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CHAPTER 2 FUNCTIONS & OPERATION
2) Double Feed Detection
There are 2 double feed detection
methods: the document length detection
by the registration sensor and the
document overlapping detection by the
ultrasonic sensor.
Registration sensor
The registration sensor uses the first
document length of the scanned batch as
a reference to detect the document
length. The 35 mm or more difference
from the standard is interpreted as a
double feed.
Ultrasonic sensor
The ultrasonic drive sensor transmits the
ultrasonic and the ultrasonic receive
sensor receives the ultrasonic signal to
gain a specific signal level. When
overlapping documents are fed, the
signal level is different from when
properly feeding a single document. This
machine interprets this difference as a
double feed.
Note that since this level of difference
occurs depending on the presence of a
layer of air, a double feed will not be
detected if the document is tightly
adhered by static electricity or adhesive.
Furthermore, “double feed” is judged if
this level of difference is detected
continuously for a specific amount of time.
As a result, if the overlap between sheets
is less than 50 mm when a document is
being fed, it might not be judged as a
“double feed” because the detection time
is short. Furthermore, the ranges within
10mm from the leading and trailing
edges are not judged.
Ultrasonic drive sensor
(transmission)
Ultrasonic receive sensor
(reception)
Figure 2-305
3) Skew Detection
Skewed documents are detected by the
skew sensors (L and R). This makes it
possible to both prevent damage to the
document if it is skewed, and to detect
documents that are held by staples.
If multiple A4 or LTR size documents are
fed stapled together in a single location,
the uppermost document will become
skewed. This is detected by the skew
sensor to prevent the documents from
becoming damaged.
The following figure shows positions of
the skew sensors.
Registration roller
Skew sensor (L) Skew sensor (R)
Retard roller
Figure 2-306
2-12
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CANON ELECTRONICS INC. 2011 CANON DR-M140 FIRST EDITION