Specifications

Principles of Operation Print Process - 4
2 Exposure
During this stage, the laser beam scans across the negatively charged drum surface.
The laser beam is emitted from the laser diode in the laser/scanner assembly. This diode is
stationary. Its beam reflects off the face of a rapidly rotating scanning mirror, through a
correction lens, and outward off a stationary mirror which directs the beam onto the
surface of the drum.
The laser beam is modulated according to the video signal from the printer controller,
switched on when the video signal denotes a black pixel and off when it denotes a white pixel.
The laser beam that strikes the drum surface generates electron-hole pairs in the
photoconductor layer, exciting electrons to the conduction band and thereby creating holes
in the valence band. The electrons are attracted by the electric field and move toward the
inner conductor of the drum to flow into it. The holes move toward the outside surface of the
photoconductor layer and recombine with the negatively charged electrons at the surface to
decrease the negative charge at the surface. The resultant less-negatively charged parts
(parts whose potential has risen relative to the inner conductor) in the drum surface form
an invisible electrostatic latent image.
Conductor Layer
Photoconductor
Layer
Laser Light
Electron
Recombination
Decrease of
Negative Charge
Electron-hole pair