
3
4
2
/Toner Supply Rate) + 50 ms
DRUM UNIT
A294/A295