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READING SECTION
3. CONTACT SENSOR
3.1
Structure of Contact Sensor
The structure of the contact sensor is designed to prevent dirt and dust
from collecting on the sensor surface or entering the inside. The inside of
the contact sensor comprises an LED array, contact glass, rod lens array
and photo-transistor array. The LED array emits the light for reading the
document, the contact glass refracts the light emitted from the LED array
to irradiate the document, the rod lens array picks up and channels the light
reflected from the document, and the photo-transistor array receives the
reflected light. (See Fig. 3-13)
3.2
Features of Contact Sensor
There are two types of contact sensor, the multi-chip type and the -Si
(Amorphous Silicon) type.
The following describes the strengths and weakness of each type.
(1) Multi-chip type
(2)
3–10
• Unevenness of the sensor chip is less than that of the -Si type.
• Image quality is good as the
• Documents can be read even if they rise off the glass surface slightly.
(This is dependent, though, on the performance of the rod lens array.)
• The document need not be held down by rollers. So, photographs need
not be pasted onto a sheet for reading.
• The density level differs among the sensor chips. So, a density differ-
ence may occur between sensor chips which may affect the image if
the density is not compensated.
-Si (amorphous silicon) type
• Costs can be reduced as a rod lens array is not required in the structure
of the contact sensor.
• The contact sensor can be designed to be thinner as the rod lens array
is not required.
• Light irradiated from the read surface of the copyboard glass is
reflected internally on the contact sensor to enter the photo-transistor
array. So, there is the possibility that even black originals will be
reproduced as gray.
gamma characteristics
are proportional.
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