Document Size Identification - Canon NP6320 Service Manual

F.

Document Size Identification

1. Outline
The copier is equipped with auto paper selection and auto reproduction ratio selection mecha-
nisms. These mechanisms call for identification of the document size as described below.
To enable such identification, three circuits are attached under the copyboard glass (Figure 3-
305); when the copyboard cover is lowered, the DC controller checks the output of these circuits
twice, thereby identifying the document as A3, A4, A4R, or A5R.
The document identification circuit causes its LED to emit light to illuminate the document;
the reflected light is then checked by the phototransistor, whose output is sent to the DC controller.
2. Mechanism
The DC controller checks the output of the document identification circuit when the copyboard
cover is lowered to about 20°. (SW4 ON) and about 1 second after the over has been lowered to
about 5°. (SW5 ON).
The DC controller recognized the presence of a document if the two measurements are identi-
cal; conversely, it recognizes the absence of a document if the measurements are different.
Copyboard cover
Document
SW4 ON
SW5
OFF
When a document is present, the light reflected by the document is checked by the document
identification circuit; therefore, the output of the circuit is constant regardless of the angle of the
copyboard cover.
When no document is present, the output of the circuit from the first measurement is low or
none at all; the output of the circuit from the second measurement, on the other hand, is high
because the light is reflected by the document sheet.
If the document is too thick and, therefore, if only SW4 goes ON, the document size is identi-
fied based on the current output level.
COPYRIGHT © 1999 CANON INC.
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Document
identification
circuit
DC controller PCB
(The thickness of the arrows represents the degree of the level.)
Figure 3-305
CANON NP6320 REV.0 DEC. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 3 EXPOSURE SYSTEM
20°
SW4 ON
SW5
ON
DC controller PCB
5°
3-11