Table of Contents
Advertisement
Chapter 2
2) Automatic power control (APC)
3) Horizontal synchronization control
4) Image mask control
2.2.2.2 Laser Emission Control
In this control, the laser diodes (LD1, LD2) are turned on/off based on the VIDEO signals.
When the laser drive IC goes into print mode, the laser driver PCB turns on the laser diodes with a specified amount of light or turns it off according to the VIDEO
(VDO1, /VDO1, VDO2, /VDO2) signals sent from the SCNT Board.
2.2.2.3 Automatic Power Control (APC)
This control is utilized to maintain amount of light emitted from the laser diodes at a specified amount.
There are two kinds of the APC, initial APC (Note: 1) and between-lines APC (Note: 2). They perform in the same way. The control procedures are described below.
1) When the laser driver IC goes in to LD1 force on mode, the laser driver circuit emits light from the LD1 forcefully.
2) The light amount of the laser diode is detected by the photo diode (PD). Then it is converted to voltage level and compared with the reference voltage (voltage
level equivalent to a target laser light amount) in the comparator.
3) The laser driver circuit controls the laser current until the voltage level of the LD1 laser light amount reaches the standard voltage.
4) Then, when the laser driver IC goes into LD force off mode, the LD1 is turned off forcefully. The laser driver circuit stores the adjusted laser light amount in the
C16.
5) After the light amount adjustment of the LD1, the laser driver IC goes into LD2 force on mode and the laser driver circuit emits light from the LD2 forcefully.
The laser light amount of the LD2 is adjusted in the same way the LD1 is done. The laser driver circuit stores the adjusted laser light amount of the LD2 in the
C18.
Note 1. The APC performed at scanner motor start-up. It adjusts the laser light amount and detects a laser failure.
Note 2. The APC performed during the print period. It performs the laser light amount adjustment for one line before the first line starts to be written.
2.2.2.4 Horizontal Synchronous Control
This control is utilized to determine a starting position in the image horizontal direction.
The control procedures are described below.
1) The DCNT Board outputs the LASER CONTROL signals in a combination of which the laser drive IC goes into LD1 force-on mode or LD2 force-on mode
during the unblanking period (Note) and emits light from the laser diodes (LD1, LD2) forcefully.
2) Each laser beam is sent to the BD PCB located on the scanning path of laser beams.
3) The BD circuit detects these laser beams and generates the BD INPUT (/BDI) signal. The signal is sent to the DCNT Board.
4) The DCNT Board generates the HORIZONTAL SYNCHRONOUS (/BDO) signal based on the/BDI signal and sends the /BDO signal to the SCNT Board.
5) The SCNT Board, after inputting the /BDO signal, outputs the VIDEO (VDI1, /VDI1,VDI2, /VDI2) signals to the DCNT Board so that the starting position in
the image horizontal direction is determined.
The unblanking period is a period while light is emitted from the laser diodes in non-image areas.
2.2.2.5 Image Mask Control
This control is utilized to avoid laser beam emission on the non-image areas during periods other than the unblanking period.
The DCNT Board let the laser driver IC go into LD force off mode to turn off the laser diodes (LD1, LD2) forcefully while the laser beam scans on non-image areas
during periods other than the unblanking period. This status is called an image mask status, which the laser diodes (LD1, LD2) do not emit light even though the
VIDEO (VDI1, /VDI1, VDI2, /VDI2) signals are input during this period. Control timing for the image masking is determined based on paper size information sent
from the SCNT Board.
If the length of paper measured with the registration sensor (PS711) is longer than paper size information, the DCNT Board puts the image masking forcefully to
avoid soiling the secondary transfer roller.
1. The shaded areas indicate areas in which an image can be written by the laser beams.
2. Times T1 to T3 vary according to a paper size.
3. When the multi-purpose tray is selected as a pick-up source, the paper width cannot be determined if a paper size specification command is not sent from the
SCNT Board. In this case, values of T1 to T3 are set to be that of universal size.
2.2.2.6 Laser Failure Detection
The DCNT Board detects a condition of the control in order for the laser control to be performed properly.
If the laser current monitor signal (PDOUT) cannot be detected when the scanner motor is started up or when APC is under way, the DCNT Board will assume the
condition to indicate a fault in the scanner block and stop the printer engine; at the same time, it will communicate the fact to the SCNT Board.
2-6
/BD
LEFT/RIGHT
T2
MARGIN
MASKING signal
T1
2 mm
F-2-10
2 mm
0008-1542
0008-1543
0008-1544
0008-1545
0008-1546
Advertisement
Chapters
Table of Contents
