D.
Sìze Identification
1. Outline
The
with auto paper selection
and auto reproduction ratio selection mechanisms.
These mechanisms
for identification of the
document size as
below.
To enable
identification, three circuits are
attached under the copyboard
(Figure 3-21);
when the copyboard
lowered, the DC
troller checks the output of these circuits
thereby identifying the document as Ledger, Legal,
Letter, or Mini.
C o p y b o a r d
The document identification circuit causes its
LED to emit light to illuminate the document; the
flected light then checked by the phototransistor,
whose output sent to the DC controller.
2. Mechanism
The DC controller checks the output of the
ment identification circuit when the copyboard
lowered to about 20 deg. (SW4
and about 1
second
has
lowered to about
5 deg. (SW5
The DC controller recognized the
of a
document if the two measurements are identical:
conversely, it recognizes the absence of a document
if the measurements are different.
D C
P C B
(The thickness of the arrows represents the degree of the
Figure 3-19
When a document present, the light
by the document checked by the document
tification circuit; therefore, the output of the circuit
regardless of the angle of the copyboard
When no document present, the output of the
circuit from the first measurement low or
at
ment,
the other hand, high
the light
by the document sheet.
If the document too thick and, therefore, if only
thedocument sizeis identified based
the output
of this time.
1992 CANON INC.
C A N O N
R N . 0
I N
3-21
Summary of Contents for NP-2120
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