Canon PC740 Service Manual - Page 51

Exposure, System

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OPERATIONS AND TIMINGM II. EXPOSURE SYSTEM A. Varying the Reproduction Ratio The reproduction ratio in the direction of the drum axis is varied by the lens drive system and that around the drum, by the scanner drive system. The lens drive system holds a lens array and changes the location of the lens and the optical path length as shown in Figure 3-201 to vary the reproduction ratio in the direction of the drum axis; the length of the optical path is changed by moving the No. 4 and No. 5 mirror units as shown in Figure 3-202. The scanner drive system changes the reproduction ratio around the drum by moving the No. 1 mirror faster (reduction) or slower (enlargement) relative to the peripheral speed of the drum. DIRECT Optical path I 4 length REDUCE Optical path r" length LI t. I L2 N. I Reference: 1. In DIRECT, the speed at which the No. 1 mirror is moved is the same as the peripheral speed of the drum. 2. The length of the optical path is longer in both REDUCE and ENLARGE than in DIRECT. ENLARGE Optical path L3 length Optical path: LI< L2, LI< L3 Figure 3-201 COPYRIGHT @ 1994 CANON INC. CANON PC72074017501770 REV.O AUG.1994 PRINTED IN JAPAN pmPHImE AU JAPON) 3 - 11

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OPERATIONS
AND
TIMINGM
II.
EXPOSURE
SYSTEM
A.
Varying
the
Reproduction
Ratio
The
reproduction
ratio
in
the
direction
of
the
drum
axis
is
varied
by
the
lens
drive
sys-
tem
and
that
around
the
drum,
by
the
scan-
ner
drive
system.
The
lens
drive
system
holds
a
lens
array
and
changes
the
location
of
the
lens
and
the
optical
path
length
as
shown
in
Figure
3-201
to
vary
the
reproduction
ratio
in
the
direction
of
the
drum
axis;
the
length
of
the
optical
path
is
changed
by
moving
the
No.
4
and
No.
5
mirror
units
as
shown
in
Figure
3-202.
The
scanner
drive
system
changes
the
reproduction
ratio
around
the
drum
by
mov-
ing
the
No.
1
mirror
faster
(reduction)
or
slower
(enlargement)
relative
to
the
periph-
eral
speed
of
the
drum.
Reference:
1.
In
DIRECT,
the
speed
at
which
the
No.
1
mirror
is
moved
is
the
same
as
the
peripheral
speed
of
the
drum.
2.
The
length
of
the
optical
path
is
longer
in
both
REDUCE
and
ENLARGE
than
in
DIRECT.
DIRECT
Optical
path
length
RE-
DUCE
Optical
path
length
EN-
LARGE
t.
I
I
4
LI
N.
I
r"
L2
Optical
path
length
Optical
path:
LI<
L2,
LI<
L3
L3
Figure
3-201
COPYRIGHT
@
1994
CANON
INC.
CANON
PC72074017501770
REV.O
AUG.1994
PRINTED
IN
JAPAN
pmPHImE
AU
JAPON)
3
-
11