Technical information

OPERATIONS AND TIMING m
D. Document Sìze Identification
1. Outline
The copier is equipped with auto paper selection
and auto reproduction ratio selection mechanisms.
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 3-21);
when the copyboard cover is lowered, the DC con-
troller checks the output of these circuits twice,
thereby identifying the document as Ledger, Legal,
Letter, or Mini.
Copyboard cow?
[ DCcontroller PCB / 1
The document identification circuit causes its
LED to emit light to illuminate the document; the re-
flected 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 docu-
ment identification circuit when the copyboard cover
is lowered to about 20 deg. (SW4 ON) and about 1
sec second afterthe over has been lowered to about
5 deg. (SW5 ON).
The DC controller recognized the presente of a
document if the two measurements are identical:
conversely, it recognizes the absence of a document
if the measurements are different.
DC conlroller PCB
(The thickness of the arrows represents the degree of the level.)
Figure 3-19
When a document is present, the light reflected
by the document is checked by the document iden-
tification 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;theoutputofthecircuitfromthesecondmeasure-
ment, 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
SW4goesON. thedocument sizeis identified based
on the output level of this time.
COPYRIGHT 8 1992 CANON INC.
CANON NP2120/2070 RN.0 MAY 1590 PRINTEO IN JAPAN IIMPRIME AU JAPON]
3-21