Sharp AR-651 (serv.man23) Service Manual ▷ View online
AR-651/810 IMAGE PROCESSING 7 - 8
7. 5. Scanning Section
Light reflected from original surface is directed to the CCD which performs the opto-electronic conversion,
and the optical image data is converted into an electrical signal. This analog signal undergoes the A/D
conversion processing and is changed into a digital signal. The signal then undertakes various corrective
processes necessary for image formation.
(1) Opto-electronic conversion
The CCD elements convert the optical signal (light) into electrical signal (voltage). (
Chap.6.5.1)
(2) Signal amplification
Amplifies the electrical signals received from the CCD.
(3) A/D conversion
Converts the analog signal into a digital signal.
(4) Shading correction
Shading correction is applied to the signal received front the CCD. (
Chap.6.5.2.)
7. 6. Writing Section
The image signal is processed by the PLG board ASIC for the writing operation. The laser is controlled
based on this signal, writing the image data on the drum.
(1) Setting the effective image area ........................ • Top, bottom, left and right margins
(2) Horizontal synchronization signal (H-Sync) ....... • The reference clock signal in the printer section
clock generation section
is synchronized with the H-Sync signal from the
LSU.
(3) Laser drive section ............................................ • The ON/OFF control of the semiconductive laser
and APC (Auto Power Control) control is performed
based on the processed image data.
CCD
Signal
amplification
A/D
conversion
Shading
correction
Next stage
AR-651/810 LASER & OPTICAL UNIT 8 - 1
8. LASER & OPTICAL UNIT
8. 1. General Description
The laser optical unit radiates the laser beam onto the photoconductive drum responding to the digital
image signals, which have been sent from the scanner, printer controller, etc., to create a latent image.
The Image signal is converted into the light emission signal of the laser diode on the laser driver board,
and it is radiated on the drum through the optical elements such as cylinder lenses, polygonal mirror and f
Ø
lens.
Caution: This unit must not be disassembled in the field since it is finely adjusted and very sensitive to
dust.
[Laser optical unit exterior view]
AR-651/810 LASER & OPTICAL UNIT 8 - 2
f
Ø lens 1
f
Ø lens 2
Laser emission unit
1st laser diode
Finite focus lens
2nd laser drive PC board
2nd laser diode
Finite focus lens
Half mirror
Galvanic mirror
Cylinder lens
Polygonal motor
H-Sync detection PC board
1st laser drive PC board
Front side
H-Sync turnup mirror
1st turnup mirror
2nd turnup mirror
Slit glass
(Laser light exit)
Front side
Rear side
[Laser optical unit overview]
AR-651/810 LASER & OPTICAL UNIT 8 - 3
[CAUTION]
•
Do not place reflective tools near the path of the laser beam.
•
Take off your watches, rings, bracelets, etc. when handling the unit.
8. 2. Structure
(1) Laser emission Unit
This unit consists of the laser diode, finite focus lens and aperture.
a. Laser diode
This laser diode features low droop, small laser variation and low threshold current.
An aperture determines the shape of the laser beam at the laser emission position.
The laser diode radiates the laser beam responding to the laser emission control (ON/OFF) signals
from the laser drive board. The laser beam which passed through the finite focus lens are focused
on the drum surface.
b. Caution:
The beam of the semiconductor laser is very weak (about 5 mW), but focused parallel rays can
create enough energy to be hazardous.
Some material of the components of the laser optical unit are metal. Since the unit is in a sealed
container, there is no danger of laser leakage during normal operation.
Note: The laser beam is not visible. Pay the close attention when handling the laser unit components or
performing operations such as adjustment of the laser beam. This kind of operation, which can be
very dangerous, must be performed only by specially trained staff.
The warning label shown below is attached on the front side left inner cover.
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