Optical: systems and elements – Deflection using a moving element
Reexamination Certificate
1999-07-27
2001-01-09
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
C355S057000, C355S060000, C355S066000, C355S067000, C355S071000
Reexamination Certificate
active
06172784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus suitable for an apparatus such as a flatbed image scanner or digital copying machine, which reads the image information of an original using an integrated scanning optical system unit in which a light source, a plurality of mirrors, imaging lens, image sensor, and the like are integrally accommodated.
2. Related Background Art
Conventionally, various image reading apparatuses such as flatbed image scanners or digital copying machines have been proposed.
FIG. 1
is a view schematically showing the arrangement of the main part of a conventional image reading apparatus of this type. Referring to
FIG. 1
, an original
103
placed on an original glass table
104
is illuminated with direct light from a light source
106
and a light beam that has passed through a reflector
107
from both sides. The image of the light beam reflected by the original
103
is formed on an image sensor
114
such as a CCD by an imaging lens
113
through a first mirror
108
, second mirror
109
, and third mirror
110
for scanning, and is converted into an electrical signal in accordance with a level light and shade (density) of the original
103
. With this operation, image information of one line in the main scanning direction (direction perpendicular to the drawing sheet of
FIG. 1
) is read. Image reading in the sub-scanning direction (direction indicated by an arrow C in
FIG. 1
) is done in the following way. The first mirror table formed from the light source
106
, reflector
107
, and first mirror
108
is moved relative to the original
103
in the sub-scanning direction, and the second mirror table formed from the second mirror
109
and third mirror
110
is moved in the same direction at a speed ½ that of the first mirror table. With this operation, the image information of the original is read while maintaining a constant optical path length between the original
103
and image sensor
114
.
The scanning optical system of this type is called a so-called 1:2 scanning optical system as a known technique. Even when the optical path length between the original and image sensor is increased, the apparatus size in the sub-scanning direction can be reduced.
However, since an original must be scanned while changing the relative positional relationship between the reading section comprising the imaging lens and image sensor that are fixed with respect to the original and the three scanning mirrors, color registration misalignment, density level variation, and defocus may occur due to vibration, angle error, and surface precision error of the scanning mirrors. To prevent this, the component precision or driving accuracy of the scanning mirrors must be increased.
FIGS. 2 and 3
are views schematically showing the arrangements of the main part of image reading apparatuses having an integrated scanning optical system unit, which relax the problem of the above 1:2 scanning optical system. Each of the integrated scanning optical system units shown in
FIGS. 2 and 3
integrally accommodates components including a light source, reflector, a plurality of scanning mirrors, imaging lens, and image sensor, so an original is scanned without changing the relative positional relationship between the components.
FIG. 2
is a view schematically showing the arrangement of the main part of an image reading apparatus having an integrated scanning optical system unit disclosed in, e.g., Japanese Patent Application Laid-Open No. 63-217872. An integrated scanning optical system unit
118
shown in
FIG. 2
integrally accommodates a light source
106
and reflector
107
for illuminating an original
103
placed on an original glass table
104
, image sensor
114
for reading a light beam from the original
103
illuminated with the light source
106
and reflector
107
, a plurality of scanning mirrors
115
,
116
, and
117
for guiding the light beam from the original
103
, and imaging lens
113
for forming the image of the light beam from the original
103
, which is based on image information, on the image sensor
114
.
Referring to
FIG. 2
, the plurality of scanning mirrors comprise the first mirror
115
, second mirror
116
, and third mirror
117
. A light beam from the original
103
travels from the first mirror
115
to the second mirror
116
and then from the second mirror
116
to the third mirror
117
. The light beam from the third mirror
117
strikes the second mirror
116
again. After this, the light beam passes between the first mirror
115
and third mirror
117
and enters the imaging lens
113
to form its image on the image sensor
114
. A plane connecting the second mirror
116
, imaging lens
113
, and image sensor
114
is substantially parallel to the original surface.
FIG. 3
is a view schematically showing the arrangement of the main part of an image reading apparatus having an integrated scanning optical system unit disclosed in, e.g., Japanese Patent Application Laid-Open No. 9-69915. An integrated scanning optical system unit
122
shown in
FIG. 3
integrally accommodates a light source
106
and reflector
107
for illuminating an original
103
placed on an original glass table
104
, image sensor
114
for reading a light beam from the original illuminated with the light source
106
and reflector
107
, a plurality of scanning mirrors
119
,
120
, and
121
for guiding the light beam from the original
103
, and imaging lens
113
for forming the image of the light beam from the original
103
, which is based on image information, on the image sensor
114
.
Referring to
FIG. 3
, illumination light by the light source
106
and reflector
107
illuminates the lower surface of the original
103
and is diffused and reflected. Some components of the light beam travel downward in the vertical direction in
FIG. 3
, are reflected by the first mirror
119
, and reach the second mirror
120
. The light beam incident on the second mirror
120
is reflected at a predetermined angle and strikes the first mirror
119
again. The light beam incident on the first mirror
119
again is further reflected at a predetermined angle. The light beam is reflected by the third mirror
121
in the horizontal direction and is incident on the imaging lens
113
. A reduced image of the original
103
is formed on the image sensor
114
through the imaging lens
113
, thereby reading the image information of the original
103
.
These conventional image reading apparatuses have various problems to be described below.
In Japanese Patent Application Laid-Open No. 63-217872 shown in
FIG. 2
, the optical path from the original
103
to the first mirror
115
and that from the second mirror
116
to the imaging lens
113
cross each other, and additionally, the light beam is reflected by the second mirror
116
twice. For this reason, a space is required between the second mirror
116
and imaging lens
113
, and consequently, the distance from the second mirror
116
to the image sensor
114
increases, resulting in a bulky integrated scanning optical system unit
118
. Accordingly, the image reading apparatus using the integrated scanning optical system unit also becomes bulky.
In addition, the light beam from the second mirror
116
passes between the first mirror
115
and third mirror
117
and enters the imaging lens
113
. With this arrangement, light components other than those contributing to image formation may be irregularly reflected by the edge portion of the first mirror
115
or third mirror
117
and enter the imaging lens as hazardous light. This generates ghost or flare to degrade the read image.
In Japanese Patent Application Laid-Open No. 9-69915 shown in
FIG. 3
, the third mirror
121
, imaging lens
113
, and image sensor
114
are parallel to the original surface and disposed immediately under the original glass table
104
. The light source
106
and imaging lens
113
must therefore be arranged close to each
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Schuberg Darren
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