Sharp AR-5132 Service Manual page 8

Data flow (flowchart)
<White level correction>
15. Halogen lamp <ON>
16. CCD
A/D convertor
17.
18. GA1
19. SRAM
20. CPU
21. FIFO
22. D/A convertor
<Document scanning>
23. Halogen lamp <ON>
24. CCD
25. A/D convertor D/A convertor
Latch
26. GA 1
Histogram
CPU
27. Density
conversion LUT
<White level correction>
15. Halogen lamp
For white level correction, the halogen lamp is lighted at the voltage obtained in the light
quantity adjustment under the shading plate and the shading plate is scanned.
16. CCD
CCD PWB
The reflected light from the shading plate is received by the CCD as photo energy and
converted into electrical energy (analog voltage).
17. The analog voltage is divided into 256 sections (0 ∼ 255) to be digital data.
18. Gate array 1
The digital data are inputted to gate array 1 and thinned out every 16 lines.
19. SRAM
Stores data. Thinning out every 16 lines is performed in order to minimize the bad effect
by dirt on the shading plate.
20. CPU
The optimum white reference of 5048 pixels in the main scanning direction is obtained
ICU PWB
from the SRAM data. At that time, the correction of variations between odd/even num-
bers is performed as well as the correction of the halogen lamp and the lens. These
corrections are made in order to prevent against darkness at both ends. In addition, the
correction for variations between the document surface and the shading plate previously
obtained by SIM 63-2 is performed.
21. FIFO
The correction data of one line are stored in the line memory (FIFO).
22. D/A convertor
The correction data of FIFO are converted into analog values to be the white reference
value (+ reference) in 17. The white reference value is switched for every pixel.
<Document scanning>
23. Halogen lamp
The halogen lamp is lighted at the voltage obtained by procedures 1 ∼ 6 to radiate the
document.
24. CCD
CCD PWB
The scanned image data are sent to the ICU PWB with the analog signals.
25. A/D convertor, D/A convertor, latch, FIFO
Procedures 1 ∼ 22 are performed at the specified timings such as turning on the power.
The values obtained in 1 ∼ 22, however, the black reference values of odd/even num-
bers are stored in the latch, and the white reference value is stored in the FIFO.
Therefore, shading correction is performed in copying. The white/black reference values
FIFO
of the A/D convertor are switched for every pixel to correct unevenness of the optical
system and converted into digital values.
26. Gate array 1
Takes data of the density level of the scanned document.
ICU PWB
Density value A
A judgment is made whether the document is of A type (an document of characters with
much white area) or of B type (a photo document with much half tone area) or of C type
(newspapers with much background area) to select the most suitable look-up table for
density conversion.
27. CPU/SRAM
Converts the density.
For an document of A type, an LUT (look-up table) which provides clear characters is
selected. For an document of B type, an LUT which provides clear half tone images is
selected. For an document of C type, an LUT which removes background. Since
process is performed for every several lines. the most suitable LUT may not be selected
for some documents. In that case, the manual exposure mode is selected.
Content
Density value B
1 – 5
Density value C