2. Operation
The DC controller PCB measures the outputs of the original detection circuits at
intervals of 0.2 sec until the Copy Start key is pressed or for 15 sec after the copyboard
cover open/closed sensor (PS5) has turned on while the copyboard cover is being
closed.
Figure 3-402
If an original exists over a sensor, the original detection circuit receives the light
reflected by the original so that the output of the detection circuit remains the same
regardless of the angle of the copyboard cover.
If no original exists over the sensor, on the other hand, the output of the detection
circuit immediately after PS5 turns on is small. When the copyboard cover is fully closed
thereafter, the light reflected by the detection circuit receives the light reflected by the
copyboard sheet, and the output will be larger.
Accordingly, the DC controller will assume the presence of an original if the output of
the detection circuit remains the same, while assuming the absence of an original if the
output changes.
This type of detection enables identification of the size of even a black original.
Reference:
1. If the original is thick and, as a result, the copyboard cover will not fully close after
PS5 has turned ON, the level of the sensor output will not change regardless of
the size of the original. If none of the levels (of the three sensors) does not
change, the DC controller identifies the size of the original by comparing the
measurement taken when PS5 has turned on against the slice level.
2. If the copyboard cover is opened (PS5 is off), the cassette containing the
maximum size paper will be selected.
,,
DC controller PCB
Output
Original
detection
circuit
PS5
ON
Original
Copyboard cover
30° (approx.)
(The thickness of the output arrow represents the size of the level.)
,,
,
Output
PS5
ON
DC controller PCB
Output
(constant)
Output
(varied)
COPYRIGHT © 1997 CANON INC. CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 3 EXPOSURE SYSTEM
3-21
