Canon LBP-800 Service Manual page 85

2. Operation
a. Generation of voltage applied to primary charging roller
When the pick-up command is sent from the interface controller, the INITIAL ROTATION period
(INTR) starts, and the PRIMARY HIGH VOLTAGE (AC) DRIVE signal (PRACC) is input to the pri-
mary high-voltage circuit via the power operational amplifier. The PRIMARY HIGH-VOLTAGE
(DC) DRIVE signal (PRDCC) sent from the CPU is input to the primary high-voltage circuit. As
a result, the combined primary high-voltage of the AC bias and the DC bias is applied to the pri-
mary charging roller.
The IC302 compares the primary high-voltage (DC) with the PRIMARY HIGH-VOLTAGE (DC)
DRIVE signal (PRDCC) sent from the CPU to control the voltage value of the primary high-volt-
age (DC).
When the cartridge is installed, a current flows into the J304. Whether the cartridge is
installed or not can be detected by detecting the current with the CRGSNS.
b. Generation of developing bias
The DEVELOPING BIAS (AC) DRIVE signal(DVACC) is input to the developing bias circuit via the
power operational amplifier. The constant developing DC bias is generated in the DC generation
circuit on the developing bias circuit. As a result, the combined voltage of the developing AC
bias and the DC bias is applied to the developing cylinder.
c. Generation of voltage applied to transfer charging roller
The negative bias, print bias, and between-page bias are applied to the transfer charging roller
according to each print sequence.
The negative bias (negative voltage) is applied to the transfer charging roller with the speci-
fied timing in order to clean the roller by removing the toner adhered to the roller onto the pho-
tosensitive drum.
The print bias (positive voltage) is applied to the transfer charging roller in order to transfer
the toner on the photosensitive drum onto the paper.
The between-page bias (positive voltage lower than the print bias) is applied with the speci-
fied timing to prevent the residual toner on the photosensitive drum from adhering to the trans-
fer charging roller.
When the pick-up command is sent from the interface controller, the INITIAL ROTATION peri-
od (INTR) starts. At the same time, the CPU outputs the TRANSFER NEGATIVE VOLTAGE
DRIVE signal (TRNFOT), and the negative bias is applied to the transfer charging roller for the
specified period of time in order to clean the roller.
During the print sequence, the CPU outputs the TRANSFER POSITIVE VOLTAGE DRIVE sig-
nal (TRPWM), and the print bias is applied to the transfer roller. The between-page bias is
applied to the roller between pages.
After the end of printing, the negative bias is reapplied to clean the transfer charging roller.
d. Generation of fixing bias
The CPU outputs the PRIMARY HIGH-VOLTAGE (DC) DRIVE signal (PRDCC), and the primary
DC bias is output from the DC generation circuit on the primary high-voltage circuit. At the
same time, the fixing bias and the negative DC voltage are applied to the pressure roller.
e. Cartridge detection
When the PRIMARY HIGH-VOLTAGE (AC) DRIVE signal (PRACC) is output from the CPU and the
primary AC bias is output from the AC generation circuit on the primary high-voltage circuit,
the primary high-voltage circuit feeds back the CARTRIDGE DETECTION signal (CRGSNS) to the
CPU.
The CPU checks the voltage of the CRGSNS signal when the primary AC bias is output dur-
ing WAIT period in order to detect the presence/absence of the cartridge.
CHAPTER 2
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