Unit Mechanisms - Fuji Xerox DocuPrint M355df Service Manual

10.5 Unit Mechanisms

■ Scanner
The SCANNER consists of the Image Input Terminal (IIT) and the Auto Document Feeder (ADF). Document
scanning is performed by the Carriage Assy in the Image Input Terminal.
A CCD Image Sensor is a light-receiving element that produces an electrical signal in response to light.
The white areas of the original document reflect the light from the lamp. The black areas reflect no light. The
CMOS Image Sensor read the light reflected from the original, outputting sequentially to the control circuit
which areas are white and which black as binary data (1/0 digital data: 1 bit).
NOTE
To scan the original, the Carriage Assy (CCD Image Sensor Unit) must be shifted a distance of one line
after each line is scanned. When the original is scanned on the platen glass (as for a flatbed scanner), the
Carriage Assy is moved with respect to the original. In the case of a FAX equipped with the DADF (Auto-
matic Document Feeder), scanning via the DADF is performed by moving the original with the Carriage
Assy fixed at one position. This is known as constant velocity transport (CVT).
NOTE
During scanning, the finer the grid into which the original is divided, the greater the scanning precision of
the original image. For a G3 FAX (normal mode: G3 Normal), scanning is performed at the resolution of 8
divisions per millimeter (200 dpi) in the horizontal direction and 3.85 divisions per millimeter in the vertical
direction. This means that the 200 dpi in-line Carriage Assy is shifted approximately four times per millime-
ter in the vertical direction. For an A4 original, the data amounts to approximately two million pixels. In the
high-quality mode (G3 Fine), scanning resolution is 8 divisions per millimeter in the horizontal direction and
7.7 divisions per millimeter in the vertical direction, where the data amounts to approximately four million
pixels. As resolution increases, the amount of data also increases, lengthening the transmission time.
■ Control Circuit
The control circuit executes scanning of image data by controlling the image scanner. A line of CCD Image
Sensor scans the original image one line at a time. When scanning of one horizontal line is completed, the
next line below is scanned. As this continues, the original is scanned from end to end one line at a time and
converted to digital data as black-and-white information.
Because this image data is a set of digital signals, it cannot be transmitted using an analog telephone line. It
must be subjected to DA conversion (modulation). On the other hand, the receiving FAX machine must per-
form AD conversion to restore the incoming digital data to analog data.
DA conversion, analog signal transmission, analog signal reception, and AD conversion are all performed by
a modem (modulator/demodulator) in the control circuit. A modem consists of a network control unit (NCU) for
connecting to the telephone line and an A/D conversion unit for performing DA and AD conversions.
Chapter 10 Principle of Operation
10-11
10.5 Unit Mechanisms