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 Clock of 1,18KHz is always outputted. PMCLK PMD_ (Scanning motor) APCSTT (Laser power control) LEND_ 2.0sec 0.5sec After about 0.5sec of turning on the LEND_ signal, the LEND process is started. 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 operation 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 controlling the print left margin is made and when the print image is drawn on the photoconductor. FO-2970MU • 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. SYNC A B 1st dot 2nd dot last dot VIDEO C D 1 line data Next line Keep low level. SAMP 2 µs 2 µs LEND_ Line end off Fig. 11 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 electrostatic 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 Time B C D Line end off 600dpi 846.7µs 3 ~ 10µSec (29.97µSec) (84.3nSec) 510µs 406.4x 1298.7524µs 4.6 ~15.3µSec (45.971µSec) (190.907nSec) 720µs 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