About The Scanner Cartridge; Scanner Block Diagram And The Data Flow - Canon BJC-3000 Service Manual

Part 5: Appendix

1.5 About the Scanner Cartridge

The scanner cartridge is a replaceable scanner unit. It carries a one-line 256 pixel CCD,
and by scanning the same line three times, switching each of the three RGB primary
colors of the LED, it separates one line of the color image into three RGB colors, output
in 8-bit signals (256 gradation in each RGB color). For a monochrome image, the image
is output either as an 8-bit or 1-bit signal by lighting the green (G) LED and scanning
once.

1.5.1 Scanner block diagram and the data flow

When scanning, the light source LED lights up and illuminates the document on the
platen. Reflected light rays pass through the field lens and the imaging lens, and are
converged onto the CCD. The CCD converts the converged light rays to analog signals,
which are then converted to digital signals by the scanner controller, and the scanned
image is processed. The image data is then passed through the scanner cartridge's I/F
controller to the printer. The printer then sends the image data to the computer
through the USB interface or the Centronics interface. Data in each line of the image
will be transferred per RGB color; therefore, three transfers are executed per line of
data.
Operations within the scanner block are shown below in order of data processing:
1) LED Illumination Lens
LED illumination lens consists of the light source LED and the illumination lens.
The LED part uses red, green and blue LEDs as light sources to illuminate the
scanning document. Only the green LED is used for monochrome scanning.
The illumination lens part is a "D" shaped lens which converges the light from the
LED light source.
2) Field Lens
This lens prevents magnification/reduction caused by changes in the head to paper
gap when scanning a folded or bent document.
3) Diffusion Board
The light intensity of the LED is brighter at the center than at the edges. The
diffusion board allows even distribution of light from the document.
4) Imaging Lens
This lens is used for forming an image of the light rays converged by the field lens
onto the CCD.
5) CCD
The scanner cartridge uses a semiconductor type image sensor, one-line 256 pixel
CCD (Charge Coupled Device). Depending on the light amount of the image formed
on the CCD, voltage signals are sent to the scanner controller as image signals.
Scanner Cartridge (Optional)
Scanner Controller
I/F Controller
1bit
Image Processing
(10bit->8bit)
A/D Converter (10Bit)
Analog Signal Control
Amplifer
Sensor Control
LED (R, G, B)
Illumination Lens
Figure 5-11 Scanner Block Diagram
5-12
Printer
+24V DC
+5V DC
CCD (Image Sensor)
Imaging Lens
Diffusion Board
Field Lens
Scanning Document
BJC-3000