Ricoh FT4215, Service Training Manual

Page: 39 / 208

2.5 GRID VOLTAGE CONTROL
The main board controls the grid voltage for a copy image and the toner
density detection through the CC/Grid/Bias power pack. As the grid voltage
for the image density control becomes less, the copy image becomes lighter
and vice versa.
As the grid voltage for the toner density detection becomes less, the toner
concentration in the developer becomes higher and vice versa.
The grid voltage is based on the standard grid voltage and the correction
factor as follows:
2.5.1 Image Density Control
Grid Voltage = Standard image density grid voltage (–920 volts [SP60 = 5])
+
Vr correction factor
Vr Correction Factor
L Change of grid voltage
100 to 89 (%)
88 to 76 (%)
75 to 62 (%)
61 to 45 (%)
44 to 0 (%)
±
0 (volt)
–40 (volts)
–80 (volts)
–120 (volts)
–160 (volts)
L = Vrp/Vsg x 100 (Vr correction ratio)
Vrp: ID sensor output for Vr correction pattern
Vsg: ID sensor output for bare drum
NOTE: The grid voltage for between copies (non-image area) is 0 volt
(Fixed).
2.5.2 Toner Density Detection
Grid Voltage = Standard ID sensor grid voltage (–560 volts [SP62 = 5])
+
Vp correction factor
Drum counter Vp correction factor
0 to 1,999 (copies)
Over 2,000 (copies)
±
0 (volt)
–20 (volts)
2.5.3 Vr Detection
Grid Voltage = –500 volts (Fixed)
FT4220/4222 2-8 STM