Konica Minolta 7075/FORCE 75, Service Manual

Page: 96 / 844

2 - G - 6
DEVELOPING UNIT
[7] Gradation Correction Control
Gradation correction control is performed by the TCSB
(toner control sensor board), M2 (drum), M3
(developing), and so on. These parts are controlled
by the PRCB (printer control board).
1. Operation
The gradation characteristics of the toner density
versus exposure amount at the image forming
section (drum area) are detected to obtain a linear
relation between the image density on a
document and the copying image density (toner
density).
(1) Method
Exposure is performed with the laser PWM varied
in several steps, and development is performed
at the toner transfer sleeve speed obtained by
Dmax correction.
Next, each density is read by
γ
sensor (PD2) on
the TCSB to detect the gradation characteristics
of image density.
The gradation characteristics obtained here are
used as the values for correcting the laser
exposure amount.
PRCB
DCPS2
DCPS1
DPSB
DPS
TCSB
24VDC
24VDC
PGND
12VDC
5VDC
SGND
M2 CONT
M2 F/R
SGND
M2 EM
M3 CONT
M3 CLK
M3 EM
DPS DRIVE A
DPS DRIVE B
DPS ANG 1
DPS ANG 2
DPS ANG
AGND
5VDC
MS2 MS1
M2
M3
/Dmax LED Vref
LED CONT
SIG/MONI
(2) Timing
a) When the fixing temperature is lower than 50°C
at power ON
b) At the end of job after every 20,000 copies.
2. Signals
a. PRCB Input signals
(1)
γ
SIG/MONI (TCSB to PRCB)
Output voltage from the
γ
sensor (PD2) on the
TCSB. This signal monitors the light reflected
by the drum surface (without toner).
The voltage applied to the gradation detection
LED is corrected by
γ
/Dmax LED Vref so that the
output voltage becomes 4.5V (calibration).
Reference voltage: 4.5V
<Timing>
Before gradation correction.