Sharp FO-2970M Service Manual page 49

3) Starting operation
Warm-up operation of laser scanning is described below.
The operation is made when the cover is closed from the open state,
and is made before starting printing.
The PMCLK signal is the clock signal for scanner motor speed control.
It is rectangular waveform of 1.18kHz.
1
The PMD_signal is to turn on/off the scanner motor. When this signal
is outputted, the scanner motor is operated.
2
After 2 sec of starting the scanner motor, the laser power control
signal APCSTT and the laser diode ON signal VIDEO (LEND) are
outputted to output laser beams.
3
After 0.5sec from outputting the VIDEO (LEND) signal and turning
on the laser diode, the LEND process operation is started.
Stop Start
PMCLK
PMD_
(Scanning motor)
APCSTT
(Laser power control)
LEND_
2.0sec
Fig. 10
4) LEND process operation
The LEND process operation means outputting the HSYNC (HSYNC_)
signal for left margin control.
To control the left margin, the scanning position of the scanning mirror
on the virtual area of the left side out of the margin must be precisely
detected when the scanning motor reaches the stable rpm. Therefore,
the dummy laser beam must be outputted to detect the position.
The laser beam scanning position is detected by the laser beam sensor,
and the SYNC signal is outputted.
The dummy laser beam is outputted for every scanning of one line only
when the scanning position of the scanning mirror is outside the left
area of virtual paper. (The laser is forcibly turned on by the PCU when
the laser beam scanned by the scanning mirror come in front of the
laser beam sensor (left margin reference).)
Note: The laser beam is not outputted continuously during printing op-
eration of one paper. It repeated ON and OFF for every scanning
of one line.
The laser beam is outputted only when the LEND process for con-
trolling the print left margin is made and when the print image is
drawn on the photoconductor.
Clock of 1,18KHz is always outputted.
0.5sec
After about 0.5sec of turning on the LEND_ signal,
the LEND process is started.
• Laser control signal
LEND signal is controlled based on HSYNC signal.
For simultaneous APC control, SAMP signal is also controlled.
These timings are made by ASIC. The line-end-off section is set by the
register.
B
SYNC
1st dot 2nd dot
VIDEO
C D
SAMP
2 s
LEND_
Line end off
1
When the LEND_ signal is on, the dummy laser beam is outputted,
and the scanned laser beam is detected by the laser beam sensor to
output the SYNC signal. When the SYNC signal is outputted, the
CPU detects the scanning position.
2
At the rising of the SYNC signal, the CPU turns off the LEND_signal.
By this, the dummy laser beam is turned off. When the CPU detects
the scanning position with the SYNC signal, the dummy laser beam
becomes unnecessary.
3
The draw signal Video_ is made from the DDATA_ signal of one line
outputted from the ASIC. When it is outputted, the laser beam is turned
on off accordingly. This corresponds to the making of latent electro-
static images on the photoconductor drum.
4
When making of latent electrostatic images for one line is completed,
the CPU turns on the LEND_ signal before the output timing of the
SYNC.
1 4
Procedures ~ are repeated.
Resolution
A
600dpi 846.7 s 3 ~ 10 Sec (29.97 Sec) (84.3nSec)
406.4x 1298.7524 s 4.6 ~15.3 Sec (45.971 Sec) (190.907nSec)
391.16dpi
5) Automatic acknowledgment of resolution
The CPU control 600dpi/400dpi when starting the LEND process.
When the scanner motor rotation is stabilized, the SYNC interval is
judged.
5 – 13
FO-2970MU
A
last dot
1 line data Keep low level.
2 s
Fig. 11
Time
B C D
Next line
Line end off
510 s
720 s