Toshiba E-STUDIO190F Service Manual page 188

6.3.4. Laser Scan Unit (Exposure)
6.3.4.1. Operation Theory
The light beam from the Laser Diode (light source) is modulated by the digital signal (nVIDEO) and
converted to parallel light waves by the Collimator Lens. The beam is then sent to the rotating Polygon
Mirror (polygon scanner), where it is reflected through the
surface. The diameter of the beam is about 80 µm, and the light moves across the surface of the OPC Drum
in the scanning direction of right to left. As the drum rotates (sub-scans), a static image is formed where the
laser beam touches the drum surface.
The laser beam is also deflected to the Timing Sensor. This sensor controls the start timing of scanning on
the drum, providing a consistent left margin. The CPU uses the Timing Sensor to detect abnormal signals.
6.3.4.2. Laser Beam
The laser beam is pulsed On and Off by the digital signal (nVIDEO) to form a latent image of two different
voltage potentials on the drum, as shown below.
Item
Oscillation Wavelength
Output Light Power
(OPC Drum Surface)
Laser Diode Specification
Minimum
770
0.315
188
Lens and then focused onto the OPC Drum
Standard Maximum
785 800
0.350 0.385
nm
mW