Gradation Control (Laser Power Modulation) - Gestetner A193 Service Manual

LASER EXPOSURE

3.3 GRADATION CONTROL (LASER POWER MODULATION)

PM
(8 levels)
Data: 0 Data: 3
7
5
3
1
0
0 7 1
PWM
(8 levels) 1 dot
Black
White
To create the latent image, the laser beam illuminates the image area of the
drum surface. The longer the laser is on and the stronger its intensity is, the
darker the developed pixel becomes. Modulating (changing) the width of the
pulse changes the on time of the laser longer or shorter (PWM). There are
eight pulse width levels in this machine.
While the laser is on to make one dot, the intensity of the laser is controlled
by power modulation (PM). The laser's intensity is controlled by the amount
of current sent to the laser diode. Modulating the power makes the laser
brighter or dimmer. There 8 power levels, or laser intensity levels. The power
is modulated only on the final part of the laser pulse (example: see data 11 in
the diagram).
The machine uses the 8 pulse width levels and 8 power levels to create the
64 possible grayscale values for each pixel.
(A193)
Data: 7 Data: 11
2
1
2-20
Data: 15 Data: 34
2 5
63
A193d520.wmf
Data: 63
7
A193D519.wmf
SM