Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-08-26
2002-10-22
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C358S475000, C359S601000, C359S613000
Reexamination Certificate
active
06469774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to removal of flare in an image reading apparatus using a slit exposure optical system.
2. Related Background Art
FIG. 1
is a schematic view showing the main part of a conventional image reading apparatus used in a digital copying machine, flat bed scanner, or the like.
Referring to
FIG. 1
, an original
118
placed on an original glass table
112
is illuminated from the two sides with a direct light beam from a light source
171
and a light beam incident through a reflector
172
. The light beam reflected by the original
118
passes through a stop (slit)
174
and is focused on the surface of a CCD (line sensor)
113
by an imaging lens
111
through first, second, and third scanning mirrors
114
,
115
, and
116
. The optical image formed on the surface of the CCD
113
is converted into an electrical signal in accordance with the density of the original
118
, and one-line image information (in the main scanning direction (direction perpendicular to the drawing sheet of
FIG. 1
) is read. Image information in the sub-scanning direction (direction indicated by an arrow Y in
FIG. 1
) is read as follows. The first mirror table comprised of the light source
171
, a reflector
172
, the stop
174
, and the first scanning mirror (full-speed scanning mirror)
114
is moved in the sub-scanning direction with respect to the original
118
. The second mirror table comprised of the second and third scanning mirrors (half-speed mirrors)
115
and
116
is moved in the sub-scanning direction at a speed half (moving speed ratio of 2:1) that of the first mirror table. The image information of the original
118
is read while the optical path length from the original
118
to the CCD
113
is kept constant.
The light source, reflector, slit, first to third scanning mirrors, and CCD in the image reading apparatus of this type stretch in a direction (main scanning direction) perpendicular to the page of drawing to read the entire line of the original in the main scanning direction and the entire area of the original by scanning the first and second mirror tables. This optical system is a so-called slit exposure optical system.
The CCD pixel array is composed of one line for a monochrome image read and three adjacent lines (monolithic 3-line sensor) of R, G, and B for a color image read. The magnification of the imaging lens is determined by the original read pitch and CCD pixel pitch. For example, when the read pitch is 600 DPI and the CCD pixel pitch is 7 &mgr;m, the imaging magnification &bgr; is ×0.16535.
The above image reading apparatus suffers from the following various problems. Such a problem is described with reference to FIG.
2
.
FIG. 2
is a schematic view showing the main part of the optical system of the image reading apparatus in
FIG. 1
from the viewpoint of paraxial optics. For the descriptive convenience, as the main constituent elements in
FIG. 1
, only the imaging lens
111
, original glass table
112
, and CCD
113
are extracted. At the same time, an optical axis O of the imaging lens
111
, marginal light rays
10
, and typical light rays
14
,
15
, and
16
are illustrated.
Along with the higher integration of recent CCD substrates, the semiconductor process techniques have been re-examined to increase the yield, and the surface precision of electrodes on the CCD substrate has improved. As the CCD surface has become an almost mirror surface, the imaging light beam incident on or near the CCD pixel array is partially reflected by the CCD surface. For example, the light ray
14
(travelling in the A direction) as part of the imaging light beam is partially reflected by a pixel array
131
of the CCD
113
and becomes a reflected light ray (flare ray)
15
(travelling in the B direction). Most of the reflected light ray
15
is refocused near a surface
121
of the original glass table
112
by the imaging lens
111
. The light ray
15
reflected by the surface
121
of the original glass table
112
travels as the light ray (propagating in the C direction) tracing nearly the same optical path as the light ray
14
, and reaches the surface of the CCD
113
.
As described above, a flare due to multiple reflection between the original glass table
112
and the CCD
113
tends to be produced on or near the axis, but is hardly produced at an off-axis position due to the following reason. That is, as an off-axis light beam has a larger incident angle on the CCD
113
due to increased field angle, the light ray
15
reflected by the surface of the CCD
113
can hardly enter the imaging lens
111
again.
For example, when an image having a uniform intermediate density is read, streaks of a white flare appear near the central portion of the resultant image. This interferes with high image quality.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low-cost, compact image reading apparatus in which a reading means is not perpendicular to the optical axis of an imaging optical system, or the optical axis between an original glass table and a first scanning mirror is not perpendicular to the original glass table to eliminate the multiple reflection flare between the original surface and reading means surface and improve the image quality of the image reading apparatus.
According to the present invention, an image reading apparatus for causing illumination means to illuminate an original placed on an original glass table, causing an imaging optical system to focus a light beam based on image information of the original surface on a surface of the reading means, and causing the reading means to read the image information is characterized in that the reading means is not perpendicular to an optical axis of the imaging optical system, and the following condition is satisfied:
&thgr;
i
≧sin
−1
(
NA
i
)
where &thgr;
i
is the tilt angle of the reading means with respect to the optical axis of the imaging optical system, and NA
i
is the numerical aperture of the imaging optical system on a reading means side. In particular, the following condition is satisfied:
&thgr;
0
≧sin
−1
(NA
0
)
where &thgr;
0
is the tilt angle of the original glass table with respect to the optical axis of the imaging optical system when the original glass table is not perpendicular to the optical axis of the imaging optical system, and NA
0
is the numerical aperture of the imaging optical system on an original side.
The image reading apparatus is characterized in that a light-shielding member is inserted between the imaging optical system and the reading means, and a normal to the reading means is directed toward the light-shielding member. Alternatively, the image reading apparatus is characterized in that a plurality of scanning mirrors are inserted between the original glass table and the imaging optical system.
According to the present invention, an image reading apparatus for causing illumination means to illuminate an original placed on an original glass table, causing an imaging optical system to focus a light beam based on image information of an illuminated original surface on a surface of the reading means through a plurality of scanning mirrors, and causing the reading means to read the image information is characterized in that an optical axis between the original glass table and a first scanning mirror of the plurality of scanning mirrors which opposes the original glass table is not perpendicular to the original glass table, and the following condition is satisfied:
&thgr;
0
≧sin
−1
(NA
0
)
where &thgr;
0
is the angle a normal to the original glass table makes with the optical axis between the original glass table and the first scanning mirror, and NA
0
is the numerical aperture of the imaging optical system on an original side.
According to the present invention, an image reading apparatus for moving an integral scanning optical system unit in a scanning direction to read image informat
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Roy
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