Canon fax basic 2000 サービスマニュアル
RECORDING SECTION
4–30
The LASER beam scans one line of the image at a time to form the image
on the photosensitive drum. If the scanning start position in the Horizontal
scanning direction is different for each line of the image during scanning,
then the image will not be able to be drawn correctly on the photosensitive
drum.
Fig. 4-31 Scanning Start Position
For this reason, the nBD signal is required for making the scanning start
position in the Horizontal scanning direction the same for each line of the
image.
The nBD signal is the signal generated by irradiating the LASER beam on
a small mirror (BD mirror) at the end of the photosensitive drum and
detecting it.
Fig. 4-32 nBD Signal
Scanning direction
Normal
When the start position
has shifted partially
When the start position
of the entire image
has shifted
Drum
BD detection
circuit
Control
section
nBD signal
BD mirror
LASER unit
Scanning
mirror
mirror
nBD signal
Fixed period
of time
As the scanning mirror rotates at a
fixed speed, this nBD signal is output
at each fixed time period.
fixed speed, this nBD signal is output
at each fixed time period.