Optical: systems and elements – Lens – With support
Reexamination Certificate
2003-04-28
2004-10-05
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
C359S819000, C359S694000, C359S704000
Reexamination Certificate
active
06801375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to an image formation optical system and, an image reading apparatus using the same. In particular, the invention is suitable for an image reading apparatus such as an image scanner, a copying machine or a facsimile which is adapted to sufficiently exhibit the optical performance of an image formation optical system having a rotation asymmetric lens such as an anamorphic lens.
2. Related Background Art
FIG. 20
is a schematic view showing a construction of a main portion of a conventional image reading apparatus.
In the figure, reference numeral
92
designates an original table glass on the surface of which an original
91
is placed. Reference numeral
97
designates a carriage in which an illumination system
93
, a plurality of reflecting mirrors
94
a
,
94
b
,
94
c
,
94
d
and
94
e
, an image formation optical system (image reading lens)
95
, a reading unit
96
, and the like all of which will be described later are integrally accommodated. Image information of the original
91
is read by scanning the carriage
97
in a sub-scanning direction indicated by an arrow in the figure by a sub-scanning mechanism
98
such as a motor. The image information which has been read is sent to a personal computer or the like as an external apparatus through an interface (not shown).
Reference numeral
93
designates an illumination system composed of a xenon tube, a halogen lamp, an LED array or the like. By the way, a reflecting plate such as an aluminium evaporation plate may be combined with the illumination system
93
. Reference numerals
94
a
,
94
b
,
94
c
,
94
d
and
94
e
designate reflecting mirrors, respectively, which serve to fold optically the luminous flux from the original
91
in the inside of the carriage
97
. Reference numeral
95
designates an image formation optical system which serves to image the light from the original
91
on the surface of the reading unit
96
. Reference numeral
96
designates a linear sensor such as a CCD (Charge Coupled Device) as the reading unit which is constructed by arranging a plurality of light receiving elements in a main scanning direction as a direction perpendicular to the paper surface.
For miniaturization of the image scanner in the above-mentioned construction, the carriage
97
must be miniaturized. For miniaturization of the carriage
97
, for example, there is a method of increasing the number of reflecting mirrors, or a method of reflecting the light plural times by one reflecting mirror to ensure an optical path length.
However, in these methods, there is encountered a problem in that since the internal construction of the carriage
97
becomes complicated, it becomes difficult to achieve accurate assembly and hence the cost is greatly increased. In addition, there is also encountered a problem in that the image formation performance becomes worse in proportion to the profile irregularity of the reflecting mirror and the number of times of reflection, which exerts an influence on the read image as well.
Then, the applicant of the present invention made such a proposal that in the formerly proposed image reading apparatus shown in the Japanese Patent Application Laid-Open No. 2000-171705, an anamorphic lens having at least one surface which is rotation asymmetric with respect to an optical axis is introduced into an image formation optical system to increase the field angle of the image formation optical system (image formation system)
97
to shorten the distance between object and image, thereby shortening the optical path length itself.
However, if the lens having the anamorphic surface is incorporated in the image formation optical system, then the image formation performance of the image formation optical system will become rotation asymmetric with respect to an optical axis. For this reason, the main scanning direction of the image formation optical system, and the direction of arrangement of a plurality of light receiving elements constituting a CCD of the image reading apparatus need to be controlled so as to be aligned with each other.
Various image reading apparatuses for fixing accurately the above-mentioned image formation optical system in the main scanning direction along which a CCD is arranged have been proposed Application Laid-Open No. 2000-307823 and Japanese Patent Registration No. 307,828 for example. In accordance with these references, the positional relationship among an anamorphic lens, a lens barrel and an image reading apparatus is accurately fixed.
In addition, there has been proposed, e.g., in Japanese Patent Application laid-Open No. 2002-314765, a method of maintaining the high image formation performance of the above-mentioned image formation system even under the conditions in which the temperature environment is severe.
However, these techniques described in these references have the following problems.
First of all, the description will hereinbelow be given with respect to a conventional image formation optical system
101
constituted only by rotation symmetric lenses with reference to FIG.
21
. If rotation symmetric lenses a, b, c and d included in a lens barrel
100
are manufactured as designed, as shown in a shaded dot portion in the figure, the sufficient image formation performance is exhibited in the whole image formation area
105
. However, as shown in the rotation symmetric lens c in the figure, in general, in the image formation optical system, the lens decentering occurs through the manufacture process. If the lens decentering occurs, then the image formation performance within the image formation surface becomes nonuniform. For this reason, in the image formation optical system
101
constituted by only the lenses each having the rotation symmetric shape, the lenses each having the rotation symmetric shape needs to be rotated with the optical axis as a center to carry out the adjustment indicated by an arrow in the figure (hereinafter, referred to as “the rotation adjustment”) so that the best image formation line
104
having high image formation performance overlaps the direction of arrangement of a plurality of pixels of the CCD within the image formation area
105
(hereinafter, referred to as “the CCD arrangement direction”).
Next, the description will hereinbelow be given with respect to a prior art using the rotation asymmetric lenses such as the anamorphic lenses with reference to FIG.
22
.
In the figure, objects shown in the form of circles are lenses each having a rotation symmetric shape (rotation symmetric lenses) a, b, c and d, and an object shown in the form of a quadrilateral is a lens having a rotation asymmetric shape (rotation asymmetric lens) e. The main scanning direction of the rotation asymmetric lens e is indicated by a long broken line x in the quadrilateral. In the image formation optical system
101
using the rotation asymmetric lens e, the image formation area
105
becomes a flattening area determined by the rotation asymmetric lens e.
In this image formation optical system
101
, when the lens decentering as exemplified by the rotation symmetric lens c occurs, the sufficient image formation performance can not be obtained. Even if the rotation adjustment is carried out, since both the best image formation line
104
and the image formation area
105
are rotated, there is a problem in that the CCD arrangement direction
106
and the best image formation line
104
are not necessarily aligned with each other.
Thus, for the image formation optical system
101
using the rotation asymmetric lens e, the molding accuracy, the assembly accuracy and the like of the lens barrel need to be rigidly managed so that a quantity of occurrence of the decentering becomes very small. Thus, that image formation optical system
101
can not be safely said as the image formation optical system which is excellent in mass production due to an increase in processing cost and a reduction in yield.
In addition, the above-mentioned problem is also the problem aris
Mack Ricky
Thomas Brandi
LandOfFree
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