Canon DADF-B1 Service Manual page 20

b. Identifying the Size of an Original
The ADF identifies the size of an original
in terms of length (feeding direction) and
width.
The length is computed in reference to the
number of clock signals from the pre-
registration sensor (U502) and the registration
roller.
When the pre-registration sensor detects
the leading edge of an original (ON) and the
trailing edge (OFF), the ADF controller
computes the time taken by the original to
move past the pre-registration sensor with
reference to the number of clock signals from
the feed motor clock sensor (SR1) to find out
the size in the lengthwise direction (feeding
direction).
The ADF controller uses the result to
identify a default size, and communicates it to
the copier so that copy paper of the appropriate
size may be selected.
ADF controller PCB
Original
Pre-registration
Prism
sensor
U502
Feed motor
BK M2
Registration roller
SR4
Figure 2-203
COPYRIGHT © 1999 CANON INC. CANON DADF-B1 REV.0 APR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
Feed motor clock
sensor
CHAPTER 2 BASIC OPERATION
The ADF refers to the original width
detecting volume (U508) located inside the
original tray to find out the width of an original.
The original width detecting volume
operates in conjunction with the slide guides,
and the resistance of the voltage varies in
analog mode. The ADF controller uses
changes occurring in the resistance as the
original size detection signal (WIDE), and uses
them to find out the width of a specific original.
Original width detecting volume
Figure 2-204
2-7